Cytomegalovirus infection and NK cells

Natural killer (NK) cells are a key component of the innate immune system that are capable of rapid recognition and elimination of target cells without prior sensitization. Compelling evidence that NK cells limit viral replication in vivo has come from studies involving cytomegalovirus (CMV) infection. Human CMV (HCMV) is a pathogen responsible for causing significant morbidity and mortality in immunocompromised individuals. This chapter discusses some of the mechanisms used by NK cells to identify CMV-infected cells and describes the escape mechanisms employed by the CMVs to evade detection. Human cytomegalovirus (HCMV) is a common human pathogen typically encountered during childhood. Primary HCMV infection is rapidly controlled by the immune system but not eliminated, resulting in the establishment of a latent infection that persists for the life of the host. Reactivation of HCMV in healthy individuals is usually asymptomatic. However, in immune-compromised patients, HCMV reactivation is a significant clinical problem causing diseases such as interstitial pneumonitis, encephalitis and retinitis. Since CMVs are strictly species specific, animal models have been used to investigate various aspects of viral pathogenesis. In particular, the study of murine CMV (MCMV) has provided valuable insights into how the immune system responds to CMV infection and has helped to define the immune evasion mechanisms used by CMV to ensure that viral replication proceeds successfully. NK cells play a critical role in controlling immune responses, including the resolution of such responses.