CELLULAR-DISTRIBUTION OF PROTEIN-KINASE-C ISOZYMES IN CD3-MEDIATED STIMULATION OF HUMAN T-LYMPHOCYTES WITH AGING

Protein kinase C (PKC) is involved in a variety of cellular responses, such as the expression and secretion of IL-2, the regulation of cytot oxic killing and cell proliferation, It is known that these immune fun ctions are altered with aging, Here, me show that anti-CD3-triggered T cell proliferation is significantly decreased with aging and that H7, an inhibitor of PKC, impairs the anti-CD3-induced T cell proliferatio n in a differential manner, lymphocytes of healthy young subjects bein g more sensitive to the PKC inhibitor than those of elderly subjects. We examined (Western blot) the presence and the cellular distribution of PKC isozymes in T lymphocytes of healthy young and elderly subjects in the resting state and after anti-CD3 mAb stimulation using antibod ies directed against PKC alpha, beta, delta, epsilon and zeta isoforms in the cytosol and the plasma membrane fractions, These five PKC isot ypes were present in human T cells of young and elderly subjects, Howe ver, their distribution between the cytosolic and membrane fractions v aried according to the isozymes and the age of the subjects, In restin g lymphocytes of young subjects, all the PKC isozymes mere found in th e cytosolic fraction, except PKC-zeta. In resting lymphocytes of elder ly subjects PKC-delta and -epsilon were almost equally distributed bet ween the cytosolic and the membrane fractions, whereas PKC-alpha and - zeta were mainly found in the membrane fraction and PKC-beta was almos t exclusively located in the cytosolic fraction, The translocation of PKC-alpha, -beta, -delta and -epsilon could be observed under anti-CD3 mAb stimulation in lymphocytes of young subjects, while in the case o f elderly subjects only the PKC beta isoform was translocated, Our res ults suggest that the decreased availability of cytosolic PKC may cont ribute to the diminished PKC-dependent responses to CD3-triggered stim ulation of human T lymphocytes with aging.