Fas/FasL pathway is the main mechanism of CD8-induced cytotoxicity in cutaneous lichen planus

Background: Lichen planus (LP) is an inflammatory dermatosis involving either the skin and/or the mucosal epithelial surfaces. Apoptosis of keratinocytes by cluster of differentiation (CD) 8+ T cells may be mediated by the release of cytotoxic molecules such as perforin and granzyme B or by the Fas/Fas ligand (FasL) system. Objective: To evaluate the degree of expression of both Fas/FasL and granzyme B in CD8+ infiltrating cells in lichen planus. Patients and methods: Skin biopsies were taken from lesional skin of LP patients and from normal skin of normal control individuals. Immunofluorescence staining of CD8 with Fas/FasL or granzyme B (double markers) as well as TUNEL assay were performed. Results: Immunofluorescence staining showed that CD8+ cells were strongly represented in the dermal infiltrate of LP patients. The difference in the mean number of FasL+ CD8+ cells between LP patients and healthy controls was significant (P=0.013), whereas the difference for granzyme B was not significant (P=0.11). Although apoptotic cells were significantly higher in LP patients (P=0.031), there was no significant correlation between FasL expression and the number of these apoptotic keratinocytes in the lesions. Comparison within the LP group revealed significant difference between FasL+ CD8+ cells and granzyme B+ CD8+ cells in LP dermal infiltrate (P=0.002). Conclusion: The Fas/FasL pathway has the upper hand over the perforin/granzyme pathway in CD8 + -mediated cytotoxicity in cutaneous LP.