Human placental trophoblasts express the immunosuppressive cytokine IL-35

Studies of maternal-fetal tolerance focus on defining mechanisms for establishment of immunological privilege within the uterus during pregnancy. Fetal trophoblasts play a key role in maternal tolerance, in part through cytokines production. As a novel inhibitory cytokine, IL-35 is produced by Foxp3(+) regulatory T cells (Tregs) and mediates maximal suppression of Tregs. The purpose of the study is to analyze the expression of IL-35 in first-trimester human placental trophoblasts. IL-35 expression was detected at both protein and mRNA levels by immunohistochemical staining and quantitative real-time PCR method, respectively and secretion of IL-35 was measured by ELISA assay. Our results demonstrated that human trophoblasts constitutively expressed IL-35. Ebi3 and p35 (two subunits of IL-35) mRNA was shown to be co-expressed in trophoblast cells. Moreover, large amounts of secreted IL-35 were detected in the supernatants of trophoblast cells. But we did not detect the constitutive expression of IL-35 in decidual stromal cells. Our findings confirmed for the first time that first-trimester human trophoblast cells expressed and secreted IL-35, which might contribute to their suppressive capacity to maternal immune cells. Therefore, IL-35 may be an important factor of the cytokine network regulating local immune responses during human pregnancy. (c) 2013 American Society for Histocompatibility and Immunogenetics. Published by Elsevier Inc. All rights reserved.