In vitro IgM and IgM rheumatoid factor production in response to Staphylococcus aureus Cowan I: evidence for the role of Leu-2-positive T suppressor cells and radiosensitive T helper cells.

Staphylococcus aureus Cowan I (SAC) is a potent stimulus of B cell proliferation and differentiation, the latter being T cell-dependent. It has been suggested that immunoglobulin and IgM rheumatoid factor (RF) production in response to SAC involves radiosensitive T helper cells. We studied normal peripheral blood mononuclear cell (PBMC) cultures to assess the roles of radiosensitive T cells and Leu-2 positive suppressor cells in the cellular control of SAC-stimulated IgM and IgM RF responses. Depletion of Leu-2 positive T cells from reconstituted autologous PBMC cultures resulted in an increase in SAC-stimulated IgM production in the majority of individuals, implying the involvement of Leu-2 positive suppressor T cells in this system. Suppression by Leu-2 positive cells is less evident in the SAC-induced IgM RF response, suggesting qualitative differences between IgM and IgM RF SAC-stimulated responses in PBMC cultures from the same normal individuals. Irradiation (1000 rads) of the T cell-enriched subpopulation, either with or without Leu-2 positive cell depletion, resulted in statistically significant decreases in IgM and IgM RF production in response to SAC in reconstituted autologous cultures, providing further evidence of a Leu-2 negative radiosensitive sheep-cell rosetting cell active in in vitro SAC responses. In contrast, PWM-stimulated PBMC cultures showed almost exclusively increases in total IgM and IgM RF production when T cells were irradiated (1000 rads) before culture, consistent with the radiosensitive T suppressor cell involved in the in vitro immunoglobulin responses to PWM. The same five out of nine individuals produced IgM RF, under different culture conditions, in response to PWM and SAC, suggesting that the ability of an individual to produce IgM RF lies intrinsically within the B cell.