Phorbol ester and calcium ionophore are sufficient to promote cell replication in cultures of quiescent human B lymphocytes.

Highly purified, resting B cells could be induced to grow for up to 10 days by culturing in the presence of a synergistic combination of a tumour-promoting phorbol ester and the calcium ionophore ionomycin. In spite of evident cell death occurring, four to five times as many viable B lymphocytes could be harvested at the end of culture than were initially plated. Soluble factors derived from T cells (interleukin-2, commercial B-cell growth factor) or monocytes (interleukin-1) failed to augment further the growth-promotion observed. Evidence is presented to suggest that an autocrine component might be necessary for maintenance of the cell-cycle and growth initiated by the phorbol ester and calcium ionophore combination. The significance of these findings to B-cell physiology are discussed.