Plasmacytoid dendritic cells mediate the tolerogenic effect of CD8(+)regulatory T cells in a rat tolerant liver transplantation model

Background: Tolerance is more easily induced in liver transplant models than in other organs; CD8+CD45RClowregulatory T cells (Tregs) have been shown to induce tolerance in heart allografts. Whether CD8+CD45RClowTregs could induce tolerance in a liver transplant model and how dendritic cells (DCs) mediate the CD8+CD45RClowTregs effect remains to be investigated. Methods: A rat liver transplantation model was established and used to test tolerance and acute rejection compared to control groups. Liver function and histopathological changes of allograft were examined by enzymelinked immunosorbent assay (ELISA) and haematoxylin and eosin (H&E) staining, respectively. The distribution and proportion of CD8+CD45RClowTregs and plasmacytoid dendritic cells (pDCs) in the allografts and spleen were determined using flow cytometry. Cytokine secretion levels were determined using ELISA and real-time quantitative PCR (qRT-PCR). Results: The rat liver transplantation model was well established, with a success rate of 93.3% (28/30). The mean survival time of the tolerant and acute-rejection rats were 156 and 14 days, respectively. The proportions of CD8+CD45RClowTegs were higher in the allografts of tolerant rats than in those of acute-rejection rats (33.1 +/- 4.3 and 12.4 +/- 4.6, respectively; P = 0.04). Significant accumulation of pDCs was observed in tolerant liver graft rats compared to that in acute-rejection rats (1.46 +/- 0.23 and 0.80 +/- 0.20, respectively; P = 0.02). Importantly, CD8+CD45RClowTregs were positively associated with the frequency of pDCs (P = 0.001, r2 = 0.775). The protein and mRNA expression of IL-10 and TGF-8 in the allograft group were increased, possibly being responsible for tolerance induction. Conclusion: CD8+CD45RClowT cells interact with pDCs through the induction of IL-10 and TGF-8 expression and are responsible for inducing immune tolerance in rat liver transplantation.