Comparison of phorbol myristate acetate and phytohaemagglutinin as stimulators of in vitro T lymphocyte colony formation of human peripheral blood lymphocytes. I. Surface markers of colony cells.

Human T lymphocyte colonies were grown in methylcellulose semi-solid cultures in the presence of phytohaemagglutinin (PHA) and/or phorbol myristate acetate (PMA). Surface marker analysis showed lower percentages of OKT3- and OKT4-positive cells in PMA-induced colonies than those in PHA-induced colonies. The percentage of OKIa1-positive cells in PMA-induced colonies was approximately twice that in PHA-induced colonies. The percentage of OKT9-positive cells in PMA-induced colonies was significantly lower than that in PHA-induced colonies. These data suggest that the subsets of PMA-induced colony cells express a more immature phenotype than that of PHA-induced colony cells and that, among PMA-induced colony cells, there are fewer T cells in the proliferative status at the time tested. When 3 X 10(5)/ml monocyte-depleted T cells, at which concentration of seeded cells neither PHA nor PMA could induce colony growth, were cultured in the presence of both PHA and PMA, T cell colony growth was observed. In T cell colonies induced by a combination of PHA and PMA, the percentages of OKT3-, OKT4- and OKT8-positive cells were different from those in colonies induced by either PHA or PMA alone. These results suggest that PMA acts not only as a substitute for monocytes and/or interleukin-1, but may directly affect lymphocyte proliferation induced by a combination of PHA and PMA.