Fig. 2.

Life cycle of human papillomaviruses

HPVs infect basal layer keratinocytes when the basal layer of stratified epithelia is exposed to the virus. On the left, a normal uninfected epithelium is shown for the regular differentiation. On the right, the HPV-infected epithelium is shown with the progress of HPV viral proteins expression. After persisting infection, HPVs replicate with cellular chromosomes in basal cells. Upon the differentiation, more viral genes are observed in differentiated cells. The late gene expression and viral replication are activated, followed by virion assembly and release of newly synthesized virions from the top layers of epithelium