More than 70% of decidual lymphocytes are NK cells characterized by CD56(bright)CD16(-) phenotype, but the mechanisms by which these NK cells are recruited in the decidua are still almost unrevealed. In this study, we first analyzed the transcription of 18 chemokine receptors in the first-trimester decidual CD56(bright)CD16(-) NK cells. Among these receptors, CXCR4 and CXCR3 were found highly transcribed, and the expression of CXCR4 was verified in most of the decidual CD56(bright)CD16(-) NK cells by flow cytometry. The first-trimester human trophoblasts were found expressing CXCL12/stromal cell-derived factor 1, the specific ligand of CXCR4, by way of in situ hybridization and immunohistochemistry. The primary cultured trophoblast cells were also found to secrete stromal cell-derived factor 1alpha spontaneously, and its concentration was 384.6 +/- 90.7 pg/ml after the trophoblast cells had been cultured for 60 h. All of the ligands for CXCR3 were below the minimal detectable concentration when trophoblast cells were cultured for up to 48 h. Both recombinant human SDF-1alpha and supernatants of the cultured trophoblast cells exhibited chemotactic activity on decidual CD56(bright)CD16(-) NK cells. Our findings suggest that human first-trimester trophoblast cells produce CXCL12, which in turn chemoattracts decidual CD56(bright)CD16(-) NK cells. This activity could contribute to the recruitment mechanism of decidual lymphocytes, especially CD56(bright)CD16(-) NK cells, in decidua, and may be used at a local level to modulate the immune milieu at the materno-fetal interface.