Lipopolysaccharide = Lipid + Polysaccharide. The Innate Immune Response is Conserved Throughout Evolution and is Triggered by Pattern Recognition

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1 Lipopolysaccharide = Lipid + Polysaccharide The Innate Immune Response is onserved Throughout Evolution and is Triggered by Pattern Recognition E.coli ell wall organization Lipopolysaccharide Outer membrane Peptidoglycan Inner membrane Lipid A Architecture of LPS O-specific side chain ore region Lipid A From: Beutler and Rietschel, ature Reviews Immunology 3; (2003) Diversity of Pathogen-associated Molecular Patterns (PAMPs) Innate Immune Receptors for PAMPs Toll-like receptors (TLRs) omplement ollectins (e.g., Surfactant Protein-A) Scavenger receptors Pentraxins (e.g., RP) Lectins (e.g., Dectin-1) D14 OD-like receptors (LRs) RIG-1-like receptors From: Akira et al., ell 124:783, 2006 ollectins and Innate Immune Recognition ollectins an Serve as Opsonins SP-D SP-D Globular heads bind to: Ag/Ab complexes Apoptotic cells Pathogens -reactive protein Virus Bacterium Apototic cell SP-A ollagen-like tails bind to: 1q receptors on phagocytes (to promote phagocytosis) 1r/1s (to initiate the classical pathway) SP-A SP-D 1q Surfactant proteins Opsonization Modified from: Wright, ature Rev. Immunol. 5:58,

2 The Scavenger Receptor Superfamily Recognizes PAMPs OxLDL: Oxidized LDL AGE: Advanced glycation end-products KEY TO DOMAIS Innate Immune Receptors Also Trigger a Systemic Response to Infection LTA LPS Gram-positive bacteria Gram-negative bacteria Bacterial DA OxLDL AGE E. coli S.aureus -omplement control protein (P) -Somatomedin B --type Lectin -Epidermal growth factor (EGF) -Partial Epidermal growth factor (EGF) -Potential -linked glycosylation -Potential O-linked glycosylation E. coli S.aureus OxLDL HDL E. coli S.aureus OxLDL * * SR-A I SR-A II SR-A III MARO D36 SR-B1 dsr- I D68 LOX-1 SRE SR-A SR-B SR- SR-D SR-E SR-F Innate Immune Functions of Reactive Protein (RP), an Acute Phase Protein Synthesized by Hepatocytes o-localization of RP and Activated omplement in Infarcted Human Myocardium 1q omplement activation RP MBL omplement activation Phosphocholine RP 4d RP acts as a bridge between phosphocholine on bacterial targets and 1q Adapted from: Black et al., J. Biol. hem. 47:48487, 2004 J = jeopardized; = normal From: ijmeijer et al., Am. J. Pathol. 163:269, 2003 Treatment of Experimental Myocardial Infarction with a RP-binding Analog of Phosphocholine Limits Infarct Size History of Endotoxin Research 3H/HeJ Primary mutation structure of reported LPS reported TLR2 is the receptor for PG Pasteur, Koch: the germ theory of disease Pfeiffer describes endotoxin Endotoxin = LPS TF mediates Discovery LPS-induced shock of D14 The post-microbial era began with the discoveries of Koch and Pasteur (1865). Four phases of discovery are depicted: the recognition that infection is poisonous (red); search for poisons culminating in the identification of endotoxin (green); the chemical and biological characteriztaion of endotoxin (orange); the identification of the endotoxin receptor and its role in promoting the immune response (purple) LPS = TLR4 From: Kitsis and Jialal, ew Engl. J. Med. 355:513, 2006 Modified from: Beutler and Rietschel, ature Reviews Immunology 3; (2003) 2

3 A Re-interpretation of the Endotoxin Research Timeline Discovery of the F-κB signaling pathway by Toll in Drosophila by Hoffman and colleagues Use of adjuvant to stimulate the immune response Molecular basis of adjuvant discovered by Medzhitov and Janeway Infectious-non-self model of immunity described by Janeway Primitive Specificity in Target Recognition by the Innate Immune System 3H/HeJ mutation reported Primary structure of LPS reported TLR2 is the receptor for PG Endotoxin = LPS TF mediates septic shock Discovery of D14 LPS = TLR4 Modified from: Beutler and Rietschel, ature Reviews Immunology 3; (2003) Recruitment of TLR2 to Yeast Phagosomes Ligand Specificity of TLRs Adaptor proteins, kinases From: Underhill et al., ature 401:811,

4 Specificity of TLR Transcriptional Programs TLR Signaling: Two Major Pathways artoon of major signal transduction pathways following engagement of TLRs. TLR4 is the major sensor of LPS. TLR3 recognizes dsra and is important in the anti-viral response. The IRF pathway leading to production of Type I IFs (i.e., IF-α/β) is particularly prominent in a minor subset of dendritic cells (called plasmacytoid Ds ) that are the major source of these IFs in response to viral infections. From: Luster, urr. Opin. Immunol. 14:129, 2002 Do not memorize this cascade but rather appreciate that it consists of two parallel pathways, one that activates F-κB, leading to production of most pro-inflammatory proteins, and one that activates the IRF pathway, leading to production of Type I IFs. From: Moynagh,Trends Immunol. 26:469, 2005 TLRs Sense Microbial Pathogens and Trigger Expression of Pro-inflammatory ytokines and hemokines ewly Recognized omponents of the Innate Immune System Adapted from: reagh and O eill, Trends Immunol. 27:352, 2006 OD Proteins: Intracellular Peptidoglycan Sensors ytosolic Bacterial Recognition Systems and the Inflammasome od Protein OD-1 ARD LRR; Ligand Recognition OD-2 ARD = caspase-recruitment domain LRR = leucine-rich repeat OD = OD2-like domain MDP = muramyl dipeptide RIK ytoplasm I-κB p50 p65 F-κB Polymorphisms in od-2 are associated with up to 30-40% of cases of rohn s disease (an inflammatory bowel disease) ARD, caspase-recruitment domain; LRR, leucine-rich repeat; RIK, a ARD-containing protein kinase From: Akira et al., ell 124:783,

5 Mutations in Pyrin, Another ARD-containing Innate Immune-like Protein, is Responsible for Familial Mediterranean Fever Another Disease Associated with Activation of the Inflammasome ontrast-enhanced abdominal T from a 31 year-old patient with Familial Mediterranean Fever suffering an acute attack of abdominal pain, nausea, vomiting, and arthritis. ote mesenteric vessel with thickened mesenteric fold (white arrow). Histopathology demonstrated neutrophilic infiltrate and associated vasculitis. Treatment with an IL-1 receptor antagonist (Anakinra) resulted in prompt cessation of symptoms. Pathogenesis of Gout Uncovered in 2006: Monosodium Urate rystals Activate the Inflammasome od-like Receptors (LRs) Sense Microbial Products, Activate the Inflammasome, and Trigger Maturation of IL-1 From: Martinon and Glimcher J. lin. Invest. 116:2073, 2006 Adapted from: reagh and O eill, Trends Immunol. 27:352, 2006 Dendritic ell Maturation The Dendritic ell and Development of The Primary Immune Response: Wisdom Through Maturity From: Mellman & Steinman, ell 106:255,

6 The Innate Immune Response Orchestrates D Trafficking to Secondary Lymphoid Organs Question: What Triggers Maturation of Ds? From: Luster, urr. Opin. Immunol. 14:129, 2002 Functional Differences Between Immature and Mature Ds The (Primary) Acquired Immune Response is Initiated by Innate Immune Recognition Expression of R7 Migration towards T-cell zone of lymph node hemokines Direct Trafficking of Immune ells The Early Antiviral Response and the Innate Immune System Pathogen IL-12 IF-γ IF-γ From: Luster, urr. Opin. Immunol. 14:129, 2002 K cells are a major source of a rapidly mobilizable pool of pro-inflammatory cytokines 6

7 Innate Immune Receptors for dsra ooperate to Initiate the Immune Response to RA Viruses The Antiviral Response: a ascade of Transcriptional Events Double-stranded RA products of virus infection bind to RIG-I or MDA5, which in turn bind to IPS-1 via ARD domain interactions. This complex then signals the activation of IKK-ε and TBK1 or other kinases to phosphorylate IRF-3, possibly through direct recruitment of signaling effectors, leading to IRF-3 dimerization, nuclear translocation and assembly onto the IF-β enhancer. IPS-1 might also signal the activation of the IKK c o m p l e x v i a d i r e c t b i n d i n g o f I K K components or through recruitment of RIP-1, FA D D a n d / o r T R A F 6, c a u s i n g t h e phosphorylation of IκB, the inhibitor of FκB. Phosphorylated IκB is then ubiquitinated and targeted to the proteosome for degradation, releasing the active F-κB complex to translocate to the nucleus. During virus infection, dsra products can signal through TLR3 to activate IRF-3 and F-κB by the actions of the TRIF adaptor protein and RIP-1, respectively..b.: Do not memorize this cartoon, but a p p r e c i a t e h o w c y t o s o l i c d s R A receptors (RIG-1, MDA5) and plasma membrane-associated dsra receptors (TLR3) cooperate to activate IRF- and FκB-dependent gene expression. Some targets of IRFs Gene Function p21 ell cycle arrest IL-15 K cell maturation FasL ell death IL-12 Th1 immune response Multiphasic induction of murine type I IF genes can be divided into three phases. (a) The immediate early phase. Virus infection stimulates a phosphorylation cascade, leading to the activation of at least three families of transcription factors, including F-κB, AP-1 and IRF3. Activation of the IF-α promoter requires all three transcription factors. (b) IRF7 induction phase. Secretion of early IF produces an autocrine response through stimulation of the JAK-STAT pathway. Among the pathway s target genes is IRF7, itself. (c) Delayed early (amplification) phase. Many members of the IF-α gene family possess promoter binding sites for activated IRF7 and become transcriptionally active. From: Johnson and Gale, Trends Immunol. 27:1, 2006 RIG-1-like Receptors (RLRs) Sense Viral Products, Activate the IRF Pathway, and Trigger Production of Antiviral Proteins Summary 1. Innate immunity is conserved throughout evolution and is triggered by recognition of pathogenassociated molecular patterns (e.g., LPS) by pattern recognition receptors. 3. ollectins (e.g., SP-A, 1q, MBP) recognize carbohydrates on pathogen surfaces and perform multiple anti-microbial functions (e.g., opsonization). ollectins are essential for innate immunity, but also help clear apoptotic debris. 5. Members of the Scavenger Receptor superfamily recognize bacteria as well as glucose-modified proteins and oxidized lipoproteins. They are implicated in the response to infection as well as atherosclerosis and other degenerative diseases. 7. TLR4 is the major LPS receptor in mammalian cells. TLR4 triggers activation of F-κB (leading to production of TF-α, for example). Other TLRs recognize additional microbial products. OD-like receptors (LRs) are intracellular sensors of bacterial products that activate the inflammasome, triggering caspase-dependent maturation of IL Dendritic cells undergo a maturation program: immature Ds, which traffic to the periphery, capture antigen, and mature Ds, which traffic to the lymph node, present antigen. Innate immune stimuli trigger D maturation, which upregulates co-stimulatory molecules and facilitates antigen presentation. Thus, the innate immune response ushers in the acquired immune response. 6. K cells, a component of innate immunity, especially to viruses, represent an early source of IF-γ and serve to stimulate macrophages and Ds in inflammatory sites. Additional components of the antiviral response include intracellular dsra sensors (RIG-like proteins) that activate the IRF pathway to signal antiviral gene expression. Adapted from: reagh and O eill, Trends Immunol. 27:352,