Though IL-1β is mainly produced by alveolar macrophage, alveolar epithelia may play more important role in the progress of BPD as followed: (1) alveolar epithelial type II cells (AECII)-derived chemokine Monocyte chemoattractant protein-1 (MCP-1) was identified as a main factor in activating alveolar macrophages (37); (2) alveolar epithelial type II cells more sensitive to hyperoxia (38). Here, CCL2 is linked to bronchopulmonary dysplasia.