Abstract: GUAN Hai-hong, LI Hui, LI Hong-xin, LIN Lin*, WANG Hong-sheng, ZHOU Wu-qing. *Institute of Dermatology, Chinese Academy of Medical Sciences and Peking Union Medical College, Nanjing 210042, China Corresponding author: LIN Lin, Email:dllon3@yahoo.com.cn 【Abstract】 Objective To investigate the expression of CD200 in peripheral lymphocytes and hair follicles from patients with alopecia areata （AA）. Methods Flow cytometry was used to detect the expression of CD200 in peripheral lymphocytes from 43 patients with AA and 43 healthy controls. Immunohistochemistry was carried out to quantify the expression of CD200 and cytokeratin 15（CK15, a marker for basal cells of the outer root sheath） in resected scalp specimens from 8 patients with AA and 8 healthy controls. Differences in the expression of CD200 and CK15 between the patients and controls were assessed by independent-samples t test and rank sum test. Data were processed by the software SPSS17.0. Results The percentage of CD200-expressing cells in peripheral blood lymphocytes and T lymphocytes was significantly lower in the patients with AA than in the healthy controls （5.73% ± 3.46% vs. 12.01% ± 4.9%, 8.85% ± 4.8% vs. 12.31% ± 3.12%, t = 6.865, 3.964, respectively, both P < 0.05）. However, no significant difference was observed in the percentage of CD200-expressing cells in peripheral blood B lymphocytes between the patients and controls （74.676% ± 8.122% vs. 75.750% ± 9.447%, t = 0.570, P > 0.05）. Further more, the patients showed a lower expression of CD200 （P < 0.05）, but a similar expression of CK15 （P > 0.05） in hair follicles compared with the controls. Conclusion The decrease in CD200 expression in peripheral lymphocytes and hair follicles may be involved in the pathogenesis of AA. 【Key words】 Alopecia areata; CD200; Lymphocytes; Hair follicle

Key words: alopecia areata, CD200