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Problem: Decidual natural killer (dNK) cells play key roles in maternal-fetal immune regulation, trophoblast invasion, and vascular remodeling, and most dNK cell populations are CD56 bright CD16 − NK cells. However, the enrichment and redistribution of dNK cells in the local decidua have not been clarified yet. Method of study:A total of 45 women with normal pregnancies and 8 unexplained recurrent spontaneous abortion (RSA) patients were included. We isolated primary human dNK (n = 53) and peripheral blood NK (pNK) cells (n = 5) from specimen and analyzed CD56, CD82, and CD29 by flow cytometry (FCM). We assessed their adhesion ability by cell counts of NK cells adhered to decidual stromal cells (DSCs) in a co-culture system. Results:We found that RSA patients had more CD56 dim dNK cells with lower CD82 and higher CD29 than women with normal pregnancies. There were negative correlations of CD82 to CD29 on CD56 dim and CD56 + dNK cells. In normal pregnancies, dNK cells had lower CD82 and higher CD29 expression with a stronger adhesion ability than pNK cells. Blocking CD82 on dNK cells increased the adhesive ability and CD29 expression, while blocking CD29 decreased the adhesive ability. Co-culturing dNK cells with trophoblast cells decreased CD82 expression and increased the adhesive ability of dNK cells and the percentage of CD56 bright NK cells, while blocking trophoblast-derived CXCL12 increased CD82 expression, decreased CD29 expression, and impaired the adhesive ability of NK cells. Conclusion: Trophoblast cells enhance the adhesive ability of NK cells to DSCs viathe CXCL12/CD82/CD29 signaling pathway and contribute to CD56 bright NK cell enrichment in the uterus. K E Y W O R D S abortion, adhesion, CD29, CD82, CXC12, decidua, NK, trophoblasts How to cite this article: Lu H, Jin L-P, Huang H-L, et al. Trophoblast-derived CXCL12 promotes CD56 bright CD82 − CD29 + NK cell enrichment in the decidua.Am J Reprod Immunol. 2020;83:e13203.

Objective: The maternal-fetal interface undergoes dynamic changes to allow the fetus to grow and develop in the uterus. The interaction between decidual γδ T cells and trophoblasts plays a pivotal role during successful pregnancy; however, their physiological functions in early-term human pregnancy are still not completely illustrated. This study was undertaken to illustrate the functional roles of CXCL16/CXCR6 to prevent pregnancy loss via the crosstalk between decidual γδ T cells and HTR8/SVneo trophoblast cells. Methods: The percentile of CXCR6+ γδ T cells in the peripheral blood from normal female and recurrent spontaneous abortion (RSA) patients was analyzed by flow cytometry. The expression of CXCR6 was detected in decidual immune cells via flow cytometry, and the expression of CXCL16 was analyzed in HTR8/SVneo trophoblast cells and lentivirus (LV)-HTR8/SVneo trophoblast cells via enzyme-linked immunosorbent assay. Reverse transcriptase-polymerase chain reaction was used to verify the expression of the CXCL16 gene in LV-HTR8/SVneo trophoblast cells. Expression of granzyme B and cytokines and proliferation of decidual γδ T cocultured with HTR8/SVneo trophoblast cells were analyzed by flow cytometry. Invasion of HTR8/SVneo trophoblast cells was assessed via Matrigel transwell assay. Adoptive transfer was induced in vivo further to illustrate that the normal expression of CXCL16/CXCR6 could prevent pregnancy loss. Results: The percentile of CXCR6+ γδ T cells in the peripheral blood from RSA patients was lower than normal pregnancies. The expression of CXCR6 was highest in the decidual γδ T cells among decidual immune cells, and the expression of CXCL16 increased as the amount of HTR8/SVneo trophoblast cells increased. Expression of granzyme B in the decidual γδ T cells was downregulated by cocultured with HTR8/SVneo cells dependent of CXCL16, and HTR8/SVneo trophoblast cells induced the Th2 cytokines production in the decidual γδ T cells. Both the expression of CXCR6 in the decidual γδ T cells and proliferation of the decidual γδ T cells were promoted by HTR8/SVneo trophoblast cells. On the other hand, decidual γδ T cells enhanced the invasion of HTR8/SVneo trophoblast cells and thus promoted embryo implantation. In vivo study was taken further and shown that low expression of CXCL16/CXCR6 results in pregnancy loss because of dialog disorder between decidual γδ T cells and trophoblasts. Conclusions: Low expression of CXCL16/CXCR6 results in pregnancy loss because of the dialog disorder between decidual γδ T cells and trophoblasts, and it showed a light on the effective strategy of adoptive transfer of CXCR6+ γδ T cells on the treatment of RSA. This observation provides a scientific basis on which a potential strategy can be applied to the early-detect and treatment of RSA.