Objective. We sought to compare the frequencies of precursors producing IgM rheumatoid factors (IgM-RFs) in synovial fluid and peripheral blood B cells from patients with rheumatoid arthritis (RA).
Methods. We used limiting-dilution analysis of Epstein-Barr virus—activated B cells from seropositive and seronegative patients. B cell precursors producing IgM against insulin, an irrelevant autoantigen, were also assessed for comparison.
Results. On average, IgM-RF—producing precursors were 15-fold higher in the synovial fluid than in the peripheral blood of seropositive RA patients, but not in seronegative RA patients. The frequency of B cell precursors producing IgM against insulin was lower in the synovial fluid than in the peripheral blood of both the seropositive and the seronegative patient groups; moreover, the concentrations were similar in both groups.
Conclusion. The findings provide evidence against a nonspecific accumulation of IgM-producing cells in the synovial fluid, and suggest that there is an active attraction of the RF-producing B cell precursors toward sites of inflammation in RA.