Phagocytosis: An Evolutionarily Conserved Mechanism to Remove Apoptotic Bodies and Microbial Pathogens Phagocytosis of IgG-coated Targets by Macrophages 3 min 10 min Mast Cells Can Phagocytose Too! Extension of an F-actin-rich Phagocytic Cup Around Phagocytic Targets Motor Proteins and Exocytosis Power Phagocytosis From: Chavrier, Nature Cell Biol. 4:E169, 2002 Elie Metchnikoff, Phagosome-Lysosome Fusion? Post-phagocytic Events: Phagosome-Lysosome Fusion Lysosomes Pathogen Macrophage Phagolysosomes 0-3 min1-5 min30 min-hrs Phagocytosis of Bacteria is Followed by Phagosome-Lysosome Fusion From: Allen et al., J. Exp. Med. 191:115, 2000 Granulomatous inflammation consists of epithelioid macro- phages, giant cells, lymphocytes, plasma cells, and fibroblasts. Epithelioid cells accumulate around the center of a granuloma. They get their name from the fact that they have pink cytoplasm similar to squamous epithelia. Langhans-type giant cells represent fused macrophages. The nuclei are lined up around the peripheryof the cell. The Granuloma: a Delayed Response to Indigestible Pathogens and Particles in Macrophages Epithelioid CellsGranulomas Langhans-type Giant Cells Oxidant-dependent Killing of Bacteria and Fungi From: Lekstrom-Himes and Gallin, N Engl J Med, 343:1703, 2000 Post-phagocytic Events: Phagosome-Oxidase Fusion NADPH oxidase Pathogen Macrophage 2O 2 2O H + Post-phagocytic Events: Generation of H 2 O 2 NADPH oxidase Pathogen Macrophage 2O 2 2O H + O 2 - + O 2 - + 2H + H 2 O 2 + O 2 Superoxide dismutase Post-phagocytic Events: Myeloperoxidase Activity NADPH oxidase Pathogen Macrophage 2O 2 2O H + O 2 - + O 2 - + 2H + H 2 O 2 + O 2 Superoxide dismutase H 2 O 2 + Cl - HOCl + OH Myeloperoxidase Post-phagocytic Events: Peroxynitrite Production NADPH oxidase Pathogen Macrophage 2O 2 2O H + O 2 - + O 2 - + 2H + H 2 O 2 + O 2 Superoxide dismutase H 2 O 2 + Cl - HOCl + OH Myeloperoxidase 2O NO ONOO - Peroxynitrite Bacterial Virulence Factors Subvert Host Defenses Phagosome maturation stalled (M. tuberculosis; Legionella) Ingestion phase impaired (Yersinia) Resistance to lysosomal degradation (Salmonella) Modification of phagocytic receptors (P. aeruginosa) Escape from phagosome into cytosol (Listeria, Shigella) Immunological Consequences of Phagocytosis Death of pathogenic microbe Persistence of pathogenic microbe Resolution of infection Failure of resolution of infection Clearance of pathogens Clearance of apoptotic corpses Suppression of inflammationInappropriate inflammation ToleranceBreak in tolerance Dendritic Cells Engulf Influenza-infected Monocytes and Cross-present Antigen From: Albert et al., Nature 392:86, 1998 Percent cytotoxicity Infected M + uninfected DC Unifected M + uninfected DC Ininfected DC Uninfected DC Ininfected M Uninfected M Biology of Fc Receptors C1q binding site Glycosylation site Fc R binding site Functional Sites on the IgG Molecule VHVH VLVL Y Y YPYPYPYP YPYPYPYP Y Y Fc RIIIA subunit Src family TK YYYYYYYYYYY Opsonized Bacterium Fc Receptor Signaling: ITAM Phophorylation PYPPYP PTPase PYPPYP PYPPYP PYPPYP PYPPYP Y Y Y TK substrates Fc RIIA ligand- binding domain YYYYYYYYYYY Opsonized Bacterium PPYPPY PYPPYP PYPPYP Syk Fc Receptor Signaling: Syk Activation SykSHIP Phagocytosis Activating Fc R Inhibitory Fc R ITAM ITIM Ig Ig Ig Ig ITAM Ag Clustering of the BCR by Antigen Initiates Signaling Ig Ig Ig Ig ITAM Ig- Activating BCR Inhibitory Fc RIIB Syk Ca 2+, Proliferation Ig- ITAM ITIM PLC- P PIP 3 BTK SHIP PI3-kinase Ig Ig Ig Ig CD21 (CR2) ITIM CD19 Ag C3d PI 3-kinase - + SHP-1 CD22 Positive and Negative Regulation of the BCR Ag SHIP Fc RIIB ITAM Y IgG SHP-1: PI 3-kinase: SHP-1: A protein tyrosine phosphatasePI 3-kinase: Generates PIP 3 SHIP: SHIP: A phosphoinositide phosphatase The Dark Side of Fc Receptors: Immune Complex-mediated Injury Hypersensitivity Diseases The Arthus Reaction: A Model of Type III Hypersensitivity 1-2 hr Absence of the subunit of Fc receptors leads to enhanced survival in the F1 generation of NZB/NZW (lupus-prone) mice, a model for autoimmune, immune complex-mediated glomerulonephritis. Requirement of Activating Fc Rs in Immune Complex-mediated Glomerulonephritis From: Clynes et al., Science 279:1052, 1998. Glomerulonephritis is blocked in chain-deficient NZB/NZW (lupus-prone) mice. Pathological features include mesangial thickening and hypercellularity evolving into end-stage sclerotic and crescentic changes. Requirement of Activating Fc Rs in Immune Complex-mediated Glomerulonephritis From: Clynes et al., Science 279:1052, Strain: C57Bl/6 NZB/NZW NZB/NZW chain: -/- -/- +/- Summary 1.Phagocytosis is a component of innate and aquired immunity. It is the principal means of destroying pathogenic bacteria and fungi. Phagocytosis initiates the process of antigen presentation. 2.Many phagocytic receptors recognize a diverse array of microbial pathogens. Some pathogens (e.g., S. pneumoniae) require opsonization for their clearance. 3.Bugs fight back. 4.Phagocytosis is an essential component of development and tissue remodeling. Ingestion of apoptotic bodies is immunologically silent and is normally accompanied by a suppression of inflammation. 5.Failure of this mechanism may result in autoimmunity. 6.Fc receptors come in two basic types: activating (ITAM-associated) and inhibitory (ITIM-associated). 7.The relative expression of activating and inhibitory Fc receptors determines the outcome of a given engagement of Fc receptors. 8.Fc receptor-driven pathology includes formation and deposition of immune complexes, which play a major role in autoimmunity.