Cellular distribution of protein kinase C isozymes in CD3‐mediated stimulation of human T lymphocytes with aging

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Abstract
Protein kinase C (PKC) is involved in a variety of cellular responses, such as the expression and secretion of IL‐2, the regulation of cytotoxic killing and cell proliferation. It is known that these immune functions are altered with aging. Here, we 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 proliferation in a differential manner, lymphocytes of healthy young subjects being 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 antibodies directed against PKC α, β, δ, ϵ and ζ isoforms in the cytosol and the plasma membrane fractions. These five PKC isotypes were present in human T cells of young and elderly subjects. However, their distribution between the cytosolic and membrane fractions varied according to the isozymes and the age of the subjects. In resting lymphocytes of young subjects, all the PKC isozymes were found in the cytosolic fraction, except PKC‐ζ. In resting lymphocytes of elderly subjects PKC‐δ and ‐ϵ were almost equally distributed between the cytosolic and the membrane fractions, whereas PKC‐α and ‐ζ were mainly found in the membrane fraction and PKC‐β was almost exclusively located in the cytosolic fraction. The translocation of PKC‐α, ‐β, ‐δ and ‐ϵ could be observed under anti‐CD3 mAb stimulation in lymphocytes of young subjects, while in the case of elderly subjects only the PKC β isoform was translocated. Our results suggest that the decreased availability of cytosolic PKC may contribute to the diminished PKC‐dependent responses to CD3‐triggered stimulation of human T lymphocytes with aging.