The mechanisms underlying immune tolerance during pregnancy are poorly understood. In this regard, Treg seem to play an important role in mediating maternal tolerance to the fetus. We proposed a crucial role of T regulatory cells (Treg) in avoiding immunological rejection of the fetus after observing diminished number and function of Treg in abortion-prone mice. We further confirmed the protective role of Treg during pregnancy by transferring pregnancy-induced Treg into abortion-prone mice, which prevented rejection. Here, we analyzed the mechanisms involved in Treg-mediated protection. As expected, Treg therapy prevented abortion, while expanding the peripheral and thymic Treg population. Surprisingly, the decidual levels of the Th1 cytokines IFN-c and TNF-a were not diminished after therapy. Interestingly, the mRNA levels of leukemia inhibitory factor, TGF-b and heme oxygenase-1 at the fetal-maternal interface were dramatically up-regulated after Treg transfer, while the levels of indolamine 2,3-dioxygenase remained unchanged. Our data suggest that Treg treatment can not prevent T cell infiltration or high Th1 levels but is able to create a privileged tolerant microenvironment at the fetal-maternal interface, further shedding light onto the molecular mechanisms involved in pregnancy tolerance.

We previously reported that B lymphocyte chemoattractant (BLC; CXCL13) was highly and ectopically expressed in aged (NZB × NZW)F1 (BWF1) mice developing lupus nephritis, and that B1 cells were preferentially chemoattracted toward BLC. We demonstrate in this study that B1 cells fail to home to the peritoneal cavity in aged BWF1 mice developing lupus nephritis, and that they are preferentially recruited to the target organs including the kidney, lung, and thymus when injected i.v. In contrast, B1 cells homed to the peritoneal cavity in aged BALB/c mice as effectively as in young mice. Accumulation of B1 cells to the omentum milky spots was also impaired in aged BWF1 mice compared with young mice. CD11bhighF4/80high cells with macrophage morphology were confirmed to be a major cell source for BLC in the peritoneal cavity both in young and aged BWF1 mice. However, the number of BLC-producing peritoneal macrophages was markedly decreased in aged BWF1 mice. These results suggest that the decreased number of BLC-producing peritoneal macrophages together with ectopic high expression of BLC in aged BWF1 mice result in abnormal B1 cell trafficking during the development of murine lupus.

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