Although HMGB1 stimulation prevented engraftment of WT islets, TLR2/4−/− islets engrafted in all animals, normalizing serum glucose levels with similar kinetics to untreated WT islets (Fig. 7D). Our results delineate several new insights into the pathogenesis R788 chemical structure of early islet graft failure, including the notable result that TLR2 and TLR4 are key participants in this process. We demonstrated that stimulation via either TLR2 or TLR4 initiated a proinflammatory milieu, likely via chemokines and cytokine release at the graft site, associated with graft apoptosis

and early graft failure (Fig. 2), but did not directly affect islet viability or function in vitro (Fig. 1). In experiments mimicking physiological islet injury by adding exocrine debris (Fig. 3) or by alloimmune response (Fig. 4), TLR2/4−/− islets reduced proinflammatory cytokine production and/or improved islet survival. Recipient T cells and principally CD8+ T cells mediated the graft destruction, because TLR-stimulated islets restored euglycemia

in CD8−/− mice (Fig. 5). Although the specific T-cell targets are not known, our data demonstrate Metformin datasheet that the CD8+ T cells did not require DC (Fig. 6). The data newly revealed that HMGB1, a highly conserved chromosomal protein, could be released from islets in response to hypoxic stress or transplantation and that through signaling via TLR2 and TLR4 this endogenous Florfenicol DAMP prevented primary

engraftment (Fig. 7). These studies extend our previous report in mice 10 and of others in humans 13 that isolated pancreatic islets produce chemokines, following short-term culture, and high pretransplant CCL2 concentrations correlated with poor islet graft function. Our previous data showed that the damage to the islets could not be completely accounted for by the interaction of CCL2 with its receptor CCR2, suggesting a role for other cytokines or chemokines 10. Our current findings explain this previous study by implicating islet-expressed TLR as the mechanistic link between pre and peri-transplant events and increased expression of proinflammatory genes, attracting macrophages and T cells. Although we demonstrated that early islet graft loss occurred in CD4−/− but not in CD8−/− recipients (Fig. 5), indicating a pathogenic role for CD8+ T cells, the specific mechanisms underlying this observation remain to be elucidated. We speculate that the local inflammation associated with the transplant procedure, compounded by the absence of CD4+ Treg in CD4−/− animals facilitates activation of autoreactive CD8+ T cells. The primed CD8 cells are attracted to the inflamed graft, where they elicit effector functions that mediate injury and amplify the local inflammation.