Changes in SRBC binding capacity and T-surface antigen expression on human peripheral blood lymphocytes stimulated by 12-0-tetradecanoilphorbol-13-acetate (TPA).

The expression of surface markers was analyzed on human peripheral blood lymphocytes after exposure to 12-O-tetradecanoylphorbol-13-acetate (TPA), a tumor promoter which is known to have a mitogenic effect on human T-cells. A significant decrease in the proportion of cells capable of binding to SRBC under different experimental conditions (active (EA), high affinity (EH), total (ET) rosettes) was observed after 20 hr exposure to TPA. After 4 days incubation, the ability to form EH and ET rosettes was recovered, while a significant increase in the proportion of EA and temperature stable (ES) rosettes compared with control cultures was observed. Using monoclonal antibodies directed against different T-lymphocyte subpopulations, a depression in the proportion of cells reacting with OKT3 (pan T) and OKT4 (helper/inducer) antibodies was observed, after both early and late exposure to TPA. On the contrary, the positivity with OKT8 (suppressor/cytotoxic) antibody was not affected at any time of culture. These findings suggest that, in normal blood, TPA can modulate the expression of T-cell receptors, and that T-lymphocytes with helper/inducer phenotype appear to be the target of the TPA-induced membrane changes.