To investigate the relationship of the expression of peripheral T helper type 9 (Th9) cells and their related cytokines with the severity and clinical course of alopecia areata, and to explore their significance in the occurrence of alopecia areata.

From May to December in 2017, 74 outpatients with alopecia areata enrolled from Department of Dermatology, Huashan Hospital, Fudan University served as the alopecia areata group, and 57 health checkup examinees in Huashan Hospital served as the control group. Peripheral blood samples were obtained from the patients and controls. Enzyme-linked immunosorbent assay (ELISA) was performed to detect the serum levels of interleukin (IL) -9, IL-4, transforming growth factor (TGF) -β1 and interferon (IFN) -γ, flow cytometry to determine the proportion of Th9 cells (CD4⁺ IL-9⁺ T helper cells) in peripheral blood mononuclear cells (PBMC) , and real-time fluorescence-based quantitative PCR to measure the mRNA expression of IL-9 and PU.1 in the PBMCs. Data were recorded in Microsoft Excel 2017 software, and statistically analyzed with SPSS17.0 software using two-sample t test and Spearman rank correlation analysis. Statistical charts were drawn with Graphpad prism 6 software.

Compared with the control group, the alopecia areata group showed significantly decreased serum level of IL-9 (190.40 ± 12.33 ng/L vs. 288.10 ± 17.38 ng/L, t= 4.71, P < 0.01) , but significantly increased serum levels of TGF-β1 (6 191.00 ± 355.50 ng/L vs. 4 026.00 ± 258.00 ng/L, t= 4.41, P < 0.05) and IFN-γ (15.71 ± 3.00 ng/L vs. 8.79 ± 0.60 ng/L, t= 2.001, P < 0.05) . However, there was no significant difference in the serum level of IL-4 between the alopecia areata group and control group (P > 0.05) . The serum level of IFN-γ was significantly lower in the patients with severe alopecia areata than in the patients with mild alopecia areata (P= 0.02) , and the serum level of IFN-γ in the patients with alopecia areata was negatively correlated with the severity of alopecia tool (SALT) score (r_s = -0.298, P = 0.010) . There were no significant differences in the serum levels of IL-9, IL-4 and TGF-β1 between the patients with severe alopecia areata and those with mild alopecia areata (all P > 0.05) . The serum levels of IL-9, IL-4, TGF-β1 and IFN-γ did not differ between the patients with active alopecia areata and those with stable alopecia areata, as well as between the patients with clinical course of < 6 months and those with clinical course of > 6 months (P > 0.05) . The alopecia areata group showed significantly decreased proportion of Th9 cells in the PBMCs (t= 2.04, P= 0.045) and mRNA expression of IL-9 and PU.1 (t= 2.12, 2.178, both P < 0.05) compared with the control group.

The serum level of IL-9 and proportion of peripheral blood Th9 cells both decrease in patients with alopecia areata, and Th9 cells and their related cytokines may be involved in the occurrence of alopecia areata.

Alopecia areata; Cytokines; Interleukin-9; Interleukin-4; Transforming growth factor beta1; Interferon-gamma; Th9 cells