Term
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Definition
| Bb is a serine protease and the active enzyme of C3 and C5 convertase in the alternative pathway |
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Term
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Definition
| plasma serine protease which cleaves Factor B when it is bound to C3b |
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Term
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Definition
stabilizes the C3 convertase (C3bBb) when it is on microbial surfaces
THE ONLY POSITIVE REGULATOR oF COMPLEMENT |
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Term
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Definition
| C1qr2s2: initiates the classical pathway; C1q binds to Fc portion of Ab; C1r and C1s are serine proteases that lead to C4 and C2 activation |
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Term
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Definition
covalently binds to surface of microbe or cell where Ab is bound and complement is activated
C4b binds to C2 for cleavage by C1s
C4a stimulates inflammation |
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Term
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Definition
| C2a is a serine protease functioning as an active enzyme of C3 and C5 convertase |
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Term
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Definition
| initiates the lectin pathway; MBL binds to terminal mannose residues of microbial carbohydrates; an MBL-associated protease activates C4 and C2, as in the classical pathway |
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Term
| what is the net result of the early steps of complement activation? |
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Definition
| opsonization of the microbe with C3b |
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Term
| what complement receptor does the macrophage have? |
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Definition
| CR1 (CD35) that binds the C3b covering microbes; found on the surface of macrophages |
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Term
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Definition
CR2 receptor on the surface of B cells, and binding stimulates B lymphocyte response (B cell activation and Ab production).
this binding process is an example of innative enhacing adaptive immune function |
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Term
| what does a deficiency of C2 or C4 (early complement proteins) results in? |
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Definition
| increased incidence of immune complex diseases (like SLE) because the classical pathway functions to eliminate immune complexes from circulation |
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Term
| what does a deficiency in C9 result in? |
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Definition
| increased susceptibility to Neisseria infections due to loss of MAC formation, which is effective against Neisseria and other bacteria with thin cell walls |
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Term
| what prevents complement proteins from attacking normal cells? |
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Definition
| the presence of complement regulatory proteins that are absence on the surface of microbes |
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Term
| what is DAF(CD55) and what does it do? |
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Definition
Decay accelerating factor: prevents binding of Bb to C3b (it displaces Bb as it associates with C3b; also C3b from binding to C4bC2a
terminates complement activation of alternative and classical pathways |
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Term
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Definition
| membrane co-factor P is a cofactor for the proteolysis of C3b into inactive fragments, which involves Factor I |
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Term
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Definition
regulatory protein; stops complement at an early stage of C1 activation
THE ONLY REG PROTEIN THAT DIRECTLY BLOCKS SERINE PROTEASE ACTIVITY via covalently binding to C1r and C1s
it binds with C1r2,C1s2 and prevents them from becoming proteolytically active (blocking their association with C1q) |
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Term
| Hereditary angioneurotic edema |
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Definition
| deficiency of C1 INH; excessive C1 activation and the production of vasoactive protein fragments leads to fluid leakage in the larynx and other tissues |
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Term
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Definition
along with cofactor MCP (membrane cofactor protein), Factor I mediates a proteolytic cleavage of C3b into inactive fragments: iC3b, C3f
THE ONLY PROTEASE THAT REGULATES |
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Term
| paroxysmal noctural hemoglobinuria |
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Definition
| results from a deficiency in an enzyme that synthesizes key glycolipid anchors critical for regulatory proteins: DAF, MCP |
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Term
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Definition
C4 binding protein: causes dissociation of classical pathway C3 convertase components
cofactor for Factor I mediated cleavage of C4b |
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Term
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Definition
| blocks C9 binding and prevents MAC |
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Term
| name the regulatory proteins in plasma |
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Definition
-C1 INH
-Factor I
-Factor H
-C4BP |
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Term
| name the regulatory proteins in membrane |
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Definition
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Term
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Definition
-many roles; found on almost all hematopoietic cells
-on phagocytes, it is an opsonic receptor
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causes dissociation of C3 convertase subunits; co-factor for factor I |
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Term
| what are the serine proteases? |
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Definition
| C1r, C1s, C2a, Factor Bb, Factor D, MASP |
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Term
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Definition
mannose-binding associated serine proteases
MASP1 is activated by the association of MBL with microbe; it cleaves/activates MASP2
MASP2: cleaves both C4 and C2 (just like C1s) |
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Term
| what are the anaphylatoxins and what functions do they serve? |
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Definition
C3a, C5a (and to a lesser extent C4a...remember they are all homologous)
role: vasodilation, chemoattraction, mast cell degranulation, induction of molecules on endothelia allowing diapedesis |
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Term
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Definition
displaces Bb from C3b, making it susceptible as a substrate for Factor I cleavage into inactive fragments iC3b, C3dg
helps to regulate complement and to keep the circulating levels of C3b "homeostatic" |
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Term
| what regulators inhibit MAC formation? |
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Definition
-CD59
-S protein
-clusterin |
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Term
| how is complement activation protective? |
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Definition
-prevents normal cells from being attacked by complement
-due to C3b "tickover" (meaning a little C3 is continuously cleaved by low levels of C3bBb activity); were it not for regulation, all C3 could be depleted
-they serve to regulate the intensity of the response bc if all C3 were cleaved thus amplifying the response, the inflammatory outcome would be overwhelming for the host |
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Term
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Definition
-found on B cells and FDCs
-highest affinity for C3d--> binding lowers the activation potential to enable stimulation
-also the receptor for EBV |
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Term
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Definition
| integrins found on surface of neutrophils and macrophages that bind strongly to iC3b |
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Term
| how does C3 bind to pathogen? |
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Definition
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Term
| how many and what type of Igs do C1 bind to? |
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Definition
| at least 2 ANTIGEN BOUND IgG1 and IgG3 (inflammatory Abs) need to be bound to microbe surface; alternatively, at least 1 IgM may activate classical pathway complement |
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Term
| what are potential cofactors of Factor I? |
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Definition
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Term
| what is the function of C3dg and C3d? |
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Definition
stimulate B cells
hang out on DCs |
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Term
| CR 1 binds what fragments and has what function? |
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Definition
| CR1 binds C3b, C4b, iC3b. Main role is enhancing phagocytosis and immune clearance from the liver |
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Term
| CR3 binds what to what end? |
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Definition
| CR3 binds iC3b and works in opsonization, phagocytosis, and cellular migration |
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Term
| CR2 binds what to what end? |
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Definition
| CR2 binds C3d and also EBV. It is on the surface of B cells and helps to stimulate them (activation and proliferation). C3d lowers activation threshold for B cells. |
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Term
| what are the complement anaphylatoxins? |
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Definition
C5a
C3a
C4a
They induce smooth muscle contraction, increase vascular permeability, activate mediator-release by mast cells; initiative adaptive immune response.
They bind to C5aR and C3aR (anaphylatoxin receptors) |
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Term
| loss of what anchor protein results in paroxysmal noctural hemtoglobinuria? |
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Definition
| loss of PIG-A (a GPI) anchor protein |
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