Advancing age leads to predominance of inhibitory receptor expressing CD4 T cells.

Decline in CD4 T cell function is the hallmark of aging. In this study, we compared the proportion and absolute number of inhibitory receptor expressing splenic CD4 T cells in unprimed young (2 months) and aged (20 months) C57BL/6 mice. Our results showed a predominance of PD-1, ICOS and CTLA-4 expressing conventional and regulatory CD4 T cells in aged mice. Furthermore, the expression of these molecules was localized to memory but not naïve CD4 T cell subset. Since aging is associated with decline in naïve but accumulation of hyporesponsive memory phenotype (MP) CD4 T cell, we hypothesize that inhibitory receptors can account for the senescence noted in MP subset of CD4 T cell.