Spontaneous hydrolysis of C3 thioester
Factor B binds to C3(H2O)
Factor D cleaves C3(H2O)-bound Factor B
C3(H2O):Factor Bb cleaves C3 to C3b and C3a
C3b binds to cell surface
Factor B binds to surface-associated C3b
Factor D cleaves C3b-bound Factor B
Properdin stabilizes C3b:Bb bound to cell surfaces
Formation of alternative pathway C5 convertase
Alternative complement activation