It is speculated by these authors that in vivo, CTLA-4 could originate from TRegs to stimulate see more IDO from decidual DCs. The protective role for CTLA-4 in pregnancy is supported by the fact that both the number of TRegs and the level of CTLA-4 on TRegs are lower in the decidua in cases of spontaneous abortion.36 CTLA-4 expression by placental fibroblasts has also been reported,37 providing another potential source of ligand to mediate reverse signaling at the maternal–fetal interface. IDO production following reverse signaling may also occur in placental macrophages. Hofbauer cells express both IDO22 and B7-2,25 suggesting that CLTA-4 ligation of B7-2 on

placental macrophages may induce IDO from these cells in the same manner as in decidual DCs.35 The role of B7-1 and B7-2 in pregnancy has been investigated in the ‘abortion-prone’ CBA × DBA mouse model using blocking antibodies administered at approximately the time of implantation. It was reported that blocking the signaling pathway of both B7-1 and B7-2

or B7-2 alone improved viability of fetuses38. This was accompanied by an increase in the percentage of CD4+ CD25+ Treg cells expressing CTLA-4 as well click here as skewing toward a Th2 response. These authors also found that unfractionated T cells transferred from anti-B7-1/-2-treated mice into subsequent CBA × DBA matings were protective, suggesting that an anti-B7 antibody-induced population of TRegs was able to suppress endogenous maternal immune reactivity to the fetus.39 However, these results were not supported in another abortion-prone

model of allogeneic pregnancy, where blocking B7-2 did not improve fetal viability in CBA × B6 breedings.40 B7-H1 was identified 10 years ago through searches of the expressed sequence tag database for molecules containing homology to B7-1 and B7-2.41,42 It shares approximately 20% amino acid sequence identity with B7-1 and B7-2. Such low levels of sequence homology are commonly seen among members of the B7 family, which instead share high levels of similarity in their secondary and tertiary structures.43 B7-H1 mRNA has been found P-type ATPase to be broadly distributed among many tissues, but its protein distribution is more restricted, suggesting that post-transcriptional mechanisms may have an important role in controlling B7-H1 expression, an idea that has received experimental support from our laboratory and others.44,45 However, its expression can also be induced in parenchymal cells of most organs under inflammatory conditions. Constitutive B7-H1 expression occurs on only a few cells: APCs, lymphocytes, cardiac endothelial cells, and, notably, trophoblast cells. The cellular expression on both APCs and parenchymal cells reflects the ability of B7-H1 to interfere with T-cell activation at both the priming and effector stages of the immune response within lymphoid organs and peripheral tissues, respectively.