The CXCL12/CXCR4 axis is involved in the maintenance of Th2 bias at the maternal/fetal interface in early human pregnancy

The regulatory mechanism of Th2 bias at the maternal/fetal interface remains unclear. In this study, we characterized cytokine production in decidual stromal cells （DSCs）, decidual immune cells （DICs） and embryo-derived trophoblast cells, and investigated the regulation of CXCL12/CXCR4 interaction on Th2 bias at the maternal/fetal interface in early human pregnancy. We found differential production of Th 1-type and Th2-type cytoki nes by trophoblasts, DSCs and DICs. The secretion of these cytokines varied in different cell cocultures, conduced to Th2 bias. Flow cytometry showed that coculture of trophoblasts with DSCs and DICs significantly increased IL-4 and IL-IO production in trophoblasts, and IL-IO production in DSCs. However, the coculture of trophoblasts with DSCs and DICs significantly increased interferon （IFN）-7 expression in DSCs, and tumor-necrosis factor （TNF）-a expression in DICs. No change was seen in Thl-type cytokine production in trophoblasts, and in Th2-type cytokine production in DICs in all cocultures. Furthermore, pre-treatment with anti-CXCR4 neutralizing antibody upregulated the production of the Thl-type cytokines IFN-y and TNF-a, and downregulated the production of the Th2-type cytokines IL-4 and IL-IO, in trophoblasts, DSCs, DICs or their cocultures. Interestingly, rhCXCL12 inhibited production of the Thl-type cytokine TNF-a and enhanced the expression of the Th2-type cytokines such as IL-4 and IL-IO in DICs; this effect was abrogated by anti-CXCR4 antibody. Our present study has elucidated the individual contributions of component cells to the shaping of Th2 bias, and uncovered a complicated cross-talk viathe CXCL12/CXCR4 signal at the maternal/fetal interface in early human pregnancy.

CD56^brightCD25^＋ NK cells are preferentially recruited to the maternal/fetal interface in early human pregnancy

Decidual natural killer （dNK） cells are believed to be critical for maintaining maternal/fetal tolerance and regulating placental vascular remodeling based upon their abundance and unique phenotype during early pregnancy. However, the mechanism for how the dNK cells play such important roles in successful pregnancy remains undefined. Here, we identified a subtype of dNK cells characterized as having a CD3-CD56^brightCD25^＋ phenotype. We found that CD56^brightCD25^＋ NK cells preferentially localize to the maternal/fetal interface during early human pregnancy. CD25^＋ dNK cells account for approximately 75% of CD25-expressing decidual immune cells （DICs）. However, less than 5% of CD25-positive peripheral blood mononuclear cells are CD25^＋ NK cells. Furthermore, CD25^＋ and CD25^- dNK cells exhibit distinct phenotypes： CD25^＋ dNK cells display a more activated phenotype and greater cytokine-secreting capacity. Interestingly, coculture of peripheral NK （pNK） cells with primary trophoblasts upregulates the percentage of CD25-expressing pNK cells, resulting in increased expression of activation markers and cytokine production by pNK cells. In addition, we demonstrated that the CXCL12/CXCR4 axis is crucial for the recruitment of CD25^＋ dNK cells and contributes to the accumulation of CD3^-CD56^brightCD25^＋ dNK cells at the maternal/fetal interface. Thus, our data reveal that the crosstalk between trophoblasts and pNK cells leads to the accumulation of CD3^-CD56^brightCD25^＋ dNK cells, which exert a regulating effect at the maternal/fetal interface.