Differences in Treg levels and pregnancy outcome do not correlate with changes in hormonal levels. In addition, as Treg augmentation takes place early and it is observed mainly in the decidual component of the fetal-maternal interface, IDO does not seem to be the pathway underlying Treg protective activity as proposed for humans.

Our data confirm comparable number of Tregs during pre-eclampsia and normal pregnancy in peripheral blood. Other regulatory mechanisms might be involved during late pregnancy.

Several burning questions remain unanswered in pregnancy-related research. Pro-and anti-inflammatory cytokines orchestrate an intriguing interaction leading either to the development of a normal individual or to its rejection. Augmented Th1 cytokines' production is involved in immunological rejection of the foetus. Excessive production of Th1 cytokines, particularly of tumour necrosis factor (TNF)-a, also triggers apoptosis. Thus, in the present work we investigated the incidence of apoptosis in a well-known experimental model of Th1-induced abortion, characterized by increased local TNF-a levels. Apoptosis of lymphocytes as well as their Th1 and Th2 cytokine production were analysed by flow cytometry. TNF-a mRNA levels were additionally analysed by real time reverse transcription-polymerase chain reaction (RT-PCR) in placental and decidual samples. Total placental apoptosis activity was investigated by measuring caspase-3 activity and by TdT-mediated dUTP nick end label staining. Immunohistochemistry, Western blot and real time RT-PCR were used to localize and quantify several anti-and pro-apoptotic molecules at the foetalmaternal interface. Despite elevated Th1 levels at the foetal-maternal interface, mice undergoing abortion presented comparable apoptotic rates. Interestingly, we found a significant upregulation of the anti-apoptotic Bcl-2 protein at the foetal-maternal interface from abortion-prone mice, while no changes could be observed for pro-apoptotic molecules. In the light of our results, we conclude that there is no evidence of increased apoptosis in mice undergoing immunological abortion in spite of elevated TNF-a levels. This is probably due to a selective upregulation of anti-apoptotic pathways (i.e. Bcl-2) at the foetal-maternal interface as a compensatory and/or protective mechanism.