Age-dependent changes in T cell homeostasis and SIV load in sooty mangabeys

Sooty mangabeys (Cercocebus atys) showed age-dependent changes in T cell re generation. Younger animals had a high percentage of CD4 + CD45RA + T cells and a high concentration of T cell receptor excisional circles (TRECs) in peripheral blood, which indicated active thymopoiesis. In contrast, older a nimals had an increased T cell turnover, which suggested that most T cell p roduction occurred in the periphery. In addition, the number of peripheral CD4 + T cells naturally decreased with age. Non-pathogenic SIVsm infection did not significantly change the T cell proliferation rate or the TREC conc entration, though it did cause a moderate loss of peripheral CD4 + T cells. The viral load correlated negatively with age, which could be accounted fo r by the reduced availability of CD4 + target cells in older mangabeys. Thu s, the number of susceptible target cells may be a limiting factor in natur al SIV infection.