['Our previous studies have demonstrated that cyclosporin A (CsA) can increase the cell number in and invasion by human first-trimester trophoblasts and induce maternal-fetal tolerance. C-X-C chemokine receptor type 4 (CXCR4) and C-X-C chemokine ligand 12 (CXCL12) are important mediators at the maternal-fetal interface during early pregnancy. In this study, we further investigate the molecular mechanisms underlying modulation by CsA of the crosstalk between human cytotrophoblast and decidual stromal cell (DSC).', 'Human first-trimester cytotropoblast and DSC were treated with CsA in the absence or presence of U0126 pretreatment, and then the mRNA and protein levels of CXCL12 and CXCR4 were measured by RT-PCR, qPCR, in-cell western blots and enzyme-linked immunosorbent assay (ELISA), respectively. 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide and Matrigel invasion assays were used to determine the invasiveness of cytotrophoblast, respectively. The activity of matrix metalloproteinase (MMP)-9 and MMP-2 was detected by gelatin zymography. A co-culture with direct contact between cytotrophoblast and DSC was established and used to investigate the interaction between these two cells.', 'CsA up-regulated CXCL12 and CXCR4 expression in human first-trimester cytotrophoblast cells, but not in DSCs. Blocking the mitogen-activated proteinkinase/extracellular signal-regulated kinase (MAPK/ERK1/2) signaling by U0126 abrogated the CsA-induced increase in CXCL12 and CXCR4 expression and neutralizing antibodies to CXCL12 or CXCR4 completely inhibited the CsA-induced increase in cell number, invasion and MMP-9 and MMP-2 activity of cytotrophoblast. CsA also significantly promoted the activity of MMP-9 and MMP-2 in DSCs, but this was unaffected by CXCL12 or CXCR4 neutralizing antibody. Furthermore, the CsA-induced MMP-9 and MMP-2 activity and the invasiveness of cytotrophoblast in the cytotrophoblast and DSC co-culture were significantly increased compared with CsA-treated trophoblast cultured alone, and CXCR4 blocking antibody effectively abolished the increased MMP activity and invasion of cytotrophoblasts in the cytotrophoblast-DSC co-culture stimulated by CsA.'] Does cyclosporin A promote crosstalk between human cytotrophoblast and decidual stromal cell through up-regulating CXCL12/CXCR4 interaction?