The role of perforin-mediated apoptosis in lichen planus lesions

Lichen planus is recognized as a T-cell-mediated disease. Histologically, it is characterized by the formation of colloid bodies representing apoptotic keratinocytes. The apoptotic process mediated by CD8⁺ cytotoxic T lymphocytes (CTLs) and NK cells mainly involves two distinct pathways: the perforin/granzyme pathway and the Fas/FasL pathway. So far, little is known regarding the role of perforin-mediated apoptosis in lichen planus. In the present study, the expression and distribution of perforin, T and NK cell subsets in the epidermis and dermis of lesional and nonlesional lichen planus skin were studied. Skin biopsy specimens from lesional and nonlesional skin of ten patients with lichen planus and eight healthy persons were analysed by immunohistochemistry. Significant accumulation of T cells, particularly of CD4⁺ and CD8⁺ subsets, was found in both epidermis and dermis of lichen planus lesions compared with nonlesional and healthy skin. There were no significant differences in the incidence of NK cells (CD16⁺ and CD56⁺) between lesional, nonlesional and healthy skin. Perforin expression was significantly upregulated in the epidermis of lichen planus lesions. In conclusion, accumulation of perforin⁺ cells in the epidermis of lichen planus lesions suggest a potential role of perforin in the apoptosis of basal keratinocytes.