The role and association of plasma level of IL-19 and pro-inflammatory cytokines (IL-17A, IL-4 and IL-1β) with severity of atopic dermatitis in children

Interleukin-19 (IL-19) is known as a pro-inflammatory cytokine produced mainly by monocytes and keratinocytes and stimulated by IL-4, IL-13 and IL-17. IL-19 promotes the development and function of Th2 cells and thus can play a role in pathogenesis of allergic diseases. However, no clinical studies have analyzed plasma levels of IL-19 in larger series of children with atopic dermatitis (AD). This study was performed to clarify whether plasma levels of IL-19 and cytokines associated with IL-19 are reflecting on disease severity. Children diagnosed with atopic dermatitis in the active phase of the disease and healthy children were enrolled in the study. The diagnosis of atopic dermatitis was made by a physician according to criteria by Hanifin and Rajka. Demographic data including age, gender, sex, family history of atopy, age of onset, plasma eosinophil level were recorded. Disease severity was measured by SCORAD index. IL-19 plasma levels were measured with human IL-19 ELISA kit (R&D Systems), IL-17A, IL-4 and IL-1β plasma levels were measured with flow cytometry (CBA Human Enhanced Sensitivity Mater Buffer Kit, BD Biosciences), according to manufacturers’ instructions. The study consisted of 23 children with atopic dermatitis and 12 healthy children (with mean age 5.91 years ±3.61 and 8.56 ±4.89, respectively, p>0.05). Mean IL-19 plasma level was 61.1 pg/mL ± 105.7 in AD patients and 2.1 ± 5.9 pg/mL in healthy controls. Mean IL-17A, IL-4 and IL-1β plasma levels in AD children were 129.4 fg/mL ± 86.1, 26.4 fg/mL ± 31.6, 67 fg/mL ± 82.8, respectively. In healthy controls mean plasma cytokines levels were 18.8 fg/mL ± 36.6, 21.5 fg/mL ± 32.2, 8.9 fg/mL ± 31, for IL-17A, IL-4 and IL-1β respectively. IL-17A and IL1β plasma levels differed significantly between AD and control group (p<0.001, p<0.05 respectively) however cytokine levels were not significantly correlated with SCORAD index. IL-4 plasma levels did not differ significantly between AD and control group. Overall IL-19 levels were significantly increased in patients in the top quartile of SCORAD (36,7-55,8), compared to those in the bottom quartile and the control group (ANOVA, p<0.001 for all four comparisons). Plasma IL-19 level was found to be significantly elevated in children with high SCORAD. Our findings indicate that plasma IL-19 may play a role in AD pathogenesis and become a novel indicator for evaluating disease activity.