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ACTIVATION OF THE COMPLEMENT CASCADE Classical Pathway The classical pathway starts with C1; C1 binds to immunoglobulin Fc (primarily IgM and IgG); C1 is recognition complex composed of 22 polypeptide chains in 3 subunits; C1q, C1r, C1s. C1q is the actual recognition portion, a glycoprotein containing hydroxyproline and hydroxylysine that looks like a tulip flower. Upon binding via C1q, C1r is activated to become a protease that cleaves C1s to a form that activates (cleaves) both C2 and C4 to C2a/b and C4a/b. C2b and C4b combine to produce C3 convertase (C3 activating enzyme). C4a has anaphylactic activity (inflammatory response).
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Unformatted text preview: C3 is central to both the classical and alternative pathways. In classical, C4b2b convertase cleaves C3 into C3a/b. C3a is a potent anaphylatoxin. C3b combines with C4b2b to form C4b2b3b complex that is a C5 convertase. C3b can also bind directly to cells making them susceptible to phagocytosis. C5 is converted by C5 convertase (i.e. C4b2b3b) to C5a/b. C5a has potent anaphylatoxic and chemotaxic activities. C5b functions as an anchor on the target cell surface to which the lytic membrane-attack complex (MAC) forms. MAC includes C5b, C6, C7, C8 and C9. Once C9 polymerizes to form a hole in the cell wall, lysis ensues....
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This note was uploaded on 11/05/2011 for the course BIOLOGY MCB2010 taught by Professor Jessicadigirolamo during the Fall '10 term at Broward College.

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