Recognition of Pathogens I&I L2 PDF

Recognition of Pathogens by cells of the innate immune system Dr. Sreepoorna Pramodh Acknowledgements: Dr. Paul Harrison  Immune System - 3 Levels Of Defence 1 2 3 1014 >99% 10...

Recognition of Pathogens by cells of the innate immune system Dr. Sreepoorna Pramodh Acknowledgements: Dr. Paul Harrison  Immune System - 3 Levels Of Defence 1 2 3 1014 >99% 1012-1015 Protozoan Fungi 10-200m Worms 2m - cm Flukes 1cm - 3m Pathogen-Associated Molecular Patterns (PAMPS) (common microbial components) Unique structures present in proteins (unique microbial signatures) Repeating molecular patterns Absent in humans but present in microbes E.g. Lipopolysacharide (LPS)- Gram-negative bacteria Lipoteichoic acid (LP) and peptidoglycan- Gram-positive bacteria Flagellin- bacteria ds and ssRNA of viruses British Society for Immunology Express: Pattern Recognition Receptors (PRRs) (Evolved over time >600m yrs – genes encoded in DNA) Receptors expressed on the plasma membrane of cells of innate immune system such as macrophages, dendritic cells and neutrophils Other than on cell surface, they are also expressed in cellular compartments such as cytosol, endosomes and lysosomes Able to detect extracellular and intracellular PAMPS Each type of PRR can recognize multiple pathogenic species that share a molecular pattern like LPS or flagellin Types of PRR Toll-like receptors (TLR)- detect bacteria, virus and protists C-type lectin receptors (CLR)- detect fungi Nucleotide-binding oligomerization domain (NOD)-like receptors (NLR)- cytosolic receptors that detect intracellular bacterial invasion and stress signals RIG-1 like receptors (RLR)- soluble PRRS that exist in cytosol and detect viruses British Society for Immunology  PATHOGEN Bacteria (extra) Surface Expressed Pattern Recognition Receptors (PRR’s) Toll-like Receptors (TLRs) – 6 Bacteria (Intra) (TLR 1, 2, 4, 5, 6, 10) Surface/Secreted components (PAMP’s) DNA viruses RNA viruses TLRs Fungi Parasites  Detection of Pathogen PAMPs By Surface TLR’s Coat proteins Coat proteins (TLR 2, 4) (TLR 2, 4) LTA = Lipoteichoic acid TLR 1, 2, 4, 5, 6, 10  PATHOGEN Endosome expressed Bacteria (extra) Pattern Recognition Receptors(PRR’s) Bacteria (Intra) Exposed nucleic acids RNA Endosomes TLRs DNA DNA viruses Lysosomes RNA viruses Toll-like Receptors (TLR’s) - 4 (TLR 3, 7, 8, 9) Fungi Parasites Phagocytic Immune Cells (Neutrophils, Macrophages & dendritic cells) Detection of Pathogen Nucleic Acid PAMPs By Endosomal TLR’s TLR 3, 7, 8, 9  PATHOGEN Bacteria (extra) Surface Expressed Pattern Recognition Receptors (PRR’s) Recognize carbohydrate components of fungi, bacteria and parasites Bacteria (Intra) DNA viruses C-Type lectin Receptors (CLRs) - >12 RNA viruses CLR Sugars Mannose Fructose -glucan Fungi Parasites CLR’s expressed on Macrophages & Dendritic cells  C-Type Lectin Receptors Mannose receptor (mannose) Glucan Receptor (-glucan) Fungi Parasites Mycobacteria -glucan (S. mansoni) Viruses Cord Factor (Dengue) C-Type Lectin domains Are carbohydrate binding proteins Dectin 1 Dectin 2 MINCLE CLEC5a Detect Sugar Moieties (PAMP’s) On Surface of Pathogens  PATHOGEN PAMP PRR Bacteria (extra) (example) Detection LPS of pathogens Bacteria (Intra) DNA/RNA TLR Flagellin TLR DNA viruses DNA NLR’s RNA viruses DSR’s RNA RLR’s Fungi Sugars CLR TLR Parasites GPI-linked All PRR’s are expressed by Proteins Macrophages & Dendritic cells  Cell PATHOGEN Bacteria (extra) Response Bacteria (Intra) TLR4 DNA viruses NLR’s DNA Inflammation RNA viruses sensors Interferons Adaptive immunity RLR’s Fungi CLR TLR2 Parasites Pathogen clearance Immunity PAMP-PRR-Inflammation Pathogen Recognition Receptors & Innate immune Response || Toll-like Receptors (youtube.com) TLR-Mediated Effector Functions Activated macrophages produce many cytokines (IL-1, TNF , IL-6, IL-12, CXCL8 etc that have local and systemic effects microbe NFk’s http://upload.wikimedia.org/wikipedia/commons/0/0e/Macrophage.png Pro-inflammatory Cytokines/chemokines TLR Inflammation IL1, IL6 IL8,TNF Cytokines: Low‐molecular‐weight proteins that stimulate or inhibit the differentiation, proliferation or function of immune cells. chemokines: A family of structurally related cytokines that selectively induce chemotaxis and activation of leukocytes Acute Inflammation TLR-Mediated Effector Functions (TLR3, TLR4, TLR7, TLR8, TLR9) Ribonuclease Protein kinase vRNA microbe http://upload.wikimedia.org/wikipedia/commons/0/0e/Macrophage.png TLR mRNA degraded Protein synthesis inhibited Virus replication inhibited IRF’s Anti-viral cytokines Inhibit viral replication IFN & IFN Same Effector Functions Mediated By RLR’s & DSR’s  PRRs on Produce sentinel Trigger Activated PAMPs on Recognized cytokines Pathogens by PRRS cells bind to PAMPs signal transduction sentinel cells and Inflammation chemokines Goals of inflammatory response: 1. Prevent initial establishment of infection 2. Prevent spread of infection from invasion site 3. Recruit effector cells for assistance 4. Alert and mobilize B cells and T cells Cardinal signs of inflammation 1. Redness- Increased blood flow 2. Warm- Decreased blood flow velocity 3. Swelling- Increased vascular permeability 4. Pain- Increased vascular diameter Signs and Symptoms Of An Infection An infected wound may be characterized by: pain, redness, warm to the touch (heat) and swelling, – Infection Associated Inflammation PAMP activation of Sentinel PRR’s triggers local inflammation Infection Associated Inflammation PAMP activation of Sentinel PRR’s triggers local inflammation 1. Cytokines secreted by macrophages act on neighboring cells including endothelial cells of blood vessels 2. Endothelial cells begin to express specific adhesion molecules and chemokines that are selective leucocytes and adhere to free moving leucocytes 3. Leucocytes slow down, adhere to adhesion molecules and chemokines, and squeeze in between endothelial cells and enter site of infected tissue 4. Fluid from blood also enters infected site providing soluble components like antibodies Blisters - Sterile inflammation No Infection Also Characterised by: Pain, redness, heat & swelling Inflammatory response elicited by physical damage to tissue cells Cell Lysis (necrosis) Release: Damage Associated Molecular Patterns (DAMPs) Intracellular Cell Components Exposed Following Lysis DAMPs are usually nuclear or cytoslic cell components released to the extracellular environment Intracellular Cell Components Exposed Following Lysis ATP DNA Heat shock proteins Uric acid Cell Lysis Cytosol Mitochondria nucleus Histones Nucleic acids (DNA & RNA) Act as “Danger Signals” to immune system of cell damage  DAMPs Are Ligands For Some TLR’s, CLR’s & NLR’s Signaling pathways of Toll-like receptors E.g. TLR signalling General structure of Toll-like receptors DAMP TIR domain SIGNAL DAMP RESPONSE chemokines Inflammation File:Cutaneous abscess MRSA staphylococcus aureus 7826 lores.jpg Abscess - pocket of pus (necrotic neuts + dead & live bacteria). Staph aureus bacteria resist killing by neutrophils Enzymes released by necrotic neutrophils cause cell liquefaction forms pus DAMPs & PAMP’s both promote inflammation Natural Killer Cell (NK cell) Large granular lymphocytes Recognise and kill virus-infected & transformed cells Natural Killer (NK) Cells express 2 sets of receptors- recognise molecules on surface of infected or malignant cells Inhibitory ligand One set are inhibitory and one set activating  If inhibitory signal is reduced ( MHC Class I) the killer activating signal prevails Inhibitory receptor Activating receptor Dead Cytolytic mechanisms of NK cells NK Cell Lytic FasL is present in the lytic granule membranes of NK cells Trimer Target Cell Apoptosis PRR Signalling Triggers Dendritic Cell Activation and Promotes An Adaptive Immune Response Tissue Pathogen Dendritic cell Lymph node Proliferation Adaptive immunity Summary - Pattern Recognition Receptors Four families of PRR’s: Toll-like (TLRs), Nod-like (NLRs), RIG-I-like (RLRs) and DNA sensing (DSR’s) Initiate innate immunity, the inborn host response to common pathogens such as viruses, bacteria, and fungi General features: Directly recognize common antigen determinants of virtually all classes of pathogens (pathogen-associated molecular patterns, PAMPs) and initiate immune response against them via specific intracellular signalling pathways that induce expression of pro-inflammatory cytokines as well as the type-I interferon response. Act to attracts immune cells to the site of infection, and activate the adaptive immune response. Some also recognize endogenous ligands released in cells under stress, which are known as damage-associated molecular patterns (DAMPs). Therefore, a subset of PRR-mediated immune response can be activated without an influence of infectious agents Exit Slip For revision Complement : Overview ◼ The complement system is part of the innate immune system (vs adaptive) ◼ It is named “complement system” because it was first identified as a heat-labile component of serum that “complemented” antibodies in the killing of bacteria ◼ It is now known that it consists of over 30 proteins and contributes 3 g/L to overall serum protein quantities  The Complement System (35 proteins total) Complement cascade 13 proteins (9 pro-enzymes) Triggered Pro-enzymes Enzyme amplify the response Cascade at each stage Effector Functions Complement proteins (pro-enzymes) C protein Attachment site Ca Cb Enzyme site Activates next proenzyme in cascade Binds Microbe surface 3 initial pathways of complement activation Innate Humoral Response Pre-Specific antibody formation 3 Initiator molecules Lectin Pathway Classical Pathway Alternative pathway CRP MBL C3b Microbe MBL = Mannose Binding Lectin CRP = C-reactive protein 3 initial pathways of complement activation Adaptive Response Lectin Pathway Classical Pathway Alternative pathway MBL Specific Ab C3b Specific Antigen Sugar PAMP Foreign Surface Microbe Acute Phase Proteins In response to inflammation and infection, inflammatory cytokines affect liver and in responseliver produces acute phase response proteins MBL Liver Blood Tissue CRP (Plasma) (Fluids) IL-1 IL-6 Target & activate the C’-system to surface of microbes Infection/inflammation Production increased in response to infection (x1000) All Three Activation Pathways Converge To Form C3 convertases Lectin Pathway Classical Pathway Alternative Pathway MBL Antibody C3b Plasma Concn of C3 1.5mg/ml Microbe surface C3 Convertase X100-1000 C3 Massive amplification of C3b response C3 Convertases Classical & Lectin Pathway - C4bC2a Alternative Pathway - C3bBb C3 protein Attachment site C3a C3b Enzyme site Activates next proenzyme in cascade Binds Microbe surface C5 Convertases Classical & Lectin Pathway - C4bC2aC3b Alternative Pathway - C3bBbC3b C5 protein Attachment site C5a C5b Enzyme site Activates next proenzyme in cascade Binds Microbe surface The Complement System Can Be Activated In One of Three Ways Initiators Maximises 1 initiator Recognition 1 2 3 molecule of any Pathogen Complement cascade 5mins Enzyme Cascade Effector Functions 106-108 Effector Molecules Opsonisation Lysis Inflammation Invading Microbes rapidly become coated in complement proteins (Opsonised) (cell wall) Complement Bacteria (C3b) Phagocytosis of Complement Opsonised Pathogens Complement Receptors (CR’s) On Phagocytes Trigger Phagocytosis of Complement (C3b) Coated Pathogens Neutrophils, macrophages & dendritic cells express Complement Receptors (CR’s) Actions of Membrane Attack Complex - C5b,C6,C7,C8,C9n Lipid Also viral bilayer envelopes MAC - barrel shaped insertion complex Surface of microbe (after MAC formation) Healthy bacteria Lysis of bacteria (surface blebs) Actions of Membrane Attack Complex - C5b,C6,C7,C8,C9n Lipid Also viral bilayer envelopes MAC - barrel shaped insertion complex Surface of microbe (after MAC formation) Healthy bacteria Lysis of bacteria (surface blebs) Complement-mediated Inflammation - C3a & C5a Bi-products of Complement Cascade C3a & C5a Tissue 3. Neutrophil Chemotaxis 2. Endothelial cell activation 1. Mast cell degranulation Blood Adhesion Vasodilation molecules Neutrophils Actions of C3a & C5a 1. Activate Tissue Mast Cells 2. Activate Endothelial Cells + More Complement proteins flow into tissue site 3. Attract innate immune cells from blood into infection site Downloaded from: Student Consult (on 19 September 2009 01:48 PM) © 2005 El sevier  Innate immunity KEY FEATURE : Always present, all the time (Rapid Response) A set repertoire of PRR responses to common Pathogen molecules (PAMPs) (No memory Response Generated) Probably the major pathway by which invading organisms are cleared If you end up inducing acquired immunity, you have a disease! The humoral Innate Immune System Comprises of 2 groups of soluble plasma proteins: The complement enzyme cascade system – (C1-C9) & Acute Phase proteins – Mannose binding lectin (MBL) & C-reactive protein (CRP) Function of MBL & CRP – target & activate the C’-system to surface of microbes Functions of the complement system: (Mast cell degranulation) neutrophils