In vitro rheumatoid factor synthesis in patients taking second‐line drugs for rheumatoid arthritis

Rheumatoid arthritis (RA) patients whose unstimulated peripheral blood mononuclear cells produce high levels of IgM rheumatoid factor (IgM‐RF) in vitro have more severe disease activity. RA patients being treated with second‐line agents, including gold salts, penicillamine, or methotrexate, tend to be low producers or nonproducers of IgM‐RF in vitro. The possibility that low production or nonproduction of IgM‐RF in vitro may be explained by treatment with second‐line agents alone, irrespective of disease activity, was analyzed in 133 RA patients whose disease status was assessed by multiple laboratory and clinical measures. The results indicate that treatment with second‐line agents and in vitro IgM‐RF synthesis are independently associated with disease activity.