Phagocytosis: An Evolutionarily Conserved Mechanism to Remove Apoptotic Bodies

1. Phagocytosis: An Evolutionarily Conserved Mechanism to Remove Apoptotic Bodies and Microbial Pathogens

2. Phagocytosis of IgG-coated Targets by Macrophages 3 min 10 min

4. Mast Cells Can Phagocytose Too!

5. Extension of an F-actin-rich “Phagocytic Cup” Around Phagocytic Targets

6. Motor Proteins and Exocytosis Power Phagocytosis From: Chavrier, Nature Cell Biol. 4:E169, 2002

7. Phagosome-Lysosome Fusion? Elie Metchnikoff, 1845-1916

11. Post-phagocytic Events: Phagosome-Lysosome Fusion Pathogen Macrophage Lysosomes Phagolysosomes

12. Phagocytosis of Bacteria is Followed by Phagosome-Lysosome Fusion 0-3 min 1-5 min 30 min-hrs From: Allen et al., J. Exp. Med. 191:115, 2000

13. The Granuloma: a Delayed Response to Indigestible Pathogens and Particles in Macrophages Langhans-type Giant Cells Granulomas Epithelioid Cells Langhans-type giant cells represent fused macrophages. The nuclei are lined up around the peripheryof the cell. 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. Granulomatous inflammation consists of epithelioid macro- phages, giant cells, lymphocytes, plasma cells, and fibroblasts.

14. Oxidant-dependent Killing of Bacteria and Fungi

15. From: Lekstrom-Himes and Gallin, N Engl J Med, 343:1703, 2000

17. Post-phagocytic Events: “Phagosome-Oxidase Fusion” Pathogen Macrophage 2O2  2O2- + H+ NADPH oxidase

18. Post-phagocytic Events: Generation of H2O2 Pathogen Macrophage 2O2  2O2- + H+ NADPH oxidase O2- + O2- + 2H+  H2O2 + O2 Superoxide dismutase

19. Post-phagocytic Events: Myeloperoxidase Activity Pathogen Macrophage 2O2  2O2- + H+ NADPH oxidase H2O2 + Cl- HOCl + OH Myeloperoxidase O2- + O2- + 2H+  H2O2 + O2 Superoxide dismutase

20. Post-phagocytic Events: Peroxynitrite Production Pathogen Macrophage 2O2  2O2- + H+ NADPH oxidase 2O2- + NO ONOO- Peroxynitrite H2O2 + Cl- HOCl + OH Myeloperoxidase O2- + O2- + 2H+  H2O2 + O2 Superoxide dismutase

21. Bacterial Virulence Factors Subvert Host Defenses Modification of phagocytic receptors (P. aeruginosa) Escape from phagosome into cytosol (Listeria, Shigella) Ingestion phase impaired (Yersinia) Phagosome maturation stalled (M. tuberculosis; Legionella) Resistance to lysosomal degradation (Salmonella)

22. Clearance of pathogens Death of pathogenic microbe Persistence of pathogenic microbe Resolution of infection Failure of resolution of infection Clearance of apoptotic corpses Suppression of inflammation Inappropriate inflammation Tolerance Break in tolerance Immunological Consequences of Phagocytosis

23. Dendritic Cells Engulf Influenza-infected Monocytes and Cross-present Antigen Percent cytotoxicity Infected Mf + uninfected DC Unifected Mf + uninfected DC Ininfected DC Ininfected Mf Uninfected DC Uninfected Mf From: Albert et al., Nature 392:86, 1998

24. Biology of Fcg Receptors

25. Functional Sites on the IgG Molecule VH VL C1q binding site FcgR binding site Glycosylation site

26. Fcg Receptor Signaling: ITAM Phophorylation Opsonized Bacterium FcgRIIIA Y Y Y Y Y Y Y Y Y Y Y g subunit Y YP Y Y YP Y Src family TK

27. Fcg Receptor Signaling: Syk Activation Opsonized Bacterium Y Y Y Y Y Y Y Y Y Y Y FcgRIIA ligand- binding domain PTPase Y PY YP YP Syk YP YP YP Y YP Y YP TK substrates

29. Activating FcgR Inhibitory FcgR g g Syk SHIP ITAM ITIM + - Phagocytosis

30. Clustering of the BCR by Antigen Initiates Signaling Ag Igb Iga Iga Igb Igb Iga Iga Igb ITAM ITAM

31. Activating BCR Inhibitory FcgRIIB PIP3 Syk ITAM BTK + SHIP - ITIM Ig-b Ig-a PI3-kinase P PLC-g Ca2+, Proliferation

32. Positive and Negative Regulation of the BCR C3d Ag Ag IgG Y CD21 (CR2) FcgRIIB CD22 CD19 Igb Iga Iga Igb SHIP ITAM PI 3-kinase - + ITIM SHP-1 SHP-1: A protein tyrosine phosphatase PI 3-kinase: Generates PIP3 SHIP: A phosphoinositide phosphatase

33. The “Dark Side” of Fc Receptors: Immune Complex-mediated Injury

34. Hypersensitivity Diseases

35. The Arthus Reaction: A Model of Type III Hypersensitivity 1-2 hr

36. Requirement of Activating FcgRs in Immune Complex-mediated Glomerulonephritis Absence of the g 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. From: Clynes et al., Science 279:1052, 1998.

37. Requirement of Activating FcgRs in Immune Complex-mediated Glomerulonephritis Strain: C57Bl/6 NZB/NZW NZB/NZW g chain: -/- -/- +/- Glomerulonephritis is blocked in g chain-deficient NZB/NZW (lupus-prone) mice. Pathological features include mesangial thickening and hypercellularity evolving into end-stage sclerotic and crescentic changes. From: Clynes et al., Science 279:1052, 1998.

38. Summary 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. Many phagocytic receptors recognize a diverse array of microbial pathogens. Some pathogens (e.g., S. pneumoniae) require opsonization for their clearance. Bugs fight back. 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. Failure of this mechanism may result in autoimmunity. Fc receptors come in two basic types: activating (ITAM-associated) and inhibitory (ITIM-associated). The relative expression of activating and inhibitory Fc receptors determines the outcome of a given engagement of Fc receptors. Fc receptor-driven pathology includes formation and deposition of immune complexes, which play a major role in autoimmunity.