Modified spontaneous and mitogen-stimulated IgG synthesis in lymphocytes from rheumatoid synovial fluid

Lymphocytes from rheumatoid synovial fluid (RASFL) synthesized lower levels of IgG than normal or rheumatoid peripheral blood lymphocytes (PBL) when cultured in vitro with a plant lectin, pokeweed mitogen (PWM). Conversely, RASFL produced higher levels of IgG than normal or rheumatoid PBL when the plant mitogen was omitted. B cell rich fractions from RASFL showed an enhancement in both spontaneous and PWM-induced IgG synthesis when they were combined with normal PBL T cells, suggesting that the RASFL B cells had already been partially activated in vivo. Presumably, RASFL T cells are defective in that they are not able to assist B cells effectively in the response to PWM stimulus. We also found that rheumatoid synovial fluid contains some humoral factors which render normal PBL T cells capable of helping normal PBL B cells synthesize IgG spontaneously. These findings may contribute to the inflammatory process of rheumatoid synovitis.