The role of chorionic gonadotropin in the formation of immunological tolerance during pregnancy

We have studied the role of pregnancy hormone (chorionic gonadotropin, CG) in the control of expression of Foxp3 (a marker of T-regulatory lymphocytes, Treg), synthesis of interleukin-4 (IL-4) and interferon-gamma (IFH-γ) in lymphocytes, and secretion of indolamine-2,3-dioxygenase (IDO) by monocytes. Moreover, we evaluated the phagocytic and oxidative activities of these cells. It was shown that incubation of CG at a dose of 100 IU/ml with mononuclear cells from peripheral blood (MPC) resulted in a rise in the relative number of IL-4+CD3+CD4+T-lymphocytes whereas the number of IFN-γ+CD3+CD4+T-cells remained unaltered; the intracellular production of IFN-γ and IL-4 in the subpopulation of CD3+CD8+T-lymphocytes did not change either. In vitro, CG (10 and 100 IU/ml) significantly increased percentage of CD4+CD25 brightFoxp3+ cells and enhanced activity of indolamine-2,3-doxygenase in lipopolysaccharide-stimulated MPC. CG suppressed phagocitosis of E. coli lux+ by monocytes and simultaneously inhibited the production of active oxygen species in the reaction of spontaneous luminol-dependent chemiluminescence. Taken together, these properties of CG account for its role in the promotion of the formation of immunological tolerance during pregnancy.