REGULATION OF APOPTOSIS IN-VITRO IN MATURE MURINE SPLEEN T-CELLS

Previously it has been shown that thymocytes undergo apoptosis, a form of programmed cell death, in response to glucocorticoids. This classi c form of apoptosis is prevented by inhibition of protein synthesis. T he current paper demonstrates that mature T cells also undergo apoptos is, but that the regulation of apoptosis in spleen T cells differs fro m that of thymocytes. Mature mouse spleen T cells were shown to die by apoptosis, not necrosis, when cultured without an added stimulus. Ass ays for apoptosis included internucleosomal DNA cleavage by gel electr ophoresis, percent fragmentation of DNA by the diphenylamine method, a nd percent of cells with hypodiploid DNA by flow cytometry. The percen t of apoptotic cells was 2% in fresh spleen T cells, and increased at least until 16 h, when 21 % were apoptotic. Dexamethasone caused apopt osis in both thymus and spleen T cells, but only thymocytes showed a r equirement for protein synthesis in dexamethasone-induced death. Cyclo heximide increased apoptosis in spleen T cells, indicating that apopto sis was controlled by newly synthesized protective proteins. Spontaneo us apoptosis was decreased in spleen T cells by protein kinase C activ ation, and was increased by H7 and staurosporine, which inhibits prote in kinases, in contrast with the behavior of thymocytes. The protein k inase A/G inhibitor HA1004 also decreased spleen T cell apoptosis. The contrasting effects of cycloheximide on thymocytes and spleen T cells occurred over the same concentration range, and the same was true for PMA. The dexamethasone dose-response curves were similar, except that a greater proportion of spleen T cells were dexamethasone-resistant. These data support the hypothesis that the apoptosis program in T cell s undergoes a transition during their maturation, such that apoptosis in mature T cells is regulated more like that of mature B cells than t hat of thymocytes.