Effect of macrophages on phorbol ester-stimulated comitogenesis in bovine lymphocytes

12-O-Tetradecanoylphorbol-13-acetate (TPA) added together with mitogenic lectins to bovine lymph node lymphocytes causes a synergistic increase in DNA synthesis. This comitogen effect is due to an increase in cell proliferation. To determine the role of macrophages in comitogenesis, lymphocyte preparations were depleted of macrophages by sequential adherence to glass, plastic, and nylon wool. Phagocytic cells were removed by incubation with carbonyl iron and a magnet. After macrophage depletion, the lymphocyte response to lectins decreased, indicating the accessory function of macrophages in mitogenesis. The addition of TPA or macrophages to the depleted cultures restored its response to that of the unfractionated cells. TPA was still comitogenic with lectin in lymphocyte preparations from which all residual macrophages were removed by antimacrophage serum and complement. Therefore, the comitogenic effect of TPA is independent of macrophages in these cultures.