Proliferation of leukemic B cells in response to SAC and anti-mu. Evidence for different modes of action and comparison to proliferation and differentiation induced by conditioned medium.

We investigated the proliferative responses and immunoglobulin production of highly purified E-rosette negative largely leukemic B cells from patients with CLL to Staphylococcus aureus Cowan I (SAC) or to SAC in combination with anti-mu or conditioned medium (CM). The latter was derived by stimulating human peripheral blood mononuclear leukocytes with PHA. We observed: (1) that purified E-rosette negative largely leukemic B cells from 25% (five out of 20) of the patients exhibited proliferative responses to SAC; (2) inhibition of SAC-induced proliferation by anti-mu in certain patients, whereas synergism between SAC and anti-mu in inducing proliferative responses in others; (3) the lack of synergism between SAC and CM in inducing proliferative responses, which is in contrast to the strong synergism that was observed between anti-mu and CM in inducing proliferation; and (4) induction or enhancement by SAC alone of Ig production by largely leukemic B-cell populations from few patients with CLL and purified tonsillar B lymphocytes, but not peripheral blood B cells from normal donors. These results suggest that SAC and anti-mu induce proliferation of B cells by different mechanisms and that B-cell proliferation and differentiation is dependent not only on the mitogen but also on the activation state of the cells.