- Enzymes of the protein kinase C (PKC) family have a decisive role in the activation process of T cells. Under physiological conditions. PKC undergoes activation by diacylglycerol (DAG) which is transiently produced following activation of an antigen receptor-coupled phosphatidylinositol 4,5-bisphosphate (PIP 2 )-specific phospholipase C (PLC) and hydrolysis of PIP 2 . In vitro activation of distinct PKC isoenzymes is differentially regulated by various synthetic DAGs and membrane phospholipids. We tested whether exogenous PLC obtained from Bacillus cereus can affect PKC-dependent functions in mouse lymphocytes. The results indicated that B. cereus PLC, which preferentially hydrolyzes phosphatidylethanolamine (PE) and phosphatidylcholine (PC), induces the expression of functional cell surface IL2 receptors and that, in the presence of exogenous IL2, it leads to cell proliferation. The PE/PC-PLC reversed the inhibitory effect of PC on enzymatic activity of T cell-derived PKC in vitro. Furthermore, it augmented the activity of PKC over the background level suggesting that the PC-derived DAG may function as a positive regulator of T cell-specific PKC isoenzymes.