Abstract: 【Abstract】 Objective To investigate the relationship between eosinophil cationic protein （ECP） levels in sera and blister fluids and bullous pemphigoid （BP）. Methods From January 2012 to October 2019, 40 patients with newly diagnosed BP and 40 healthy individuals were enrolled from Department of Dermatology, Peking Union Medical College Hospital, and serum ECP levels were detected by enzyme-linked immunosorbent assay. Meanwhile, another 33 patients with newly diagnosed BP and 41 patients with non-autoimmune bullous diseases were enrolled, and the ECP level was detected in blister fluids by enzyme-linked immunosorbent assay. Pathological sections of skin lesions of 1 patient with BP and 1 with contact dermatitis were subjected to immunohistochemical staining for ECP. Normally distributed data were compared between 2 groups by using t test or t′ test, while enumeration data were comparedby using chi-square test. Pearson's correlation coefficients was used to analyze the relationship between serum levelsof ECP and proportions of peripheral blood eosinophils in patients with BP. Results The serum level of ECP was significantly higher in the BP group （116.9 ± 19.3 ng/L） than in the healthy control group （93.3 ± 15.9 ng/L, t = 5.96, P＜0.001）, and the blister fluid level of ECP was also significantly higher in the BP group （665.8 ± 189.0ng/L） than in the non-autoimmune bullous disease group （547.5 ± 240.6 ng/L, t = 2.31, P = 0.02）. Immunohistochemical study showed more brown-yellow particles in the cytoplasm of ECP-positive cells in the BP group than in the contact dermatitis group. There was no significant correlation between the serum level of ECP and proportion of peripheral blood eosinophils in the BP patients （r = -0.15, P = 0.35）. Conclusion The levels of ECP in the sera and blister fluids markedly increased in the patients with BP, and blister fluid levels of ECP were much higher than serum levels of ECP, suggesting that ECP may be involved in the occurrence of BP.

Key words: Pemphigoid, bullous, Eosinophils, Eosinophil cationic protein