HNP inhibits C1q hemolytic activity and CH50. To determine the effect of HNP-1 on CH50, EA diluted in normal serum, were incubated with various concentrations of HNP-1 and assessed for hemolysis. Alternatively, AP50 was determined by incubation of rabbit erythrocytes in the presence of different concentrations of HNP-1 (A). Also, the effect of HNP-1 on specific complement components was determined (B). Dilutions of serum were incubated with increasing concentrations of HNP-1 and after incubation, the hemolytic activity of either C1q or C3 was determined. The data are expressed as the percentage inhibition of lysis, compared with values obtained in the absence of HNP-1.