Cytotoxicity of anti-Fab antibodies against B lymphocytes in rheumatoid arthritis

Anti-Fab antibody titers were positive in 70% of rheumatoid arthritis patients (54 of 77) and 3% (1 of 35) of healthy donors. Their specificity was examined by inhibition of the radioimmunoassay for anti-Fab antibodies, which demonstrated that they are against the Fd region of the intact immunoglobulin molecule. In addition, anti-Fab antibodies have broad specificities for IgG antigens, shown by inhibition with myeloma IgG. They are cytotoxic against B (20% of B cells from most healthy donors) but not T lymphocytes, with cytotoxicity greater at 5 degrees C than 37 degrees C. These studies show that the anti-Fab antibodies interact with allotypic or idiotypic determinants on subpopulations of B lymphocyte cell surface antigens.