Effects of Senescence on Immune Parameters in Baboons Shows Differential Susceptibilities (P1321)

Abstract Vaccine efficacy declines significantly with age, yet old baboons immunized with Yersinia pestis LcrV antigen generated vigorous humoral responses [JI 181:109 (2008)] while aged rhesus macaques did not. To assess whether these non-human primate (NHP) species are differentially impacted by immunosenescence, animals were immunized with Y. pestis F1, a plasmid-encoded protein which is known to elicit naïve B and T cell responses. Interestingly, age-associated decreases in antibody titers to F1 were observed in both species. However, defects in T cell proliferative responses were seen only in the macaques; T cell reactivity to both mitogen and antigenic stimulation was similar in the old and young baboons. We therefore asked whether other aspects of immune regulation are affected by age. The loss of naive, relative to memory, T cells was seen, as expected. Moreover, there was a decrease, albeit relatively small, in the production of naive T cells (TRECs). However, several parameters known to change with aging were not affected. For example, AID induction was maintained in most, but not all, old baboons. Moreover, the T cell fine specificity was similar in old and young animals. Lastly, TCR-Vβ spectratype analysis revealed that the age-associated repertoire skewing reported in old rhesus and humans is not seen in baboons, even in the CD8+ T cell subset. Thus, baboons do appear to be less affected by aging and this NHP species may provide novel insights into healthy immune aging.