CD8A and cytomegalovirus infection: In addition, older individuals who are sero-positive for CMV compared to CMV-negative elderly, exhibit poor antibody responses to influenza vaccination and an accumulation of terminally differentiated CD8+ T cells (largely driven by the response to persistent CMV infection); these CD8+ T cells express granzyme B, which has toxic effects when non-specifically released into the extracellular space in response to an inflammatory stimulus.