 Other CCPs prevent the activity of terminal effectors of the complement system, CD59 for example blocks oligomerization of the complement peptide C9 stalling the formation of the Membrane Attack Complex (MAC).For example, C3b.Bb is an important convertase that is part of the alternative pathway, and it is formed when factor B binds C3b and is subsequently cleaved.To prevent this from happening, factor H competes with factor B to bind C3b; if it manages to bind, then the convertase is not formed.