Evaluation of merkel cell count and distribution in the skin with CD200 expression in alopecia areata patients

Alopecia areata is a chronic, immune mediated disease targeting anagen hair follicles and characterized by non-cicatricial alopecia. In the etiopathogenesis of alopecia areata hair cycle disruption which is thought to be the result of T cell mediated peribulbar inflammation is held responsible. Merkel cells are horizontally located in the basal layer of the epidermis, and stained with CK20 in the skin. CD200 is a transmembrane glycoprotein expressed on the surface of Merkel cells and keratinocytes located in the touch dome. CD200 attenuates inflammatory reaction and maintains immune tolerance through binding to its receptor CD200R. This study was founded on the hypothesis that Merkel cells play the central role in autoimmune diseases of the skin, hence Merkel cell count and CD200 expression were evaluated in alopecia areata. 20 alopecia areata and 19 androgenetic alopecia as a control group cases were enrolled in this study. 28 cases were female and 11 cases were male. Mean age in alopecia areata was 29.2 (range: 10-67) and 32.2 (range: 11-53) years in androgenetic alopecia patients. Mean Merkel cell count was 0.8 cells (range: 0-4) in alopecia areata and 4.15 cells (range: 0-16) in androgenetic alopecia cases (p=0.092). CD200 expression was not detected in any of the alopecia areata cases while CD200 expression was present in the outer root sheath of hair follicles in 4 androgenetic alopecia cases (p=0.113). In conclusion, although Merkel cell count and CD200 expression results were not statistically significantly different between alopecia areata and androgenetic alopecia cases, we believe that our hypothesis can be proved with large-scale studies with larger number of patients.