The
INFLAMMASOMES
Guardians of the Body
Fabio Martinion, Annick Mayor, Jurg Tschopp
Annual Reviews Immunology 2009
Marcin Cebula
Innate immunity

Toll like receptors – extracellular sensing (PAMPs, DAMPs)

RIG-like helicases (RIG-I, MDA5 viral sensors) – intracelular sensing

NOD - like receptors – intracellular sensing
- microbial products
- danger signals
- metabolic stress

Some NLR form large cytoplasmatic complexes
INFLAMMASOMES

Link between sensing of microbial products with proteolytic activation of
proinflammatory cytokines
IL-1 and IL-18
Structure of NLR family (I)

Multidomain proteins
1) C-terminal region (Leucin rich repeats 20-30 - LRR)
2 ) NACHT – belongs to STAND family of NTPases

3) N-terminal effector domain

LRR – ligand sensing, autoregulation of NLR signaling,
LRR domains are formed by tandem repeats
Structures of NLR
Ligand sensing domain
Responsible for NLR
oligomerization
Effector domain
Two sub families
I PYD containing NALPs (14 in human)
II 5 members of NODs + CIITA
IPAF, and BIR containing NAIP form
remaining NLR members
PYD – pyrin domain
CARD – caspase recruitment domain
FIIND – function to find
BIR – baculovirys IAP repeat
AD- activation dmain

No experimental data have convincingly
demonstrated direct interaction between LRRs
of NLRs and their respective activators,
suggesting that sensing of patogens by NLRs
may be indirect.

It is believed that the crucial step in NLRs
activation lies in the oligomerization of the
NACHT domains

Formation of active high molecular wieght
complexes - INFLAMMASOMES
NALPs



NALP1, NALP2, NALP3
are central scafold of caspase-1activating complex known as
INFLAMMASOMES
Have PYD domain
NALP1 posses additionaly CADR
domain
IPAF, NAIP




Evolutionary seperates
from other NLRs
IPAF – CARD domain
NAIP – BIR damain (often
found in proteins involved
in apaptosis
Both form
INFLAMMASOMES alone
or in combination of both
CARD-containing NLRs




NOD1,2,4 and CIITA and
separated NOD3, NOD5
NOD1 and NOD2 once
activated recruits kinase RIP2
through CARD-CARD
interaction. Oligomerization of
RIP2 in NOD signalosomes
activate NFBb
NOD1, NOD2 detects PNG
NOD2 detects MDP
NLRs expression pattern and gene
regulation

NLRs are expressed in cell and tissues that have role in
immunity such as phagocytes

Epitelial cells - the first barrier

NAIP, IPAF – brain, spleen, lung, liver

Some like NALP5, 8, 4, 7, 10, 11 have restricted
expression – germ cells and preimplantation embryos

Regulation – TLR stimulation increases the expression
of NLRs (NOD1, NOD2 NALP3)
In Plants…

NLRs genes have similarities to plant genes involved in
immune defenses (R-genes)

Contain: LRR, oligomerization domain NB-ARC, and TIR
domain (recruitment domain involved in the TLR and ILR1 family of immune mediators)

Convergent evolution

No NLR-like proteins in insects
Prototypical inflammasomes (II)
Biochemistry and diversity if
inflammasomes is poorly understood,
three prototypes
 NALP1
 NALP3
 IPAF

Prototypical inflammasomes NALP3

Assumed that PYD of NALPs
recruits adaptor ASC
(apoptosis assiciated speclike protein containing
caspase recruitment domain)

The CARD within ASK binds
and recruits caspase-1 to the
inflammasomes

NALP1 has C-terminal
extension with CARD that
rectuits caspase-5 or second
caspase-1 to inflammasomes
Prototypical inflammasomes IPAF

Direct way of recruitment of
caspase-1
 Both IPAF and NALP3 bind
ATP/dATP what is necessary
for oligomerization of NACHT
domain. Signal for this comes
from LRR that are proposed to
sense activating signal
Both IPAF and NALP3 bind
SGT1 and HSP90 and activity
of HSP90-SGT1 complex is
essential for NALP3 activation
(by keeping inflammasomes
inactive but competent for
activation)
Heterocomplexes – diversity?
Sensors of Danger signals (III)





How innate immune system discriminate
between pathogenic and self nonpathogenic
microbes
Matzinger suggest DANGER hypothesis
Presentation of an antigen in the context of
danger signal triggrs efficient immune response
- not only the foreignnes of antigen
Signals released by damaged or stressed
tissues
First evidence found in plans
MSU – monosoduim urate crystals
CPPD – calcium pyrophosphate dihydrate crystals
Sensing extracellular ATP





Extracellular ATP released by damage or cellular stress
hydrostatic pressure, hypotonic shock
Danger signal binds to purinoreceptor P2X7 thereby
activating NALP3 and caspase-1
Extracellular ATP in vivo my be rapidly hydrolyzed.
Other ATP sourses
- insulin containing granules from pancreatic  cells
- microbial flora and pathogenes
ASC deficient mice demonstrated that ATP mediated
caspase-1 activation requires ASC and is therefore
dependent on activation of NALP
Uric Acid – a danger signal
involved in gout (Arthritismus)




Uric acid form supernatant of dying cells tiggers adjuvanticity.
Uric acid with free sodium in extracellular enviroment form
monosodium urate MSD crystals
MSU adjuvanticity depends on NALP3 inflammasome
activation → IL-1
ASC, NALP3 deficient mice have reduced crystal induced IL-1

Examples
- Erytrocytes infected with Plasmodium contain high levels of
hipoxanthine which is released from damaged cells and converted
to uric acid – results in inlamation
- DC incubated with alum also release uric acid

Aluminium particles act as adjuvant by augumented production of IL-1
Alum-induced caspase -1 is dependent on NALP3 inflammasome
activation

Silica and Asbestos
Inflamation in the lung

Alveolar macrophages reside on barrier between body
and the external enviroment

This phagocytes are important defence against
microorganisms, dust particles

Silica, asbestos dust are strong inflamation inducers in
the lungs.

This compounds act as activators of NALP3
and skin inflamations


UV activate NALP3 in keratinocytes
Inflammasomes play a role in contact hypersensitivity an inflammatory
disease caused by irritant chemicals penetrating skin and inducing T cell
response

Two phases
- sensitization (chamicals as adjuvants and foreign hapten)
- activation (after reexpousure)

SENSITIZATION phase depends on functional:
– caspase-1 IL-1, IL-18
– confirmed role of ASC, NALP3 inflammasome
DNFB (dinitrofluorobenzene) shown to promote release IL-1 in caspase-1
dependent manner in DC and keratinocytes.
Suggestion that inflammasomes may detect such a compound directy or
recognise the danger signals produced by irritants
Reactive oxygen species

ROS production occurs upon expousure of macrophages to:
silica, asbestos, MSU, alum, ATP, toxin nigericin, UV, DNCB

ROS production is signal involved in stress and damage sensing

Knockdown of NADPH oxidaze subunits or use of antioxidants
inhibit inflammasome activation by mentioned above compound

It is proposed that ROS is directly sensed by NALP3 or indirectly
sensed by cytoplasmic modulators of inflammasome activity
Sensors of Pathohens (IV)

Extracelular PAMPs and danger signals – TLR,
RAGE (receptor for advanced glycation end product)

NLRs samples PAMPs reaching cellular compartments
(invasion, degradation products from phagocytosed
bacteria, viruses)

Additionaly to PAMPs inflammasomes detects toxins and
signals restricted to certain pathogens
PAMPs & toxins

Mainly bacterial PGNs and nucleic acids (indirect).

PGN is degraded to MDP that is sensed by NLR
- NOD2 results in activation of NFB
- NALP3 results IL-1 activation via caspase-1 (but NOD2 is required)

Sugesstion that NOD2 and NALP3 can cooperate
directly or indirectly as part of the same complex

PORE-FORMING bacterial toxins antivate NALP3 inflammasome
- -toxin
Staphylococcus aureus
- aerolysin
Aeromonas hydrophila
- listeriolysin O
Listeria monocytogenes
-potassium efflux, calcium influx (danger signals)

Antrax lethal toxin activates NALP1
MDP - Muramyl dipeptide
IPAF inflamasomme activation by injected
virulent factors

Gram negative pathogens that activate IPAF require
type III or type IV secretion system for injection of
virulent factors activating IPAF

Mainly flagellin activates IPAF but not only.
INFLAMMASOME regulators (V)
POPs – poxoviral gene product
 – viral PYD
vPYDs
What are the mechanisms silenting
the inflamation iduced by
inflammasomes


Factors: proteins that interfere with
inflammasome assembly and
inflammatory caspase activation
MAIN inflamasome regulators are
those containing CARD domain, and
those with PYD domain
Pi9 – serpin protease inhibitor
vCrmA – cowpox virus-encoded inhibitor of caspase-1
•Targeted disruption of Pyrin in mice
causes increased endotoxin
sensitivity and enhanced caspase-1
activation
•But Pyrin overexpression can be
proinflamatory
•vPYD defficient poxoviruses –
enhanced activation of caspase-1
& inflamatory diseases

Autoinflammatory but not autoimmune
disorders
Inflammasomes & Adjuvanticity






Adjuvants: alum, oil based emulsions
TLR agonist ?
IL-1 has adjuvant properties. Mice immunization
together with IL-1 results in higher antibody production
Inflammasome activators have adjuvant properties
(MDP, MSU)
MSU, alum (ASC,NALP3,caspase-1) biases immune
response towards Th2 type via IL-1, IL-18, IL-33
Inflammasomes are important in linking innate immunity
to adaptive immunity
Pyroptosis

Apoptosis – silent death

Pyroptosis – „Pyro” Fire
Cell death dependent on caspase-1, associated with
high inflammatory state

Shigella f. infects colon epitelium, evades phagosome to
enter cytosol where tigers death requires caspase-1 but
not apoptotic caspase-3

Salmonella induced pyroptosis in infected macrophages
(ASC, IPAF) is blocked in IPAF defficient mice

Bacillus anthracis induces pyroptosis dependent on
NALP1
Emerging inflammasomes
functions

Research on IL-1 and inflammatory caspases revealed
its role as mediators in neurodegenerative disorders,
cancer and fertility-associated conditions

Amyloid- in Alzheimer’s disease similary to
phagocytosed uric acid crystals, activate NALP3
inflammasome, might be important for inflamation and
tissue damage

IL-1 perfusion in rabbit ovary blocks embryo
development. Inflammasomes may link innate immunity
to reproductive biology
Thank you
PAMPs & DAMPs
The Caspase-1 Inflammasome: Apilotof innate immune response
B. Brett Finlay et al. Cell Host & Microbe 2008
General mechanisms of
Inflammasome activation