Editing Alternative complement pathway (section)

==Signaling cascade==
This change in shape allows the binding of plasma protein [[Complement factor B|Factor B]], which allows [[Factor D]] to cleave Factor B into Ba and Bb.

Bb remains bound to C3(H<SUB>2</SUB>O) to form C3(H<SUB>2</SUB>O)Bb. This complex is also known as a fluid-phase [[C3-convertase]].  This convertase, the alternative pathway C3-convertase, although only produced in small amounts, can cleave multiple C3 proteins into C3a and C3b.  The complex is believed to be unstable until it binds [[properdin]], a serum protein.  The addition of properdin forms the complex C3bBbP, a stable compound which can bind an additional C3b to form alternative pathway C5-convertase.

The C5-convertase of the alternative pathway consists of (C3b)<SUB>2</SUB>BbP (sometimes referred to as C3b<sub>2</sub>Bb). After the creation of C5 convertase (either as (C3b)<SUB>2</SUB>BbP or C4b2a3b from the classical pathway), the complement system follows the same path regardless of the means of activation (alternative, classical, or lectin).  C5-convertase cleaves C5 into C5a and C5b.  C5b binds sequentially to C6, C7, C8 and then to multiple molecules of C9 to form [[membrane attack complex]].