['Pregnancy hormones were proposed to be crucially involved in fetal tolerance. Recently, we showed that human chorionic gonadotropin (hCG) not only increases the number and activity of regulatory T cells (Treg) but also retains tolerogenic dendritic cells (DCs). Here, we investigate whether the highly homologous luteinizing hormone (LH) modulates Treg number and DC phenotype and thereby supports pregnancy.', 'Abortion-prone females were treated with LH or PBS on different gestation days. Pregnancy outcome and the number and phenotype of Treg and DCs were evaluated in the periphery and locally.', 'We discovered that LH application completely prevented fetal rejection in abortion-prone females. This protective effect was associated with a Treg augmentation peripherally and locally. Moreover, LH reduced the number of total and mature DCs.'] Does luteinizing hormone contribute to fetal tolerance by regulating adaptive immune responses?