[Academic Presentation] Detection of Serum IL-25 and IL-31 Levels in Patients with Chronic Urticaria

Article reprinted from: Chinese Medical Abstracts – Dermatology, Issue 1, 2017.

Authors: Zhu Lianhua, Nan Meilan, Jin Zhehu

Urticaria is a common allergic skin disorder with complex etiology and pathogenesis that remain incompletely understood. Its hallmark symptoms are wheals and pruritus; when the course lasts ≤6 weeks, it is classified as acute urticaria (AU), whereas a duration exceeding 6 weeks defines chronic urticaria (CU). In recent years, numerous novel cytokines have been identified, and many studies suggest a close association between interleukins and allergic diseases. Interleukin‑25 (IL‑25), also known as IL‑17E, is a newly recognized member of the IL‑17 family. It is widely believed to play a significant role in allergic disorders, though its precise mechanisms have yet to be fully elucidated. Interleukin‑31 (IL‑31) is a helical‑structured cytokine belonging to the IL‑6 family, and its biological functions remain incompletely characterized. Some studies indicate that IL‑31 may be involved in atopic dermatitis, pruritus, and allergic asthma by regulating cytokine and chemokine production, cell proliferation and differentiation, hematopoiesis, inflammatory responses, and immune reactions. In this study, we measured serum levels of IL‑25 and IL‑31 in patients with CU from the Yanbian region to further investigate their relationship with the pathogenesis of CU.

1 Materials and Methods

1. 1 General Information

The CU patient group comprised 110 cases, all of whom were patients of Yanbian origin who attended the dermatology outpatient clinic at the Affiliated Hospital of Yanbian University between May 2015 and January 2016; their ages ranged from 13 to 70 years, with a disease duration of 2 to 8 years. The normal control group consisted of 105 subjects, selected from healthy volunteers in the Yanbian region who underwent routine health examinations at our hospital during the same period; these individuals had no history of allergies and were aged 18 to 65 years. Inclusion criteria for the CU patient group were as follows: ① episodic or persistent recurrent wheals that resolve within 24 hours; ② at least two episodes per week lasting for more than six weeks; ③ urticaria not clearly associated with medication; ④ urticaria not induced by physical factors; ⑤ exclusion of other specific types of urticaria; ⑥ absence of systemic organ involvement; and ⑦ no use of glucocorticoids, antihistamines, or immunosuppressants within two weeks prior to testing. All participants provided informed consent for the study procedures.

1.2 Instruments and Reagents

Enzyme‑linked immunosorbent assay (ELISA) plates (Coated Wells), 10× sample diluent, standards, biotinylated antibody working solution, enzyme‑conjugate working solution, 20× concentrated wash buffer, TMB substrate solution, and stop solution. ELISA kits for IL‑25 and IL‑31 (Shanghai Xitang Biotechnology Co., Ltd., Shanghai). The microplate reader used was the DENLEY DRAGON Wellscan MK 3 model manufactured by Thermo Fisher Scientific.

1. 3 IL-25 and IL-31 assays

Five milliliters of venous blood were collected from each subject, transferred to centrifuge tubes, allowed to stand for 30 minutes, and then centrifuged at 3,000 rpm for 15 minutes. The resulting serum was aliquoted into Eppendorf tubes and stored at −70°C. IL‑25 and IL‑31 were measured by ELISA, with all procedures performed in strict accordance with the kit instructions.

1. 4 Statistical Analysis

Statistical analyses were performed using SPSS 19.0. Continuous data are presented as mean ± standard deviation, and group comparisons were conducted using the t-test; a P-value less than 0.05 was considered statistically significant.

2 Results

The peripheral blood IL‑31 level in the CU patient group [1.44 ± 0.52 ng/L] was significantly higher than that in the healthy control group [(1.07 ± 0.42 ng/L)], with a statistically significant difference (t = 5.812, P = 0.000 < 0.01). However, there was no statistically significant difference in peripheral blood IL‑25 levels between the two groups: the CU group (2.08 ± 0.32 ng/L) versus the healthy control group (2.15 ± 0.24 ng/L) (t = 1.858, P = 0.065 > 0.05).

3 Discussion

The etiology and pathogenesis of chronic urticaria (CU) remain unclear, but they may be associated with autoimmune factors, infections, food and inhalant allergies, and psychological stressors. IL‑31 belongs to the IL‑6 cytokine family, yet it exhibits low sequence homology with other members of this family. It is primarily secreted by activated CD4+ T lymphocytes, particularly Th2 helper cells, mast cells, monocytes/macrophages, and dendritic cells. IL‑31 exerts its effects by activating three major signaling pathways: JAK‑STAT, MAPK, and PI3K/Akt. Following skin scratching, Th2 cells can shift toward a Th1 phenotype, and both Th2 and Th1 cells are capable of secreting IL‑31; thus, IL‑31 may play a role in regulating the interconversion between these two cell subsets. Although experimental evidence has demonstrated that IL‑31 is critically involved in allergic conditions such as dermatitis, pruritus, and allergic asthma, domestic research on the relationship between IL‑31 and CU remains virtually nonexistent. In this study, we measured serum IL‑31 levels in CU patients from the Yanbian region using ELISA and found that the CU group exhibited significantly higher serum IL‑31 concentrations than the healthy control group (P < 0.01). Similarly, Dillon et al. reported elevated serum IL‑31 levels in CU patients compared with healthy controls, findings consistent with our results. These observations suggest that IL‑31 may contribute to the pathogenesis of CU in the Yanbian area. However, the precise roles and underlying mechanisms of IL‑31 in CU require further experimental investigation in the future.

IL‑25, also known as IL‑17E, is a newly identified member of the IL‑17 family. Unlike other members of this family, IL‑25 can both elicit Th2‑type immune responses and suppress pro‑inflammatory reactions. Innate immune cells—including epithelial cells, eosinophils, mast cells, and basophils—express IL‑25. By binding to its receptor, IL‑17Rβ, IL‑25 mediates the crosstalk between innate and adaptive immunity and facilitates interactions among eosinophils, basophils, and Th2 memory cells, thereby establishing a positive feedback loop between innate and adaptive immunity that further amplifies allergic responses. Previous studies have demonstrated that dysregulation of Th2 responses associated with IL‑25 is implicated in atopic dermatitis, asthma, and autoimmune diseases. In recent years, research on IL‑25 expression in chronic urticaria (CU) has increased, with findings consistently showing elevated levels in the peripheral blood of CU patients, positively correlated with disease severity. However, investigations in ethnic minority regions remain scarce. In the present study, repeated measurements revealed no significant difference in serum IL‑25 levels between CU patients from the Yanbian region and healthy controls, a result that contrasts with earlier reports. This discrepancy may stem from variations in disease stage, assay methodologies, or the sensitivity of the detection kits; alternatively, it could reflect regional differences in the association between serum IL‑25 levels and CU, possibly attributable to dietary habits or climatic conditions—factors that may account for higher IL‑25 levels in southern populations but lower or undetectable levels in Yanbian residents. Furthermore, the small sample size of this study may have precluded identification of a genuine link between IL‑25 and the pathogenesis of CU in the Yanbian area. Consequently, the relationship between IL‑25 and the onset of CU in Yanbian remains an open question requiring further investigation.

This study focused on chronic urticaria (CU) in the Yanbian region. The results showed that serum IL‑31 levels were higher in CU patients than in the healthy control group, suggesting that serum IL‑31 may play a role in the pathogenesis of CU in this population. In contrast, no significant difference was observed in serum IL‑25 levels between CU patients and the control group, indicating that IL‑25 might not be expressed in the serum of these patients. Further research is needed to elucidate the relationship between IL‑31 and IL‑25 and the pathogenic mechanisms underlying CU and other types of urticaria. Additionally, future studies could expand the sample size in the Yanbian region or employ more sensitive assays for IL‑31 and IL‑25 to obtain more precise findings. At present, the interrelationships among Th cell subsets remain incompletely understood and warrant further investigation, with the aim of providing new theoretical insights for the treatment of CU.