IMMUNOGLOBULINS
CLASSICAL ALTERNATE AND LECTIN PATHWAYS
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Dissociates C1r from C1q
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Cofactor with I to inactivate C3b
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Acts as cofactor with I to inactivate C4b
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cofactor for factor I; mediates transport of immune complexes
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Detailed explanation-1: -C4BP functions as a co-factor for factor I in proteolytic inactivation of both soluble and cell surface-bound C4b, thus restricting the formation of the C3-convertase, C4b2a. C4BP also accelerates the natural decay/dissociation of the C3 convertase.
Detailed explanation-2: -C4BP binds apoptotic and necrotic cells as well as DNA, to clean up after injury. The interaction with apoptotic and necrotic cells is mediated by the Gla domain of protein S and does not affect the ability of C4BP to inhibit complement.
Detailed explanation-3: -Factor I (FI) is a crucial inhibitor controlling all complement pathways due to its ability to degrade activated complement proteins C3b and C4b in the presence of cofactors such as factor H, C4b-binding protein, complement receptor 1 or CD46.
Detailed explanation-4: -In the classical and MB-lectin pathways, the C3 convertase is formed from membrane-bound C4b complexed with C2b.