Mansbach JM, et al. - This work was planned to assess the association of serum LL-37 levels with the severity of bronchiolitis and viral etiology. Results from this large multicenter study of infants hospitalized with bronchiolitis suggested that lower levels of serum LL-37 were associated with increased severity of illness. Observations, in addition, revealed an inverse relationship between LL-37 levels and the most common virus causing bronchiolitis, respiratory syncytial virus (RSV). The role of LL-37 in the pathogenesis of bronchiolitis seemed evident from these findings.