Viral genes involved in immune evasion of cytomegalovirus

Cytomegaloviruses (CMVs) are prototypes of the beta-subgroup of herpesviruses. After immune control of primary CMV infection, viral genomes persist in a latent state for lifetime of the infected host. From the non-productive state of latency, CMV replication is occasionally reactivated folowed by virus shedding and transmission to other hosts. To replicate in the face of a repeatedly primed immune system and despite the protracted replication cycle of their large DNA genomes expressing more than 200 potentially antigenic proteins, CMVs have devised a multitude of fascinating mechanisms to evade immunity. Among these strategies are methods of blocking pathways of antigen presentation to cytotoxic T lymphocytes as well as inhibition of signalling pathways of antivoiral cytokines. More than 20 CMV genes have been identified which code for immune modulators, and this collection is certainly incomplete. In addition, CMVs even exploit immune functions utilized by the host for their own advantage. These sophisticated and highly adapted strategies secure the permanent coexistence of CMVs with their host and provide the opportunity to sspread to naive individuals.