The heterogeneity of the germinative compartment in human epidermis and its implications in pathogenesis.

In mouse epidermis keratinocytes of the basal layer seem to belong to 3 different subpopulations: stem cells, transit cells and postmitotic cells. Each subpopulation assumes a specific role in epidermal homeostasis. Recent data tend to display a similar heterogeneity among basal keratinocytes in human epidermis. This concept opens the door to an integrated understanding of epidermal renewal but also suggests new hypotheses in pathogenesis. Psoriasis, a typical example of epidermal hyperplasia, is considered from this point of view.