FIG. 2.   Keratin expression in primary human vaginal keratinocytes can be identified by immunofluorescence. Primary vaginal keratinocytes were examined by direct immunofluorescence for expression of CD4 and members of the keratin protein family. Analyses were conducted as described in Materials and Methods. (A) Representative field under visible light; (B, C, and D) direct immunofluorescent micrographs of vaginal keratinocytes in the absence of antibody, labeled with CD4 antibodies, or labeled with pan cytokeratin antibodies, respectively. The arrow in panel C indicates a cell weakly positive for CD4 expression. The field of cells in panel C was selected specifically to show the cells that expressed low levels of CD4 and is not representative of a typical field; cells in most fields were devoid of any detectable CD4 expression.