The 3 pathways of complement activation converge on the cleavage of C3 by C3 convertases. C3 convertase cleaves C3 into C3a and C3b - a central step of complement activation. C3a remains in the fluid phase and acts as an anaphylatoxin, whereas C3b can form additional C3 convertases hastening the production of C3b. Besides, C3b binds to C3 convertases to form C5 convertase, which can act as an opsonin, or is degraded into fragments which cannot form an active convertase.
Lesavre, PH, Hugli, TE, Esser, AF, Muller-Eberhard, HJ
Fujita, T, Matsushita, M, Endo, Y
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