Systemic IL-10 and IFN-γ Levels in Respiratory Syncytial Virus- and Rhinovirus-Infected Bulgarian Children with Acute Bronchiolitis and Their Impact on Clinical Manifestation

Respiratory syncytial virus (RSV) and rhinovirus (RV)-the two primary causative viruses of bronchiolitis in children-have been studied extensively in terms of their associations with disease severity and serious late disease outcomes. In this study, we explored the differences in the clinical values of IFN-γ and IL-10 serum levels in RSV and RV bronchiolitis in the Bulgarian childhood population. Eighty-eight children with acute bronchiolitis, aged two months to two years, who were admitted to the General Pediatrics Clinic of University Hospital "Prof. St. Kirkovich", Stara Zagora, Bulgaria served as this study's subjects. The degree of wheezing and respiratory failure were classified. Naso-pharyngeal swabs were collected from all participants, and molecular identification of viruses was performed using real-time PCR. Serum samples were used to determine IFN-γ and IL-10 quantities using ELISA kits, and data are presented as the median IQR (25-75%). The total serum IL-10 levels were significantly enhanced in RSV-infected children compared to those infected with RV (14.4 (12.2-24.0) vs. 8.9 (7.2-12.5); <i>p</i> < 0.001) and the other viral bronchiolitis groups (14.4 (12.2-24.0) vs. 6.65 (3.9-15.3); <i>p</i> = 0.003). The highest IL-10 levels (14.4 (12.8-27.9)) were found in RSV-positive patients with first-degree respiratory failure. Almost identical serum IFN-γ levels were determined for RSV- and RV-positive bronchiolitis patients (3.2 (1.6-6.8) and 2.8 (1.1-7.3); <i>p</i> = 0.781). Variance analysis of IL-10 serum levels revealed statistically significant differences among the patient groups depending on the type of viral infection, concerning respiratory failure (<i>p</i> = 0.005) and wheezing severity (<i>p</i> = 0.017). Our findings show that the IL-10 levels and the type of virus have a combined effect on disease severity. These data might contribute to patients' personalized/individualized therapy and the prevention of recurrent wheezing later in life.