Polyions regulate the alternative amplification pathway of complement.

Polyanion has previously been shown to inhibit generation of amplification pathway convertase of complement and to inhibit H-mediated decay of this complex. Polycations, protamine sulfate, and poly-l-lysine (PLL) were examined in this study for direct effects on alternative amplification pathway mechanisms and for ability to regulate polyanion-induced inhibiton; they were found to inhibit generation of EAC4b,3b,Bb, and EAC4b,3b,Bb,P in a dose-related manner. The generation of EAC4b,3b,B was also inhibited by higher doses but was augmented by lower doses of polycation. Polycation interfered with the effective consumption of B in the fluid phase, bound minimally to EAC4b,3b, and did not cause accelerated decay of a preformed convertase. Polycation diminished the ability of polyanion (heparin) to inhibit generation of both cell-bound and fluid-phase amplification pathway convertase. In contrast, polycation enhanced the ability of polyanion to cause decay of preformed convertase even though polycation had no effect itself. These studies demonstrate that both polyionic substances have the capacity to regulate amplification pathway mechanisms directly.