The degree of monocyte participation in human B- and T-cell activation by phorbol myristate acetate.

The DNA synthetic responses of mononuclear cells (MNC), highly purified B and T lymphocytes, and T-cell subsets--OKT4+ and OKT8+ cells--and immunoglobulin production by a tumor-promoting agent, phorbol myristate acetate (PMA), were investigated. The following results were obtained: (1) PMA induced a significant DNA synthesis in MNC, pure B cells, pure T cells, and OKT4+ and OKT8+ cells. (2) Addition of monocytes to B cells did not increase the mitogenic responses more significantly than that of pure B cells alone. (3) PMA induced DNA synthesis in purified T cells significantly, but the addition of monocytes to the T cells augmented the responses markedly. (4) PMA induced polyclonal IgM production but the level of IgM synthesis was lower than that induced by PWM (about 45% at Day 6 culture). (5) Cyclosporin A (CyA) inhibited DNA synthesis induced by Con A and PHA, but did not inhibit the PMA-induced DNA synthesis. It was concluded that although there is a possibility that monocytes are not depleted completely, PMA did not seem to require monocytes for B-cell activation, whereas the level of T-cell activation was potentiated by monocyte addition and PMA probably activated T cells via receptors that are different from those used by Con A and PHA or probably activated T cells without HLA-DR antigen receptors.