Trogocytosis-mediated acquisition of MHC class II molecules from plasmacytoid dendritic cells confers donor-specific immune tolerance to CD8+CD45RClow/- regulatory T cells

Abstract

Objective

Donor-specific suppression by MHC-II⁺CD8⁺CD45RC^low/-regulatory T cells (Tregs) was observed in our prior study, here we endeavor to investigate the mechanism underlying generation of the MHC-II⁺CD8⁺CD45RC^low/-Tregs.

Methods

The presence of MHC-II⁺CD8⁺CD45RC^low/-Tregs within tolerated grafts was confirmed using a multicolor immunofluorescence technique in spontaneous tolerant rat liver transplant model. We aimed to elucidate the generation mechanism of MHC-II⁺CD8⁺CD45RC^low/-Tregs by purifying naive CD8⁺CD45RC^low/-Tregs and plasmacytoid dendritic cells (pDCs) from recipients and co-culturing them to induce trogocytosis. Initially, we examined the immunophenotype and cytokine secretion of MHC-II⁺CD8⁺CD45RC^low/-Treg using flow cytometry. Trogocytosis of peptide-MHC class II complexes was visualized using a confocal microscope. Subsequently, we analyzed the donor-specific inhibitory effect of MHC-II⁺CD8⁺CD45RC^low/-Tregs using CFSE-based lymphocyte proliferation analysis. Finally, we explored the possible transfer mechanisms of MHC class II using IFN-γ stimulation and 1-MT to block indoleamine-(2,3)-dioxygenase (IDO).

Results

In the spontaneously tolerant rat liver transplants, MHC-II⁺CD8⁺CD45RC^low/-Tregs and IL-10 expression were upregulated. Our in vitro study revealed that trogocytosis occurring between naive CD8⁺CD45RC^low/-Tregs and pDCs could induce MHC-II⁺CD8⁺CD45RC^low/-Tregs. The semi-direct pathway represents the primary mode of Trogocytosis-mediated transfer of MHC-II molecules from pDCs to CD8⁺CD45RC^low/-Tregs. The MHC-II⁺CD8⁺CD45RC^low/-Tregs exhibited high secretion of IL-10 and IFN-γ. Co-culturing with MHC-II⁺CD8⁺CD45RC^low/-Tregs significantly suppressed the proliferation of CD4⁺CD25^-effector T cells. Moreover, this inhibitory effect was donor-specific and could be overcome in the presence of third-party antigen-presenting cells. Our data also suggested that blocking the IFN-γ/IDO signaling pathway could inhibit the generation of trogocytosis-mediated MHC-II⁺CD8⁺CD45RC^low/-Tregs.

Conclusions

MHC-II⁺CD8⁺CD45RC^low/-Tregs generated through trogocytosis exhibit donor-specific suppressive function. Moreover, in vitro generation of MHC-II⁺CD8⁺CD45RC^low/-Tregs offers a potential alternative approach to induce donor-specific immune tolerance through adoptive transfer.