A role for IL-17 in induction of an inflammation at the fetomaternal interface in preterm labour

Chorioamnionitis (CAM) is a major cause of preterm delivery. Inflammatory cytokines and chemokines play important roles in the pathogenesis of preterm delivery. Interleukin (IL)-17 is a key cytokine which induces inflammation and is critical to host defense. In this study, we examined the role of IL-17 in the pathogenesis of preterm delivery. The levels of cytokines including IL-17, IL-8 and tumor necrosis factor (TNF) α were measured by ELISA in amniotic fluid from 154 cases of preterm labor. Flow cytometry and immunohistochemical staining were performed to determine the distribution of IL-17-producing cells. IL-8 secretion was evaluated in primary cultured human amniotic mesenchymal (HAM) cells and human amniotic epithelial (HAE) cells stimulated with IL-17, TNFα or IL-1β. We also studied the signaling pathway of IL-17 and TNFα in HAM cells. Levels of inflammatory cytokines in amniotic fluid were higher in preterm delivery cases than in term delivery cases. Furthermore, IL-8, IL-17 and TNFα levels were significantly higher in the preterm cases with CAM stage II or III than those without CAM. Flow cytometry and immunohistochemical staining revealed that CD3⁺CD4⁺ T cells were the main source of IL-17 in the chorioamniotic membrane. Interestingly, TNFα-induced IL-8 secretion was enhanced by IL-17 in a dose-dependent manner in HAM cells. The IKK inhibitor BMS-345541 and mitogen-activated protein kinase (MAPK) inhibitors p38, JNK and p42/44 (ERK1/2 pathway) reduced IL-8 secretion by IL-17-stimulated and TNFα-stimulated HAM cells. These results indicate that IL-17, produced by T cells, promotes inflammation at the fetomaternal interface in preterm delivery.