Response of human B cells to Staphylococcus aureus Cowan I: T-independent proliferation and T-dependent differentiation to immunoglobulin secretion involve subsets separable by rosetting with mouse erythrocytes.

We separated T-depleted mononuclear cells into subsets by rosetting with mouse erythrocytes and studied proliferation and differentiation responses to Staphylococcus aureus Cowan I (SAC), pokeweed mitogen (PWM), and a combination of the two polyclonal activators. All of the T cell-independent proliferation of unfractionated B cells in response to SAC was attributable to mouse erythrocyte rosette-forming cells (BMR+). BMR- cells were not stimulated to proliferate by SAC in the presence or absence of T cells, but did proliferate to PWM plus irradiated T cells. Co-stimulation of BMR+ cells with SAC and PWM in the presence of autologous T cells did not lead to immunoglobulin secretion. The B cells stimulated to divide by SAC apparently do not become responsive to B cell differentiation factors and are distinct from those that undergo T cell-dependent differentiation.