Evaluation of merkel cell number and distribution and cd200 expression in lichen planopilaris and discoid lupuserythematosus

Lichen planopilaris (LPP) and discoid lupus erythematosus (DLE) are diseases that cause primary cicatricial alopecia.In pathogenesis of these diseases, deterioration of immune privilege in the bulge region of the follicle may cause an aggressive immune response. CD200 is a transmembrane protein that binds to CD200 receptor and promotes immune tolerance and creates an immune-privileged environment in the "bulge" region of hair follicle. Merkel cells are located in the outer root sheat of hair follicle and are thought to play a role in immune response.In this study, based on hypothesis that Merkel cells play a central role in inflammatory diseases of the skin, number and distribution of Merkel cells in the LPP and DLE (staining with CK20 immunohistochemistry) and CD200 expression were compared with control group. A total of 119 patients were included in thestudy, 31 in DLE group, 60 in LPP group and 28 in control group. In immunohistochemical examinations, there was no significant difference between groups in terms of epidermal Merkel cell number. Number of follicular Merkel cells, total Merkel cells (epidermal + follicular), mean follicular Merkel cells (follicular Merkel cell number / follicle number) were significantly lower in case groups (DLE and LPP) compared to control group.CD200 expression was also significantly lower in the case groups.In CD200 (-) cases, follicular Merkel cell numberand total Merkel cellnumber were found to be significantly lower than CD200 (+) cases. In conclusion, findings supported relationship between Merkel cells and CD200 molecule and effect of Merkel cells on immune response.Despite its limitations, our study was first to examine role of Merkel cells in cicatricial alopecia. However, new studies are needed.