To obtain targeted information on the relevance of these variables during severe RSV bronchiolitis, we compared the transcriptional levels of six IFN-I ISGs and of type III IFNs, of HERV sequences, in particular of env genes of SYN1 and SYN2, and of pol genes of HERV-H, -K, and -W (the three retroviral families most widely studied), as well as of TRIM28 and SETDB1 in children hospitalized for acute RSV bronchiolitis versus healthy children (HC). The gene discussed is SYN2; the disease is respiratory syncytial virus bronchiolitis.