The immunological burden of human cytomegalovirus infection.

Cytomegalovirus (CMV) is a persistent DNA virus that has evolved with humans to establish a finely balanced host-virus relationship. This balance is maintained by host immune surveillance since deficiencies in these processes can result in life-threatening disease, as observed in immunologically immature neonates and pharmacologically immunosuppressed transplant recipients. Both T cells and natural killer cells are intimately involved in maintaining asymptomatic infection by specific and non-specific recognition of infected cells. Under pressure from such host immune responses, CMV appears to have evolved elaborate strategies to subvert these responses in order to persist in the host. CMV target antigens are well characterized, with many CD8 T cell and CD4 T cell epitopes reported. This information is now being exploited to treat immunocompromised patients in order to boost virus-specific immunity. This review also discusses our current understanding of how virus carriage may skew lymphocyte populations in immunocompetent subjects and the association of CMV-seropositivity with immunosenescence.