Assessment of interferon gamma and indoleamine 2,3-dioxygenase 1 analysis during respiratory syncytial virus infection in infants in Italy: an observational case–control study

OBJECTIVES: The aim of this study was to measure interferon gamma (IFN-γ) and indoleamine 2,3-dioxygenase 1 (IDO1) values in the White blood cells of infants during respiratory tract infections and to compare these with healthy age-matched controls. DESIGN: This was a prospective, observational case–control study conducted in 2019–2020. SETTING: The study took place at Regina Margherita Children’s Hospital, Turin, Italy. PARTICIPANTS: The study comprised 63 infants, including 26 patients hospitalised for bronchiolitis due to a respiratory syncytial virus (RSV) infection and 37 age-matched controls. The inclusion criteria included a positive RSV test for an infant with bronchiolitis. METHODS: We collected peripheral blood and measured the relative quantification of messenger RNA (mRNA) expression of IFN-γ and IDO1 with TaqMan real-time PCR amplification. The data were collected on the first day of admission. RESULTS: The mean age of the 26 patients with RSV bronchiolitis (53.8% female) was 85 (9–346) days when they were admitted to the hospital. Their mean gestational age at birth was 38 weeks and their mean birth weight was 3100 (2780–3730) g. The expression of IFN-γ was significantly reduced in patients with bronchiolitis RSV compared with healthy controls (p=0.0132). However, there was no significant difference between the two groups when the IDO1 mRNA expression values in their WCC were measured (p=0.0642). CONCLUSION: Our findings did not clarify whether IDO1 expression was related to the early stage of the disease or to the young age of the infants. The data provide evidence that IFN-γ was significantly reduced in infants with bronchiolitis due to RSV, compared with age-matched healthy controls, but the IDO1 was not different. New investigations that focus on subjects infected with RSV at different stages of infancy would help to clarify whether IDO1 expression can be related to age.