DIVERSE ANTIGEN-SPECIFICITY OF ERYTHROCYTE-REACTIVE MONOCLONAL AUTOANTIBODIES FROM NZB MICE

The specificities of a panel of erythrocyte-reactive MoAbs derived fro m NZB mice with autoimmune haemolytic anaemia (AIHA) were determined b y immunoprecipitation and immunoblotting. Of the eight antibodies, two (IgG1 MoAb 105-2H and IgG2a MoAb 34-3C) immunoprecipitated a 105-kD c omponent identified as the erythrocyte anion channel band 3. A similar band was also immunoprecipitated by the 1gG2b MoAb 34-2B when used at relatively high concentrations, but none of the remaining hybridoma a ntibodies precipitated any labelled erythrocyte components. In immunob lotting experiments only 34-2B reacted with band 3, indicating that th e epitope recognized by this MoAb is robust and differs from the deter minant(s) recognized by 105-2H and 34-3C. The remaining MoAbs to react by immunoblotting were the IgM antibodies IE10 and 4C8, both of which bound to a doublet corresponding to band 4.1 from the internal erythr ocyte membrane skeleton. Of the three MoAbs which gave negative result s in immunoprecipitation and immunoblotting, the IgM antibodies 103-7E and 106-10E reacted poorly with intact erythrocytes by Bow cytometry, but the IgG1 antibody 31-9D bound well. ELISAs demonstrated that all four IgM MoAbs are polyreactive, since they bound to histones from a p anel of nuclear antigens, and additionally 103-7E reacted with phospha tidyl choline. It is concluded that band 3 is an important autoantigen in NZB AIHA. However, since 3/5 haemolytic MoAbs failed to precipitat e this antigen, either these antibodies represent minor components of the total autoantibody response, or responses to diverse possibly non- protein surface antigens also contribute to the pathogenesis of the di sease.