Atopic dermatitis (AD) is closely related to many systemic diseases, such as other allergic diseases, autoimmune diseases, infectious diseases, cardiovascular diseases and mental disorders, and the underlying mechanism is very complex. AD is considered to be a starting point of the allergy march, and affects the occurrence of various allergic diseases such as food allergies, allergic rhinitis and allergic asthma. AD is associated with the occurrence of many autoimmune diseases, decreased incidence of some malignant tumors and low serum levels of vitamin D. AD is not only a potential risk factor for multiple organ infections and osteoporosis, but also increases the risk of cardiovascular diseases, nephrotic syndrome, and skin dryness. In addition, mental disorders such as anxiety and depression are also common complications of AD. To recognize and investigate into the associations between AD and systemic diseases is of great significance for improving the prognosis and quality of life of AD patients.

Objective:To determine the expression of transglutaminase 2 (TGM2) in peripheral blood mononuclear cells (PBMCs) from patients with atopic dermatitis (AD), and to analyze its correlation with AD-related inflammatory factors and disease severity.Methods:A total of 29 AD patients and 15 healthy controls were collected from the First Affiliated Hospital of Fujian Medical University from July 2020 to January 2021. Ten milliliters of peripheral blood samples were collected from each subject, so was the clinical information, including age, gender, course of disease, eosinophil counts, basophil counts, total IgE levels, Scoring AD index (SCORAD), etc. PBMCs were isolated by density gradient centrifugation. Fluorescence-based quantitative PCR was performed to determine the mRNA expression of TGM2 and AD-related inflammatory factors (interleukin [IL]-1β, IL-4, IL-6, IL-8, IL-10, IL-13, IL-17, thymic stromal lymphopoietin [TSLP], P2RX7 [purinergic receptor P2X, ligand-gated ion channel, 7], etc.) in PBMCs from 29 AD patients and 15 healthy controls, and flow cytometry to determine TGM2 protein expression on PBMCs. Mann-Whitney U test was used to analyze differences between groups, and Spearman correlation analysis to evaluate the correlation. Results:The relative mRNA expression of TGM2 in PBMCs did not differ between the AD group and control group ( M[ Q1, Q3]: 0.509 [0.325, 0.958] vs. 0.475 [0.328, 1.051], U = 210.50, P = 0.872). Compared with the control group, the AD group showed significantly decreased IL-4 mRNA expression (0.171[0.049, 0.449] vs. 0.824 [0.397, 1.378], P < 0.001), but significantly increased mRNA expression of IL-8 and IL-13 ( P = 0.011, 0.006, respectively). Spearman correlation analysis showed that the mRNA expression level of TGM2 in PBMCs was positively correlated with the mRNA expression levels of IL-4 and P2RX7 in the AD group ( rs = 0.42, 0.40, P = 0.024, 0.034, respectively), while there were no correlations between TGM2 mRNA expression and AD severity-related indicators (all P>0.05), such as age (21[16, 29] years), course of disease (4[1,10] years), eosinophil counts (0.33[0.18, 0.65] × 10 9/L), basophil counts (0.04[0.03, 0.06] × 10 9/L], SCORAD scores (60.5[46.98, 66.13] points), and serum total IgE levels (373 [40, 1 815] IU/ml). The relative protein expression levels of TGM2 on the surface of PBMCs did not differ between the AD group and control group (54.9 [47.6, 62.8] vs. 55.55 [51.5, 60.25], U = 112.00, P = 0.922) ], and no correlations were observed between the protein expression of TGM2 on PBMCs and AD severity-related indicators in the AD group (all P > 0.05) . Conclusion:No significant differences were observed in TGM2 mRNA expression in PBMCs or TGM2 protein expression on the surface of PBMCs between the AD patients and healthy controls, and there were no correlations between the TGM2 mRNA and protein expression and AD severity.