Herbst V, Kissling S, Stutz N, Hoffmann R, Zöller M, Freyschmidt-Paul P
Department of Dermatology, Philipp University, Marburg, Germany

Alopecia areata (AA) is regarded as a T-cell mediated autoimmune disease, involving perifollicular CD4+ and CD8+ cells. Homing of T-cells is mediated by the homing-receptors CD44s and CD44v10. The most effective treatment of AA is the elicitation of a contact dermatitis by application of a contact sensitizer like diphenylcyclopropenone (DCP). The immunological mechanisms underlying this treatment are so far poorly understood. In order to elucidate the cellular mechanisms involved in AA-treatment with a contact sensitizer, we performed immunohistochemical studies on scalp biopsies of AA-patients before and after DCP-treatment. We compared the expression of CD4, CD8, CD1a, CD68, CD44s, CD44v7, CD44v10, Fas and FasL within the perifollicular infiltrate in i. untreated patients and successfully treated patients ii. 1 day and iii. 3 days after application of DCP. Furthermore the number of apoptotic lymphocytes was assessed by TUNEL-staining. Double staining for CD4+CD25+ was performed to identify regulatory T-cells. Compared to untreated AA, one day after application of DCP there was a striking increase in perifollicular CD4+ cells and CD68+ cells, the expression of CD44s, CD44v7, CD44v10, Fas and FasL was upregulated. TUNEL staining revealed a large number of apoptotic cells within the perifollicular infiltrates, many of these cells co-expressed CD4 and CD8. Three days after DCP-application the number of infiltrating CD4+ cells and CD68+ cells was reduced and showed the same density as in untreated AA but CD8+ cells were almost absent and there was still a large number of apoptotic lymphocytes. Our data suggest that the elicitation of a contact dermatitis by DCP-application induces apoptosis in perifollicular lymphocytic infiltrates in AA resulting in a removal of CD8+ cells. The apoptosis-inducing cells seem to be part of the early inflammatory infiltrate of the contact dermatitis and might be CD4+CD25+ regulatory T-cells.