Functionally active C1 on the surface of human peripheral lymphocytes: Its role in the complement-mediated inhibition of the Fc receptor of B lymphocytes

Abstract

Guinea pig and fresh human serum inhibit the binding of aggregated human IgG to human peripheral B lymphocytes. It has been confirmed that this inhibition is mediated through the activated complement system. The presence of functionally active C1 was demonstrated on the surface of human peripheral lymphocytes. The role of surface C1 was studied in the activation of the complement system during the complement-mediated inhibition of the binding of IgG aggregates to Fc receptors of human B lymphocytes. Elimination of C1 from the surface of lymphocytes by EDTA treatment almost fully eliminated the inhibitory effect of serum on the aggregated IgG binding. The significance of the C1 on lymphocytes in the modulation of the immunoglobulin binding function of Fc receptors is discussed.