HPV Infection

HPV has a distinct life cycle. Most viruses infect target cells and produce progeny from that same cell. However, HPV has to rely on the mitosis and differentiation of the basal epithelial cells to produce new virions. Understanding of the HPV lifecycle is mainly derived from research on the high-risk group of HPV viruses, in particular HPV 16. However, with slight modifications, life cycle models of HPV 16 can be applied to other HPV groups as well.17 The principal route of transmission for HPV is skin to skin contact. Epidemiologic evidence shows that sexual behavior greatly influences the incidence and prevalence of HPV infections.18 To develop infection, infectious particles must find their way to cells in the basal layer of skin. Usually this access is provided through breaks in the stratified epithelium as a result of micro-abrasions or micro-traumas.
However, L1 and L2 capsid proteins, alpha-6 integrin cellular receptors and heparan sulfate proteoglycans/heparin sulfate play a major role in the binding process.19 After binding, through endocytosis the virus enters basal epithelial cells, and endosome/lysosome cause capsid disassembly. Next, the L2 protein facilitates transfer of the viral genome to nuclei of keratinocytes,20 and with the help of early viral proteins (E1 and E2), the virus maintains its episomal form and replicates in synchrony with host