Programmed death 1 regulates memory phenotype CD4 T cell accumulation, inhibits expansion of the effector memory phenotype subset and modulates production of effector cytokines.

Memory phenotype CD4 T cells are found in normal mice and arise through response to environmental antigens or homeostatic mechanisms. The factors that regulate the homeostasis of memory phenotype CD4 cells are not clear. In the present study we demonstrate that there is a marked accumulation of memory phenotype CD4 cells, specifically of the effector memory (T(EM)) phenotype, in lymphoid organs and tissues of mice deficient for the negative co-stimulatory receptor programmed death 1 (PD-1).