The effect of antiidiotypic antibody on the in vitro production of rheumatoid factor was studied in rheumatoid arthritis patients with cross-reactive idiotypic determinants. Antiidiotypic antibodies (ascites IgG) were developed against monoclonal rheumatoid factor (Ka m-RF) by a cell fusion procedure. These antibodies were idiotype-specific, since: 1) they reacted only with F(ab')2 fragment of Ka m-RF; 2) they failed to react with normal IgM without rheumatoid factor activity; and 3) their F(ab')2 fragment inhibited the rheumatoid factor activity of Ka m-RF. The antiidiotypic antibody strongly suppressed the in vitro production of rheumatoid factor by lymphocytes from unrelated rheumatoid arthritis patients with cross-reactive idiotypes. The suppression was specific, since ascites IgG failed to suppress in vitro anti-keyhole limpet hemocyanin antibody production by the lymphocytes. These results indicate that antiidiotypic antibody may influence the regulation of rheumatoid factor production in patients with rheumatoid arthritis.
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