Characterization of the subpopulations of human peripheral blood B lymphocytes which react to staphylococcus aureus Cowan I and T-cell help.

Staphylococcus aureus Cowan I strain (SAC) activates human peripheral blood B lymphocytes to proliferate but does not induce secretion of immunoglobulin (Ig) unless pokeweed mitogen (PWM)-activated T cells are added. Using a Percoll gradient separation method, we show that a B-cell subpopulation isolated at 50/60% Percoll interface is the target for SAC stimulation. After SAC activation, small, dense B cells become larger, less-dense B cells which proliferate. These activated B blasts differentiate into Ig-secreting cells when cultured with PWM-activated T cells. The culture supernatant of PWM-activated T cells is capable of supporting proliferation and Ig secretion of the activated B blasts but not of resting small B cells. This result suggests that the culture supernatant contains B-cell growth factors.