Peripheral blood mononuclear cells in early pregnancy promote invasion of human choriocarcinoma cell line, BeWo cells

BACKGROUND: During the establishment of the maternal blood circulation around the implanting human embryo, maternal peripheral blood mononuclear cells (PBMC) directly contact trophoblasts. To determine the physiological significance of this interaction, the effects of PBMC obtained from pregnant women on the proliferative and invasive properties of a human choriocarcinoma cell line, BeWo cells, were examined. METHODS AND RESULTS: PBMC were obtained from women in early pregnancy and from women in the secretory phase of the menstrual cycle. PBMC from pregnant women significantly increased the number of invading BeWo cells in an invasion assay without affecting the proliferation of BeWo cells (P +/- 0.05). No significant changes were observed in the co-cultures with PBMC from non-pregnant women. The addition of conditioned medium, which was prepared by 2 days of incubation with PBMC from pregnant women, also enhanced BeWo cell invasion in a dose-dependent manner. Moreover, when PBMC obtained from non-pregnant women were incubated with recombinant HCG (0-10 IU/ml) for 2 days, significant augmentation of the effect on BeWo cell invasion was observed in the conditioned medium from HCG-treated PBMC (P +/- 0.05). CONCLUSION: This study indicated that soluble factor(s) secreted from PBMC promote BeWo cell invasion. It also showed the possible involvement of HCG in the regulation of BeWo cell invasion by PBMC. These findings suggest crosstalk between maternal PBMC and trophoblasts via soluble factor(s), which may play an important role in early embryo implantation.