Phagocytosis: An Evolutionarily Conserved Mechanism to Remove Apoptotic Bodies

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Phagocytosis An Evolutionarily Conserved
Mechanism to Remove Apoptotic Bodies and
Microbial Pathogens
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Phagocytosis of IgG-coated Targets by Macrophages
3 min 10 min
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Mast Cells Can Phagocytose Too!
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Extension of an F-actin-rich Phagocytic Cup
Around Phagocytic Targets
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Motor Proteins and Exocytosis Power Phagocytosis
From Chavrier, Nature Cell Biol. 4E169, 2002
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Phagosome-Lysosome Fusion?
Elie Metchnikoff, 1845-1916
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Post-phagocytic Events Phagosome-Lysosome Fusion
Pathogen
Macrophage
Lysosomes
Phagolysosomes
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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. 191115, 2000
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The Granuloma a Delayed Response to
Indigestible Pathogens and Particles in
Macrophages
Langhans-type Giant Cells
Epithelioid Cells
Granulomas
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.
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Oxidant-dependent Killing of Bacteria and Fungi
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From Lekstrom-Himes and Gallin, N Engl J Med,
3431703, 2000
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Post-phagocytic Events Phagosome-Oxidase Fusion
Pathogen
Macrophage
2O2 ????????? 2O2- H
NADPH oxidase
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Post-phagocytic Events Generation of H2O2
Pathogen
Macrophage
2O2 ????????? 2O2- H
NADPH oxidase
O2?- O2?- 2H ???????????? H2O2 O2
Superoxide dismutase
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Post-phagocytic Events Myeloperoxidase Activity
Pathogen
Macrophage
2O2 ????????? 2O2- H
NADPH oxidase
H2O2 Cl- ????????? HOCl OH?
Myeloperoxidase
O2?- O2?- 2H ???????????? H2O2 O2
Superoxide dismutase
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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
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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)
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Immunological Consequences of Phagocytosis
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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 39286, 1998
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Biology of Fcg Receptors
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Functional Sites on the IgG Molecule
VH
VL
C1q binding site
FcgR binding site
Glycosylation site
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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
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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
YP
Y
Y
YP
TK substrates
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Activating FcgR Inhibitory FcgR
g g
Syk
SHIP
ITAM ITIM

-
Phagocytosis
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Clustering of the BCR by Antigen Initiates
Signaling
Ag
Igb
Iga
Igb
Iga
Igb
Iga
Igb
Iga
ITAM
ITAM
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Activating BCR Inhibitory FcgRIIB
PIP3
Syk
ITAM
BTK

SHIP
-
ITIM
Ig-b
Ig-a
PI3-kinase
P
PLC-g
Ca2, Proliferation
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Positive and Negative Regulation of the BCR
C3d
Ag
Ag
IgG
Y
CD21 (CR2)
FcgRIIB
CD22
CD19
Igb
Iga
Igb
Iga
SHIP
ITAM
PI 3-kinase
-
ITIM
SHP-1
SHP-1 A protein tyrosine phosphatase PI
3-kinase Generates PIP3 SHIP A phosphoinositide
phosphatase
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The Dark Side of Fc Receptors Immune
Complex-mediated Injury
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Hypersensitivity Diseases
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The Arthus Reaction A Model of Type
III Hypersensitivity
1-2 hr
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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 2791052, 1998.
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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 2791052, 1998.
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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