Changes in a t-cell subpopulation marker induced by tumor-promoting phorbol esters

We observed a significant reduction in one specific T-cell rosetting marker after treatment of bovine lymph node lymphocytes with 12-O-tetradecanoylphorbol-13-acetate (TPA). There was a dose-dependent reduction in the formation of neuraminidase-treated sheep erythrocyte rosettes (En), but not aminoethylisothiouronium bromide-treated sheep rosettes (Ea) after as little as 10 min of incubation with TPA. A maximum of ∼50% reduction was reached after 1 h. When several phorbol esters and mezerien were tested, we found that the reduction in En rosetting induced by the compounds correlated with their in vivo tumor-promoting activity. The reduction in En rosetting appears to be ∼50% reversible for up to 6 h of treatment with TPA when the cells were incubated in TPA-free medium for an additional 24 h, but it was irreversible after at least 12 h of treatment. Addition of the tumor promoters directly to the rosetting assay had no detectable effect on the sheep erythrocytes or the percentage of Ea rosettes. This specific change in En rosetting marker may represent the maturation of a T-cell subpopulation to T-suppressor cells in the presence of tumor-promoting phorbol esters.