Pokeweed mitogen-induced secretion of IgG- and IgM-rheumatoid factors by synovial fluid and blood B lymphocytes in rheumatoid arthritis

Summary Lymphocytes from patients with rheumatoid arthritis (RA) were assayed for their ability to secrete Ig and rheumatoid factors (RF) upon polyclonal activation in vitro. B lymphocytes secreting IgM-RF and IgG-RF were enumerated using hemolytic plaque forming cell (PFC) assays. The sensitivity of RF-PFC formation was similar to that of a reverse PFC assay detecting all cells secreting Ig. Blood mononuclear cells from RA patients generated a median of 12 IgM-RF and 15 IgG-RF-secreting cells/10⁶ after 6 days culture with pokeweed mitogen (PWM). Thus a median of approximately 0.5% of IgM- and IgG-secreting cells were identified as RF-PFC. Synovial fluid B lymphocytes co-cultured with autologous blood T lymphocytes in the presence of PWM generated higher numbers of RF-secreting cells; medians of 43 IgM-RF and 441 IgG-RF secreting cells/10⁶ were found. Thus, 8–9% of IgM- and IgG-secreting cells from synovial fluid were identified as RF-PFC. In co-cultures containing synovial fluid T cells, PWM-induced RF secretion was low. The data indicate that both blood and SF B cells have the potential for RF secretion.