Objective:To observe the differences of immunological activity of trans-endothelial trafficking monocyte-macrophage from mid-term placenta and late placenta. Methods:Umbilical vein endothelial cells were isolated and cultured for establishing endothelial cell monolayer. CD14+ monocyte-macrophage cells were separated from the mid-term placenta and late placenta and induced to differentiate by trafficking through the endothelial cell monolayer. We detected IL-12 and IL-10 levels of the culture supernatants with ELISA method before and after trafficking of monocyte-macrophages through endothelial cell monolayer. Flow cytometry was performed to detect the expressions of CD69 molecule and nuclear factor Foxp3 by allogeneics cord blood T lymphocyte co-cultured with differentiated monocyte-macrophages through transendothelial trafficking. Results:① In the culture supernatant of monocyte-macrophages from late pregnancy placenta,IL-12 level was remarkably higher,while IL-10 level remarkably lower than those in the supernatant of the cells from mid-term pregnancy placenta,respectively. The ratio of IL-10/IL-12 was 2.59 ± 0.71,remarkably lower than that in the supernatant of cells from mid-term placenta (71.4 ± 8.49). After trafficking through endothelial monolayer,IL-12 level increased,while IL-10 level decreased significantly in the supernatants of both cells from late placenta and mid-term placenta,and IL-10 level decreased more significantly in the supernatants of the cells from late pregnancy placenta than that from mid-term pregnancy placenta[(92.1 ± 8.2)% vs. (57.8 ± 4.98)%], so that IL-10/IL-12 ratio dropped down to less than 1 (0.11 ± 0.04) while the ratio remained more than 1 (3.16 ± 0.96) in the supernatants of the cells from mid-term placenta. ②After trafficking through endothelial monolayer,both cells from late placenta and mid-term pregnancy placenta activated allogenic cord blood T lymphocytes to express CD69,and CD69 expression level of T cells stimulated by the cells from late pregnancy placenta was significantly higher than that by the cells from mid-term placenta [(73.59 ± 3.52)% vs (45.32 ± 7.47)%]. ③After trafficking through endothelial monolayer,compared with the cells from late placenta,the cells from mid-term placenta induced allogenic cord blood T cells to differentiate into more Foxp3+ T cells. Conclusion:By trafficking through endothelial monolayer,monocyte-macrophages from mid-term and late pregnancy placenta differentiate into different cells with distinctively immunologic characteristics. After trafficking through endothelial monolayer,monocyte-macrophages from late pregnancy placenta differentiate into a kind of immunologically stimulatory cells which could fully stimulate T cells to activate and express high level of CD69,while monocyte-macrophages from mid-term pregnancy placenta differentiate into a kind of immunologically regulatory cells which are capable for inducing Treg.