Presentation of Allogeneic MHC On Cross-Dressed Recipient APCs vs. Passenger Leukocytes After Skin Transplantation.

Abstract

We studied the trafficking of donor cells to recipient’s lymphoid organs and its relationship to the direct T cell alloresponse in mice transplanted with a fully allogeneic skin graft. First, we investigated the presence of donor passenger leukocytes in different lymph nodes and the spleen of BALB/c mice transplanted with a B6-GFP or B6-MHC class II-GFP skin allograft, using intra-vital microscopy. Very few donor cells were detected (MHC class II+, n < 5) in draining ipsilateral lymph nodes and only 5 days after transplantation. This did not reflect a lack of sensitivity of our method, given that many more passenger leukocytes were detected in all lymph nodes and spleen, as early as 1 day after transplantation of vascularized solid organs. Alternatively, in skin-grafted mice, imaging flow cytometry (Amnis ImageStream X Mark II) analysis revealed the presence of many recipient cells (B cells and dendritic cells, n > 1,000) displaying donor MHC class I and class II MHC molecules. These “cross-dressed” cells were found in several hosts’ lymphoid organs, as early as 36 hours after transplantation. Next, kinetics studies of direct T cell alloresponses were performed using an ELISPOT assay. Significant numbers of activated donor-specific activated T cells producing gIFN were observed starting at 48 hours post-transplantation. Altogether, these results suggest that, at least at an early time point, presentation of donor MHC molecules by cross-dressed recipient APCs represents the driving force behind direct T cell alloreactivity in skin transplantation.