Massive load of functional effector CD4+ and CD8+ T cells against cytomegalovirus in very old subjects

A progressive, systemic, and low-grade proinflammatory status is one of the major characteristics of immunosenescence. Emerging data suggest a possible contribution of CMV, known to chronically infect a large proportion of humans, lifelong from newborns to centenarians. To test this hypothesis, we evaluated functional T cell responses to two CMV immunogenic proteins, pp65 and IE-1, in 65 chronically infected subjects aged 25-100 years. PBMC were stimulated with mixtures of peptides spanning the entire sequence of both proteins, and Ag specificity and magnitude of intracellular IFN-γ- and TNF-α-positive cells were then analyzed within both CD4⁺ and CD8⁺ T cells. Results indicate that pp65 and, to a lesser extent, IE-1 constitute major Ags against which aged people target functionally efficient T cell effector responses with massive production of Th1 cytokines and exhibition of CD107a degranulation marker. As a result, the production of IFN-γ induced in T cells by both Ags was seven to eight times greater in very old than in young subjects. The comparative analysis of pp65-specific responses in these very long-term carriers revealed a reciprocal relationship between CD4⁺ and CD8⁺ producing IFN-γ in the same individuals. These results indicate that CMV represents an important pathogen responsible for a strong immune activation in human aging. Such a remarkable burden of effector CD4 ⁺ and CD8⁺ T cells may be necessary to protect the elderly from CMV endogenous reactivation, but can turn detrimental by giving a substantial contribution to the proinflammatory status that accompanies the main age-related diseases.