Airway mir-155 responses are associated with TH1 cytokine polarization in young children with viral respiratory infections

Background MicroRNAs (miRs) control gene expression and the development of the immune system and antiviral responses. MiR-155 is an evolutionarily-conserved molecule consistently induced during viral infections in different cell systems. Notably, there is still an unresolved paradox for the role of miR-155 during viral respiratory infections. Despite being essential for host antiviral TH1 immunity, miR-155 may also contribute to respiratory disease by enhancing allergic TH2 responses and NFkB-mediated inflammation. The central goal of this study was to define how airway miR-155 production is related to TH1, TH2, and proinflammatory cytokine responses during naturally occurring viral respiratory infections in young children. Methods Normalized nasal airway levels of miR-155 and nasal protein levels of IFN-gamma, TNF-alpha, IL-1 beta, IL-13, IL-4 were quantified in young children (<= 2 years) hospitalized with viral respiratory infections and uninfected controls. These data were linked to individual characteristics and respiratory disease parameters. Results A total of 151 subjects were included. Increased miR-155 levels were observed in nasal samples from patients with rhinovirus, RSV and all respiratory viruses analyzed. High miR-155 levels were strongly associated with high IFN-gamma production, increased airway TH1 cytokine polarization (IFN-gamma/IL-4 ratios) and increased pro-inflammatory responses. High airway miR-155 levels were linked to decreased respiratory disease severity in individuals with high airway TH1 antiviral responses. Conclusions The airway secretion of miR-155 during viral respiratory infections in young children is associated with enhanced antiviral immunity (TH1 polarization). Further studies are needed to define additional physiological roles of miR-155 in the respiratory tract of human infants and young children during health and disease.