Studies on the inhibition of C56-initiated lysis (reactive lysis). V. The roleof C567-INH in the regulation of complement-dependent haemolysis initiated by cobravenom factor.

Activation of the alternative pathway of complement by a factor from cobra venom (CVF) can lead to lysis of unsensitized erythrocytes (E) of some species. In these studies we observed that alterations in CVF-induced lysis could be produced by manipulation of C567-INH, a naturally occurring inhibitory activity which acts on fluid phase C567 complexes. Venom lysis of sheep and guinea-pig E was markedly inhibited by serum fractions having C567-INH activity. Microgram quantities of poly-L-lysine (PLL), molecular weight 180,000, a polycation which is a functional antagonist to C567-INH in serum, potentiated CVF lysis of sheep and guinea-pig E, and permitted the lysis of human E, which are otherwise not suscepticle to CVF lysis. The potentiation of venom lysis by PLL seemed not to be due to alterations in the target cell membrane; furthermore, it in turn was reversed by substances with C567-INH activity. This suggests that the generation of fluid phase C567 complexes contributes to the CVF-induced lysis of erythrocytes of these species, and that the haemolytic potential of fluid phase C567 generated during alternative pathway activation by this means is regulated by C567-INH.