Age associated decline in CD25 and CD28 expression correlate with an increased susceptibility to CD95 mediated apoptosis in T cells

Abstract

Immunosenescence is believed to contribute to increase susceptibility to infectious diseases and cancer in the elderly, and is caused mainly by changes in the T cell compartment. Longitudinal studies were undertaken to examine T cell surface receptor expression and apoptotic susceptibility using Staphylococcal enterotoxin B (SEB) activated human T cells as an in vitro model of an ageing T cell culture. An intracellular stain Carboxyfluorescein diacetate succinimidyl ester (CFSE) was used to assess the number of population divisions (PD) occurring in the ageing T cell culture. One major biomarker of aged T cells is a decrease in expression of CD28 and since this is an essential co-stimulatory molecule, its decreasing expression with age could compromise their activation and apoptotic capacity. Activation of T cells resulted in initial up-regulation of CD25, CD95 and CD28, although expression of CD25 and CD28 subsequently decreased with increasing PD. CD4 and CD8 T cells expressed similar CD25 profiles although CD28 expression was unique in each subset. CD4+ cells expressed the highest CD28 levels, and showed a gradual decline in expression with increasing PD, whereas CD8+ cells were low CD28 expressers, but did not appear to lose their expression as they aged. To determine T cell susceptibility to apoptosis via CD95/CD95-L interactions with increasing age, cells were challenged with CD95-L transfected CHO cells at various PD. Increased death was observed as they aged, which correlated with the decreased expression of activation markers CD25 and CD28.