Potentiation of C56-initiated lysis by leucocyte cationic proteins, myelin basic proteins and lysine-rich histones.

Synthetic polycations such as poly-L-lysine (PLL) have recently been shown to enhance C56-initiated lysis by neutralization of serum-derived inhibitors of the C567 complex, collectively designated C567-INH. In the present report we have examined the effect of several naturally occurring polycations on C56-initiated lysis. Lysosomal granule extracts from rabbit peritoneal exudate cells were found to potentiate C56-initiated lysis via counteraction of C567-INH in the fluid phase; this was dependent upon the amount of C567-INH present and independent of cell concentration. The basic proteins of guinea-pig, bovine, and monkey myelin as well as lysine-rich histones also potentiated EC567 formation, but this effect seemed to occur predominantly at the cell surface. The presence of biologically derived cationic proteins at sites of complement activation during inflammation thus might lead to enhanced tissue damage by favouring the formation of cell-C567 intermediates by either or both of these mechanisms.