IgA on the surface of erythrocytes from IgA nephropathy patients

Erythrocytes (RBCs) have been reported to play a role in the transport of both IgG and IgA immune complexes in primates. Therefore they investigated the IgA on the surface of RBCs from IgA nephropathy (IgA NP) patients. Surface immunoglobulins were detected by radioimmunoassay using radiolabeled monoclonal anti-IgA1, anti-IgA2 and protein A. The RBCs from one-third of IgA NP patients examined had over 10 ng IgA1/4 x 10/sup 8/ RBCs, which was more than on RBCs from normal individuals. There was no surface IgA2 and the level of IgG on their surfaces was the same as that of normal RBCs. IgA1 present on patients' RBCs was displaced from the surface by incubation with monoclonal IgA1, but not with IgG, IgA2, IgM or C3. Furthermore, incubation with factor I (C3b inactivator) did not affect the binding of IgA1 on RBCs. Polyethylene glycol precipitates from the sera of IgA NP patients, which contained IgA1, IgG and C3, were able to bind to the RBCs from an IgA deficient patient. This binding was also inhibited by IgA1, but not IgG, IgA2, IgM or C3. These results suggest that the RBCs from IgA NP patients have IgA1 or IgA1 immune complexes on their surface andmore » that the binding is mediated through the interaction of IgA1 and an IgA receptor on the surface of RBCs.« less