Objectives: The cytokine milieu at the implantation site plays a role in human pregnancy. Th2 cytokines, such as interleukin (IL)-4 and IL-10, stimulate growth and development of placenta, whereas Th1 cytokines, such as tumor necrosis factor-alpha (TNF-alpha), are associated with pregnancy complications. Natural killer (NK) cells predominate at the implantation site. The aim of the present study is to investigate cytokine expression in NK cells when they are in close contact with JEG-3 trophoblast-like cells using an in vitro coculture model.
Methods: Female peripheral blood mononuclear cells (PBMCs) were cocultured with JEG-3 cells for 24 hours. PBMCs were harvested from the cocultures and stimulated with 25 ng/mL phorbol myristate acetate and 1 micromol/mL ionomycin in the presence of 2 micromol/mL monensin. NK cells were analyzed by flow cytometry for intracellular TNF-alpha, interferon-gamma (IFN-gamma), and IL-4 and IL-10 cytokines. Controls were PBMCs cultured without JEG-3 cells.
Results: The proportion of CD56+/TNF-alpha(+) NK cells was significantly decreased when they were in coculture with JEG-3 cells (26.1%) as compared to without JEG-3 cell coculture (40.8%) (P < .05). There was no difference in the proportion of CD56(+) NK cells expressing intracellular IFN-gamma, IL-4, and IL-10. Down-regulation of CD56+/TNF-alpha(+) NK cell levels was dependent on direct cell-to-cell contact between NK cells and JEG-3 cells. The expression of human leukocyte antigen (HLA)-G on trophoblast cell lines did not affect CD56+/TNF-alpha(+) NK cell levels under these experimental conditions.
Conclusion: We report that JEG-3 cells induce down-regulation of intracellular CD56+/TNF-alpha(+) NK cell levels. It is speculated that trophoblasts may secure themselves from NK cell cytotoxicity via this mechanism.