Role of membrane lipids in cold agglutination of human erythrocytes

Abstract

The membrane lipid fluidity of normal human erythrocytes was modified by enrichment and depletion in cholesterol. and the expression of I and Sp₁ antigens was assayed by quantitative hemagglutination from 4° to 24°C by use of a continuous flow system. Below 16°-18°C. cholesterol enrichment increased and cholesterol depletion decreased percent agglutination. As temperatures approached approximately 18°-2O°C. differences in agglutination between modified and unmodified erythrocytes became insignificant despite marked differences in lipid fluidity at that temperature. Thus. fluidity changes alone cannot be responsible for the effect of membrane cholesterol on cold agglutination. In an additional study, the temperature dependence of a relative equilibrium association constant, estimated by probit analysis of percent agglutination at various antisera concentrations. was biphasic with a sharp break at 16°C. Our studies are consistent with the hypothesis that I and Sp₁, antigens preferentially partition into a lipid domain that forms during lateral phase separation of membrane lipid developing at low temperature. A resulting increase in antigen density would then become responsible for augmented agglutination by specific antibody.