Immunohistochemical detection of keratins 1 and 13 as differentiation markers in the hormone-dependent human vaginal epithelium. 
Human vaginal epithelium provides a good model to study hormonally regulated differentiation.  Differentiation in this tissue can be characterized by the expression of the keratins 1 and 13 which represent the epidermal and nonkeratinizing pathway in stratified epithelia, respectively.  In the present study immunohistochemistry was applied on sections of vaginal epithelium derived from women at various stages of the menstrual cycle or during pregnancy.  Our results demonstrate that both pathways are realized simultaneously during sexual maturity and that the maximum for synthesis of keratins 1 and 13 is seen during the first half of the cycle.  In contrast keratin 1 is not detectable at the end of pregnancy, thus reflecting a completely suppressed epidermal differentiation.  As the levels of the female sex hormones, i.e. estrogens, is significantly increased in pregnant women over that in nonpregnant women, these results suggest a possible role of estrogens in downregulating the epidermal differentiation pathway.