Antibodies from patients and mice with autoimmune diseases react with recombinant hnRNP core protein A1

Sera from autoimmune patients and normal volunteers were tested for antibodies to the A1 core protein of heteronuclear ribonucleoprotein (hnRNP) particles by ELISA and Western blot assays. The A1 protein used in these studies was produced by recombinant DNA technology. Thirty-seven per cent of patients with systemic lupus erythematosus produced anti-A1 antibodies, compared to 7% of normal controls. Several strains of autoimmune mice were also analysed. They spontaneously made high-titered responses to A1. Normal strains showed very low anti-A1 response unless they were specifically immunized with the antigen. Following immunization, normal mice also made high-titered responses to the A1 protein. These studies demonstrated that the A1 protein itself is an autoantigenic component of hnRNP particles. Our studies uncovered no evidence of linkage between the production of anti-A1 and of anti-DNA antibodies.