| Objective: To observe the expression of IL-18 in bleomycin-induced pulmonary fibrosis in rats , discuss its possible role in the pathogenesis of pulmonary fibrosis; To study the effect of recombinant rat IL-18 on rat lung fibroblasts.Method: Firstly, the female SD rats were randomly divided into two experimental groups of 60rats.30 rats per group received intratracheal instillation of single dose bleomycin A5(BLM) 5mg·kg-1 and 30 rats per group received normal saline. On day 1,3,7,14,28 after administration, 6 rats of each group were sacrificed and the lung tissues were harvested respectively. Immunofluorescence was performed to investigate the expression of IL-18 protein in the lung. RT-PCR examined the expression of IL-18 mRNA. Then, lung fibroblasts of neonatal rats was isolated and cultivated in vitro, the expression of IL-18 mRNA in normal lung fibroblasts was detected by RT-PCR. The method of MTT was adopted to detect the influence of rrIL-18 on proliferation of lung fibroblasts. The expression of type III collagen,TNF-a,MMP9,IL-13 mRNA was tested by semi-quantitative RT-PCR., and the untreated sample served as control.Results:①IL-18 was expressed in bronchoalveolar epithelium, alveolar macrophages, and the endothelium of small vessels in control subjects, and was abundantly expressed in the majority of pulmonary cells in rats with pulmonary fibrosis, especially in the fibroblastic foci(FF).The expression of IL-18 mRNA significantly increased rapidly from day 1, reached peak on day 7,than decreased gradually and still more than normal level on day 28(vscontrol,P<0.01),as well as the expression of IL-18 protein.②The lung fibroblasts of neonatal rats was cultivated in vitro successfully. IL-18 mRNA in normal fibroblasts was not detected. The rrIL-18 can promote the proliferation of rat lung fibroblasts (P<0.05). The results of semi-quantitative RT-PCR showed that in forepart, rrIL-18 enhance the synthesize of type III collagen,TNF-a,in fibroblasts significantly (P<0.01). IL-18 can not cause the synthesize of MMP9 and IL-13 mRNA in lung fibroblasts.Conclusion:①The proinflammatory cytokine IL-18 plays an important role in the lung pathology of pulmonary fibrosis.②Participation of IL-18 in the formation of pulmonary fibrosis involved in promoting the proliferation of fibroblasts and deposition of collagen.? TNF-a is one of the primary cytokine in the proliferation of fibroblasts mediated by IL-18.
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