OBJECTIVETo investigate the effect of macrophages on embryo implantation by observing the distribution of macrophages in mouse uterine tissues during the peri-implantation period.

METHODSUterine tissues were collected from pregnant (n=30) and pseudopregnant mice (n=30) during the peri-implantation period. The distributions of macrophages, iNOS and leukemia inhibitory factor (LIF) were determined by immunohistochemistry and the correlations of macrophages with iNOS and LIF were analyzed.

RESULTSMacrophages were located mainly in the endometrium before D4.5 in the pregnant rats with D0.5 defined as the morning when a vaginal plug was observed. After D4.5, the macrophages was significantly reduced in number (P<0.05) in the endometrium and gradually migrated to the perimetrium. In the psudopregnant mice, macrophages were located mainly in the endometrium. Before D4.5, iNOS-positive cells were detected mainly in the endometrium and the myometrium in the pregnant rats and became significantly reduced on D4.5 (P<0.05); in the pseudopregnant mice, the positive cells were mostly detected in the endometrium. Significant differences were found in the distribution of the macrophages and LIF between the implantation and non-implantation sites (P=0.013). LIF was mostly located in the endometrium in the pregnant mice but scarcely detected in the pseudopregnant mice.

CONCLUSIONMacrophages are located mainly in the endometrium and the implantation site where iNOS and LIF are expressed, suggesting the important role of macrophages in the determination of implantation.