Phenotypic characterization in situ of inflammatory cells in pityriasis (tinea) versicolor

The cellular response in pityriasis (tinea) versicolor lesions was analysed in situ with an immunohistochemical double staining technique combined with periodic acid-Schiff staining in frozen sections of skin biopsies from 9 patients. The proportions of B and T cells and subpopulations of T cells in the blood were normal as were the proliferative responses of blood mononuclear cells against various B- and T-cell mitogens and antigens. Fungi were observed in stratum corneum in all lesions, and there were moderate cell infiltrates in both epidermis and dermis as compared to biopsies from normal-looking skin. The majority of the infiltrating perivascular cells reacted with anti-Leu 1 antibodies (all mature peripheral T cells). Anti-Leu 2a reactive cells ('suppressor/cytotoxic' phenotype) were few and scattered, whereas anti-Leu 3a reactive cells ('helper/inducer' phenotype) dominated. This investigation demonstrates that pityriasis versicolor is not a simple overgrowth of the fungus in stratum corneum, but is accompanied by infiltrating immunocompetent cells in both epidermis and dermis.