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Innate Immunity1 Self-Test Questions: A: both B1: all B2-3: 1 - 6, 9 B4: 1 - 4 B5: 1 - 5 B6: 1 Review on your own: Clathrin-mediated endocytosis Endomembrane transport system Also review slides on innate immunity in previous ppt Note about the alternative pathway of Complement: You are not responsible for knowing the specific steps that are unique to this pathway.

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Innate Immunity2 What is inflammation? An Innate response involves cellular & physiological elements Localized -- infection or wounding can trigger Capillary vasodilation redness (erythrema) Capillary vasopermeation swelling (edema) Cell influx Vasoactive molecules released by WBC Systemic -- infection only Fever Increase in WBC Changes in serum proteins (e.g., Acute phase proteins) Diagnostic for infection Excessive inflammation causes immunopathogies Inflammation around a wound Copyright 2003, Georgetown University

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Innate Immunity3 Danger signals activate innate cells Danger signals = PAMPs Pathogen-associated molecular patterns -- molecules of pathogens or wounding -- general structure/widespread occurrence PAMPS bind to Receptors called PRRs Pattern Recognition Receptor -- e.g., Toll-like receptors (TLR) -- other types also Very important to DC activation -- upregulates MHC expression -- allows T-cell activation Some Danger Signals (See Table 3-1 & Table 7-3) Viral dsRNA Viral ssRNA Bacterial LPS, flagellin, pilin Bacteral and fungal cell wall components Microbial polysaccharides Reactive oxygen molecules H 2 0 2, OH -, O 2 - Certain cellular molecules

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Innate Immunity4 Macrophage killing mechanisms External -- mediator secretion Internal: requires phagocytosis -- Receptor mediated, or not -- Antibody Fc receptors, PRR, etc. O 2 dependent vs independent -- respiratory burst -- enzymes

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Innate Immunity5 Neutrophil mechanisms -- rapid responders Degranulation & phagocytosis Extracellular Traps -- Chromatin & antimicrobial enzymes Images from Brinkman et al. 2004 Science 333:1532 Neutrophil granule contents Antimicrobial enzymes defensins lysozyme etc. Acid hydrolases proteases, etc. Myeloperoxidase -- produces HOCl & much more

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Innate Immunity6 Effectors of Mast cells and Eosinophils Target parasites Degranulation and secretion -- releases mediators of anaphylaxis Histamine Seratonin Prostaglandins etc Effects: Sneezing Cramping Tearing Scratching Etc Also cause allergies

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Innate Immunity7 Acute Phase Response --Systemic inflammatory response Fever, Changes in Acute Phase Proteins e.g., CRP, Complement proteins, plasminogen, fibrinogen, etc Fibrinogen causes RBCs to stick together form Rouleaux (Ru-Lo) = Black bile Fast sedimentation rate Was bled to cure illness Rouleaux The Acute Phase Response, Black bile, & Medieval bleeding

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Innate Immunity8 What is complement? What are the 4 principal functions of complement?

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Innate Immunity9 Complement involves a proteolytic activation cascade C1 activates C4, which activates C2 to C9 What are the 3 pathways of initiation? Classical (acquired) -- initiated by Ab bound to AG Alternative (innate) -- does not involve Ab binding Lectin (innate) -- activated by mannose-binding lectin C3

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Innate Immunity10 The Classical Pathway involves 3 stages Initiation begins with C1 binding to Ab bound to Ag Bind to Fc part of Ab

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Innate Immunity11 Activated C1 triggers activationof C4 and then C2 -- to form C3 Convertase Activation of C3 is an important amplification step C3 convertase activates C3 -- which acts as an opsonin and becomes part of C5 convertase

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Innate Immunity12 C5b triggers formation of the Membrane Attack Complex MAC is most effective against Gram-negative bacteria Nucleated cells Enveloped viruses

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Innate Immunity13 The Alternative Pathway C3 spontaneously fragments into C3a and C3b -- which can bind to AGs -- pathogens and Immune complexes Binding to other protein factors creates alternative C3 & C5 Convertases -- leading to MAC formation Lectin pathway is initiated by Mannose-Binding Lectin -- binds to bacterial glycoproteins Creates C1-like activator -- activates C4, C2, etc McGraw-Hill Complement Activation

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Innate Immunity14 How is Complement regulated? 1) Lability of protein fragments -- rapid, spontaneous inactivation 2) Sialic acid in glycoproteins -- inactivates C3b on body cells 3) Regulatory proteins -- e.g., C1 inhibitor (see table 3-3) Hereditary Angioedema Complement receptors mediate other functions -- immune complex clearing -- chemotaxis -- opsonization

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Innate Immunity15 How does C3b cause opsonization by phagocytic cells? Roles for both Fc and Complement receptors C3b is primary opsonin binds to CR1 receptor Coating of viruses blocks receptors and enhances opsonization

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Innate Immunity16 RBCs and CR1 play major role in immune complex clearance Immune complexes generate C3b -- via classical or alternative pathways Transport to spleen & liver Phagocytosis Deficiencies in complement-mediated IM-complex clearing are major cause of Systemic Lupus Erythromatosus (SLE)