Serum Levels of Selected Cytokines and Chemokines and IgG4 in Children With Recurrent Respiratory Tract Infections

Background: Respiratory tract infections are a common health problem. Cytokines/chemokines play a critical role in the regulation of the immune system. Their defective production may predispose to recurrent respiratory tract infections (RRIs), and an excessive immune response may lead to chronic inflammation and cause damage to the respiratory tract. Another biomarker of respiratory infections may be immunoglobulin-IgG4. Its meaning has still been little explored. We wanted to assess the suitability of the levels of biomarkers tested: interleukin (IL)-17A, IL-18, IL-23, normal T cells expressed and secreted (RANTES), and induced protein (IP)-10, as well as immunoglobilun G4 (IgG4) to predict recurrent infections. Methods: The study group (SG) included a total of 130 children (68 girls, 62 boys) between 3 and 17 years of age with RRI. The control group (CG) included 86 healthy children with no symptoms of inflammatory or allergic diseases (44 girls and 42 boys) of the same age. Blood samples were collected in fasting state and then serum samples were frozen and stored until biomarker assay. Results: Serum RANTES, IL-18, IL-23, and IgG4 concentration were higher in all children with recurrent infections vs. those in the CG (p  < 0001). Serum levels of IL-17A and IP-10 were also significantly higher in the SG than in the CG, but only in the youngest children. Among the six serum markers, RANTES demonstrated the highest area under the receiver operating characteristic curve (area under curve) value (0.998, 95% confidence interval [CI]: 0.98-1.0, p < 0.001) for the diagnosis of RRIs, followed by IL-23 (0.99, 95% CI 0.966-0,999, p < 0.001) and IL-18 (0.957, 95% CI 0.921-0.980, p < 0.001). Conclusions: RANTES, IL-23, and IL-18 could be strong predictors of respiratory infections recurrence in children.