The anti-erythrocyte autoimmune response of NZB mice. Identification of two distinct autoantigens

With age, Neu Zealand black (NZB) mice spontaneously develop anti-mouse red blood cell (RBC) autoantibodies resulting in the development of autoimmune haemolytic anemia (AIHA). Previously, we characterized a panel of monoclonal autoantibodies derived from unimmunized, adult NZB mice. One of these antibodies (Gs) was shown to be pathogenic, inducing AIHA in a non-autoimmune-prone mouse strain (BALB/c). Using GS, and two other antibodies from our panel, we have characterized two distinct autoantigens on the surface of mouse RBCs. The autoantigen, historically referred to as antigen X (AgX), was found to be partially hidden on the surface of the mouse RBC because glycosidase treatment or mild digestion with proteinase K resulted in increased reactivity with autoantibodies. One of the monoclonal antibodies (3H5G1) was found to immunoprecipitate a 110000 MW protein identified as the erythrocyte anion transporter (band 3)whereas the pathogenic antibody (G8) as well as a third monoclonal antibody (2E6m) were shown to immunoprecipitate a 60000 MW protein that was not reactive with the anti-band 3 serum. Finally, we show that the autoantigen recognized by GS is expressed on differentiated mouse erythroleukaemia (MEL) cells. The results suggest that a protein distinct from band 3 can serve as a target for AIHA in NZB mice.