As shown in Figures 5, the serum level of IL-18 in infants with different severity of BPD were always different on days 1, 7, 14, and 28, and infants with severe BPD were significantly associated with a higher serum level of IL-18 than those with mild BPD (P < 0.05). Here, IL18 is linked to bronchopulmonary dysplasia.