Studies have demonstrated that VD could attenuate lung injury in an animal model of BPD through the suppression of interferon-gamma (IFN-γ) production (19) or downregulation of Toll-like receptor 4 (TLR4) (20); however, the mechanism of VD in BPD remains poorly understood and uncertain. This evidence concerns the gene TLR4 and bronchopulmonary dysplasia.