Fig. 3.

Diversity of host cells and environments affect viral pathogenicity at cervix. Most cervical cancers arise at the cervical transformation zone, where is maintained by a specialized type of tissue stem cell known as the reserve cell (shown in purple), and possibly also by a cluster of cuboidal cells (yellow) localized more precisely at the squamo-columnar junction. These cells can maintain either the columnar epithelium or the stratified epithelium (metaplasia) of transformation zone depending on their extracellular environment. The cells in the ectocervix maintain the conventional stratified epithelium, in contrast the cells in endocervix lack the ability to stratify. Current thinking suggests that the cells at the transformation zone fail to properly regulate viral gene expression, leading to a non-productive rather than a productive infection, which can be seen in ectocervix, and are more likely to progress to malignant transformation. The cells at the endocervix also fail to properly regulate viral gene expression, suggesting that high-risk HPV infection at this site might not develop an LSIL precursor, but adenocarcinoma in situ