Editing Classical complement pathway (section)

=== Formation of C3-convertase. ===
Surface-bound C4b acts as a receptor for the binding of C2.<ref name=":1" /> The binding of C2 and C4b results in C2 being cleaved by C1s into C2a and C2b. C2b diffuses into the plasma as a protein inflammatory mediator while C2a remains attached with C4b, forming the C3-convertase (C4b2a). The function of the membrane-bound C3-convertase is the cleavage of many many molecules of C3 into C3a and C3b. C3a is a smaller fragment of C3 is a potent inflammatory mediator.