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properdin
stabilizes alternative C3 convertase allowing for more C3b to be deposited on the pathogen surface
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Factor H
Factor I
Factor H binds to C3b. This allows for Factor I to bind. I inactivates C3b converting it to iC3b.
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Decay accelerating factor (DAF)
Binds to the C3b component of the alternative convertase, causing its dissociation and inactivation.
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Membrane co-factor protein (MCP)
Same function as DAF, but in addition, factor I can bind and inactivate C3b to iC3b.
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C3 convertase
- structure: Bb-C3 in the plasma
- function: cleaves C3 depositing C3b on the pathogen surface
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alternative C3 convertase
- structure: Bb-C3b on the pathogen surface
- function: cleaves C3 depositing C3b on the pathogen surface.
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Complement Receptor 1 (CR1)
- CR1 binds to C3b allowing for opsonization of bacteria
- On your own cells, it disrupts C3 convertase activity by making it susceptible to Factor I.
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alternative C5 convertase
- structure: 2 molecules of C3b and 1 molecule of Bb
- function: cleaves C5 to C5b and C5a
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Membrane Attack Complex
- structure: C5b, followed by binding of C6, C7, C8. C9 is polymerized forming a pore.
- function: kills pathogen by allowing water to flow in.
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CD59
On human cells, CD59 binds to the C5b678 complex and prevents the binding of C9 to form the pore.
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Homologous Restriction Factor
same function as CD59
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S protein
prevents soluble C5b-6-7 from binding on human cell membranes
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clusterin
prevents soluble C5b-6-7 from binding on human cell membranes
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Factor J
prevents soluble C5b-6-7 from binding on human cell membranes
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a2-macroglobulin
- a protease inhibitor (proteases are produced de novo by bacterium for the purpose of spreading infection)
- mechanism: protease cleaves the bait region of the a2-macroglobulin, which is then enshrouded by it.
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What are the ligands that the following Toll-like receptors bind to (plus where are they located):
TLR1:TLR2 heterodimer
TLR2:TLR6 heterodimer
TLR3
TLR4:TLR4 homodimer
TLR5
TLR7
TLR8
TLR9
TLR10
- TLR1/TLR2 heterodimer: lipopeptides
- TLR2/TLR6 heterodimer: lipoteichoic acid (found in gram positive bacteria)
- TLR3: double stranded viral RNA
- TLR4/TLR4 homodimer: lipopolysaccharide (found in gram negative bacteria)
- TLR5: Flagellin
- TLR7: single stranded viral RNA
- TLR8: single stranded viral RNA
- TLR9: unmethylated CpG-rich DNA
- TLR10: ??
- TLR 3, 7, 8, 9 are found on endosomes
- the rest are found on plasma membranes.
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Describe the TLR4/TLR4 pathway:
- - bacterial LPS is recognized by a complex of TLR4, MD2, and CD14
- - MyD88 binds to TLR4 and initiates a signaling cascade (if TRIF binds, then antiviral type I interferons are produced)
- - NFkB release, which activates transcription of inflammatory cytokines.
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X-linked ectodermal dysplasia and immunodeficiency
dysfunctional NFkB activation
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Paraoxysmal nocturnal hemoglobinuria
impaired synthesis of HRF, CD59, DAF
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Hereditary angioneurotic edema (HANE)
impaired synthesis of C1 inhibitor
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What binds to cause the "rolling effect" for neutrophils?
selectins (on endothelial cells) binds to s-Lex (on neutrophil)
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CD31
channel in the endothelial cell which allows the neutrophil to move into the site of infection.
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Describe the Lectin Pathway
- On sensing bacteria, macrophages release IL-6, which causes the release of acute phase proteins (C-reactive protein, and mannose binding lectin) in the liver.
- Mannose Binding lectin froms a complex with MASP-1 and MASP2, which binds son the pathogen surface
- MASP-2 cleaves C4 --> C4b which binds on the pathogen surface
- MASP-2 cleaves C2 --> C2a, which binds to C4b, forming the classical C3 convertase.
- Now C3 can be cleaved to C3b and be bound on the pathogen surface
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Describe the Classical Pathway
- C1 binds to C-reactive protein.
- this complex can cleave C4 --> C4b and C2--> C2a, thus forming the classical C3 convertase
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C1 inhibitory protein (C1INH)
- disables C1r (remember C1 binds to C-reactive protein as C1q, C1r, C1s).
- mechanism: C1r cleaves C1INH forming a covalently bonded intermediate, which is stable
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Type I interferon
activates natural killer cells
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NKG2D
- activating cell surface receptor on natural killer cell that binds to MIC-A and MIC-B of virus infected cells.
- Binding causes the NK cell to attack the virus infected cell by releasing lytic granules.
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MIC-A and MIC-B
- ligand expressed on the surface of virus infected cells.
- Binding with NKG2d of the NK cell, causes it to attack the virus infected cell by releasing lytic granules
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