In vitro synthesis of IgM rheumatoid factor in response to Staphylococcus aureus, by lymphocytes from healthy adults

Peripheral blood mononuclear cells from 20 healthy adults were tested in vitro for the production of IgM rheumatoid factor (RF) in response to Staphylococcus aureus Cowan I (SAC) or pokeweed mitogen. Fifteen of the 20 normal subjects produced greater than or equal to 4 ng/ml IgM-RF (mean +/- SD 46 +/- 55 ng/ml) in response to SAC, compared with only 2 of 20 who produced greater than or equal to 4 ng/ml IgM-RF (mean +/- SD 2 +/- 4 ng/ml) in response to pokeweed mitogen (P = 0.0001). Separation and reconstitution of autologous T and B cell-enriched fractions, with and without prior T cell irradiation, provided evidence for a radiosensitive T helper/inducer cell involved in the IgM-RF response to SAC in 70% of the normal subjects studied. SAC appears to be a potent stimulus of IgM-RF production, with a cellular mechanism distinct from that of other in vitro systems.