Characterization of Lymphocyte Stimulation by Phorbol Related Compounds

1. The stimulation of (3H)-thymidine incorporation by lymphocytes in response to phorbol and seven other phorbol related compounds was investigated. 2. Lymphocytes from each of a small group of individuals were treated with the test compounds over wide concentration ranges. 3. All the tested compounds, including the most active, 12-0-tetradecanoylphorbol-13-acetate, were far less effective lymphocyte mitogens than the plant lectin phytohaemagglutinin. 4. Inter-individual differences were detected in the maximum response to the phorbols but not in their stimulating potency, as estimated by the concentration producing a half maximal response. 5. The rank order of the lymphocyte stimulating potency of the tested compounds was similar to the rank order of both tumour promoting activity and irritant potency in mouse skin. 6. Lymphocyte stimulation was paralleled equally well by these two mouse skin responses.