Abnormal Expression of Indoleamine 2, 3-Dioxygenase in Human Recurrent Miscarriage

Indoleamine 2, 3-dioxygenase (IDO), an immunosuppressive enzyme that mediates the conversion of tryptophan to kynurenine, was shown to play a key role in placental development during normal pregnancy. However, little is known about the pattern of IDO expression in the endometrium and its attendant functional significance in pregnancies complicated with recurrent miscarriage (RM). Immunohistochemical studies of IDO, Foxp3, CD56, and CD163 expression were performed in endometrial samples from women with RM and healthy fertile controls. Our study found that IDO was localized in glandular epithelial cells, surface epithelial cells, and a small number of cells within the stromal compartment (including stromal cells and leukocytes) in endometrium. Indoleamine 2, 3-dioxygenase expression in the RM group was significantly lower than control group. The Foxp3 and CD56 expression were significantly increased with the elevated IDO expression in controls but not in RM. The percentage of Foxp3+ Tregs was significantly correlated with the level of IDO expression in the control group. Comparatively, no correlation was found between the percentage of CD56+ cells, CD163+ cells, and the level of IDO expression, no matter in controls and RM patients. This study demonstrated that the downregulation of IDO expression and noncoordinated association between IDO and other endometrial immune cells were associated with RM. Our findings provide insights into the contribution of IDO in immune regulation to maintain normal pregnancy, which could be used to develop potential therapeutic methods for RM.