Administration of TSG-6 protein in BPD mice at PN2 and PN4 (Fig. 5a) significantly decreased the total cell count (Fig. 5b), infiltration of neutrophils (Fig. 5c) and protein leak (Fig. 5d) in the BALF of the TSG-6-injected group versus BPD, thus demonstrating decreased hyperoxia-induced alveolar-capillary leakage and preserved alveolar-capillary barrier in the lung. The gene discussed is TNFAIP6; the disease is bronchopulmonary dysplasia.