Immunohistochemical characterization of the cellular infiltrate in severe alopecia areata before and after minoxidil treatment.

The mechanism of minoxidil-induced hair regrowth in alopecia areata (AA) is unknown. In vitro studies suggest that pharmacologic tissue levels of minoxidil may have both epithelial and T cell effects. Response in 36 of 47 patients with severe AA to topical minoxidil 5% b.i.d. was characterized by a return toward normal of hair follicle diameter, depth and structure, and an apparent shift in T cell populations from the skin into the peripheral blood. Nonresponders showed none of these changes. Biopsies from 34 patients subsequently treated with oral minoxidil 5 mg q. 12 h showed no further changes in perifollicular total T, helper-inducer T or suppressor-cytotoxic T cell counts; they did, however, demonstrate significant decreases in perifollicular Langerhans cell and activated T cell counts, and nearly significant decreases in perifollicular monocyte counts. It is possible that minoxidil may be altering a presumed follicular chemoattractive stimulus to a variety of cell types. Decreases in activated T cell counts suggest the possibility of direct immunomodulatory effects of minoxidil on T cells which might contribute to a hair regrowth response in AA.