Requirement of Ia-positive accessory cells for T-cell stimulation with 12-O-tetradecanoyl-phorbol-13-acetate.

The cellular mechanism of lymphocyte stimulation with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) was studied using mouse spleen cells. TPA had a potent mitogenic activity on mouse spleen cells at concentrations of 10-1000 ng/ml. The maximum response was observed on Day 2. Other phorbol derivatives such as phorbol, phorbol-12-monomyristate, and phorbol-13-monoacetate had no mitogenic activity. The responder cells in the stimulation experiment with TPA were Thy-1-positive T cells. Nylon column purification of spleen cells diminished the response to TPA, but the addition of spleen cells to nylon-purified T cells restored their responding activity, suggesting that the accessory cells were required for T-cell stimulation with TPA. The accessory cells were macrophage-like adherent cells and la-positive. The mechanism of T-cell stimulation with TPA was discussed from the standpoint of the requirement of two different stimulatory signals.