Modulation of complement lysis of human erythrocytes by the membrane lipid viscosity

Human red blood cells (H-RBC), sensitized by specific rabbit antihuman hemolysin, showed a significant increase in susceptibility to complement lysis after rigidification of the membrane lipid layer by incorporation of cholesterol (p less than 0.001). Conversely, fluidization of the membrane lipid layer by treatment with phosphatidylcholine for cholesterol depletion displayed increased tolerance to the complement lysis (p less than 0.01). Antisera, obtained from 6 rabbits immunized with untreated H-RBC, were tested separately. The average serum concentration, exerting 50% hemolysis, was 1,1 +/- 0.4% for the cholesterol-enriched H-RBC and 16.3 +/- 7.5% for cholesterol-depleted H-RBC.