Abstract： Objective To explore the roles of follicular helper T cells (Tfh) in the pathogenesis of pemphigus and bullous pemphigoid (BP).Methods Venous blood was collected from 20 patients (including 10 cases of pemphigus and 10 cases of BP) and 20 age- and sex-matched normal human controls.Enzyme linked immunosorbent assay (ELISA) was performed to measure the levels of serum interleukin (IL)-21 and anti-BP180-NC16A antibody,and flow cytometry to detect the percentage of Tfh in peripheral blood mononuclear cells (PBMCs).The relationship of anti-BP180-NC16A antibody titer to Tfh and IL-21 levels was assessed by linear correlation analysis.Results The serum IL-21 level and Tfh percentage in PBMCs were significantly higher in patients with pemphigus than in the normal controls (95.33 ± 33.69 vs.54.50 ± 18.13 pg/ml,t =3.38,P＜ 0.01;12.08％ ± 4.74％ vs.6.15％ ± 1.62％,t =3.74,P ＜ 0.01),and higher in patients with BP than in the normal controls ( 106.70 ± 44.91 vs.55.37 ± 15.89 pg/ml,t =3.41,P ＜ 0.01; 11.85％ ± 3.14％ vs.6.03％ ± 1.74％,t =5.13,P ＜ 0.01 ).The titer of anti-BP180-NC 16A antibody was positively correlated with the percentage of Tfh (r =0.67,P＜ 0.05) and serum level of IL-21 (r=0.77,P＜ 0.01) in patients with BP.Conclusions There is a significant increase in the percentage of Tfh and serum level of IL-21 in patients with pemphigus and BP,hinting a certain role of Tfh and IL-21 in the pathogenesis of pemphigus and BP.