Activation of T lymphocytes by 12-O-tetradecanoylphorbol-13-acetate is resistant to inhibition by cyclosporin A.

Cultured T lymphocytes from pig blood can be activated by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Activation is additive with that induced by the mitogenic lectin phytohaemagglutinin (PHA). Activation by TPA differs from that induced by PHA or other mitogenic lectins in that it is not inhibited even by high concentrations of the immunosuppressive drug cyclosporin A (CS-A). Neither co-culture of lymphocytes with PHA and TPA nor addition of culture supernatants from TPA-stimulated cultures affected the sensitivity to CS-A of the response to PHA.