BackgroundRespiratory syncytial virus (RSV) is the most common cause of bronchiolitis in infants. Following RSV bronchiolitis, 50% of children develop post-bronchiolitis wheeze (PBW). Animal studies have suggested that interleukin (IL)-10 plays a critical role in the pathogenesis of RSV bronchiolitis and subsequent airway hyperresponsiveness. Previously, we showed that ex vivo monocyte IL-10 production is a predictor of PBW. Additionally, heterozygosity of the single-nucleotide polymorphism (SNP) rs1800872 in the IL10 promoter region was associated with protection against RSV bronchiolitis.MethodsThis study aimed to determine the in vivo role of IL-10 in RSV pathogenesis and recurrent wheeze in a new cohort of 235 infants hospitalized for RSV bronchiolitis. IL-10 levels in nasopharyngeal aspirates (NPAs) were measured at the time of hospitalization and the IL10 SNP rs1800872 genotype was determined. Follow-up data were available for 185 children (79%).ResultsLocal IL-10 levels during RSV infection turned out to be higher in infants that later developed physician diagnosed PBW as compared to infants without PBW in the first year after RSV infection (958 vs 692 pg/ml, p = 0.02). The IL10 promoter SNP rs1800872 was not associated with IL-10 concentration in NPAs.ConclusionThe relationship between high local IL-10 levels during the initial RSV infection and physician diagnosed PBW provides further evidence of the importance of the IL-10 response during RSV bronchiolitis.

Severity of respiratory syncytial virus (RSV) infection ranges widely. To what extent the local immune response is involved in RSV disease pathogenesis and which markers of this response are critical in determining disease severity is still a matter of debate.The local immune response was studied in nasopharyngeal aspirates (NPAs) during RSV infection. 47 potential markers of disease severity were analysed in a screening cohort of RSVinfected infants with mild disease at home (n58), hospitalised infants (n510) and infants requiring mechanical ventilation (n57). Results were confirmed in a cohort of infants hospitalised for RSV infection (n5200). Finally, genetic validation was studied in a cohort of infants hospitalised for RSV infection (n5465) and healthy controls (n5930).The concentration of TIMP-1 (tissue inhibitor of metalloproteinase) was higher in the NPAs of hospitalised infants compared with the NPAs of infants at home (1,199 versus 568 ng?mL -1 ; p,0.0001). Similar results were found for matrix metalloproteinase (MMP)-3 (765 versus 370 pg?mL -1 ; p50.004). MMP-3 was confirmed as a marker of disease severity in a larger cohort and MMP3 gene polymorphism rs522616 was associated with severe RSV infection (OR 0.82, p,0.05).In conclusion, extracellular matrix proteinases play an important role in the pathogenesis of RSV bronchiolitis.