Regional variations in cytokeratin expression in palmo-plantar epidermis.

The cytokeratin composition of palmo-plantar epidermis from sites with different degrees of mechanically induced thickening of the stratum corneum was analysed. The urea-soluble proteins of the stratum corneum were analysed by two-dimensional electrophoresis. Viable epidermal layers were analysed by immunofluorescence microscopy with polyclonal and monoclonal antibodies. A mouse monoclonal antibody specific for cytokeratin no. 9 was prepared for the study. Significant amounts of low molecular weight cytokeratins were found in suprabasal layers at sites with the most pronounced thickening of the stratum corneum. This was taken as evidence that palmo-plantar epidermis responds to mechanical stress with hyperproliferation. At sites where stratum corneum thickness is most increased this hyperproliferation appears to involve two different populations of cells--one capable of expressing high molecular weight, differentiation-related cytokeratins in the suprabasal epidermal layers, and one population that does not express these cytokeratins. At sites with intermediate epidermal hyperplasticity the high molecular weight cytokeratins were predominant in all suprabasal cells.