Altered control of self-reactive IgG by autologous IgM in patients with warm autoimmune hemolytic anemia

Warm autoimmune hemolytic anemia (WAIHA) is characterized by an accelerated clearance of red blood cells (RBCs) associated with the presence of anti-RBC immunoglobulin (Ig)G autoantibodies. In the present study, we analyzed the self-reactive IgG and IgM antibody repertoires of patients with WAIHA using a technique of quantitative immunoblotting on a panel of whole tissue extracts as sources of self-antigens. Data were compared by means of multiparametric statistical analysis. We demonstrate that self-reactive antibody repertoires of IgG purified from plasma and of IgG purified from RBC eluates do not differ between healthy donors and patients with WAIHA, whereas autoreactive repertoires of IgM from patients exhibit broadly altered patterns of reactivity as compared with those of healthy controls. We further demonstrate that IgG purified from eluates of RBCs of healthy donors induces agglutination of RBCs in an indirect Coombs assay to a similar extent as IgG purified from eluates of RBCs of patients with WAIHA. The capability of IgG to induce agglutination of RBCs is suppressed in unfractionated eluates of healthy donors' cells, whereas it is readily found in unfractionated eluates of patients' RBCs. IgM is an essential factor in controlling the ability of IgG in unfractionated RBC eluates to induce agglutination of RBCs. These observations indicate that anti-RBC IgG autoantibodies of patients with WAIHA share extensive similarity with natural antiRBC autoantibodies of healthy donors and suggest that defective control of IgG autoreactivity by autologous IgM is an underlying mechanism for autoimmune hemolysis in WAIHA. (Blood. 2000;95:328-335)