Red blood cell membrane-bound IgG: demonstration of antibodies in patients with autoimmune haemolytic anaemia and immune complexes in patients with rheumatic diseases.

Immunoglobulin G (IgG) bound in vivo to the surfaces of red blood cells (RBC-IgG) was quantificated by an enzyme-linked immunosorbent assay (ELISA) using the cells themselves as solid phase. The method was applied on RBC from normal subjects, patients with autoimmune haemolytic anaemia (AIHA) and rheumatoid patients with and without circulating immune complexes (CIC). Small amounts of RBC-IgG were detected in normal subjects and rheumatoid patients without CIC. Fifteen out of 16 patients with AIHA had increased RBC-IgG indicating RBC sensitization with IgG antibodies, although only eight patients had a positive direct antiglobulin test (DAT) with anti-IgG. Ten out of 13 rheumatoid patients with a negative DAT and with CIC had increased RBC-IgG suggesting RBC C3 receptor-bound IC. The results provide background for further studies of the significance of RBC-IgG in health and disease.