Modulation of the formation of the human C-3 amplification convertase of complement by polyelectrolytes.

Heparin in the fluid phase inhibits generation of the C3 amplification convertase of complement C3b,Bb. The anticomplementary activity requires the presence of O-sulfate groups on the molecule and is suppressed when the negative charges of heparin are neutralized with positive charges on polycations. In the absence of heparin, polycations inhibit generation of the cell-bound or fluid phase amplification convertase at final concentrations of 1 to 2 x 10(-8) M for poly-L- lysine 50,000 (PLL). PLL is more active on the D-dependent convertase C3b,Bb than in preventing generation of C3b,B; it does not alter the stabilizing effect of properdin. As for heparin, the major site of the inhibitory action of polycations is on the binding capacity of C3b for B. The low affinity interaction of C3b and B is a privileged site for potential pharmacologic modulation of the amplification convertase of complement by polyelectrolytes.