STUDIES ON IMMUNE ADHERENCE (C3B) RECEPTOR ACTIVITY OF HUMAN-ERYTHROCYTES - RELATIONSHIP BETWEEN RECEPTOR ACTIVITY AND PRESENCE OF IMMUNE-COMPLEXES IN SERUM

Abstract

Human erythrocytes (E) have surface receptors for the third component of complement (C3b-IA receptors) which mediate immune adherence hemagglutination (IAHA). E from patients with systemic lupus erythematosus had impaired or defective C3b receptor (C3b-R) activity when circulating immune complexes (CIC) were found in serum. This phenomenon was investigated by a newly developed method involving competitive inhibition of IAHA in patients with immune complex diseases. IAHA involving sheep E coated with antibody and complement (EAC), and indicator human E was inhibited by lysates of E with normal C3b-R activity from healthy donors and a monkey. The lysates of E from 95% of patients bearing CIC did not inhibit IAHA, which indicated such E had defective or impaired C3b-R activity. This phenomenon was supported by control studies in which IAHA was not inhibited by lysates of E with absent, inactivated or occupied C3b-R. In those patients, in whom CIC disappeared during immunosuppressive therapy, C3b-R activity slowly returned to normal levels. C3b-R activity of patients'' E decreased with the reappearance of CIC during exacerbations of disease. CIC are apparently carried in vivo by the C3b-R of E and those of the mononuclear phagocyte system, and the E C3b-R may also contribute to the clearance of CIC.