The Effect of 12‐O‐Tetradecanoyl‐phorbol 13‐Acetate on the Ribormclease Activity of Circulating Human Lymphocytes

12‐O‐Tetradecanoyl‐phorbol 13‐acetate is a very effective tumor promoter and inflammatory agent and can act as a mitogen for a subset of T lymphocytes. We report here that even short exposure of lymphocytes to 12‐O‐tetradecanoyl‐phorbol 13‐acetate changes the balance between the levels of neutral ribonuclease and ribonuclease inhibitor. The most dramatic change occurs in a B‐lymphocyte‐enriched population. We find that most, if not all, of the neutral ribonuclease activity in circulating lymphocytes is associated with this population and that this activity is lost with exposure to 12‐O‐tetradecanoyl‐phorbol 13‐acetate. Both 12‐O‐tetradecanoyl‐phorbol 13‐acetate and phytohaemagglutinin increase the level of ribonuclease inhibitor in T cells. However, phytohaemagglutinin has no effect on the ribonuclease or inhibitor level of the B‐cell‐enriched population.