Endocrine Abstracts

The physiological state of pregnancy is characterised by the tolerance of the maternal immune system towards the paternal alloantigens expressed by the foetus. Recently, CD4⁺CD25⁺ regulatory T cells (Treg) were described to play an essential role for the generation and maintenance of the tolerance state. Several research groups showed that normal pregnancy in humans and mice is associated with an augmentation in the number of Treg in different organs whereas females suffering from abortion displayed diminished numbers of Treg. We showed that the adoptive transfer of Treg from normal pregnant CBA/J (H2^k) females previously mated with BALB/c (H2^d) males into abortion-prone mice (DBA/2J-mated CBA/J females) is able to protect the semiallogeneic (H2^d/H2^k) foetus from maternal immune rejection. In addition, we could confirm that Treg from virgin mice could not rescue from abortion. In the light of these results, we postulated that the expansion of Treg is either driven by the presence of paternal/fetal antigens or by pregnancy-associated hormones. We therefore mated CBA/J females either with BALB/c- or DBA/2J males and determined the levels of progesterone and estradiol by chemiluminescence at different time points of pregnancy (day 0, 2, 5, 8, 10 and 12). In addition, we defined the levels of progesterone in Treg-treated mice on day 14 of pregnancy. We observed comparable levels of progesterone, estrone and estradiol in both, normal and abortion-prone animals. Treg treatment, which was effective in diminishing the abortion rate, did not modify the hormonal levels. Our data suggest that pregnancy-associated hormones are not crucial for the expansion of the Treg population and that this is rather driven by specific paternal alloantigens.