Objective:To evaluate the effect of exogenous interleukin-18 (IL-18) binding protein (IL-18BP) on sepsis-associated lung injury and the role of NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasomes in rats.Methods:This study was performed in two parts. Experiment Ⅰ Thirty-six SPF-grade healthy male Sprague-Dawley rats, aged 6-8 weeks, weighing 200 g, were allocated into 3 groups ( n=12 each) using a random number table method: sham operation group (S group), sepsis-associated lung injury group (SLI group), and sepsis-associated lung injury+ IL-18BP group (SI group). The rat model of sepsis-associated lung injury was developed using cecal ligation and puncture. The rats in group S underwent laparotomy without the subsequent ligation and puncture procedures. IL-18BP 1.5 mg/kg was intraperitoneally injected immediately after surgery in group SI. Experiment Ⅱ The aforementioned 36 rats were allocated into 3 groups ( n=12 each) using a random number table method: sepsis-associated lung injury + IL-18BP + vehicle group (SIV group), sepsis-associated lung injury + IL-18BP + MCC950 group (SIM group), and sepsis-associated lung injury + IL-18BP + nigericin group (SIN group). In SIV group, SIM group and SIN group, solvent, MCC950 (NLRP3 inhibitor, 5 mg/kg) and nigerin (NLRP3 agonist, 2 mg/kg) were intraperitoneally injected at 30 min before surgery respectively, and IL-18BP 1.5 mg/kg was intraperitoneally injected after operation. HE staining was used to observe the lung injury at 24 h after operation. The left lung tissues were obtained for calculation of the wet/dry weight (W/D) ratio. The concentrations of IL-18 and IL-18BP in broncho-alveolar lavage fluid (BALF) were determined by enzyme-linked immunosorbent assay. The percentage of NLRP3 positive cells in lung tissues was detected by immunofluorescence. The expression of IL-18, IL-18BP, cl-caspase-1 and gasdermin D (GSDMD) in lung tissues was detected by Western blot. Results:Experiment Ⅰ Compared with group S, the injury score of lung tissues, W/D ratio, concentrations of IL-18 and IL-18BP in BALF, and percentage of NLRP3 positive cells were significantly increased, and the expression of IL-18, IL-18BP, cl-caspase-1 and N-GSDMD was up-regulated in group SLI ( P<0.05). Compared with group SLI, the injury score of lung tissues, W/D ratio, concentrations of IL-18 and IL-18BP in BALF, and percentage of NLRP3 positive cells were significantly decreased, the expression of IL-18, cl-caspase-1 and N-GSDMD was down-regulated, and the expression of IL-18BP was up-regulated in group SI ( P<0.05). Experiment Ⅱ Compared with group SIV, the injury score of lung tissues, W/D ratio, concentrations of IL-18 in BALF, and percentage of NLRP3 positive cells were significantly decreased, and the expression of IL-18, cl-caspase-1 and N-GSDMD was down-regulated in group SIM, and the injury score of lung tissues, W/D ratio, concentrations of IL-18 in BALF, and percentage of NLRP3 positive cells were significantly increased, and the expression of IL-18, cl-caspase-1 and N-GSDMD was up-regulated in group SIN ( P<0.05). Conclusions:Exogenous IL-18BP can reduce sepsis-associated lung injury, and the mechanism is related to inhibition of activation of NLRP3 inflammasomes in rats.