Direct mitogenic effect of ionophore A23187 on isolated human T helper lymphocytes.

The Ca2+ ionophore A23187 induces only a weak mitogenic response in cultures of unfractionated mononuclear leukocytes from human blood. When a comitogen, 12-O-tetradecanoyl-phorbol-13-acetate, which by itself is nonmitogenic, is added, a greatly increased cell proliferation is obtained. Highly purified T lymphocytes respond by proliferation to A23187 alone. Studies on functional subsets of T cells, fractionated by using the monoclonal antibodies OKT4/OKT8, revealed that A23187 is a strong mitogen for pure T helper cells (T4+). This suggests that increased cytosolic Ca2+ directly triggers a proliferative response in T helper cells with no apparent need for accessory cells.