Inflammation and Innate Immunity (part I)
• Inflammation
• Innate immunity and the initial response to
infection
• Cytokines that induce inflammation and direct
inflammatory cells
• Recognition of microbes by Toll-like receptors
(TLRs) and other innate recognition elements
• Inflammation and recruitment of phagocytes
• Uptake and killing of bacteria by phagocytes
• Innate immunity against fungi, helminths, at
mucosal epithelium
Inflammation
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Source: Wikipedia
Inflammation
“rubor et tumor cum calore et dolore”
(redness and swelling with heat and pain)
--Cornelius Celsus in De Medicina, 1st century
A.D.
later “functio laesa” (disturbance of function)
was added
Inflammation
“rubor et tumor cum calore et dolore”
(redness and swelling with heat and pain)
--Cornelius Celsus in De Medicina, 1st century
A.D.
later “functio laesa” (disturbance of function)
was added
Inflammation is an adaptive response to noxious
conditions (infection and tissue injury)--an attempt
to restore homeostasis
Inflammation
• Inflammation can be induced by immune recognition of infection
or tissue damage (usually good)
• Inflammation can be induced by immune recognition that is
hypersensitive to environmental components or autoinflammatory
or autoimmune (=disease)
Inflammation
• Inflammation can be induced by immune recognition of infection
or tissue damage (usually good)
• Inflammation can be induced by immune recognition that is
hypersensitive to environmental components or autoinflammatory
or autoimmune (=disease)
• Acute inflammation: influx of white blood cells and fluid from
blood to fight infection and aid tissue repair
• Chronic inflammation: inducer of inflammation is not removed
– Leads to tissue damage and loss of tissue function (joint
destruction, lung fibrosis, etc.)
– Current view: aggressively fight inflammation in certain
chronic diseases to decrease/delay progressive loss of
function
Inflammation
•
Inflammation can be induced by immune recognition of infection or
tissue damage (usually good)
•
Inflammation can be induced by immune recognition that is
hypersensitive to environmental components or autoinflammatory or
autoimmune (=disease)
•
Acute inflammation: influx of white blood cells and fluid from blood to
fight infection and aid tissue repair
•
Chronic inflammation: inducer of inflammation is not removed
– Leads to tissue damage and loss of tissue function (joint destruction,
lung fibrosis, etc.)
– Current view: aggressively fight inflammation in certain chronic
diseases to decrease/delay progressive loss of function
•
Current research suggests that inflammation may play an important role
in common chronic diseases including atherosclerosis, type 2 diabetes,
neurodegeneration, and cancer
Immune sentinel cells in the tissues:
dendritic cells
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Green= dendritic cells
Blue= nuclei of all cells
Langerhans cells (epidermal dendritic cells) in the skin
WJ Mullholland et al. J. Invest. Dermatol. 126: 1541, 2006.
Infection leads to
production of inducers
of inflammation
or dendritic cell
Inflammatory mediators:
Complex and many, but include:
Lipids and
Proteins (cytokines/chemokines)
TNF
Others
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Cytokines
•“Cytokines” are soluble protein mediators secreted by immune
cells (mostly) that act on other cells to regulate their activity;
many are called “interleukins” (IL-1, IL-2, etc.) (note:
sometimes exist in cell-bound forms)
•Cytokines have many functions, we’ll focus on a few central
functions of some key cytokines (see “Cytokine primer” in
syllabus/on iROCKET)
•Name of a cytokine often doesn’t reflect its most important
function (TNF stands for “tumor necrosis factor” but main
function is to induce inflammation)
•A subfamily of cytokines primarily functions in directing
migration of cells, these are called “chemotactic cytokines” or
“chemokines”
Chemokines have systematic names: CCL1, 2, … and CXCL1, 2, …
(but older names sometimes used, including IL-8)
The Initial Response to
Infection: Innate Immunity
• Recognition of infection by hard-wired recognition
molecules or recognition of tissue damage and cell
death, “danger”
• Rapid mobilization of leukocytes to the site of
infection and influx of plasma into the tissue site.
(=inflammation)
• Recruited innate immune cells kill microbes/virally
infected cells (also can promote tissue repair but when
dysregulated can exacerbate tissue injury)
• Also, innate recognition promotes the adaptive immune
response, which is slower but more powerful
Cytokines and Inflammation
• Macrophages or DCs stimulated via innate immune
receptors make pro-inflammatory cytokines, especially
TNF (Tumor necrosis factor), IL-1, and IL-6
• TNF and IL-1 signal to endothelial cells to make them:
– Leaky to fluid (influx of plasma; containing
antibodies, complement components, etc.)
– Sticky for leukocytes, leading to influx of first
neutrophils, later monocytes, lymphocytes
• IL-6 promotes adaptive immune responses and has
systemic effects (“acute phase response” of liver,
including C-reactive protein or CRP; levels used
clinically as an indication of systemic inflammation)
Leukocyte recruitment to sites of inflammation
or DC
See Abbas and Lichtman Fig. 2-7
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Note: molecular details of leukocyte extravasation will be
covered in lecture Friday
Inflammation: Neutrophils vs. Monocytes
• Acute inflammation is initially characterized as rich in
neutrophils; later it is more monocytes and lymphocytes. This is
controlled by which chemokines are expressed by the endothelial
cells and by T cells.
• Neutrophils are dedicated to killing microbes and are shortlived. They often damage host tissue as a byproduct.
• Monocytes are multi-potential, depending on cytokine signals:
+IFN-g: assume a vigorous killing phenotype similar to
neutrophils
+IL-4: “alternatively activated macrophages”; tissue repair,
barrier immunity
+IL-10: assume a wound-healing type phenotype (to clean up
after infection is cleared)
+GM-CSF: assume a dendritic cell phenotype and propagate
adaptive immune responses
Anti-Inflammatory Therapeutics
• NSAIDs: inhibitors of inflammation and fever (block
prostaglandin synthesis)
• Glucocorticoids are also potent anti-inflammatory drugs;
natural systemic anti-inflammatory mechanism
• Agents that block TNF are effective in treating
rheumatoid arthritis, Crohn’s disease, etc.
• Agents that block IL-1 are less effective for these
diseases but are useful for some genetic inflammatory
diseases (and are currently in clinical trials for more
common conditions)
How is infection first recognized by the
immune system?
• What is seen by innate immunity?
– Microbes evolve rapidly, so innate immunity must focus on
highly conserved and essential components of microbes (cell
wall structures; nucleic acids). So-called “Pathogen-associated
molecular patterns” (PAMPs)
• What mediates the recognition?
– Diverse recognition elements; 4 key families of cellular
receptors:
•
• Toll-like receptors (TLRs; transmembrane receptors)
• C-type lectin receptors (CLRs; transmembrane receptors)
• RigI-like receptors (RLRs; cytoplasmic RNA helicases)
• NOD-like receptors (NLRs; cytoplasmic sensors)
Also, recognition of molecules released from necrotic cells, tissue damage
(“damage-associated molecular patterns” DAMPs or “danger”). Recognized
by same families of innate receptors as PAMPs (Note:tissue damage can
also be recognized by pain neurons, which can promote inflammation)
TLRs: Toll is required for innate defense
in flies
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J. Hoffmann et al. Cell 1996
Toll-like receptors and recognition
of pathogens
ssRNA
K. Takeda & S. Akira, Cell. Microbiol. 5: 143-53, 2003
Red circles: You should know these ligand/TLR pairs
Cellular localization
of Toll-like receptors
-Cell surface TLRs recognize
bacterial cell wall structures
-IntracellularTLRs recognize
pathogen nucleic acids
-Location likely aids
discrimination of viral vs.
host nucleic acids
(likely connection with SLE)
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The transcriptional activator NF-kB is a key
player in inflammatory cytokine expression
or TLR or IL-1
(Classical
Pathway)
IKK= I-kB kinase
Proteasome degrades I-kB
(Potential
therapeutic target)
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Genes regulated: Inflammatory
cytokines, chemokines, immune
effector molecules, cell survival
factors
Sepsis Syndrome: very bad
(too much of a good thing)
• Bacterial septicemia leads to activation of TLRs on
monocytes in the blood, DCs in spleen
• Systemic release of TNF and IL-1 leads to
“inflammation” all over the body
• Shock from loss of blood pressure (vasodilation and
leakage of fluid into tissues)
• TLRs also induce coagulation (via tissue factor)
– Current therapy with some efficacy: “activated protein C”:
promotes fibrinolysis, breaks down thrombi
• The combination of effects frequently leads to multiorgan failure and death
Innate recognition by CLRs (examples)
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Geijtenbeek and Gringhuis, Nat.
Rev. Immunol. 9: 465, 2009
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NF-kB
Innate recognition in the cytoplasm:
NLRs and RLRs
Modified from Abbas and Lichtman Fig. 2-2
Inflammatory cytokines
Secrete anti-microbial
peptides into lumen of
crypts of sm. intest.
(Mda5)
Interferon-
Engulfment of bacteria
invading the cytoplasm
(autophagy)
Common alleles of NOD2 are a genetic
risk factor for Crohn’s disease
•Several moderately common alleles of the NOD2 gene
(7% of total alleles) increase susceptibility to Crohn’s
disease (a form of inflammatory bowel disease)
•Two copies of these alleles increase susceptibility by 40X
•Mechanism: most evidence indicates these are loss-offunction alleles; unknown which function of NOD2 is most
relevant
Processing of IL-1 and related
cytokines: an important regulatory step
•Some “NLRs” assemble to form the “inflammasome” which
proteolytically processes IL-1 and related cytokines (IL-18) to
their active, secreted forms.
•Inflammasome in activated by cellular stress or recognition of
microbial components in the cytoplasm
Processing of IL-1 and related
cytokines: an important regulatory step
•Some “NLRs” assemble to form the “inflammasome” which
proteolytically processes IL-1 and related cytokines (IL-18) to
their active, secreted forms.
•Inflammasome in activated by cellular stress or recognition of
microbial components in the cytoplasm
•Genetic periodic fever syndromes are due to activating mutations
in the inflammasome (active when it shouldn’t be)
•Inflammasome is activated by some types of small crystals that
can be phagocytosed by macrophages, important role in Gout
The NALP3-inflammasome activates
caspase 1 in response to cellular insults
Phagocytosed crystals
Bacterial pore-forming toxins
Efflux of K+
Bacterial flagellin
Other insults/stresses
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Combinatorial Regulation of IL-1:
•TLRs and NOD1/NOD2 induce
synthesis of pro-IL-1
•Inflammasome processes it to
generate active IL-1
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Inducers of Inflammation
•Ligands for TLRs, NOD1/2 or CLRs: DCs, macrophages makeTNF
and IL-1
•Virus infections: infected cells, pDCs make IFN/ (type 1)
•Tissue damage (cell necrosis etc.): “DAMPs” activate DCs,
macrophages probably via TLRs, CLRs, inflammasomes (other
receptors?)
•Complement fragments (innate activators or IgM or IgG +
antigen)
•Mast cell activation (IgE+allergen or innate mechanisms: release
histamine, leukotrienes, cytokines): eosinophil-rich inflammation
(“type 2 immunity”)
•Effector T cells responding to antigen (TNF + other cytokines;
chemokines)
-the 3 types of effector T cells induce inflammation of
different characters (what white blood cells attracted)
Negative Regulation of Inflammation
•Cells responding to innate stimuli stop making
inflammatory mediators after short time period and
convert to making anti-inflammatory lipids (resolvins, etc.)
and anti-inflammatory cytokines (IL-10, TGF-)
•But incoming inflammatory monocytes can still respond to
stimuli if present and continue inflammation
•Killing the infectious agent and removal of the dead cells,
debris, crystals, etc. will stop stimulation of incoming
inflammatory cells
•Systemic elevation of inflammatory cytokines (esp. IL-1)
induce production of glucocorticoids, which are antiinflammatory (also by stress)
•Regulatory T cells are also anti-inflammatory, both by
blocking effector T cells and by inhibiting innate cells
Leukocyte recruitment to sites of inflammation:
neutrophils are good at killing microbes
or DC
See Abbas and Lichtman Fig. 2-7
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Phagocytosis and Killing of Microbes
Abbas and Lichtman Fig. 2-9
Phagocytosis and Killing of Microbes
Key Concepts related to phagocytosis:
1.
Opsonization: soluble immune
recognition elements tag a
particle for phagocytosis
(opsonins include: IgG, C3b,
Mannose-binding lectin, etc.)
2.
Interferon-g from NK cell or Th1
cell promotes killing of
internalized microbes by
monocytes/macrophages
3.
Killing mechanisms: ROI, NO,
proteases, anti-microbial peptides
Abbas and Lichtman Fig. 2-9
Phagocytosis and Killing of Microbes
Key Concepts related to phagocytosis:
1.
Opsonization: soluble immune
recognition elements tag a
particle for phagocytosis
(opsonins include: IgG, C3b,
Mannose-binding lectin, etc.)
2.
Interferon-g from NK cell or Th1
cell promotes killing of
internalized microbes by
monocytes/macrophages
3.
Killing mechanisms: ROI, NO,
proteases, anti-microbial peptides
Genetic defects in phagocyte
oxidase components: “chronic
granulomatous disease”
Abbas and Lichtman Fig. 2-9
Innate Immunity against fungal
pathogens
• CLRs are key innate recognition elements for
fungi/yeast (TLRs can also play a role)
• Neutrophils are important for killing most fungal
pathogens
• Some fungal pathogens can establish
intracellular infections (like some bacterial
pathogens): interferon-g is important for
defense; often also NO
Innate Immunity against helminths
• Often multicellular parasites induce a “type 2”
inflammation characterized by influx of eosinophils and
basophils instead of neutrophils and monocytes
• This type of inflammation is also seen in asthma and
allergies, as will be discussed later in the course and can
be propagated by Th2 adaptive immunity and/or IgE
• Innate recognition is not yet understood, may include
foreign polysaccharides (chitin), proteases, tissue
damage
• In some parasitic worm infections inside tissue, bacteria
in the gut/feces of the worm stimulate TLRs and
neutrophil-rich inflammation, which can cause pathology
(African river blindness)
Innate Immunity and Mucosal Epithelium
• Microbes are tolerated outside mucosal epithelium when
consistent with its function (colon; upper airways)
• Efforts to keep microbes out of some mucosal epithelial
regions (small intestines and small airways)
• Mechanisms include: actions of some surfactant proteins
in lungs (bind to foreign polysaccharides); secretion of
anti-microbial peptides by Paneth cells in crypts of small
intestines; secretion of mucus by goblet cells; g T cells
in epithelial tissue; IgA
• IL-13 is an important cytokine promoting mucus secretion
Tomorrow: Innate Immunity to Viruses