HCG secretion by peripheral mononuclear cells during pregnancy.

Peripheral mononuclear cells (MNC) in culture release a biologically active hCG. This effect is detectable during pregnancy with a maximum between the 9th and 16th wk. Peripheral MNC already secrete hCG between the 7th and 11th d after embryo transfer. The secretion of hCG is activated by the PKC-activator TPA. TPA induces hCG release into the medium, thus causing a decrease in intracellular hCG content. In contrast, db-cAMP inhibites hCG secretion into the medium. Protein synthesis inhibitors of transcription and translation suppress the production and secretion of hCG. Peripheral natural killer (NK) cells (CD56+/CD16+) and monocytes (CD14+) show the highest secretion rates. IL-1 beta, IL-4, IL-6, IL-10, TNF alpha, and GM-CSF stimulate, whereas IL-2 and INF gamma inhibit, the hCG secretion of mononuclear cells. Flow cytometric experiments with hCG antibody demonstrate a binding of hCG on the surface of monocytes more than lymphocytes. The binding capacity is improved during pregnancy. Different hCG bands are shown in the Western blot analysis. We could confirm the mRNA of beta hCG and alpha CG are in MNC as well in the placental control. Peripheral MNC, first and foremost NK cells and monocytes, produce and secrete hCG during pregnancy, which play an important role for the corpus luteum rescue during the early gestational age and possibly for the immunotolerance.