Activation of the Complement Attack Mechanism in the Fluid Phase and its Control by C5̄6̄7̄-INH: Lysis of Normal Erythrocytes Initiated by Zymosan, Endotoxin, and Immune Complexes

Abstract

Addition of zymosan-serum complexes to guinea pig erythrocytes in guinea pig complement-EDTA was found to result in substantial lysis of the bystander cells in the presence of polycations such as poly-L-lysine of 178,000 daltons. Involvement of the alternative C pathway was shown, and the optimum time, temperature, and eruthrocyte and polycation concentrations were defined; a surprising efficiency was observed at low temperatures and high cell concentrations. Several lines of evidence indicated that this hemolysis was mediated via the complex of the C system and modulated by serum inhibitors of (-INH): lysis was observed only with zymosan-serum complexes possessing C-consuming activity; it was not observed in C5-depleted guinea pig serum but was restored upon addition of purified C5; the addition of partially purified -INH substantially depressed hemolysis; and poly-L-lysine which is known to neutralize -INH in solution resulted in substantial enhancement of hemolysis. We also sought to determine whether the addition of complement activators directly to erythrocyte-serum mixtures could result in the hemolysis of bystander erythrocytes. It was found that zymosan, endotoxin, antigen-antibody complexes, and aggregated human γ-globulin each could initiate such bystander lysis under appropriate conditions. Lysis again was favored by increased erythrocyte concentrations, low temperatures, and the presence of polycations such as poly-L-lysine, and was found to be mediated via the C system. -INH blocked cytolysis whereas poly-L-lysine potentiated hemolysis by neutralization of -INH. These experiments emphasize the propensity for formation and lysis of bystander erythrocytes during C activation generally, the role of -INH in the control of this lysis, and the susceptibility of these interactions to modulation by highly charged macromolecules.