Interactions of cytomegalovirus with the human immune system.

Infection of the normal host with human cytomegalovirus (HCMV) is followed by both humoral and cellular immune responses against this herpesvirus. The importance of cell-mediated immunity against HCMV is exemplified by the occurrence of severe and prolonged HCMV infections in individuals with congenital, iatrogenic, or acquired deficiencies of this arm of host immunity. In contrast, infection in most individuals with primary B cell disorders usually is not severe. The nature of different aspects of cell-mediated immunity, including cytotoxic T cell (CTL) responses and levels of natural killer cell (NKC) and antibody-dependent cellular cytotoxicity (ADCC) during infection, has been characterized in detail in susceptible populations. To a high degree, the presence or absence of CMV-specific CTL responses correlates inversely with the severity of infection, as do levels of NKC and ADCC activity. Clinical correlates of these immune responses will be discussed. In addition, recent observations implicating HCMV as an immunosuppressive virus will be presented.