Increased T-helper cell 2 response in infants with respiratory syncytial virus bronchiolitis hospitalized outside epidemic peak

Aim: To test the hypothesis that the balance of type-1/type-2 immune response differs between infants hospitalized with respiratory syncytial virus (RSV) bronchiolitis during the peak months and those during the nonpeak months. Methods: We prospectively enrolled 90 unrelated full-term previously healthy infants hospitalized during the first year of life for RSV sole bronchiolitis over 2 epidemics (November 2016 to April 2017 and October 2017 to April 2018). We stratified infants as follows: hospitalized during the peak months (n: 71) and during the nonpeak months (n: 19). The frequencies of CD4+ producing interferon (IFN)-γ and interleukin (IL)-4 and of CD8+ producing IFN-γ T cells were measured by flow cytometry from infant peripheral whole blood. The T-helper cell (Th2) polarization index was calculated as the ratio between CD4+ T cells producing IL-4 and CD4+ T cells producing IFN-γ. Results: Infants hospitalized during nonpeak months were significantly less frequently breast-fed, had a higher eosinophils count, a significantly higher percentage of CD4+ T cells producing IL-4 and higher Th2 polarization index than infants hospitalized during the peak months. Conclusions: We elucidated the presence of different endotypes in infants with RSV sole bronchiolitis. Previously healthy full-term infants hospitalized during the nonpeak months seem to be more likely those with a possible predisposition to atopy.