Monitoring hyperproliferative disorders in human skin: Flow cytometry of changing cytokeratin expression

Background: Monitoring dynamics of different cell populations in solid tissues using flow cytometry has several limitations. The interaction and changes in epidermal subpopulations in hyperproliferative skin disorders such as psoriasis, a very common chronic inflammatory skin disease, may, however, elucidate the role of different cell populations in the pathogenesis and the effect of therapy in these disorders. We describe a new, simple method for identifying and quantifying different epidermal subpopulations in hyperproliferative skin disorders and an in vivo model for epidermal hyperproliferation by using six-parameter assessment and three-color flow cytometry. Methods: Epidermal single-cell suspensions were derived from normal human skin before and after standardized injury and from untreated and treated psoriatic lesions. Samples were stained with anti-cytokeratins 6 (K6) and 10 (K10), anti-vimentin, and 41,6-diamidino-2-phenylindole. With three-color flow cytometry, different epidermal subpopulations were further defined by six different parameters. Results: Correlations were found for mild psoriasis and K10(+)K6(-) cells and for moderate psoriasis and K10(-)K6(+) cells. Treatment of mild psoriasis resulted in a 70% increase of the K10(+)K6(-) cells and an 18% decrease of the K10(-)K6(-) cells, whereas treatment of more severe psoriasis resulted in a 77% increase of the K10(+)K6(-) cells and a 33% decrease of the K10(-)K6(+) cells. The tape-stripping model showed changes in suprabasal keratin expression before proliferative activity. Conclusions: The present flow cytometric assay permits simultaneous quantification of epidermal differentiation, inflammation, proliferation, and hyperproliferation-associated keratinization and provides information on pathogenesis and therapy of hyperproliferative skin disorders. (C) 2003 Wiley-Liss, Inc.