LL-37 levels in nasal secretions are associated with the severity of acute bronchiolitis

Objective: Τo investigate the association of serum vitamin D and nasal secretion antimicrobial peptides (AMPs) levels with the severity of acute bronchiolitis. Study design: We conducted a prospective single pediatric tertiary care center cohort study of inpatients aged 0-18 months with a first episode of acute bronchiolitis from November 1st 2014 to April 30th 2017. Disease severity was determined by the length of hospitalization and supplemental hospital data. Qualitative measurements included serum 25(OH)D and nasal secretion LL-37 and β-defensin-2 levels. Correlations were examined with the Mann-Whitney and Kruskal-Wallis criteria for qualitative and the correlation coefficient Spearman’s rho for quantitative factors. Multiple linear and logarithmic regression were performed in order to adjust for confounding factors. Results: The study population consisted of 153 infants and toddlers with mean age 3.6 months (SD: +2.8). The median level of serum 25(OH)D was 51.4 nmol/L (IQR: 29.7-72.2). No association was found between serum 25(OH)D and AMPs nasal secretions levels. Serum 25(OH)D and nasal secretion β-defensin-2 levels were not associated with the severity of bronchiolitis. In contrast, LL-37 levels were inversely associated with the length of hospitalization (rho = -0.340, p = 0.001) and the need for medication use (p = 0.001) and this association remained significant after adjustment for potential confounders. Conclusion: A significant association between LL-37 nasal secretions levels with the severity of acute bronchiolitis was found in hospitalized infants and toddlers. The role of LL-37 in the pathogenesis of bronchiolitis merits further investigation.