MUC1 and respiratory system disorder: Because MUC1 is used as a diagnostic marker for many severe respiratory diseases [6], we first found that the MUC1 protein levels were significantly up-regulated in the sputum of children with RSV-infected bronchiolitis during the exacerbation period; the levels of pro-inflammatory factors, including TNF-α, IL-1β, IL-8 and IL-6 (Fig. 1), were also increased, indicating that higher the pro-inflammatory factor levels, higher are the MUC1 protein levels.