Persistent infection

HPVs establish long-term persistent infections with low levels of virus replication as a result of immune evasion. HPV infections occur within stratified epithelia, and the mechanism of infection permits limited immune detection. The basal cells of stratified epithelia support only early virus protein synthesis, which is poorly immunogenic, while the late proteins (L1 and L2) that trigger strong immunity, are only found in high levels in the  upper layers  of the  epithelium, at a site removed from  immune surveillance. Hence the virus evades immune clearance, and the segregation of newly replicated genomes to daughter cells within the basal layer (recall that HPV stimulates mitosis) insures the pro- longed presence of the virus in the tissue.