Activation of Toll-like receptor 5 decreases the attachment of human trophoblast cells to endometrial cells in vitro

Embryo implantation in the uterus involves the trophoblast cells apposing and adhering to, then invading across the epithelium lining of the endometrium. However, ethical concerns regarding experimentation with primary human tissue during this period of life necessitates creation of in vitro models for understanding the basic mechanisms involved. Toll-like receptors (TLRs) play a crucial role in defence against pathogens invading the female reproductive tract. The objective of this study is to establish and optimize an in vitro model for studying human endometrial embryonic interactions and to understand the effect of TLR5 stimulation on the attachment of trophoblast cells to endometrial cells. By using a human telomerase immortalized endometrial epithelial cell line (hTERT-EECs) and choriocarcinoma human trophoblast cells (JAr cells), an in vitro assay of human implantation was established. In order to investigate the impact of TLR5 stimulation on attachment in this assay, bacterial flagellin was applied to the endometrial and trophoblast cells. In order to block TLR5 in the endometrial and trophoblast cells, TLR5 function-blocking antibody was applied to the cells prior to flagellin treatment. The results demonstrated that JAr spheroids attached to hTERT-EECs in a time and concentration-dependent manner. Our results also demonstrated that treatment of endometrial cells with flagellin, suppressed the attachment of JAr spheres to the endometrial cells. Application of TLR5 function-blocking antibody significantly restored the attachment of JAr spheres to the endometrium. These data suggest a novel mechanism by which the presence of intrauterine infection through TLR5 activation may result in implantation failure. These data may provide a new opportunity in the management of infertility cases.