Backgrounds. We reported the increased nitric oxide (NO) level in exhaled air of rat lung transplant recipients during acute rejection (AR). The aim of this study was to determine the site and level of NO production in the rejected graft. Methods. Rat lung transplantation was performed in isografts and allografts. Results. In isografts, no AR and no significant increase in NO production was identified. In allografts, grades I-II of AR was seen on postoperative day (POD) 3 and grade III on POD 5. NO produced by BAL cells increased on both POD 3 (11.8±2.0 parts per billion [ppb]) and POD 5 (115.3±66.9 ppb). There was a highly significant correlation between the level of NO and the severity of AR (p=0.862, P < 0.005). BAL cells from allografts expressed iNOS mRNA. Among them, macrophages, lymphocytes and neutrophils were immunostained for iNOS. Conclusion. NO produced by BAL cells was detected in the early stages of rejection. Therefore, it may serve as a sensitive indicator of AR in lung transplantation.
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