Cross-Dressing by Donor Dendritic Cells after Allogeneic Bone Marrow Transplantation Contributes to Formation of the Immunological Synapse and Maximizes Responses to Indirectly Presented Antigen

Abstract

The stimulation of naive donor T cells by recipient alloantigen is central to the pathogenesis of graft-versus-host disease after bone marrow transplantation (BMT). Using mouse models of transplantation, we have observed that donor cells become “cross-dressed” in very high levels of recipient hematopoietic cell–derived MHC class I and II molecules following BMT. Recipient-type MHC is transiently present on donor dendritic cells (DCs) after BMT in the setting of myeloablative conditioning but is persistent after nonmyeloablative conditioning, in which recipient hematopoietic cells remain in high numbers. Despite the high level of recipient-derived alloantigen present on the surface of donor DCs, donor T cell proliferative responses are generated only in response to processed recipient alloantigen presented via the indirect pathway and not in response to cross-dressed MHC. Assays in which exogenous peptide is added to cross-dressed MHC in the presence of naive TCR transgenic T cells specific to the MHC class II–peptide combination confirm that cross-dressed APC cannot induce T cell proliferation in isolation. Despite failure to induce T cell proliferation, cross-dressing by donor DCs contributes to generation of the immunological synapse between DCs and CD4 T cells, and this is required for maximal responses induced by classical indirectly presented alloantigen. We conclude that the process of cross-dressing by donor DCs serves as an efficient alternative pathway for the acquisition of recipient alloantigen and that once acquired, this cross-dressed MHC can assist in immune synapse formation prior to the induction of full T cell proliferative responses by concurrent indirect Ag presentation.

CD8 T-cell recognition of acquired alloantigen promotes acute allograft rejection

“…Trogocytosis may hold particular relevance for transplantation, because the ability to transfer allogeneic membrane proteins between donor and recipient immune cells is likely to have more profound consequences than transfer of self-proteins. Nevertheless, few studies have reported functional significance for either solid organ or hematopoietic stem cell transplantation (26,27) and our findings thus emphasize the potentially important contribution of trogocytosis in initiating adaptive alloimmunity.…”

Cross-signaling in metabotropic glutamate 2 and serotonin 2A receptor heteromers in mammalian cells

“…Imaging flow cytometry has successfully been used to quantify colocalization of proteins [2,20,27,31]. We chose to use imaging flow cytometry since it provides a unique tool to quantify colocalization in a large number of cells and is perfectly adapted to screen multiple clones.…”

“…To avoid possible effects of the trypsin and/or EDTA on distribution of the receptor, cells were re-suspended mechanically. Our group has successfully applied this technique to assess HEK293 by regular flow cytometry [27]. Cells were then stained with an anti-HA mouse IgG1 monoclonal antibody conjugated with Alexa Fluor 488 (Cell Signaling, catalog # 2350S) together with an anti-c-Myc mouse IgG1 monoclonal antibody conjugated with Alexa Fluor 647 (Cell Signaling, catalog # 2233S) (1:25 dilution for 1 hour at room temperature).…”

Graft-infiltrating host dendritic cells play a key role in organ transplant rejection

“…Activation of the latter by host DCs is possible if DCs were ‘cross-dressed' with intact donor MHC molecules in the graft. Although not formally shown here, cross-dressing has been described in vitro and in vivo and likely participates in immune responses to viruses, bone marrow transplants and organ transplants1736373839. Therefore, host DCs that replace donor DCs in the graft are not limited to engaging indirectly alloreactive T cells, which represent a minute fraction of the host's alloreactive T-cell repertoire, but can also present non-self MHC molecules to the much larger population of directly alloreactive T cells.…”