ABSTRACT
<p><b>OBJECTIVE</b>To investigate the effect of macrophages on embryo implantation by observing the distribution of macrophages in mouse uterine tissues during the peri-implantation period.</p><p><b>METHODS</b>Uterine 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.</p><p><b>RESULTS</b>Macrophages 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.</p><p><b>CONCLUSION</b>Macrophages 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.</p>