The Herpes viruses are able to evade the immune defense because, within human cells, they undergo a quiescent condition. In this state, the microorganism does not replicate and does not generate sufficient amounts of viral-derived peptides to signal their presence to cytotoxic T cells .
In fact, in order to neutralize a viral infection already established, cytotoxic T lymphocytes kill the infected cells, but some of the peptides presented by the class I MHC expressed on the surface of the infected cells must be of viral origin. This condition is easily reached during infections caused by rapidly replicating viruses, as happens, for example, during influenza (neutralized by the combined action of lymphocytes and antibodies).
The Herpes virus strategy leads to the development of a latency . In some circumstances, especially when the immune defenses are lowered, the virus will reactivate causing an episode of illness . Once the replication phase is over, the virus eventually tends to turn back and lock itself in the nerve ganglia, thus maintaining the cycle that underlies the persistence of the infection .
