Diversity of gut microflora is required for the generation of B cell with regulatory properties in a skin graft model

B cells have been reported to promote graft rejection through alloantibody production. However, there is growing evidence that B cells can contribute to the maintenance of tolerance. Here, we used a mouse model of MHC-class I mismatched skin transplantation to investigate the contribution of B cells to graft survival. We demonstrate that adoptive transfer of B cells prolongs skin graft survival but only when the B cells were isolated from mice housed in low sterility "conventional" (CV) facilities and not from mice housed in pathogen free facilities (SPF). However, prolongation of skin graft survival was lost when B cells were isolated from IL-10 deficient mice housed in CV facilities. The suppressive function of B cells isolated from mice housed in CV facilities correlated with an anti-inflammatory environment and with the presence of a different gut microflora compared to mice maintained in SPF facilities. Treatment of mice in the CV facility with antibiotics abrogated the regulatory capacity of B cells. Finally, we identified transitional B cells isolated from CV facilities as possessing the regulatory function. These findings demonstrate that B cells, and in particular transitional B cells, can promote prolongation of graft survival, a function dependent on licensing by gut microflora

Diversity of gut microflora is required for the generation of B cell with regulatory properties in a skin graft model

B cells have been reported to promote grafft rejectfion through alloantfibody productfion. However, there fis growfing evfidence that B cells can contrfibute to the mafintenance off tolerance. Here, we used a mouse model off MHC-class I mfismatched skfin transplantatfion to finvestfigate the contrfibutfion off B cells to grafft survfival. We demonstrate that adoptfive transffer off B cells prolongs skfin grafft survfival but only when the B cells were fisolated ffrom mfice housed fin low sterfilfity “conventfional” (CV) ffacfilfitfies and not ffrom mfice housed fin pathogen ffree ffacfilfitfies (SPF). However, prolongatfion off skfin grafft survfival was lost when B cells were fisolated ffrom IL-10 deficfient mfice housed fin CV ffacfilfitfies. The suppressfive ffunctfion off B cells fisolated ffrom mfice housed fin CV ffacfilfitfies correlated wfith an antfi-finlammatory envfironment and wfith the presence off a dfifferent gut mficrolora compared to mfice mafintafined fin SPF ffacfilfitfies. Treatment off mfice fin the CV ffacfilfity wfith antfibfiotfics abrogated the regulatory capacfity off B cells. Ffinally, we fidentfified transfitfional B cells fisolated ffrom CV ffacfilfitfies as possessfing the regulatory ffunctfion. These findfings demonstrate that B cells, and fin partficular transfitfional B cells, can promote prolongatfion off grafft survfival, a ffunctfion dependent on lficensfing by gut mficrolora

Regulatory T cell-derived extracellular vesicles modify dendritic cell function

Regulatory T cells (Treg) are a subpopulation of T cells that maintain tolerance to self and limit other immune responses. They achieve this through different mechanisms including the release of extracellular vesicles (EVs) such as exosomes as shown by us, and others. One of the ways that Treg derived EVs inhibit target cells such as effector T cells is via the transfer of miRNA. Another key target for the immunoregulatory function of Tregs is the dendritic cells (DCs). In this study we demonstrate directly, and for the first time, that miRNAs are transferred from Tregs to DCs via Treg derived EVs. In particular two miRNAs, namely miR-150-5p and miR-142-3p, were increased in DCs following their interaction with Tregs and Treg derived exosomes. One of the consequences for DCs following the acquisition of miRNAs contained in Treg derived EVs was the induction of a tolerogenic phenotype in these cells, with increased IL-10 and decreased IL-6 production being observed following LPS stimulation. Altogether our findings provide data to support the idea that intercellular transfer of miRNAs via EVs may be a novel mechanism by which Tregs regulate DC function and could represent a mechanism to inhibit immune reactions in tissues

What Is Direct Allorecognition?

Direct allorecognition is the process by which donor-derived major histocompatibility complex (MHC)-peptide complexes, typically presented by donor-derived ‘passenger’ dendritic cells, are recognised directly by recipient T cells. In this review, we discuss the two principle theories which have been proposed to explain why individuals possess a high-precursor frequency of T cells with direct allospecificity and how self-restricted T cells recognise allogeneic MHCpeptide complexes. These theories, both of which are supported by functional and structural data, suggest that T cells recognising allogeneic MHC-peptide complexes focus either on the allopeptides bound to the allo-MHC molecules or the allo-MHC molecules themselves. We discuss how direct alloimmune responses may be sustained long term, the consequences of this for graft outcome and highlight novel strategies which are currently being investigated as a potential means of reducing rejection mediated through this pathway