The distribution of IgG and IgA subclass plasma cells among dissociated synovial cells from 14 rheumatoid arthritis (RA) synovia was examined by immunofluorescence using mouse monoclonal anti-human subclass antibodies. Of the IgG plasma cells 81 ± 9% were IgG1, 4 ± 2% IgG2, 14 ± 9% IgG3, and 0.9 ± 0.6% IgG4. While IgG1 predom-inated in all 14 synovia (which is similar to what is seen in normal tissues), in 5 14 20% or greater of IgG plasma cells were IgG3, suggesting a selective increase in IgG3 production in the synovia of certain RA patients. Among IgA plasma cells 89 ± 5% were IgA1 and 8 ± 3% were IgA2. This distribution is similar to the distribution in normal serum. © 1985.
