CD28 and infection: In fact, extensive analysis of CD8+ T cell functional parameters revealed no relationship between age and the capacity to produce cytokines or mobilize cytotoxic mediators in response to stimulation by peptides derived from viruses responsible for both acute (WNV) and chronic (CMV, EBV) infections despite clear evidence of an immunosenescent phenotype in the bulk CD8+ T cell pool (elevated frequencies of CD28− CD57+ cells and decreased frequencies of CD45RA+ CCR7+ cells relative to the younger members of the cohort).