Downregulation of indoleamine 2, 3-dioxygenase expression in the villous stromal endothelial cells of placentas with preeclampsia

Introduction Previous studies have shown that indoleamine 2, 3-dioxygenase (IDO), an immunosuppressive enzyme that converts tryptophan to kynurenine, is expressed in the placenta and might play a role in the maintenance of pregnancy, although its associations with the pathogeneses of preeclampsia (PE) and fetal growth restriction (FGR) remain unclear. The objective of this study was to investigate the differences in IDO expression among normal, PE, and FGR placentas, and the associations between IDO expression and clinical symptoms, or the expression of fms-like tyrosine kinase receptor-1 (Flt-1). Methods Immunohistochemical studies of IDO and Flt-1 expression were performed in human placentas that were complicated with FGR alone (n = 19), PE alone (n = 20), or both PE and FGR (n = 39), and gestational age-matched controls (n = 23). Results It was found that IDO was expressed on endothelial cells in the villous stroma, while Flt-1 was located on trophoblast cells. The IDO expression level of the PE alone group was significantly lower than those of the FGR alone and control groups. The IDO expression of the PE + FGR group was significantly lower than that of the FGR alone group. Lower IDO expression was significantly correlated with more severe maternal hypertension or proteinuria in PE patients, who exhibited higher Flt-1 expression. The late onset PE patients exhibited significantly lower IDO expression than the early onset PE patients. Conclusion This study demonstrated that the downregulation of IDO expression on the endothelial cells of the villous stroma was associated with PE, but not FGR, suggesting that IDO might be involved in the pathophysiology of PE.