Immune Modulatory Effects of Human Chorionic Gonadotropin on Dendritic Cells Supporting Fetal Survival in Murine Pregnancy

Dendritic cells (DCs) are critically involved in the determination of immunity vs. tolerance. Hence, DCs are key regulators of immune responses either favoring or disfavoring fetal survival. Several factors were proposed to modulate DC phenotype and function during pregnancy. Here, we studied whether the pregnancy hormone human chorionic gonadotropin (hCG) is involved in DC regulation. In vitro, bone marrow-derived DCs (BMDCs) were stimulated in the presence or absence of urine-purified or recombinant hCG (rhCG) preparations. Subsequently, BMDC maturation was assessed. Cytokine secretion of activated BMDCs and their capability to enforce TH1, TH2, TH17, or Treg cell differentiation was determined after rhCG treatment. Moreover, the in vivo potential of hCG-modulated BMDCs to influence pregnancy outcome, Treg cell number, and local cytokine expression was evaluated after adoptive transfer in a murine abortion-prone model before and after conception. Both hCG preparations impaired the maturation process of BMDCs. rhCG treatment did neither alter cytokine secretion by BMDCs nor their ability to drive TH1, TH2, or TH17 differentiation. rhCG-treated BMDCs augmented the number of Treg cells within the T cell population. Adoptive transfer of rhCG-treated BMDCs after conception did not influence pregnancy outcome. However, transfer of hCG-treated BMDCs prior to mating had a protective effect on pregnancy. This positive effect was accompanied by increased Treg cell numbers and decidual IL-10 and TGF-β expression. Our results unveil the importance of hCG in retaining DCs in a tolerogenic state, thereby promoting Treg cell increment and supporting fetal survival.