Age-related defect of phospholipase C activity, differential expression of the beta 2 isoform in active T lymphocytes from aged humans.

The activation of phosphoinositide-specific PLC is one of the early cellular responses to various growth factors and mitogens. It is known that these functions are altered with ageing. Here we show that the beta 2 isozyme is decreased with ageing in a peculiar T lymphocyte subpopulation involved in the immune response, namely the active T lymphocytes. The presence and cellular distribution of PLC isozymes were investigated with immunochemical and immunocytochemical methods. The in situ immunocytochemistry displayed the presence of the beta and gamma isoforms in the cytoplasm, while no reactivity for the delta isoform was observed regardless of the age. The immunoblot analysis showed an increased expression in the beta 2 isoform in the young and an equal expression of the gamma 1 isoform in either age group. Our findings suggest that the age-related defect of PLC activity is possibly due to an impaired expression of isozymes in aged active T lymphocytes.