Abstract: Li Sizhe, Yan Tianmeng, Li Li, Jin Hongzhong, Zuo Yagang Department of Dermatology, Translational Medicine Center of Peking Union Medical College Hospital, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100730, China Corresponding author: Zuo Yagang, Email: zuoyagang@263.net 【Abstract】 Objective To investigate the correlations of the serum level of interleukin-21 （IL-21） with anti-BP180 antibodies, peripheral eosinophil level, bullous pemphigoid disease area index （BPDAI）in patients with bullous pemphigoid （BP）. Methods A total of 31 patients with bullous pemphigoid and 31 healthy controls were enrolled into this study. Blood samples were collected from all the subjects, and enzyme-linked immunosorbent assay （ELISA） was performed to detect the serum level of IL-21 and serum titer of anti-BP180 antibodies. BPDAI was assessed among 13 patients, and the correlation of the IL-21 level with anti-BP180 antibody titers, eosinophil count and BPDAI were analyzed. Results No significant difference in the serum level of IL-21 was observed between the patients （M［P25 - P75］: 255.28 ［156.19 - 361.59］ ng/L） and healthy controls （150.47 ［72.4 - 268.73］ ng/L, P = 0.14）. There was no correlation between the serum level of IL-21 and serum titer of anti-BP180 antibodies （82.98 ［26.82 - 132.92］U/ml, rs = 0.18, P = 0.332）. Among the 27 BP patients who underwent blood cell count, no correlation was found between the serum levels of IL-21 and whole-blood eosinophil counts （rs = 0.104, P = 0.606）. Among the 13 BP patients who underwent assessment of BPDAI, there was no correlation between the serum levels of IL-21 and BPDAI scores （rs = 0.233, P = 0.464）. Conclusion The IL-21 level is uncorrelated with anti-BP180 antibody level, peripheral eosinophil level or BPDAI in patients with BP.

Key words: Pemphigoid, bullous, Eosinophils, Interleukin?21, Anti-BP180 antibody