‘Checks and balances’ in cytomegalovirus-host cohabitation

Excerpt

Species-specific cytomegaloviruses (CMVs) and their corresponding hosts have co-speciated during eons of co-evolution adapting to each other by establishing ‘checks and balances’. Accordingly, CMVs of different host species have acquired different sets of private genes dedicated to moderate intrinsic, innate, and adaptive defense mechanisms of their respective host, and those, in turn, have found counterstrategies to keep their lodger in check. The popular term ‘immune evasion’ of CMVs is clearly an unfortunate misnomer, as immune surveillance of CMV infections prevents viral pathogenesis so that CMV disease is restricted to the immunocompromised or immunologically immature host. The immune response resolves acute infection with no overt symptoms of CMV disease, neither symptoms of viral pathogenesis nor of immunopathogenesis. Lifelong immune surveillance keeps the virus in a non-replicative state referred to as latency. Latency is defined as absence of infectious virus but durable retention of reactivation-competent viral genomes. Productive recurrent infection can be re-initiated by not yet fully defined signals resulting in virus spread and histopathology under conditions of compromised immune control. …