Neutrophil infiltration and activation in bronchiolitic airways are independent of viral etiology.

BACKGROUND: Hospitalization with bronchiolitis is linked to the development of early childhood chronic wheeze and asthma. Viral etiology and severity of inflammation are potential contributing factors. Previously we observed reduced airway neutrophil infiltration in breastfed bronchiolitic infants, with a corresponding reduction in disease severity. This study aimed to examine whether respiratory viral etiology and co-infection alters the pattern of neutrophil influx, and the inflammatory mediator profile, resulting in epithelial damage in bronchiolitis.

METHODS: Nasopharyngeal aspirates (NPAs) collected from hospitalized infants were assessed for viruses, soluble protein, cellular infiltrate, interleukin (IL)-6, -8, and myeloperoxidase (MPO).

RESULTS: NPAs were collected from 228 bronchiolitic and 14 non-bronchiolitic infants. In the bronchiolitic cohort, human rhinovirus was most prevalent (38%), followed by respiratory syncytial virus (36%), adenovirus (10%), and human metapneumovirus (6%), with 25% positive for viral co-infections and 25% negative for all screened viruses. Viral-induced bronchiolitis was associated with increased cellular infiltrate and protein, above control, and virus-negative infants (P < 0.05). Cellular infiltrate correlated to IL-6, -8, and MPO (r = 0.331, 0.669, and 0.661; P < 0.01). Protein, IL-6, -8, and MPO differed significantly between viral groups; however, the majority of marker values for all groups fall within an overlapping, indistinguishable range, precluding their use as biomarkers of viral etiology. No significant difference was found between single and viral co-infections for any parameter.

CONCLUSION: Bronchiolitic infants presenting with a detectable respiratory virus during hospitalization demonstrated elevated markers of airway tissue inflammation and injury. In this cohort, viral etiology did not discernibly modulate chemokine-mediated neutrophil infiltration and activation. Pediatr Pulmonol. 2017;52:238-246. © 2016 Wiley Periodicals, Inc.