T Lymphocyte Activation Signals

Abstract

Activation of T lymphocytes results in immediate biochemical changes including increases in intracellular calcium levels, activation of protein kinase C (PKC) and changes in tyrosine phosphorylation. In T cells recent studies have indicated that activation of the guanine nucleotide‐binding proteins p21^ras is mediated by PKC, which suggests that the p21^ras proteins may regulate intracellular signalling events downstream of PKC. The p21^ras proteins can be activated in T cells by signals generated by triggering of the T cell antigen receptor (TCR), the CD2 antigen and the interleukin 2 receptor. Experiments using a PKC pseudosubstrate inhibitor indicate that PKC does not mediate TCR‐induced activation of p21^ras. These results imply that an alternative signal transduction pathway not involving PKC can regulate the activity of p21^ras proteins in T cells.