nature reviews microbiology
https://doi.org/10.1038/s41579-025-01180-z
Review article
Check for updates
Aspergillus fumigatus biology,
immunopathogenicity
and drug resistance
Frank L. van de Veerdonk
1,2
, Agostinho Carvalho
, Joost Wauters
3,4
, George Chamilos
5
6,7
& Paul E. Verweij2,8
Abstract
Sections
Aspergillus fumigatus is a saprophytic fungus prevalent in the
environment and capable of causing severe invasive infection in humans.
This organism can use strategies such as molecule masking, immune
response manipulation and gene expression alteration to evade host
defences. Understanding these mechanisms is essential for developing
effective diagnostics and therapies to improve patient outcomes in
Aspergillus-related diseases. In this Review, we explore the biology and
pathogenesis of A. fumigatus in the context of host biology and disease,
highlighting virus-associated pulmonary aspergillosis, a newly identified
condition that arises in patients with severe pulmonary viral infections.
In the post-pandemic landscape, in which immunotherapy is gaining
attention for managing severe infections, we examine the host immune
responses that are critical for controlling invasive aspergillosis and how
A. fumigatus circumvents these defences. Additionally, we address the
emerging issue of azole resistance in A. fumigatus, emphasizing the
urgent need for greater understanding in an era marked by increasing
antimicrobial resistance. This Review provides timely insights necessary
for developing new immunotherapeutic strategies against invasive
aspergillosis.
Introduction
Department of Internal Medicine, Infectious Diseases, Radboud University Medical Center, Nijmegen, The
Netherlands. 2Radboudumc/CWZ Center of Expertise in Mycology (RCEM), Radboud University Medical Center,
Nijmegen, The Netherlands. 3Life and Health Sciences Research Institute (ICVS), School of Medicine, University
of Minho, Braga, Portugal. 4ICVS/3B’s–PT Government Associate Laboratory, Braga, Portugal. 5Medical Intensive
Care, University Hospitals Leuven and Department for Clinical Infectious and Inflammatory Disorders, University
Leuven, Leuven, Belgium. 6Institute of Molecular Biology and Biotechnology, Foundation for Research and
Technology, Heraklion, Greece. 7School of Medicine, University of Crete, Heraklion, Greece. 8Department of
Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands.
e-mail: frank.vandeveerdonk@
radboudumc.nl
1
Nature Reviews Microbiology
Aspergillus fumigatus biology
Host defence against
Aspergillus fumigatus
Virus-associated invasive
aspergillosis
Strategies to survive azole
exposure
Conclusions and outlook
Review article
Introduction
Aspergillus species are saprotrophic fungi widely present in soil, where
they play a vital role in carbon and nitrogen recycling by thriving on
decaying vegetation. While Aspergillus fumigatus typically does not
cause infection in immunocompetent hosts, it can lead to severe invasive disease in immunocompromised individuals. Traditionally, this
susceptibility has been observed in patients undergoing chemotherapy
or those with rare immunodeficiencies (Box 1). However, the landscape
is changing: new drugs in oncology and rheumatology have broadened
the population at risk for invasive aspergillosis. The COVID-19 pandemic
has brought to light a new clinical entity known as virus-associated
pulmonary aspergillosis (VAPA), highlighting the evolving nature of
these infections. To improve clinical outcomes in Aspergillus-related
infections, experts believe that a combination of antifungal therapy and
immunomodulatory treatments is needed. A thorough understanding
of the interactions between Aspergillus spp. and the host is crucial for
developing new effective treatment strategies. This Review will provide
timely updates on recent progress in host–pathogen interactions,
detailing how A. fumigatus evades host defences and adapts to the host
environment and subsequently what mechanisms are used by the host
to control and eliminate invasive infection. This will be discussed in the
context of the new clinical entity VAPA and the emergence of antifungal
drug resistance, underscoring the timely nature of this Review.
Aspergillus fumigatus biology
The life cycle of A. fumigatus begins with the germination of spores
(Fig. 1). These spores are typically formed in specialized structures
called conidiophores, which are often found in large numbers on the
surface of the fungal colony. Aspergillus species produce vast quantities
of asexual spores known as conidia, which are small unicellular structures that are highly resistant to environmental stressors, allowing them
to survive in a wide range of conditions. Recent studies have shown
heterogeneity in the conidial population produced on a single conidiophore, which results in different germination behaviours upon exit of
quiescence1,2. Once the conidia are released into the environment, they
can be dispersed by various means such as air currents, water or animal
vectors3. This enables A. fumigatus to colonize new substrates and environments. When favourable conditions are encountered, the conidia
can germinate and initiate the growth of new colonies. Germination
is triggered by environmental factors such as moisture, temperature
and nutrient availability. Upon germination, the conidium swells and
gives rise to a specialized hyphal structure known as the germ tube. The
germ tube elongates and branches, forming a network of hyphae that
infiltrates the substrate. The hyphae secrete enzymes and absorb nutrients from the environment, enabling the fungus to grow and expand its
mycelium. As the mycelium develops, it forms a complex network of
hyphae that penetrate the substrate, facilitating the decomposition of
organic matter and nutrient acquisition. Under certain conditions, such
as the presence of specific mating types or stress factors, A. fumigatus
can undergo sexual reproduction4, which involves the fusion of two
compatible mating types with the consequent formation of sexual
spores called ascospores that are enclosed within protective structures,
known as ascus4. The ascospores are released from the ascus and can be
dispersed in a similar manner to asexual conidia. These sexual spores
have the potential to contribute to genetic diversity and adaptation,
making sexual reproduction an important aspect of the A. fumigatus
life cycle5. It is worth noting that while sexual reproduction occurs in
some Aspergillus species, many others are predominantly asexual and
rely on the production and dispersal of conidia for their survival and
propagation. Although the sexual reproduction is not directly involved
in disease, understanding the biology of Aspergillus spp. life cycle is
important for studying its ecology, and can be helpful to develop effective control measures against pathogenic species6. Further research
into the molecular mechanisms and regulatory factors involved in each
Box 1 | Host genetics and Aspergillus fumigatus infections
While virulence mechanisms contribute to infection, studies in
patients with rare mutations and high-risk cohorts have unveiled the
contribution of heritable host factors to the development and clinical
course of aspergillosis. Diseases such as chronic granulomatous
disease caused by mutations in components of the nicotinamide
adenine dinucleotide phosphate (NADPH)-oxidase complex, caspase
recruitment domain 9 (CARD9) deficiency and mutations in signal
transducer and activator of transcription 3 (STAT3) lead to hyper
IgE syndrome. This predisposes individuals to severe Aspergillus
fumigatus infections and has substantially contributed to the
understanding of host defence against this pathogen186.
SNPs in the long pentraxin 3 (PTX3) remain the most robust
genetic markers identified thus far187. A haplotype in PTX3 was
reported to influence the development of invasive pulmonary
aspergillosis (IPA) after stem cell transplantation60,179, but also after
solid organ transplantation188,189 and in chronic obstructive pulmonary
disease190. This association was also observed in patients with
acute myeloid leukaemia, but only in the absence of pre-existing
neutropenia191, a finding confirming the detrimental consequences
of PTX3 SNPs to the antifungal effector functions of neutrophils60.
Because of its role in activating phagocytosis by neutrophils, SNPs
Nature Reviews Microbiology
in another pentraxin family member, the serum amyloid P, also
predisposed to IPA192.
Individuals carrying an early stop codon SNP in dectin-1, which
truncates the receptor at the recognition domain and impairs
cytokine production, displayed heightened susceptibility to IPA
across different studies110,178,179. More recently, a SNP in the MelLec
receptor that presumably affects signal transduction was also found
to impair cytokine production and predispose to IPA193. In line with its
role as a negative regulator of dectin-1 during A. fumigatus infection,
SNPs in the nucleotide-binding oligomerization domain 2 (NOD2)
were instead reported to confer resistance to IPA194.
Besides fungal recognition, genetic variants that affect processes
of immune cell activation and functional activity have also been
implicated in the risk of aspergillosis. Relevant examples include
SNPs that affect phagosome maturation and the activation of
LC3-associated phagocytosis82,118,195, post-translational modification
of proteins196 and cytokine secretion182,183,197. More recently, functional
genomics approaches that combine genome information and
immunological screenings were used to pinpoint variants that
influenced immune cell metabolism198 and ROS production199, and
that ultimately predisposed to IPA.
Review article
Habitat or niche
a
b
Lung cavity
(chronic pulmonary
aspergillosis)
Plant waste
Airways
(tracheobronchitis)
Reproduction mode and cycle
c
Swollen conidia
Conidia
Asexual
Germlings
Mycelium
Vesicle
Conidiophore
Hyphae
Hyphae
d
Fig. 1 | Habitats and life cycles of Aspergillus fumigatus. a, The lung can
be infected by inhaled conidia, leading to Aspergillus fumigatus infection in
susceptible hosts. A. fumigatus can cause a range of conditions, from allergic to
invasive diseases. The figure highlights two disease spectra that have become
increasingly difficult to treat in recent years and that are associated with specific
predisposing factors. The first is chronic pulmonary aspergillosis, in which
A. fumigatus infects a lung cavity caused by tuberculosis, sarcoidosis or other
underlying structural lung diseases. The other is invasive tracheobronchitis,
an acute and often lethal infection in the airways, especially seen in influenzaassociated aspergillosis. b, Plant waste deposits are habitats where A. fumigatus
can reproduce sexually and asexually and are environmental niches that
can substantially contribute to the genetic diversity of A. fumigatus and the
development of azole resistance. c, Asexual reproduction occurs through hyphae
called conidiophores. The tip of the conidiophore swells up into a head called
vesicle, which forms many radially arranged tubular outgrowths. From these
structures, the conidia are released into the environment, where they swell and
germinate (germlings) originating a germ tube that subsequently becomes
septated, branched and forms a mycelium. d, Sexual reproduction is rare and
occurs with the formation of a male sex organ (antheridium) and a female sex
organ (ascogonium) from the mycelium. When in close proximity, these two sex
organs can merge and the nuclei can fuse and divide and eventually form an ascus
that contains 8 haploid nuclei. These asci are present in the cleisthotecium and
the ascospores can be released from these asci into the environment. Ascospores
can form germlings that will grow and develop into mycelium.
Ascogonium
Ascogonium
Antheridium
Antheridium
Sexual
Ascospore
Ascus
Ascospores
Carbon and nitrogen recycling
Cleistothecium
Germlings
stage of the life cycle will deepen our knowledge and will help to pave the
way for innovative strategies to manage Aspergillus-related diseases.
A. fumigatus is a highly adaptable pathogen capable of adopting several molecular mechanisms to cope with host-induced and
drug-induced stresses. In this section, we summarize the main molecular aspects of nutrient recycling and cation sequestration, hypoxia
adaptation and biofilm formation by A. fumigatus, which contribute to
its adaptation to the host and fungal pathogenicity (Fig. 2). A. fumigatus
is highly efficient at recycling carbon and nitrogen and can adapt to a
wide range of substrates for its metabolic needs7. To counter nutritional
restrictions during infection, A. fumigatus utilizes organic compounds
and essential metals derived from host tissue degradation. It expresses
several proteases and enzymes (for example, serine proteases, metalloproteinases and aspartic proteases), which upon secretion, digest host
macromolecules into organic components that can be metabolized.
Besides nutrient acquisition, these proteases target host mechanisms
Nature Reviews Microbiology
to modulate the immune response. Some examples include the alkaline
protease 1 (Alp1) that can damage junctions of bronchiolar epithelial
club cells and incites eosinophilia and inflammation during fungal
allergy8; the metalloproteinase Mep1p, which can inactivate host complement proteins to restrain conidial opsonization and phagocytosis;
and fungal proteases that can cleave the dectin-1 receptor to dampen
phagocytosis and cytokine production9. Although many other examples exist and are being discovered, the ones mentioned here underscore the complex and extensive interactions between proteases and
the host in the context of Aspergillus-related diseases.
In the presence of different carbon sources, A. fumigatus uses carbon
catabolite repression to favour the utilization of selected substrates.
While this mechanism appears dispensable for initiation of infection,
the limited nutrient and oxygen availability at the site of infection
favours glucose utilization instead of alternative carbon sources, which
contributes to disease progression10. This implies that the variety of
usable carbon sources may differentially impact fungal fitness in vivo.
For example, the utilization of acetate affects cell wall composition and
resistance to oxidative stress, antifungal drugs and neutrophil-mediated
killing, while the deletion of the transcription factor facB that controls
acetate utilization impairs fungal virulence11. The relevance of nitrogen
acquisition to fungal survival within the host is illustrated by the attenuated virulence of a deletion mutant in CpcA, the transcriptional activator of the cross-pathway control system of amino acid biosynthesis12.
Moreover, deletion strains in genes involved in the biosynthesis of
histidine, lysine, tyrosine, tryptophan, isoleucine/valine, methionine,
cysteine and alanine also exhibit impaired virulence13. In certain conditions, A. fumigatus can also degrade amino acids, such as tryptophan,
to produce immunoregulatory molecules required to maintain lung
immune homeostasis14. The fact that environmental strains can be
distinguished from clinical isolates based on genome enrichment in
genes involved in carbohydrate and amino acid metabolism15, and on
Review article
a Carbon and nitrogen recycling
b Cation acquisition
Tissue degradation
Aspergillus
Proteases
Fe
FsC
TAFC
Zn
Cu
MirD
MirB
Fe
CccA
ZrfA–C
Fe
Acquisition of nutrients
FC
CtrA2
CtrC
Vacuole
Metabolic
processes
Inhibition of
neutrophil function
Antifungal drug
resistance
c Adaptation to hypoxia
Haem
biosynthesis
Hypoxia
d Biofilm formation
Carbohydrate
metabolism
Hypervirulent
conidia
Glucans
Galactosaminogalactan
Hyphae
Conidia
Galactomannan
SrbA
Nitrate
assimilation
Ergosterol
biosynthesis
Antifungal resistance
Resistance to
oxidative stress
Oxygen tension
Cell wall
remodelling
Fig. 2 | Mechanisms of Aspergillus fumigatus adaptation to the host.
a, During infection, Aspergillus fumigatus undergoes substantial rearrangements
of its metabolic pathways to cope with limited nutrient availability and survive
within the host. This metabolic plasticity is essential for cell wall remodelling,
resistance to oxidative stress, inhibition of neutrophil functions and antifungal
drug resistance. b, During infection, A. fumigatus expresses efficient molecular
machineries involved in the acquisition of nutrients and cations (iron, copper,
zinc, calcium), such as siderophore-mediated iron acquisition from the
infected tissues. c, In these conditions, hypoxia regulates the activation of
the SrbA transcription factor, which in turn coordinates fungal virulence and
contributes to processes such as carbohydrate metabolism, haem and ergosterol
biosynthesis, and nitrate assimilation. d, Hypoxia is also a crucial process involved
in the transcriptional regulation of fungal biofilm formation and composition,
contributing to antifungal resistance and activating molecular programmes that
enhance virulence. The extracellular matrix of A. fumigatus biofilms is mainly
composed of glucans, galactosaminogalactan and galactomannan.
profiles of metabolic reactions associated with nitrogen, amino acid
and nucleotide metabolism16, further highlights the importance of
these pathways to fungal fitness in vivo.
whereas HapX can activate vacuolar iron storage20. Recently, AtrR, a
transcription factor involved in ergosterol biosynthesis, azole resistance and adaptation to hypoxia, was also implicated in iron acquisition,
including siderophore biosynthesis and uptake21. Zinc is acquired from
the host through the transporters ZrfA, ZrfB and ZrfC22, whose expression is regulated by the transcription factor ZafA23. ZafA also appears
to influence genes involved in iron uptake24. The copper-responsive
transcription factors, AceA and MacA, coordinate copper import and
export, ensuring an adequate supply for copper-dependent processes
while mitigating its toxic effects25. Recently, small molecules produced
by A. fumigatus termed isocyanides were also found to bind copper and
partake in its homeostasis26. Calcium is essential for multiple biological
functions in A. fumigatus due to its role as an intracellular signalling
molecule. The calcium-responsive calcineurin–CrzA pathway influences cell morphology, cell wall composition, virulence and echinocandin resistance, and its disruption hinders virulence27,28. Several
transcription factors besides CrzA have also been reported to promote
Cation acquisition
Several cations such as iron and zinc are essential for the growth of
A. fumigatus. Although iron is an abundant trace metal, in the host it is
mostly bound to proteins such as haem and transferrin. To acquire iron,
A. fumigatus uses reductive iron assimilation and siderophore-mediated
iron acquisition, with the latter widely implicated in virulence. The
siderophore system consists of two secreted siderophores for iron
uptake (fusarinin C and triacetylfusarinin C) and two intracellular
siderophores for iron storage (ferricrocin and hydroxyferricrocin)17.
The transcription factors SreA and HapX regulate iron homeostasis
and siderophore production, although only HapX was found to affect
pathogenicity18,19. Under toxic iron concentrations, and to inhibit its utilization, SreA can repress iron uptake through the siderophore system18,
Nature Reviews Microbiology
Review article
tolerance to calcium stress, but only ZipD has thus far been linked to
reduced virulence in vivo29.
Adaptation to hypoxia
Being an obligate aerobe, oxygen is essential for A. fumigatus. However,
the restricted oxygen availability during infection implies the need for
adaptation to these conditions30,31. The inflammatory response to infection also sustains hypoxia due to tissue degradation and obstruction of
blood vessels. Moreover, the secreted secondary metabolite gliotoxin
inhibits the neovascularization of damaged tissues to further restrain
oxygen availability32. By downregulating the inflammatory response,
local tissue hypoxia decreases and improves outcomes after experimental aspergillosis33. Adaptation to low oxygen is correlated with
virulence and exposure to chronic hypoxia can restore the virulence of
fungal strains that have reduced fitness under low oxygen conditions34.
The sterol regulatory element-binding protein SrbA is required for
hypoxia adaptation and the loss of SrbA function disrupts ergosterol
biosynthesis, resistance to azoles, cell polarity and the ability to cause
disease35. Moreover, SrbA also contributes to hypoxia fitness by regulating nitrate assimilation and haem biosynthesis36. The adaptation
to oxygen stress also relies on the redirection of fungal metabolism
towards mitochondrial respiration31 and activation of the AlcC alcohol
dehydrogenase30.
Biofilm formation
Within the lung, A. fumigatus can form biofilms that enhance resistance
to antifungals and immune defences. The presence of an extracellular
matrix in biofilms mediates surface adherence and confers resistance
to antifungals and immune defences. This matrix is composed mainly
of extracellular DNA, polyols, proteins, lipids and exopolysaccharides
including α-glucans, galactomannan and galactosaminogalactan
(GAG), with the latter being a good example how complex the biology of biofilm in Aspergillus spp. is37 and how important these biofilm components can be for driving pathology in Aspergillus-related
diseases38. GAG is critical for the formation of adherent biofilms as the
deletion of Uge3, which encodes a UDP-glucose epimerase required for
GAG production, impairs the production of the extracellular matrix39.
Deacetylation of GAG mediated by Agd3 is also required for its adhesive properties and biofilm formation40, whereas GAG digestion by
the endo-α-1,4-galactosaminidase Ega3 disrupts biofilm formation41.
Biofilm formation also interplays with fungal metabolism. The alanine aminotransferase AlaA, which participates in alanine catabolism, is required for the maturation of GAG and biofilm adherence,
with an important role in resistance to echinocandins42. Besides GAG,
the role of other polysaccharides in biofilm formation has not been
detailed. The structural properties of fungal biofilms can be influenced
by environmental factors, such as oxygen tension43. The decreasing
oxygen gradient towards the base of biofilms is linked to antifungal
drug resistance44. Hypoxia drives the expression of a subtelomeric
gene cluster (hrmA-associated gene cluster, HAC) associated with the
putative transcriptional regulator hrmA, which modifies the hyphal
surface and hinders their interactions to disrupt biofilm formation45.
The increased virulence resulting from this morphotype promotes
inflammation, as well as disease progression and mortality in vivo.
The biofilm architecture factor A (BafA) within the HAC cluster is sufficient to generate the hypoxia-associated morphotype associated with
altered biofilm structure46. Moreover, the loss of SrbA entirely disrupts
biofilm maturation, while the loss of SrbB affects biofilm structure and
reduces biofilm biomass44.
Nature Reviews Microbiology
Host defence against Aspergillus fumigatus
Genetic predisposition to invasive aspergillosis in humans has revealed
many crucial mechanisms that are important for A. fumigatus antifungal
host defence (Box 1). This has directed the field of fungal immunology
towards the study of several key mechanisms that defend against the
invasion of A. fumigatus, illustrated in Fig. 3. Here, we will provide a basic
background on the innate and adaptive immune responses elicited by
A. fumigatus and provide an update and more detail of new insights
made in recent years.
Innate immunity
Inhaled A. fumigatus conidia interact with local immune defences
of the respiratory tract on a daily basis. Lung immune homeostasis
during fungal infection is conferred through a tightly coordinated
inflammatory response. Crosstalk of alveolar epithelia with alveolar
macrophages via calcium signals47 promotes timely phagocytosis of
inhaled pathogens by alveolar macrophages and restricts inflammatory neutrophil influx48. Lung tissue-resident phagocytes, including
alveolar macrophages and dendritic cells, express pattern recognition
receptors (PRRs) that recognize specific components of A. fumigatus
cell wall, such as β-glucans and galactomannans49. Toll-like receptors
(TLRs) and C-type lectin receptors (CLRs) are examples of PRRs involved
in this recognition process50. A. fumigatus conidia that escape phagocytosis by patrolling alveolar macrophages activate alveolar epithelia
and innate immune cells to release pro-inflammatory cytokines such
as tumour necrosis factor (TNF) and chemokines51. These cytokines
attract and activate other immune cells, including neutrophils inflammatory monocytes, which are recruited to the site of infection52.
Neutrophil recruitment in the lung occurs in distinct phases. The
activation of interleukin-1α (IL-1α), C-X-C motif chemokine ligand 1
(CXCL1)–CXCL5 signalling in alveolar epithelia induces early neutrophil chemotaxis53,54. A second wave of neutrophil influx is regulated by
other myeloid phagocytes via caspase recruitment domain-containing
protein 9 (CARD9)–CXCL2 signalling53,55. IL-1 signalling and type III
interferons also activate surfactant-producing alveolar epithelial to
release granulocyte–macrophage colony-stimulating factor (GM-CSF),
which enhances antifungal activity of neutrophils at the infection site56.
Autocrine and paracrine release of leukotriene B4 (LTB4)57 and C5a
anaphylatoxin58 further amplify neutrophil responses. Opsonization of
A. fumigatus conidia by PTX3 via complement activation59,60 has a crucial
role in their uptake by phagocytes. Additionally, innate B1a lymphocytes
produce natural IgG antibodies that can opsonize A. fumigatus conidia
and promote neutrophil killing61. CCR2+ inflammatory monocytes
phagocytose A. fumigatus conidia62, enhance neutrophils activity62
and initiate an adaptive immune response upon differentiation to
monocyte-derived dendritic cells (mo-DCs)63. Mo-DCs and neutrophils promote the recruitment of plasmacytoid-derived dendritic cells
(pDCs) via the release of CXCR3 ligands. pDCs64 and type I and type III
interferon signalling65 are essential for optimal antifungal effector
activity of neutrophils via STAT-1 induced transcriptional activation
of the cybb (NOX-2) subunit of NAPDH oxidase complex66. The sensing of cell wall polysaccharides via the reciprocal crosstalk of soluble,
membrane-bound and cytosolic PRRs, shapes physiological immunity
against A. fumigatus. β-glucan-mediated activation of dectin-1 signalling
regulates type I and type III interferon responses against A. fumigatus
in the lung67. A. fumigatus galactomannan can also trigger the release
of pro-inflammatory cytokine via dectin-2–Syk signalling68, which
could serve as an important compensatory host defence mechanism
when β-glucan masking occurs due to lactate or echinocandins69,70.
Review article
Conidia
AM
IL-1R–MyD88
CXCL1
CXCL5
CARD9 signalling
Alveolar epithelium
Fungal killing by AMs
• NADPH–ROS-induced LAP
• Nutritional immunity
Elimination of
germinating fungal cells
• Lateral transfer (metaphorosis)
GM-CSF
NETosis, swarming
NADPH–ROS-dependent killing
PTX3,
C5a,
LTB4
Chemotaxis of
myeloid phagocytes
CXCL2
Ly6Chi monocytes
Neutrophil
CXCL9/10
Type I and III interferons
pDC recruitment
↑ ROS
pDC
↑ ROS
Fungal killing by PMNs
• NADPH–ROS-induced apoptosis
• Antimicrobial peptides
• Nutritional immunity
Fig. 3 | Physiological innate immune response to Aspergillus fumigatus
infection. Inhaled Aspergillus fumigatus conidia are constantly phagocytosed
by alveolar macrophages (AMs) (brown). Recruited neutrophils (red) and
inflammatory Ly6Chi monocytes (yellow) eliminate conidia and germinating
A. fumigatus hyphae that escape from immune surveillance by AMs. Neutrophil
chemotaxis is regulated by sequential waves of chemokine release by epithelia
via interleukin-1 receptor (IL-1R)–MyD88 signalling and myeloid-derived cells
via caspase recruitment domain-containing protein 9 (CARD9) signalling.
Opsonization of fungal conidia by pentraxin 3 (PTX3) and other humoral
immunity effectors such as C-X-C motif chemokine ligand 1 (CXCL1) and CXCL5,
C5a and leukotriene B4 (LTB4), facilitates their uptake by phagocytes.
Plasmacytoid dendritic cells (pDCs) (grey), type I and type III interferons
and granulocyte–macrophage colony-stimulating factor (GM-CSF) released
by alveolar epithelia augment reactive oxygen species (ROS)-dependent
mechanisms of A. fumigatus killing by polymorphonuclear neutrophils (PMNs).
Germinating A. fumigatus conidia that evade phagocytosis are eliminated
by NETosis and coordinated PMN clustering (swarming), which are both
regulated by NADPH oxidase-dependent ROS. ROS-dependent activation
of LC3-associated phagocytosis (LAP) controls the killing of phagocytosed
conidia in AMs. Nutritional immunity further promotes the inhibition of fungal
growth. Furthermore, lateral cell-to-cell transfer (metaphorosis) of germinating
intracellular A. fumigatus conidia is an alternative host defence mechanism to
control invasive fungal growth by alveolar macrophages.
GAG, a signature polysaccharide of A. fumigatus produced during
germination, triggers a variety of immune responses that are specific to
different cell types. On the one hand, GAG has potent anti-inflammatory
properties mediated by the release of IL-1 receptor antagonist, which
promotes fungal pathogenicity during pulmonary infection in immunocompromised mice39,71. On the other hand, GAG induces robust CD56mediated natural killer cell activation that restricts fungal growth and
promotes antifungal responses of neutrophils72. GAG also binds to
ribosomal proteins and activates the NLRP3 inflammasome by inhibiting protein translation in macrophages, thereby conferring protective
immunity against disseminated infection73. Of interest, PTX3, released
by tissue-resident macrophages and infiltering neutrophils, specifically binds GAG on germinating hyphae, as well as surfactant protein D
(SP-D) and the complement proteins C1q and C3b on opsonized
conidia74. This activates a balanced anti-inflammatory response and
promotes infection resolution in the lung. Similarly, serum opsonization of A. fumigatus cell wall chitin shapes the coordinated activation of pro-inflammatory and anti-inflammatory responses in human
peripheral blood mononuclear cells through the activation of the Fcγ
receptor–SyK–PI3K signalling pathway75. From the pathogen perspective, A. fumigatus inhibits the activation of inflammatory signalling
pathways by masking cell wall polysaccharides with its hydrophobic
rodlet protein layer76. The release of surface-associated proteins on
A. fumigatus conidia, including a putative glycosylasparaginase, dampens pro-inflammatory cytokine responses and promote evasion from
the immune system77.
The elimination of fungal conidia is largely dependent on the activation of the nicotinamide adenine dinucleotide phosphate (NADPH)
oxidase complex and the production of reactive oxygen species (ROS)
by phagocytes78. ROS have direct antifungal activity against A. fumigatus
conidia79 and exhibit pleiotropic actions in immune cells, which
remains unexplored at the molecular level. Recently, bruton tyrosine kinase (BTK) was identified as a new regulator of NADPH oxidase
complex assembly via the phosphorylation of p40phox cytoplasmic
subunit and the activation of the GTPAse Rac2 (ref. 80). These studies
provide a mechanistic explanation on the development of invasive
aspergillosis in patients with B cell lymphoid malignancies treated
with BTK inhibitors81. Apart from acting as antifungal effectors, ROS
promote nutritional immunity via copper-mediated cytotoxicity in
the phagosome25. Furthermore, ROS activate LC3-associated phagocytosis (LAP), a pathway that promotes phagosome maturation and
fungal killing82–85.
Nature Reviews Microbiology
Phagosome biology
Following phagocytosis of A. fumigatus conidia, phagolysosome fusion
occurs rapidly, within one hour of infection. In contrast, phagosome
Review article
acidification and killing of intracellular conidia occurs with significant
delay, only after 4 to 6 hours of infection86. Importantly, intracellular
swelling of A. fumigatus is a prerequisite for conidial killing. The exposure of β-glucan and other immunostimulatory polysaccharides during
intracellular germination activates potent inflammatory responses via
C-type lectin receptor–Syk kinase signalling76,87, to promote phagolysosome fusion88 and fungal clearance89. LAP is a pathway mechanistically
distinct from classic (macro)autophagy90. Activation of LAP results in
single membrane LC3 lipidation on the phagosome membrane and has
an important role in immunity against A. fumigatus82–84. Recent studies
reveal that the vacuolar-type ATPase (V-ATPase) is a master regulator
of all single membrane LC3 lipidation processes, including LAP90–92.
Proton imbalance induced by proton consumption during NADPH
oxidase-mediated ROS production in the phagosome lumen recruits
V-ATPase on the phagosome to promote LAP90. The specific V-ATPase
inhibitor Bafilomycin completely abrogates the killing of A. fumigatus
conidia inside alveolar macrophages86.
Intercellular crosstalk facilitates the elimination of germinating
hyphae of A. fumigatus through various pathways, including the lateral
transfer of conidia between alveolar macrophages via calcineurin
signalling93, the release of neutrophil extracellular traps (NETs)94 and
the coordinated clustering (swarming) of neutrophil through the
autocrine release of LTB495,96. The killing of hyphae is largely mediated
by ROS-dependent mechanisms through the activation of NADPH oxidase and myeloperoxidase96,97. Interestingly, the deletion of the C-type
lectin inhibitory receptor MICL, which directly recognizes DNA in NETs,
resulted in protective immunity against disseminated aspergillosis
through increased ROS–protein arginine deiminase 4 (PAD4) production, which in turn triggers NETs formation98. Nutritional immunity via
calprotectin-mediated zinc and manganese chelation facilitates the
inhibition of hyphal growth99. Iron acquisition during germination
has a crucial role in the pathogenicity of A. fumigatus and is mediated
via the siderophore ferricrocin100, which is an appealing therapeutic
target101. Accordingly, iron overload is a well-established risk factor for
invasive aspergillosis101,102. In an animal model of corneal fungal infection, dectin-1-mediated IL-6 production orchestrated hepcidin release
and contributed to nutritional immunity against A. fumigatus. At the
molecular level, the release of lipocalin-1 by neutrophils neutralizes
the activity of A. fumigatus siderophores101. Nonetheless, the mechanisms that regulate iron limitation in A. fumigatus phagosome remain
unexplored. Importantly, A. fumigatus can evade neutrophil-killing
mechanisms by producing certain enzymes and toxins that impair
neutrophil function78,103. Clinical observations in patients with congenital immunodeficiencies104 (Box 1) and experiments in mice devoid of
lymphoid cells (Rag2−/− Fcγ−/−) suggest that protective immunity against
A. fumigatus is largely conferred by professional phagocytes65. However,
the substantial role of adaptive immunity and intercellular crosstalk in
fine-tuning phagocyte activity has become increasingly recognized105.
Adaptive immunity
T cell-mediated immunity could play an important role in immunity
against A. fumigatus immunity against, especially in patients with
complex acquired immune defects61,106–108. Upon activation, CD4+
T cells differentiate into subsets such as T helper (TH) 1, TH2 and TH17
cells, which produce different cytokines and play distinct roles in the
immune response109. TH1 cells produce interferon-γ (IFNγ) and help
activate macrophages to kill the fungus110. TH2 cells produce cytokines
like IL-4 and IL-13, promoting allergic responses111. TH17 cells produce IL-17 and IL-22, which are involved in recruiting and activating
Nature Reviews Microbiology
neutrophils112. On the other hand, a causative role of exuberant inflammatory immune responses mediated by overactive T cells or neutralizing auto-antibodies produced by B cells has been demonstrated in
various forms of fungal disease113,114.
Evasion of host immunity
A. fumigatus conidia have evolved several immune evasion and immune
adaptation strategies for surviving in the human host. Here, we will
highlight two examples including escape from the phagosome and
the production of toxins by A. fumigatus. The conidial surface comprises components such as hydrophobin76,89 and melanin115, which
mask immunogenic features of the cell wall from immune recognition.
Moreover, melanin was found to deplete selected chemokines from the
extracellular space to suppress the inflammatory response116. Melanin
also interferes with the production of antifungal ROS by inhibiting
Ca2+–calmodulin signalling and regulating NADPH oxidase complex
activation83. This in turn blocks phagosome maturation117 and inhibits
LC3-associated phagocytosis that is required for the intracellular killing
of conidia by myeloid phagocytes84. Conidial susceptibility to NADPH
oxidase-dependent killing was found to rely also on the expression and
activity of fungal BIR1, an anti-apoptotic protein that hinders the activation of programmed cell death pathways in engulfed conidia to promote
virulence79. More recently, the HscA protein in the conidial surface was
found to anchor to host p11(S100A10) on phagosomes and drive the
sorting of ingested conidia to the non-degradative pathway, allowing
fungal escape and transfer between cells118. Comparison of the conidial surface proteome of A. fumigatus with that of two closely related
non-pathogenic species has revealed additional proteins involved in
fungal evasion and modulation of host immunity, including a putative
glycosylasparaginase capable of modulating IL-1β secretion77. The
growth of A. fumigatus is also associated with the release of soluble GAG,
which in addition to its adhesive properties, can also induce neutrophil
apoptosis119 and mediate resistance to NETs120. The secondary metabolism of A. fumigatus is also responsible for secreting several other molecules that subvert the immune response, such as the toxic metabolites
gliotoxin, fumagillin, endocrocin, fumigaclavines, fumiquinazolines,
trypacidin and helvolic acid, among others121. Different mechanisms
have been proposed by which these metabolites impact interactions
with the immune system and disease. Among the most relevant are
the inhibition of phagocytosis, the production of pro-inflammatory
cytokines and neutrophil chemotaxis122. Gliotoxin can impair the
function, proliferation and survival of multiple immune cell types,
including neutrophils and macrophages123, with its production relying on the immune status of the host124. More specifically, gliotoxin
was recently shown to exhibit immunomodulatory properties in macrophages by either selectively suppressing the production of the lipid
mediator leukotriene (LT)B4 in activated cells or by priming them to
drive prostaglandin biosynthesis125. Deletion of GliP, which catalyses
the initial step in gliotoxin biosynthesis, was found to decrease fungal virulence in non-neutropenic mice, an observation that pinpoints
neutrophils as a major cellular target of gliotoxin124. Given its toxic
nature, A. fumigatus has evolved mechanisms to withstand gliotoxin
and transcription factors such as RglT and GliT have recently emerged
as master regulators of genes involved in gliotoxin synthesis126. The
mitogen-activated protein kinase MpkA has been shown to be essential
for gliotoxin production and self-protection127. It achieves this by physically interacting with GliT and the GtmA methyltransferase, and regulating the cellular compartmentalization of gliotoxin to prevent cell
damage. Besides gliotoxin, fumagillin is a monoterpenoid toxin that
Review article
stimulates germination and hyphal branching of A. fumigatus, and
that is also required for virulence in vivo128. Oxylipins, a large group
of oxidized fatty acids and their derivatives, are also secreted by
A. fumigatus and function as signalling molecules in developmental processes and virulence129. One such fungal oxylipin, 5,8-diHODE, has been
found to induce hyphal branching and cellular differentiation130. More
recently, an oxylipin signal mediated by the synthesis of 5,8-diHODE
through the fungal oxygenase PpoA and dependent on the transcription factor ZfpA was shown to confer protection against tip lysis by
echinocandins131. Importantly, fungal oxylipins such as 8-HODE and
5,8-diHODE share structural similarities with other lipid mediators
known to act as ligands of the host G-protein-coupled receptor G2A132.
Although the involvement of fungal oxylipins in G2A activity remains
unexplored, G2A-deficient mice exhibit improved survival during
experimental aspergillosis due to enhanced neutrophil recruitment
and increased production of inflammatory mediators132. Collectively,
these observations suggest that conserved oxylipin-directed signals
play a pivotal role in protecting against echinocandin damage and
possibly in modulating host immunity.
Virus-associated invasive aspergillosis
Invasive pulmonary aspergillosis typically occurs in severely immunocompromised patients, such as those with prolonged severe neutropenia, those taking immunosuppressants, or with specific inherited
errors of immunity133,134. However, following the 2009 H1N1 pandemic,
influenza-associated pulmonary aspergillosis (IAPA) was recognized
as a viral–fungal co-infection in patients with supposedly normal
pre-existing immunity135,136. During the pandemic, COVID-19-associated
pulmonary aspergillosis (CAPA) was also identified in critically ill
patients with COVID-19 (ref. 137). Immune dysregulation in IAPA and
CAPA is a complex phenomenon that involves interactions between the
virus, A. fumigatus, the microbiome and the host138 (Fig. 4). Although
the underlying host pathology and interactions with the virus seem
to differ139, it has been proposed in both IAPA and CAPA that the virus
and its associated immunopathology leads to defects in antifungal
immunity140,141. Moreover, a recent in vitro model showed that the influenza virus and A. fumigatus directly interact142. Although this interaction is currently under investigation, it is tempting to speculate that it
involves sialic acids interactions, similar to the way host immune cell–
A. fumigatus interactions occur through sialic acids expressed by
A. fumigatus, neuraminidases present in influenza and the host receptor
Siglec-15 (ref. 143). In addition, reduced expression of pro-inflammatory
and interferon pathways in the bronchoalveolar lavage fluid of patients
with IAPA or CAPA was observed, underscoring the altered immune
response in IAPA and CAPA144. Respiratory viral infection leads to epithelial damage, creating an environment favourable for A. fumigatus
to become tissue-invasive, as shown both in murine lung pathology
and human tracheobronchial biopsies144. Moreover, epithelial damage
also leads to impaired mucociliary clearance and decreased epithelial
production of chemokines and pro-inflammatory mediators, increasing
the susceptibility to a higher burden of A. fumigatus spores in the lower
respiratory tract53. In the lungs of patients with severe viral pneumonia,
immune cells playing a role in phagocytosis and killing of conidia can be
negatively affected. Alveolar macrophages are depleted and the influx
of hyperinflammatory monocytes that do not completely differentiate
into well-functioning macrophages leads to reduced phagocytosis of
fungal conidia145–147. Transcriptional immuno-metabolic disturbances,
which suggests potential defects in killing conidia, have been observed
in monocytes and macrophages from the bronchoalveolar lavage fluid
Nature Reviews Microbiology
of patients with CAPA, compared with patients with COVID-19 but
without CAPA107. Reduced immune cell responses to IFNγ observed in
patients with IAPA and CAPA, and impaired phagolysosomal maturation
observed in mice with IAPA, might further affect the conidial killing
capacity of phagocytes144,148. On the other hand, partial or complete
genetic ablation of early, robust influenza-induced IFNγ production
protected influenza mice from early VAPA by restoring a defective
TH17 immune response and LAP-dependent killing of conidia, highlighting the need to maintain a balanced immune response during an
infection149.
The exact role of neutrophils in VAPA remains to be determined. Autopsy from patients with IAPA and CAPA revealed that
neutrophils are abundant in human lung lavages and that neutrophilic necrotizing inflammation colocalizes with impeded fungal
growth, whereas areas without neutrophils showed high fungal
burden150. Recent animal data showed that both ROS-dependent and
ROS-independent pathways of the fungal host response are impaired
by viral infection148,151. In line, impaired neutrophil degranulation and
LC3-phagolysosome-associated transcriptional changes in critically
ill patients with IAPA were identified144. Patients with CAPA also show
significantly increased production of NETs compared with patients
with COVID-19 and without aspergillosis, and patients with CAPA that
present high NET levels have a significantly lower mortality107. Several
polymorphisms have been associated with VAPA and might provide
new opportunities for diagnostics and therapeutic strategies for VAPA
(Table 1). In observational studies, in which the fraction of all included
patients who received bronchoalveolar lavage sampling is higher than
50%, the reported incidence of VAPA is approximately 20% with a large
worldwide variation139,152. While various reasons may underlie the variations in reported VAPA incidence, numerous VAPA cases are likely to
go undetected and, therefore, untreated. Clear data on the mortality
rate attributable to VAPA is lacking. However, it is suggested that when
antifungal therapy initiation is delayed the mortality is higher, implying
that VAPA should be detected early and treated promptly153. The cornerstone for the management of VAPA is the combination of an early,
aggressive diagnostic approach and the administration of effective and
safe antifungals. Although prevention of VAPA using antifungal prophylaxis is an appealing approach, there are major caveats. A multicentric
international pilot randomized controlled trial, which randomized
patients with severe influenza to receive posaconazole prophylaxis
upon admission in the intensive care unit (ICU) versus standard of
care, found no significant difference in the incidence of IAPA in the
prophylaxis group154. IAPA develops early and is often present upon ICU
admission, making prophylaxis too late for most patients who are likely
to develop the disease154. CAPA is different, as it presents with a delay
of approximately one week between ICU admission and its diagnosis.
Several observational studies have pointed out a potential benefit of
antifungal prophylaxis in CAPA, especially for patients who are deeply
immunocompromised, such as patients with solid organ transplant and
who are admitted to the ICU with severe viral pneumonia155,156. VAPA is a
new entity which needs more attention and research to improve its high
morbidity and mortality. Lung bacterial communities also play a critical role in aspergillosis. For example, immunocompromised patients
with invasive pulmonary aspergillosis were recently found to exhibit
a markedly decreased bacterial diversity in the lower airways, which
influenced local immune profiles and disease outcomes157. However,
despite its clinical relevance, the potential of the lung microbiota as
a diagnostic and therapeutic target in aspergillosis remains largely
unexplored.
Review article
CAPA
IAPA
• Late in ICU stay
• Corticosteroids
• NETosis important
• Tissue-invasion
• Early in ICU stay
• Decreased IFNγ signalling and LAP
• Hampered neutrophil functions
• Tissue-invasion and angio-invasion
NET production
Conidia
Neutrophil
Hyphae
Alveolar
macrophage
Alveolar space
Alveolar epithelium
Interstitial space
Blood vessel
Angioinvasion
Fig. 4 | Influenza-associated and COVID-19-associated pulmonary
aspergillosis. Influenza-associated pulmonary aspergillosis (IAPA) and COVID19-associated pulmonary aspergillosis (CAPA) share similarities but are also
distinct in several features. Incidences probably lie around 10–20% in critically
ill patients and, despite antifungal therapy, both conditions are associated
with an overall mortality rate of approximately 50%, being double compared
with patients with severe viral pneumonia without virus-associated pulmonary
aspergillosis (VAPA). While IAPA occurs within the first few days after intensive
care unit (ICU) admission or even at the time of ICU admission, CAPA tends to
occur later, typically between 3 and 9 days after ICU admission. Angioinvasion of
Aspergillus fumigatus hyphae, reflected by positivity of serum galactomannan,
is rarely detected in VAPA, but more often in IAPA than in CAPA. CAPA incidence
is associated with the use of corticosteroids and tocilizumab as a treatment
for COVID-19, while in influenza patients, prolonged use of corticosteroids
Strategies to survive azole exposure
Similar to host genetics and different host responses to infection, there
are also many strains of A. fumigatus with diverse genetics and differing
induced responses, which can impact the course of the disease. In this
section, we will focus on strains in the context of antifungal therapy.
A. fumigatus may persist in the host in the presence of antifungal
azoles (Fig. 5). The formation of biofilms may enhance the resistance to
Nature Reviews Microbiology
before ICU admission has also been linked to an increased incidence of IAPA.
The pathophysiology of VAPA is complex and involves interactions between
the virus, A. fumigatus, the microbiome and the host, again showing similar
but also distinct features between IAPA and CAPA. Interestingly, CAPA patients
show higher neutrophil extracellular traps (NET) production in the lungs
compared with COVID-19 patients without CAPA, while CAPA patients with lower
bronchioalveolar lavage (BAL) NET levels had a reduced 90-day survival. On the
other hand, several genes linked to LC3-associated phagocytosis (LAP), a noncanonical form of autophagy implied in phagolysosomal fusion and subsequent
killing of A. fumigatus conidia, were downregulated in BAL fluid of IAPA patients
compared with patients presenting only influenza. Moreover, transcription of
genes related to neutrophil degranulation was significantly downregulated in
BAL fluid of patients with IAPA compared with patients with influenza only, but
this was not the case in patients with COVID-19. IFNγ, interferon-γ.
antifungals. Other mechanisms may include metabolic quiescent cells
that survive antifungal exposure by not metabolizing the drug158 or
the development of a stress response involving the upregulation of
multiple pathways that allow the fungus to survive. These pathways
may involve sterol metabolism, siderophore-mediated iron acquisition and ATP-binding cassette (ABC) and major facilitator superfamily
(MFS) transmembrane transporters, which increase efflux of cytotoxic
Review article
Table 1 | Single-nucleotide polymorphisms in immunity genes associated with viral-associated pulmonary aspergillosis
Gene
SNP(s)
Association
with IPA
Major evidence linking gene and/or SNP to VAPA
Refs.
CLEC7A
rs16910526 (p.Y238X)
Yes
Lower BAL expression of CLEC7A is associated with increased mortality after IAPA
177–180
CXCL10
rs1554013, rs3921,
rs4859588
Yes
Patients with IAPA have lower expression of CXCL10 than those with influenza alone
144,181
IFNG
rs2069705
Yes
Downregulation of IFNγ signalling in patients with IAPA and CAPA compared with those with the
viral infection alone
The rs2069705 SNP enhanced cytokine production and the fungicidal activity of macrophages
144,182
IL1B
rs16944
Yes
Patients with IAPA exhibit a blunted transcriptional response to IL-1β compared with those with
influenza alone
144,183
LGALS3
?
Not reported
Patients with IAPA have lower expression of LGALS3 than those with influenza alone
Lower BAL expression is associated with increased mortality after IAPA
144,180
PTX3
rs2305619
rs3816527 (p.D48A)
Yes
PTX3 coordinates the interaction between neutrophils and B1a cells towards the production
of natural antibodies
Neutrophils regulate the production of natural IgG against Aspergillus fumigatus by B1a cells
in IAPA
SIGLEC15
rs2919643 (p. F273I)
Not reported
Lower BAL expression of SIGLEC15 is associated with increased mortality after IAPA
Antifungal activity of immune cells is dampened by SIGLEC15 silencing
The F273I SNP impairs cytokine production after fungal stimulation
143,180
TLR2
rs5743708 (p.R753Q)
Yes
Patients with IAPA have lower expression of TLR2 than those with influenza alone
144,185
60,61,184
BAL, bronchoalveolar lavage; CAPA, COVID-19-associated pulmonary aspergillosis; CXCL10, C-X-C motif chemokine ligand 10; IAPA, influenza-associated pulmonary aspergillosis; IFNγ,
interferon-γ; IL-1β, interleukin-1β; IPA, invasive pulmonary aspergillosis; PTX3, pentraxin-related 3 protein; TLR2, Toll-like receptor 2; VAPA, virus-associated pulmonary aspergillosis.
compounds159. These stress responses are typically observed in a small
fraction of cells within a population and may be transient158. Antifungal
drug resistance can also arise from stable or inherited point mutations,
as well as insertions or deletions in target genes. Mutations that confer
antifungal drug resistance arise spontaneously within a population
of cells. When the population is exposed to an antifungal, the mutated
resistant cells will survive better than those cells without the mutation
(wild-type population), becoming dominant in the population160. This
process of resistance selection may occur in any environment that supports the growth and reproduction of A. fumigatus, although the ability
to generate genetic variation depends on the reproduction mode.
A study reported the role of sexual reproduction in the environment
in the development of multidrug-resistant haplotypes in the Cyp51A
gene5,161. Sexual reproduction is highly unlikely to take place in the
human host due to the requirement of opposing mating types and the
relatively long time needed to develop cleistothecia (closed fruit bodies
that contain sexual ascospores). Parasexual recombination is another
mechanism for fungi to transfer genetic material, without the need to
develop specific structures. Following the fusion of compatible hyphae,
a heterokaryon is formed with a diploid nucleus, which enables mitotic
recombination162. Parasexual recombination was shown to occur in
people with cystic fibrosis, where A. fumigatus genotypes may persist
over many years in the lung163. Diploid formation was associated with
increased frequency of SNPs in persistent A. fumigatus isolates and
preceded the recovery of a voriconazole-resistant isolate, suggesting a possible role in resistance development. A third reproduction
mode is asexual reproduction, characterized by mitotic mutations
and replication slippage or unequal sister chromatid recombination
at low frequency. This reproduction mode is abundantly present in the
environment and may occur in human hosts when specific conditions
are present164. Sporulation may occur in cavitary pulmonary disease
(aspergilloma) or during invasive A. fumigatus tracheobronchitis,
Nature Reviews Microbiology
where the infection mainly affects the airways. Spontaneous mutations, some of which may confer azole resistance, are likely to occur
when the population size is high. During antifungal therapy, host azole
resistance selection affects a single host, as A. fumigatus diseases rarely
spread from human to human. This contrasts with environmental
resistance selection, where exposure to azole fungicides active against
A. fumigatus has been found to migrate globally165. Various environmental hotspots for resistance selection, where resistant spores accumulate,
have been identified166. The Cyp51A gene is the most common target
for resistance mutations, including SNPs sometimes combined with
tandem repeats (TR) in the gene promoter, such as TR34/L98H and
TR46/Y121F/T289A167. These mutations confer resistance to azole fungicides, but show cross-resistance to the medical azoles, including itraconazole, voriconazole, posaconazole and isavuconazole168. Ambient
air was shown to contain ~4% of tebuconazole-resistant A. fumigatus
spores, indicating that people inhale a mixture of azole-susceptible
and azole-resistant spores169. Although most spores originate through
asexual recombination and are clonal, airborne spores are likely to
arise from multiple sources resulting in a genetically highly diverse
population. Linking patient cases to environmental sources using genotyping has proven very difficult, even during hospital outbreaks. As
a consequence, pulmonary invasive aspergillosis may present with
genetically mixed infection, including azole-resistant A. fumigatus
diseases in azole-naïve patients170. Pulmonary lesions may have developed from an azole-susceptible spore, while other lesions may have
originated from azole-resistant conidia. Azole resistance is associated
with treatment failure and mortality, both in patients with chronic
pulmonary aspergillosis and those with invasive pulmonary aspergillosis. Survival estimates of 7 clinical trials evaluating first-line
voriconazole for invasive aspergillosis were 71.8–80% at 6 weeks
and 59–70.2% at 12 weeks171–173. However, the survival of patients with
voriconazole-resistant invasive aspergillosis was 53–57.7% at 6 weeks
Review article
and 42.3–43% at 12 weeks. lower compared with the survival of patients
with voriconazole-susceptible invasive aspergillosis and in the range of
rates observed in the pre-voriconazole era174,175. This demonstrates that
voriconazole resistance has major implications for patient survival and
requires immediate treatment adjustment when diagnosed. Managing
the dual use of antifungal compounds with the same modes of action
in both agriculture and medicine is a key goal for compounds with new
modes of action. Improving the diagnosis and surveillance of resistance, as well as antifungal stewardship in agriculture, horticulture and
clinical settings, remain critical to manage and reduce azole resistance
selection in A. fumigatus.
Conclusions and outlook
This review describes the mechanisms by which A. fumigatus evades
and adapts to the hostile environment presented by its host. Through
Genetic variation
Occurrence
strategies such as molecule masking, immune response manipulation
and modulation of gene expression, A. fumigatus effectively circumvents host defences, posing notable challenges to infection treatment
and control. To expand the arsenal of antifungal drugs, it is crucial to
understand these evasion tactics, especially in the human host, in order
to develop effective targets for treating A. fumigatus infections. Another
key component to advance the treatment of invasive aspergillosis is the
elucidation of the immune response required to combat the infection.
A deeper understanding of specialized phagosome responses, which
play a pivotal role in controlling the intracellular growth of the fungus,
is needed. This includes understanding the role of WD40-mediated
single membrane LC3 lipidation in A. fumigatus immunity and how we
can modulate this process during infection176. We argue that by targeting specific evasion strategies and modulating host immune responses
with host-directed therapy, clinicians will be able to enhance treatment
Genetic
variation
Predominant mutations
in Cyp51A
Selection sites
Asexual reproduction
Azole
fungicide
TR34 and TR46
Hotspot
Conidia
Medical
azole
Spontaneous
mutation
SNPs (e.g., G54,
P216 and M220)
Cavity
Conidiophore
Parasexual reproduction
?
Hyphal
fusion
Diploidisation
via nuclear
fusion
Sexual reproduction
mat 1-1
Haploidisation
following mitotic
recombination
Unknown
Azole
fungicide
TR34 and TR46
Biofilm
Ascospore
mat 1-2
Mating types
Medical
azole
Hotspot
Meiotic recombination
Cleistothecium
Fig. 5 | Ability of Aspergillus fumigatus to generate genetic variation
according to the reproduction mode, frequency and potential sites for
resistance selection. The figure shows three modes of reproduction. Asexual
reproduction is very frequent in the environment, but as the offspring is
clonal, the genetic variation is low. Asexual reproduction occurs abundantly
in the environment, and may also occur in human infection, especially when a
cavity is present. Mutations in the Cyp51A gene, which encodes for a 14-α sterol
demethylase involved in ergosterol synthesis for the fungal cell membrane,
commonly include the TR34 and TR46 resistance mutations. In the human
host, asexual reproduction can occur in cavitary lesions and selection of
resistance may arise from long-term treatment with medical azoles. Resistance
mutations commonly involve SNPs such as G54, M220 and P216. Parasexual
reproduction requires two compatible hyphae to fuse, and therefore the
Nature Reviews Microbiology
variation achieved through this reproduction mode is limited. The occurrence
and frequency in nature are unknown, but it has been shown to occur in patients
with chronic A. fumigatus lung disease (chronic pulmonary aspergillosis) and
colonization (cystic fibrosis). In these conditions, A. fumigatus exists mainly
as hyphae in a biofilm and mitotic recombination enables the fungus to adapt
to environmental stress and persist in the host environment. Thus far, there
are no specific resistance mutations associated with this reproduction mode.
Sexual reproduction requires opposing mating types and takes several weeks to
complete, which makes it highly unlikely that this reproduction mode occurs in
the human host. As two genetically parent strains are involved, this is the most
effective way for A. fumigatus to generate genetic variation, as each ascospore
will contain genetic information from each of the parents.
Review article
efficacy and improve patient outcomes in A. fumigatus-related diseases
in the near future. Although these concepts have been studied over
the last decades and substantial progress has been made, as reviewed
here, new challenges are on the rise. A notable highlight of this review
is the exploration of VAPA, a critical condition where A. fumigatus infection complicates severe pulmonary viral infections. This emerging
phenomenon underscores the complex interplay between viral and
fungal pathogens, necessitating a nuanced understanding for effective
management. But many questions remain unanswered. How exactly
do viral infections predispose to aspergillosis? Will vaccination against
viral infection lower the incidence of VAPA? Why is there a difference
in the incidence of VAPA between different countries? Is this due to
differences in the environment?
In this review, we discussed the alarming rise of azole resistance in A. fumigatus, a trend with serious implications for treatment outcomes. By shedding light on this evolving challenge,
we underline the urgency of developing alternative strategies to
combat drug-resistant strains. We need more insight into how
azole resistance arises, not only to deepen our understanding of
A. fumigatus–host interactions but also to offer valuable perspectives for approaches that can counteract antifungal drug resistance.
The field of A. fumigatus biology and host–pathogen interaction in
relation to disease is dynamic and challenging. We are on the brink
of a transformative era in antifungal research and immunotherapy
trials that promises to revolutionize the management of A. fumigatus infections, ultimately leading to more effective therapies and
improved patient care.
Published online: xx xx xxxx
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Wang, F. et al. Transcription in fungal conidia before dormancy produces phenotypically
variable conidia that maximize survival in different environments. Nat. Microbiol. 6,
1066–1081 (2021).
Blatzer, M. & Latge, J. P. Fungal spores are future-proofed. Nat. Microbiol. 6, 979–980 (2021).
This study shows that dormant fungal spores exhibit diversity and anticipate future
conditions by activating transcriptional processes influenced by their developmental
environment.
Taha, M. P., Pollard, S. J., Sarkar, U. & Longhurst, P. Estimating fugitive bioaerosol releases
from static compost windrows: feasibility of a portable wind tunnel approach.
Waste Manag. 25, 445–450 (2005).
O’Gorman, C. M., Fuller, H. & Dyer, P. S. Discovery of a sexual cycle in the opportunistic
fungal pathogen Aspergillus fumigatus. Nature 457, 471–474 (2009).
Auxier, B. et al. The human fungal pathogen Aspergillus fumigatus can produce the
highest known number of meiotic crossovers. PLoS Biol. 21, e3002278 (2023).
Fang, W. & Latge, J. P. Microbe profile: Aspergillus fumigatus: a saprotrophic and
opportunistic fungal pathogen. Microbiology 164, 1009–1011 (2018).
Ries, L. N. A., Beattie, S., Cramer, R. A. & Goldman, G. H. Overview of carbon and nitrogen
catabolite metabolism in the virulence of human pathogenic fungi. Mol. Microbiol. 107,
277–297 (2018).
Wiesner, D. L. et al. Club cell TRPV4 serves as a damage sensor driving lung allergic
inflammation. Cell Host Microbe 27, 614–628.e616 (2020).
Griffiths, J. S. et al. Differential susceptibility of Dectin-1 isoforms to functional
inactivation by neutrophil and fungal proteases. FASEB J. 32, 3385–3397 (2018).
Beattie, S. R. et al. Filamentous fungal carbon catabolite repression supports metabolic
plasticity and stress responses essential for disease progression. PLoS Pathog. 13,
e1006340 (2017).
Ries, L. N. A. et al. Aspergillus fumigatus acetate utilization impacts virulence traits and
pathogenicity. mBio 12, e0168221 (2021).
Krappmann, S. et al. The Aspergillus fumigatus transcriptional activator CpcA
contributes significantly to the virulence of this fungal pathogen. Mol. Microbiol. 52,
785–799 (2004).
Amich, J. & Bignell, E. Amino acid biosynthetic routes as drug targets for pulmonary
fungal pathogens: what is known and why do we need to know more? Curr. Opin. Microbiol.
32, 151–158 (2016).
Zelante, T. et al. Aspergillus fumigatus tryptophan metabolic route differently affects host
immunity. Cell Rep. 34, 108673 (2021).
Barber, A. E. et al. Aspergillus fumigatus pan-genome analysis identifies genetic variants
associated with human infection. Nat. Microbiol. 6, 1526–1536 (2021).
Nature Reviews Microbiology
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
Mirhakkak, M. H. et al. Genome-scale metabolic modeling of Aspergillus fumigatus
strains reveals growth dependencies on the lung microbiome. Nat. Commun. 14, 4369
(2023).
Misslinger, M., Hortschansky, P., Brakhage, A. A. & Haas, H. Fungal iron homeostasis with
a focus on Aspergillus fumigatus. Biochim. Biophys. Acta Mol. Cell Res. 1868, 118885
(2021).
Schrettl, M. et al. SreA-mediated iron regulation in Aspergillus fumigatus. Mol. Microbiol.
70, 27–43 (2008).
Schrettl, M. et al. HapX-mediated adaption to iron starvation is crucial for virulence of
Aspergillus fumigatus. PLoS Pathog. 6, e1001124 (2010).
Gsaller, F. et al. The Janus transcription factor HapX controls fungal adaptation to both
iron starvation and iron excess. EMBO J. 33, 2261–2276 (2014).
Yap, A., Volz, R., Paul, S., Moye-Rowley, W. S. & Haas, H. Regulation of high-affinity iron
acquisition, including acquisition mediated by the iron permease FtrA, is coordinated by
AtrR, SrbA, and SreA in Aspergillus fumigatus. mBio 14, e0075723 (2023).
Amich, J. et al. The ZrfC alkaline zinc transporter is required for Aspergillus fumigatus
virulence and its growth in the presence of the Zn/Mn-chelating protein calprotectin.
Cell. Microbiol. 16, 548–564 (2014).
Moreno, M. A. et al. The regulation of zinc homeostasis by the ZafA transcriptional
activator is essential for Aspergillus fumigatus virulence. Mol. Microbiol. 64, 1182–1197
(2007).
Vicentefranqueira, R. et al. The transcription factor ZafA regulates the homeostatic and
adaptive response to zinc starvation in Aspergillus fumigatus. Genes https://doi.org/
10.3390/genes9070318 (2018).
Wiemann, P. et al. Aspergillus fumigatus copper export machinery and reactive oxygen
intermediate defense counter host copper-mediated oxidative antimicrobial offense.
Cell Rep. 19, 1008–1021 (2017).
Lim, F. Y. et al. Fungal isocyanide synthases and xanthocillin biosynthesis in Aspergillus
fumigatus. mBio https://doi.org/10.1128/mBio.00785-18 (2018).
Steinbach, W. J. et al. Calcineurin controls growth, morphology, and pathogenicity in
Aspergillus fumigatus. Eukaryot. Cell 5, 1091–1103 (2006).
Cramer, R. A. Jr. et al. Calcineurin target CrzA regulates conidial germination, hyphal
growth, and pathogenesis of Aspergillus fumigatus. Eukaryot. Cell 7, 1085–1097 (2008).
de Castro, P. A. et al. Aspergillus fumigatus calcium-responsive transcription factors
regulate cell wall architecture promoting stress tolerance, virulence and caspofungin
resistance. PLoS Genet. 15, e1008551 (2019).
Grahl, N. et al. In vivo hypoxia and a fungal alcohol dehydrogenase influence the
pathogenesis of invasive pulmonary aspergillosis. PLoS Pathog. 7, e1002145 (2011).
Grahl, N., Dinamarco, T. M., Willger, S. D., Goldman, G. H. & Cramer, R. A. Aspergillus
fumigatus mitochondrial electron transport chain mediates oxidative stress homeostasis,
hypoxia responses and fungal pathogenesis. Mol. Microbiol. 84, 383–399 (2012).
Ben-Ami, R., Lewis, R. E., Leventakos, K. & Kontoyiannis, D. P. Aspergillus fumigatus
inhibits angiogenesis through the production of gliotoxin and other secondary
metabolites. Blood 114, 5393–5399 (2009).
Gresnigt, M. S. et al. Reducing hypoxia and inflammation during invasive pulmonary
aspergillosis by targeting the interleukin-1 receptor. Sci. Rep. 6, 26490 (2016).
Kowalski, C. H. et al. Heterogeneity among isolates reveals that fitness in low oxygen
correlates with Aspergillus fumigatus virulence. mBio https://doi.org/10.1128/mBio.01515-16
(2016).
Willger, S. D. et al. A sterol-regulatory element binding protein is required for cell polarity,
hypoxia adaptation, azole drug resistance, and virulence in Aspergillus fumigatus.
PLoS Pathog. 4, e1000200 (2008).
Chung, D. et al. ChIP-seq and in vivo transcriptome analyses of the Aspergillus fumigatus
SREBP SrbA reveals a new regulator of the fungal hypoxia response and virulence.
PLoS Pathog. 10, e1004487 (2014).
Le Mauff, F. & Sheppard, D. C. Understanding Aspergillus fumigatus
galactosaminogalactan biosynthesis: a few questions remain. Cell Surf. 9, 100095
(2023).
Speth, C., Rambach, G., Lass-Florl, C., Howell, P. L. & Sheppard, D. C.
Galactosaminogalactan (GAG) and its multiple roles in Aspergillus pathogenesis.
Virulence 10, 976–983 (2019).
Gravelat, F. N. et al. Aspergillus galactosaminogalactan mediates adherence to host
constituents and conceals hyphal β-glucan from the immune system. PLoS Pathog. 9,
e1003575 (2013).
Lee, M. J. et al. Deacetylation of fungal exopolysaccharide mediates adhesion and
biofilm formation. mBio 7, e00252–00216 (2016).
Bamford, N. C. et al. Ega3 from the fungal pathogen Aspergillus fumigatus is an endo-α1,4-galactosaminidase that disrupts microbial biofilms. J. Biol. Chem. 294, 13833–13849
(2019).
Kerkaert, J. D. et al. An alanine aminotransferase is required for biofilm-specific resistance
of Aspergillus fumigatus to echinocandin treatment. mBio 13, e0293321 (2022).
Morelli, K. A., Kerkaert, J. D. & Cramer, R. A. Aspergillus fumigatus biofilms: toward
understanding how growth as a multicellular network increases antifungal resistance
and disease progression. PLoS Pathog. 17, e1009794 (2021).
Kowalski, C. H., Morelli, K. A., Schultz, D., Nadell, C. D. & Cramer, R. A. Fungal biofilm
architecture produces hypoxic microenvironments that drive antifungal resistance.
Proc. Natl Acad. Sci. USA 117, 22473–22483 (2020).
Kowalski, C. H. et al. Fungal biofilm morphology impacts hypoxia fitness and disease
progression. Nat. Microbiol. 4, 2430–2441 (2019).
Review article
46. Kowalski, C. H., Morelli, K. A., Stajich, J. E., Nadell, C. D. & Cramer, R. A. A heterogeneously
expressed gene family modulates the biofilm architecture and hypoxic growth of
Aspergillus fumigatus. mBio https://doi.org/10.1128/mBio.03579-20 (2021).
47. Westphalen, K. et al. Sessile alveolar macrophages communicate with alveolar
epithelium to modulate immunity. Nature 506, 503–506 (2014).
48. Neupane, A. S. et al. Patrolling alveolar macrophages conceal bacteria from the immune
system to maintain homeostasis. Cell 183, 110–125.e111 (2020).
49. Hatinguais, R., Willment, J. A. & Brown, G. D. PAMPs of the fungal cell wall and
mammalian PRRs. Curr. Top. Microbiol. Immunol. 425, 187–223 (2020).
50. Plato, A., Hardison, S. E. & Brown, G. D. Pattern recognition receptors in antifungal
immunity. Semin. Immunopathol. 37, 97–106 (2015).
51. Heung, L. J., Wiesner, D. L., Wang, K., Rivera, A. & Hohl, T. M. Immunity to fungi in the
lung. Semin. Immunol. 66, 101728 (2023).
52. Becker, K. L., Ifrim, D. C., Quintin, J., Netea, M. G. & van de Veerdonk, F. L. Antifungal
innate immunity: recognition and inflammatory networks. Semin. Immunopathol. 37,
107–116 (2015).
53. Jhingran, A. et al. Compartment-specific and sequential role of MyD88 and CARD9
in chemokine induction and innate defense during respiratory fungal infection.
PLoS Pathog. 11, e1004589 (2015).
54. Caffrey, A. K. et al. IL-1α signaling is critical for leukocyte recruitment after pulmonary
Aspergillus fumigatus challenge. PLoS Pathog. 11, e1004625 (2015).
55. Rieber, N. et al. Extrapulmonary Aspergillus infection in patients with CARD9 deficiency.
JCI Insight 1, e89890 (2016).
56. Mills, K. A. M. et al. GM-CSF-mediated epithelial-immune cell crosstalk orchestrates
pulmonary immunity to Aspergillus fumigatus. Sci. Immunol. 10, eadr0547 (2025).
57. Caffrey-Carr, A. K. et al. Host-derived leukotriene B4 is critical for resistance against
invasive pulmonary aspergillosis. Front. Immunol. 8, 1984 (2017).
58. Shende, R. et al. Protective role of host complement system in Aspergillus fumigatus
infection. Front. Immunol. 13, 978152 (2022).
59. Garlanda, C. et al. Non-redundant role of the long pentraxin PTX3 in anti-fungal innate
immune response. Nature 420, 182–186 (2002).
60. Cunha, C. et al. Genetic PTX3 deficiency and aspergillosis in stem-cell transplantation.
N. Engl. J. Med. 370, 421–432 (2014).
61. Sarden, N. et al. A B1a-natural IgG-neutrophil axis is impaired in viral- and
steroid-associated aspergillosis. Sci. Transl. Med. 14, eabq6682 (2022).
This study shows that viral pneumonia depletes circulating innate B1a cells and lowers
anti-A. fumigatus IgG levels, resulting in reduced opsonization and neutrophil uptake
and killing of conidia.
62. Espinosa, V. et al. Inflammatory monocytes orchestrate innate antifungal immunity in the
lung. PLoS Pathog. 10, e1003940 (2014).
63. Hohl, T. M. et al. Inflammatory monocytes facilitate adaptive CD4 T cell responses during
respiratory fungal infection. Cell Host Microbe 6, 470–481 (2009).
64. Guo, Y. et al. During Aspergillus infection, monocyte-derived DCs, neutrophils, and
plasmacytoid DCs enhance innate immune defense through CXCR3-dependent
crosstalk. Cell Host Microbe 28, 104–116.e104 (2020).
65. Espinosa, V. et al. Type III interferon is a critical regulator of innate antifungal immunity.
Sci. Immunol. https://doi.org/10.1126/sciimmunol.aan5357 (2017).
This study shows that type III interferons regulate NADPH oxidase activity in
neutrophils and are critical regulators of anti-A. fumigatus immunity.
66. Guo, Y. et al. An IFN–STAT1–CYBB axis defines protective plasmacytoid DC to neutrophil
crosstalk during Aspergillus fumigatus infection. Preprint at bioRxiv https://doi.org/
10.1101/2024.10.24.620079 (2024).
67. Dutta, O., Espinosa, V., Wang, K., Avina, S. & Rivera, A. Dectin-1 promotes type I and III
interferon expression to support optimal antifungal immunity in the lung. Front. Cell
Infect. Microbiol. 10, 321 (2020).
68. Reedy, J. L. et al. The C-type lectin receptor dectin-2 is a receptor for Aspergillus fumigatus
galactomannan. mBio 14, e0318422 (2023).
69. Dichtl, K. et al. Aspergillus fumigatus devoid of cell wall β-1,3-glucan is viable, massively
sheds galactomannan and is killed by septum formation inhibitors. Mol. Microbiol. 95,
458–471 (2015).
70. Ballou, E. R. et al. Lactate signalling regulates fungal β-glucan masking and immune
evasion. Nat. Microbiol. 2, 16238 (2016).
71. Gresnigt, M. S. et al. A polysaccharide virulence factor from Aspergillus fumigatus elicits
anti-inflammatory effects through induction of interleukin-1 receptor antagonist.
PLoS Pathog. 10, e1003936 (2014).
72. Heilig, L. et al. CD56-mediated activation of human natural killer cells is triggered by
Aspergillus fumigatus galactosaminogalactan. PLoS Pathog. 20, e1012315 (2024).
73. Briard, B. et al. Galactosaminogalactan activates the inflammasome to provide host
protection. Nature 588, 688–692 (2020).
First demonstration that galactosaminogalactan of A. fumigatus is a pathogenassociated molecular pattern molecule that activates the NLRP3 inflammasome by
binding to ribosomal proteins and inhibiting cellular translation machinery.
74. Delliere, S. et al. Interplay between host humoral pattern recognition molecules controls
undue immune responses against Aspergillus fumigatus. Nat. Commun. 15, 6966 (2024).
75. Becker, K. L. et al. Aspergillus cell wall chitin induces anti- and proinflammatory
cytokines in human PBMCs via the Fc-gamma receptor/Syk/PI3K pathway. mBio https://
doi.org/10.1128/mBio.01823-15 (2016).
76. Aimanianda, V. et al. Surface hydrophobin prevents immune recognition of airborne
fungal spores. Nature 460, 1117–1121 (2009).
Nature Reviews Microbiology
77.
Pinzan, C. F. et al. Aspergillus fumigatus conidial surface-associated proteome reveals
factors for fungal evasion and host immunity modulation. Nat. Microbiol. 9, 2710–2726
(2024).
78. Desai, J. V. & Lionakis, M. S. The role of neutrophils in host defense against invasive fungal
infections. Curr. Clin. Microbiol. Rep. 5, 181–189 (2018).
79. Shlezinger, N. et al. Sterilizing immunity in the lung relies on targeting fungal
apoptosis-like programmed cell death. Science 357, 1037–1041 (2017).
80. Desai, J. V. et al. BTK drives neutrophil activation for sterilizing antifungal immunity.
J. Clin. Invest. https://doi.org/10.1172/JCI176142 (2024).
81. Lionakis, M. S. et al. Inhibition of B cell receptor signaling by ibrutinib in primary CNS
lymphoma. Cancer Cell 31, 833–843.e835 (2017).
82. Kyrmizi, I. et al. Calcium sequestration by fungal melanin inhibits calcium-calmodulin
signalling to prevent LC3-associated phagocytosis. Nat. Microbiol. 3, 791–803 (2018).
83. Kyrmizi, I. et al. Corticosteroids block autophagy protein recruitment in Aspergillus
fumigatus phagosomes via targeting dectin-1/Syk kinase signaling. J. Immunol. 191,
1287–1299 (2013).
84. Akoumianaki, T. et al. Aspergillus cell wall melanin blocks LC3-associated phagocytosis
to promote pathogenicity. Cell Host Microbe 19, 79–90 (2016).
85. Akoumianaki, T. et al. Uncoupling of IL-6 signaling and LC3-associated phagocytosis
drives immunoparalysis during sepsis. Cell Host Microbe 29, 1277–1293.e1276 (2021).
86. Ibrahim-Granet, O. et al. Phagocytosis and intracellular fate of Aspergillus fumigatus
conidia in alveolar macrophages. Infect. Immun. 71, 891–903 (2003).
87. Hohl, T. M. et al. Aspergillus fumigatus triggers inflammatory responses by stage-specific
β-glucan display. PLoS Pathog. 1, e30 (2005).
88. Mansour, M. K. et al. Dectin-1 activation controls maturation of β-1,3-glucan-containing
phagosomes. J. Biol. Chem. 288, 16043–16054 (2013).
89. Carrion Sde, J. et al. The RodA hydrophobin on Aspergillus fumigatus spores masks
dectin-1- and dectin-2-dependent responses and enhances fungal survival in vivo.
J. Immunol. 191, 2581–2588 (2013).
90. Hooper, K. M. et al. V-ATPase is a universal regulator of LC3-associated phagocytosis and
non-canonical autophagy. J. Cell Biol. https://doi.org/10.1083/jcb.202105112 (2022).
91. Fletcher, K. et al. The WD40 domain of ATG16L1 is required for its non-canonical role in
lipidation of LC3 at single membranes. EMBO J. https://doi.org/10.15252/embj.201797840
(2018).
92. Xu, Y. et al. A bacterial effector reveals the V-ATPase–ATG16L1 axis that initiates
xenophagy. Cell 178, 552–566.e520 (2019).
93. Shah, A. et al. Calcineurin orchestrates lateral transfer of Aspergillus fumigatus during
macrophage cell death. Am. J. Respir. Crit. Care Med. 194, 1127–1139 (2016).
94. Bruns, S. et al. Production of extracellular traps against Aspergillus fumigatus in vitro
and in infected lung tissue is dependent on invading neutrophils and influenced by
hydrophobin RodA. PLoS Pathog. 6, e1000873 (2010).
95. Hopke, A. et al. Neutrophil swarming delays the growth of clusters of pathogenic fungi.
Nat. Commun. 11, 2031 (2020).
96. Song, Z. et al. NADPH oxidase controls pulmonary neutrophil infiltration in the response
to fungal cell walls by limiting LTB4. Blood 135, 891–903 (2020).
97. Gazendam, R. P. et al. Human neutrophils use different mechanisms to kill Aspergillus
fumigatus conidia and hyphae: evidence from phagocyte defects. J. Immunol. 196,
1272–1283 (2016).
98. Malamud, M. et al. Recognition and control of neutrophil extracellular trap formation by
MICL. Nature 633, 442–450 (2024).
99. Clark, H. L. et al. Zinc and manganese chelation by neutrophil S100A8/A9 (calprotectin)
limits extracellular Aspergillus fumigatus hyphal growth and corneal infection. J. Immunol.
196, 336–344 (2016).
100. Happacher, I. et al. The siderophore ferricrocin mediates iron acquisition in
Aspergillus fumigatus. Microbiol. Spectr. 11, e0049623 (2023).
101. Leal, S. M. Jr. et al. Targeting iron acquisition blocks infection with the fungal pathogens
Aspergillus fumigatus and Fusarium oxysporum. PLoS Pathog. 9, e1003436 (2013).
102. Hsu, J. L. et al. Microhemorrhage-associated tissue iron enhances the risk for Aspergillus
fumigatus invasion in a mouse model of airway transplantation. Sci. Transl. Med. https://
doi.org/10.1126/scitranslmed.aag2616 (2018).
103. Fallon, J. P., Reeves, E. P. & Kavanagh, K. Inhibition of neutrophil function following
exposure to the Aspergillus fumigatus toxin fumagillin. J. Med. Microbiol. 59, 625–633
(2010).
104. Lionakis, M. S., Drummond, R. A. & Hohl, T. M. Immune responses to human fungal
pathogens and therapeutic prospects. Nat. Rev. Immunol. 23, 433–452 (2023).
105. Desai, J. V. et al. C5a-licensed phagocytes drive sterilizing immunity during systemic
fungal infection. Cell 186, 2802–2822.e2822 (2023).
106. McDermott, A. J. & Klein, B. S. Helper T-cell responses and pulmonary fungal infections.
Immunology 155, 155–163 (2018).
107. Feys, S. et al. Lower respiratory tract single-cell RNA sequencing and neutrophil
extracellular trap profiling of COVID-19-associated pulmonary aspergillosis: a single
centre, retrospective, observational study. Lancet Microbe https://doi.org/10.1016/
S2666-5247(23)00368-3 (2024).
108. Song, L., Zhao, Y., Wang, G., Zou, W. & Sai, L. Investigation of predictors for invasive
pulmonary aspergillosis in patients with severe fever with thrombocytopenia syndrome.
Sci. Rep. 13, 1538 (2023).
109. Dewi, I. M. W., van de Veerdonk, F. L. & Gresnigt, M. S. The multifaceted role of T-helper
responses in host defense against Aspergillus fumigatus. J. Fungi https://doi.org/
10.3390/jof3040055 (2017).
Review article
110. Cenci, E. et al. Cytokine- and T helper-dependent lung mucosal immunity in mice with
invasive pulmonary aspergillosis. J. Infect. Dis. 178, 1750–1760 (1998).
111. Moss, R. B. Pathophysiology and immunology of allergic bronchopulmonary
aspergillosis. Med. Mycol. 43, S203–S206 (2005).
112. Harrington, L. E. et al. Interleukin 17-producing CD4+ effector T cells develop via a lineage
distinct from the T helper type 1 and 2 lineages. Nat. Immunol. 6, 1123–1132 (2005).
113. Break, T. J. et al. Aberrant type 1 immunity drives susceptibility to mucosal fungal
infections. Science https://doi.org/10.1126/science.aay5731 (2021).
114. Romani, L. et al. Defective tryptophan catabolism underlies inflammation in mouse
chronic granulomatous disease. Nature 451, 211–215 (2008).
115. Chamilos, G. & Carvalho, A. Aspergillus fumigatus DHN-Melanin. Curr. Top. Microbiol.
Immunol. 425, 17–28 (2020).
116. Graf, K. T., Liu, H., Filler, S. G. & Bruno, V. M. Depletion of extracellular chemokines by
Aspergillus melanin. mBio 14, e0019423 (2023).
117. Jahn, B., Langfelder, K., Schneider, U., Schindel, C. & Brakhage, A. A. PKSP-dependent
reduction of phagolysosome fusion and intracellular kill of Aspergillus fumigatus conidia
by human monocyte-derived macrophages. Cell Microbiol. 4, 793–803 (2002).
118. Jia, L. J. et al. Aspergillus fumigatus hijacks human p11 to redirect fungal-containing
phagosomes to non-degradative pathway. Cell Host Microbe 31, 373–388 e310 (2023).
The study identifies the conidial HscA protein of A. fumigatus as an anchoring factor
for host p11, which enables the fungus to divert phagosomal trafficking through the
non-degradative pathway and favour immune evasion.
119. Robinet, P. et al. A polysaccharide virulence factor of a human fungal pathogen induces
neutrophil apoptosis via NK cells. J. Immunol. 192, 5332–5342 (2014).
120. Lee, M. J. et al. The fungal exopolysaccharide galactosaminogalactan mediates virulence
by enhancing resistance to neutrophil extracellular traps. PLoS Pathog. 11, e1005187
(2015).
121. Dagenais, T. R. & Keller, N. P. Pathogenesis of Aspergillus fumigatus in invasive
aspergillosis. Clin. Microbiol. Rev. 22, 447–465 (2009).
122. Raffa, N. & Keller, N. P. A call to arms: mustering secondary metabolites for success and
survival of an opportunistic pathogen. PLoS Pathog. 15, e1007606 (2019).
123. Arias, M. et al. Preparations for invasion: modulation of host lung immunity during
pulmonary aspergillosis by gliotoxin and other fungal secondary metabolites.
Front. Immunol. 9, 2549 (2018).
124. Sugui, J. A. et al. Host immune status-specific production of gliotoxin and bis-methylgliotoxin during invasive aspergillosis in mice. Sci. Rep. 7, 10977 (2017).
125. Gunther, K. et al. Aspergillus fumigatus-derived gliotoxin impacts innate immune cell
activation through modulating lipid mediator production in macrophages. Immunology
https://doi.org/10.1111/imm.13857 (2024).
126. de Castro, P. A. et al. Regulation of gliotoxin biosynthesis and protection in Aspergillus
species. PLoS Genet. 18, e1009965 (2022).
127. Alves de Castro, P. et al. Aspergillus fumigatus mitogen-activated protein kinase MpkA is
involved in gliotoxin production and self-protection. Nat. Commun. 15, 33 (2024).
128. Guruceaga, X. et al. Aspergillus fumigatus fumagillin contributes to host cell damage.
J. Fungi https://doi.org/10.3390/jof7110936 (2021).
129. Niu, M. & Keller, N. P. Co-opting oxylipin signals in microbial disease. Cell. Microbiol. 21,
e13025 (2019).
130. Niu, M. et al. Fungal oxylipins direct programmed developmental switches in filamentous
fungi. Nat. Commun. 11, 5158 (2020).
131. Calise, D. G., Park, S. C., Bok, J. W., Goldman, G. H. & Keller, N. P. An oxylipin signal confers
protection against antifungal echinocandins in pathogenic aspergilli. Nat. Commun. 15,
3770 (2024).
132. Steffan, B. N. et al. Loss of the mammalian G-protein coupled receptor, G2A, modulates
severity of invasive pulmonary aspergillosis. Front. Immunol. 14, 1173544 (2023).
133. Arastehfar, A. et al. Aspergillus fumigatus and aspergillosis: from basics to clinics.
Stud. Mycol. 100, 100115 (2021).
134. Donnelly, J. P. et al. Revision and update of the consensus definitions of invasive fungal
disease from the European Organization for Research and Treatment of Cancer and
the Mycoses Study Group Education and Research Consortium. Clin. Infect. Dis. 71,
1367–1376 (2020).
135. van de Veerdonk, F. L. et al. Influenza-associated aspergillosis in critically ill patients.
Am. J. Respir. Crit. Care Med. 196, 524–527 (2017).
136. Schauwvlieghe, A. et al. Invasive aspergillosis in patients admitted to the intensive care unit
with severe influenza: a retrospective cohort study. Lancet Respir. Med. https://doi.org/
10.1016/S2213-2600(18)30274-1 (2018).
137. Koehler, P. et al. Defining and managing COVID-19-associated pulmonary aspergillosis:
the 2020 ECMM/ISHAM consensus criteria for research and clinical guidance.
Lancet Infect Dis. https://doi.org/10.1016/S1473-3099(20)30847-1 (2020).
138. Dewi, I. M. et al. Invasive pulmonary aspergillosis associated with viral pneumonitis.
Curr. Opin. Microbiol. 62, 21–27 (2021).
139. Feys, S. et al. Influenza-associated and COVID-19-associated pulmonary aspergillosis in
critically ill patients. Lancet Respir. Med. 12, 728–742 (2024).
140. van de Veerdonk, F. L. et al. COVID-19-associated Aspergillus tracheobronchitis:
the interplay between viral tropism, host defence, and fungal invasion. Lancet Respir. Med.
9, 795–802 (2021).
141. van de Veerdonk, F. L., Gresnigt, M. S., Verweij, P. E. & Netea, M. G. Personalized medicine
in influenza: a bridge too far or the near future? Curr. Opin. Pulm. Med. 23, 237–240 (2017).
142. Konig, S. et al. The influenza A virus promotes fungal growth of Aspergillus fumigatus via
direct interaction in vitro. Microbes Infect. 26, 105264 (2024).
Nature Reviews Microbiology
143. Dewi, I. M. W. et al. Neuraminidase and SIGLEC15 modulate the host defense against
pulmonary aspergillosis. Cell Rep. Med. 2, 100289 (2021).
144. Feys, S. et al. Lung epithelial and myeloid innate immunity in influenza-associated or
COVID-19-associated pulmonary aspergillosis: an observational study. Lancet Respir.
Med. 10, 1147–1159 (2022).
This study reveals a three-level breach in antifungal immunity in influenzaassociated and COVID-19-associated pulmonary aspergillosis, affecting epithelial
barrier integrity, spores phagocytosis and killing, and destruction of A. fumigatus
hyphae by neutrophils.
145. Wauters, E. et al. Discriminating mild from critical COVID-19 by innate and adaptive
immune single-cell profiling of bronchoalveolar lavages. Cell Res. 31, 272–290 (2021).
146. Cambier, S. et al. Atypical response to bacterial coinfection and persistent neutrophilic
bronchoalveolar inflammation distinguish critical COVID-19 from influenza. JCI Insight
https://doi.org/10.1172/jci.insight.155055 (2022).
147. Ghoneim, H. E., Thomas, P. G. & McCullers, J. A. Depletion of alveolar macrophages
during influenza infection facilitates bacterial superinfections. J. Immunol. 191,
1250–1259 (2013).
148. Liu, K. W. et al. Postinfluenza environment reduces Aspergillus fumigatus conidium
clearance and facilitates invasive aspergillosis in vivo. mBio 13, e0285422 (2022).
149. Seldeslachts, L. et al. Damping excessive viral-induced IFN-γ rescues the impaired
anti-Aspergillus host immune response in influenza-associated pulmonary aspergillosis.
eBioMedicine 108, 105347 (2024).
150. Vanderbeke, L. et al. A pathology-based case series of influenza- and COVID-19associated pulmonary aspergillosis: the proof is in the tissue. Am. J. Respir. Crit. Care
Med. 208, 301–311 (2023).
151. Wurster, S. et al. Development of a corticosteroid-immunosuppressed mouse model to
study the pathogenesis and therapy of influenza-associated pulmonary aspergillosis.
J. Infect. Dis. 227, 901–906 (2023).
152. Feys, S., Hoenigl, M., Gangneux, J. P., Verweij, P. E. & Wauters, J. Fungal fog in viral storms:
necessity for rigor in aspergillosis diagnosis and research. Am. J. Respir. Crit. Care Med.
209, 631–633 (2024).
153. Zuniga-Moya, J. C. et al. Incidence and mortality of COVID-19-associated invasive fungal
infections among critically ill intubated patients: a multicenter retrospective cohort
analysis. Open. Forum Infect. Dis. 11, ofae108 (2024).
154. Vanderbeke, L. et al. Posaconazole for prevention of invasive pulmonary aspergillosis in
critically ill influenza patients (POSA-FLU): a randomised, open-label, proof-of-concept
trial. Intensive Care Med. 47, 674–686 (2021).
155. Hatzl, S. et al. Antifungal prophylaxis for prevention of COVID-19-associated pulmonary
aspergillosis in critically ill patients: an observational study. Crit. Care 25, 335 (2021).
156. Rombauts, A. et al. Antifungal prophylaxis with nebulized amphotericin-B in solid-organ
transplant recipients with severe COVID-19: a retrospective observational study.
Front. Cell Infect. Microbiol. 13, 1165236 (2023).
157. Herivaux, A. et al. Lung microbiota predict invasive pulmonary aspergillosis and its
outcome in immunocompromised patients. Thorax 77, 283–291 (2022).
158. Gow, N. A. R. et al. The importance of antimicrobial resistance in medical mycology.
Nat. Commun. 13, 5352 (2022).
159. Hokken, M. W. J. et al. The transcriptome response to azole compounds in
Aspergillus fumigatus shows differential gene expression across pathways essential for
azole resistance and cell survival. J. Fungi https://doi.org/10.3390/jof9080807 (2023).
160. Verweij, P. E. et al. In-host adaptation and acquired triazole resistance in
Aspergillus fumigatus: a dilemma for clinical management. Lancet Infect. Dis. 16,
e251–e260 (2016).
This overview challenges current A. fumigatus management strategies and highlights
the need to study genomic dynamics during infection to understand the key factors
facilitating fungal adaptation.
161. Zhang, J., Verweij, P. E., Rijs, A., Debets, A. J. M. & Snelders, E. Flower bulb waste
material is a natural niche for the sexual cycle in Aspergillus fumigatus. Front. Cell Infect.
Microbiol. 11, 785157 (2021).
162. Zhang, J., Debets, A. J. M., Verweij, P. E. & Snelders, E. Azole-resistance development;
how the Aspergillus fumigatus lifecycle defines the potential for adaptation. J. Fungi
https://doi.org/10.3390/jof7080599 (2021).
163. Engel, T. et al. Parasexual recombination enables Aspergillus fumigatus to persist in
cystic fibrosis. ERJ Open Res. https://doi.org/10.1183/23120541.00020-2020 (2020).
164. Howard, S. J. et al. Major variations in Aspergillus fumigatus arising within aspergillomas
in chronic pulmonary aspergillosis. Mycoses 56, 434–441 (2013).
165. Fisher, M. C. et al. Tackling the emerging threat of antifungal resistance to human health.
Nat. Rev. Microbiol. 20, 557–571 (2022).
166. Schoustra, S. E. et al. Environmental hotspots for azole resistance selection of
Aspergillus fumigatus, the Netherlands. Emerg. Infect. Dis. 25, 1347–1353 (2019).
167. Rivelli Zea, S. M. & Toyotome, T. Azole-resistant Aspergillus fumigatus as an emerging
worldwide pathogen. Microbiol. Immunol. 66, 135–144 (2022).
168. Snelders, E. et al. Triazole fungicides can induce cross-resistance to medical triazoles in
Aspergillus fumigatus. PLoS ONE 7, e31801 (2012).
169. Shelton, J. M. G. et al. Citizen science reveals landscape-scale exposures to
multiazole-resistant Aspergillus fumigatus bioaerosols. Sci. Adv. 9, eadh8839 (2023).
170. Kolwijck, E. et al. Voriconazole-susceptible and voriconazole-resistant Aspergillus
fumigatus coinfection. Am. J. Respir. Crit. Care Med. 193, 927–929 (2016).
171. Herbrecht, R. et al. Voriconazole versus amphotericin B for primary therapy of invasive
aspergillosis. N. Engl. J. Med. 347, 408–415 (2002).
Review article
172. Maertens, J. A. et al. Isavuconazole versus voriconazole for primary treatment of invasive
mould disease caused by Aspergillus and other filamentous fungi (SECURE): a phase 3,
randomised-controlled, non-inferiority trial. Lancet 387, 760–769 (2016).
173. Maertens, J. A. et al. Posaconazole versus voriconazole for primary treatment of invasive
aspergillosis: a phase 3, randomised, controlled, non-inferiority trial. Lancet 397,
499–509 (2021).
174. Resendiz-Sharpe, A. et al. Prevalence of voriconazole-resistant invasive aspergillosis
and its impact on mortality in haematology patients. J. Antimicrob. Chemother. 74,
2759–2766 (2019).
175. Lestrade, P. P. et al. Voriconazole resistance and mortality in invasive aspergillosis:
a multicenter retrospective cohort study. Clin. Infect. Dis. 68, 1463–1471 (2019).
176. Hamaoui, D. & Subtil, A. ATG16L1 functions in cell homeostasis beyond autophagy.
FEBS J. 289, 1779–1800 (2022).
177. Cunha, C. et al. Dectin-1 Y238X polymorphism associates with susceptibility to invasive
aspergillosis in hematopoietic transplantation through impairment of both recipient- and
donor-dependent mechanisms of antifungal immunity. Blood 116, 5394–5402 (2010).
178. Chai, L. Y. et al. The Y238X stop codon polymorphism in the human β-glucan receptor
dectin-1 and susceptibility to invasive aspergillosis. J. Infect. Dis. 203, 736–743 (2011).
179. Fisher, C. E. et al. Validation of single nucleotide polymorphisms in invasive aspergillosis
following hematopoietic cell transplantation. Blood 129, 2693–2701 (2017).
180. Feys, S. et al. A signature of differential gene expression in bronchoalveolar lavage fluid
predicts mortality in influenza-associated pulmonary aspergillosis. Intensive Care Med.
49, 254–257 (2023).
181. Mezger, M. et al. Polymorphisms in the chemokine (C-X-C motif) ligand 10 are associated
with invasive aspergillosis after allogeneic stem-cell transplantation and influence
CXCL10 expression in monocyte-derived dendritic cells. Blood 111, 534–536 (2008).
182. Lupianez, C. B. et al. Polymorphisms in host immunity-modulating genes and risk of
invasive aspergillosis: results from the AspBIOmics Consortium. Infect. Immun. 84,
643–657 (2015).
183. Wojtowicz, A. et al. IL1B and DEFB1 polymorphisms increase susceptibility to invasive
mold infection after solid-organ transplantation. J. Infect. Dis. 211, 1646–1657 (2015).
184. Chorny, A. et al. The soluble pattern recognition receptor PTX3 links humoral innate
and adaptive immune responses by helping marginal zone B cells. J. Exp. Med. 213,
2167–2185 (2016).
185. Fischer, M. et al. Polymorphisms of dectin-1 and TLR2 predispose to invasive fungal
disease in patients with acute myeloid leukemia. PLoS ONE 11, e0150632 (2016).
186. Lionakis, M. S. Primary immunodeficiencies and invasive fungal infection: when to
suspect and how to diagnose and manage. Curr. Opin. Infect. Dis. 32, 531–537 (2019).
187. Goncalves, S. M., Cunha, C. & Carvalho, A. Understanding the genetic basis of immune
responses to fungal infection. Expert. Rev. Anti Infect. Ther. 20, 987–996 (2022).
188. Wojtowicz, A. et al. PTX3 polymorphisms and invasive mold infections after solid organ
transplant. Clin. Infect. Dis. 61, 619–622 (2015).
189. Cunha, C. & Carvalho, A. Toward the identification of a genetic risk signature for
pulmonary aspergillosis in chronic obstructive pulmonary disease. Clin. Infect. Dis. 66,
1153–1154 (2018).
190. He, Q. et al. Pentraxin 3 gene polymorphisms and pulmonary aspergillosis in chronic
obstructive pulmonary disease patients. Clin. Infect. Dis. 66, 261–267 (2018).
191. Brunel, A. S. et al. Pentraxin-3 polymorphisms and invasive mold infections in acute leukemia
patients receiving intensive chemotherapy. Haematologica 103, e527–e530 (2018).
Nature Reviews Microbiology
192. Doni, A. et al. Serum amyloid P component is an essential element of resistance against
Aspergillus fumigatus. Nat. Commun. 12, 3739 (2021).
193. Stappers, M. H. T. et al. Recognition of DHN-melanin by a C-type lectin receptor is
required for immunity to Aspergillus. Nature https://doi.org/10.1038/nature25974 (2018).
194. Gresnigt, M. S. et al. Genetic deficiency of NOD2 confers resistance to invasive
aspergillosis. Nat. Commun. 9, 2636 (2018).
195. Schmidt, F. et al. Flotillin-dependent membrane microdomains are required for
functional phagolysosomes against fungal infections. Cell Rep. 32, 108017 (2020).
196. Sueiro-Olivares, M. et al. Fungal and host protein persulfidation are functionally
correlated and modulate both virulence and antifungal response. PLoS Biol. 19,
e3001247 (2021).
197. Cunha, C. et al. IL-10 overexpression predisposes to invasive aspergillosis by suppressing
antifungal immunity. J. Allergy Clin. Immunol. 140, 867–870 e869 (2017).
198. Goncalves, S. M. et al. Genetic variation in PFKFB3 impairs antifungal immunometabolic
responses and predisposes to invasive pulmonary aspergillosis. mBio 12, e0036921
(2021).
199. Matzaraki, V. et al. Genetic determinants of fungi-induced ROS production are associated
with the risk of invasive pulmonary aspergillosis. Redox Biol. 55, 102391 (2022).
Acknowledgements
F.L.vdV. is supported by the European Union Horizon 2020 (EU H2020) programme HDM-FUN
(847507) and the Dutch Research Council and Netherlands Organisation for Health Research
CAPA (10430102110011). G.C. is supported by European Union grants (European Research
Council Consolidator Grant, iMAC-FUN (864957) and the EU H2020 programme HDM-FUN)
and a National Grant (GSRI-11412, Pro-sCAP). A.C. is supported by the EU H2020 programme
HDM-FUN and the Fundação para a Ciência e a Tecnologia, Portugal (UIDB/50026/2020,
UIDP/50026/2020, LA/P/0050/2020 and PTDC/MED-OUT/1112/2021). We thank Simon Feys for
helping with Fig. 3 and Matthaios Sertedakis for helping with Fig. 2.
Author contributions
All authors contributed equally to the preparation of this manuscript.
Competing interests
The authors declare no competing interests.
Additional information
Peer review information Nature Reviews Microbiology thanks Gustavo Goldman, Jean-Paul
Latge and the other, anonymous, reviewer(s) for their contribution to the peer review of
this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this
article under a publishing agreement with the author(s) or other rightsholder(s); author
self-archiving of the accepted manuscript version of this article is solely governed by the
terms of such publishing agreement and applicable law.
© Springer Nature Limited 2025