The Arg-1 expression decreased in BPD mice and then was inhibited when ABX was added (Fig. 4b). Then, the protein levels of iNOS and Arg-1 were detected by western blot. Consistent with the above results, iNOS increased in BPD mice and antibiotics treatment upregulated the expression of iNOS only when mice exposed to hyperoxia (Fig. 4a, P < 0.05). The gene discussed is ARG1; the disease is bronchopulmonary dysplasia.