Protein kinase C isotypes theta, delta and eta in human lymphocytes: differential responses to signalling through the T-cell receptor and phorbol esters.

The repertoire of novel and atypical protein kinase C (PKC) isotypes present in human T cells and their subcellular localization have not been fully characterized. We detected calcium-independent PKC activity in whole cell fractions from unstimulated peripheral blood lymphocytes (PBL). Towards an understanding of the role of PKC isoforms in lymphocyte activation we have studied the expression of calcium-independent PKC isoforms theta, delta and eta in PBL. With isoformspecific antibodies we detected the presence of PKC theta and delta in whole cell fractions from unstimulated human PBL by Western blot analysis. In addition, immunocytochemical analysis confirmed the presence of the novel PKC isoform PKC eta in PBL. Using immunocytochemistry, PKC theta, delta and eta had distinct patterns of redistribution following activation by phorbol myristate acetate (PMA). However, signalling through the T-cell receptor (TCR) did not appear to induce such changes in isoenzyme redistribution. These findings indicate that activation of lymphocytes either through the TCR-CD3 complex or with PMA induces different signalling pathways with respect to calcium-independent isoenzymes. Signalling through receptors other than the CD3 complex may be involved in activation of these isotypes.