High-mobility group box 1 (HMGB1), a nuclear factor released extracellularly as an inflammatory cytokine, is an endogenous ligand for Toll-like receptor 4 (TLR4). TLR4 activation mediates kidney ischemia-reperfusion injury (IRI), but whether HMGB1 contributes to IRI is unknown. Here, treating wild-type mice with neutralizing anti-HMGB1 antibody protected them against kidney IRI, evidenced by lower serum creatinine and less tubular damage than untreated mice. Mice treated with anti-HMGB1 had significantly less tubulointerstitial infiltration by neutrophils (day 1) and macrophages (day 5) and markedly reduced apoptosis of tubular epithelial cells. Furthermore, anti-HMGB1 antibody-treated IRI kidneys had significantly lower levels of IL-6, TNF␣, and monocyte chemoattractant protein 1 (MCP1). mRNA, which are downstream of HMGB1. Conversely, administration of rHMGB1 after reperfusion exacerbated kidney IRI in wild-type mice. TLR4 deficient (TLR4 Ϫ/Ϫ ) mice were protected against kidney IRI; administration of neither anti-HMGB1 antibody nor rHMGB1 affected this renoprotection. In conclusion, endogenous HMGB1 promotes kidney damage after IRI, possibly through the TLR4 pathway. Administration of a neutralizing antibody to HMGB1 either before or soon after ischemia-reperfusion affords significant protection, suggesting therapeutic potential for acute kidney injury.

Natural killer T (NKT) cells are innate-like T cells that rapidly recognize pathogens and produce cytokines that shape the ensuing immune response. IL-17-producing NKT cells are enriched in barrier tissues, such as the lung, skin, and peripheral lymph nodes, and the factors that maintain this population in the periphery have not been elucidated. Here we show that NKT17 cells deviate from other NKT cells in their survival requirements. In contrast to conventional NKT cells that are maintained by IL-15, RORγt(+) NKT cells are IL-15 independent and instead rely completely on IL-7. IL-7 initiates a T-cell receptor-independent (TCR-independent) expansion of NKT17 cells, thus supporting their homeostasis. Without IL-7, survival is dramatically impaired, yet residual cells remain lineage committed with no downregulation of RORγt evident. Their preferential response to IL-7 does not reflect enhanced signaling through STAT proteins, but instead is modulated via the PI3K/AKT/mTOR signaling pathway. The ability to compete for IL-7 is dependent on high-density IL-7 receptor expression, which would promote uptake of low levels of IL-7 produced in the non-lymphoid sites of lung and skin. This dependence on IL-7 is also reported for RORγt(+) innate lymphoid cells and CD4(+) Th17 cells, and suggests common survival requirements for functionally similar cells.

Compared with lymphoid tissues, the immune cell compartment at mucosal sites is enriched with T cells bearing the γδ T-cell receptor (TCR). The female reproductive tract, along with the placenta and uterine decidua during pregnancy, are populated by γδ T cells predominantly expressing the invariant Vγ6 + Vδ1 + receptor. Surprisingly little is understood about the function of these cells. We found that the majority of γδ T cells in the non-pregnant uterus, pregnant uterus, decidua and placenta of mice express the transcription factor RORγt and produce interleukin-17 (IL-17). In contrast, IFNγ-producing γδ T cells were markedly reduced in gestational tissues compared with uterine-draining lymph nodes and spleen. Both uterine-resident invariant Vγ6 + and Vγ4 + γδ T cells which are more typically found in lymphoid tissues and circulating blood, were found to express IL-17. Vγ4 + γδ T cells were particularly enriched in the placenta, suggesting a pregnancy-specific recruitment or expansion of these cells. A small increase in IL-17-producing γδ T cells was observed in allogeneic compared with syngeneic pregnancy, suggesting a contribution to regulating the maternal response to paternally-derived alloantigens. However, their high proportions also in non-pregnant uteri and gestational tissues of syngeneic pregnancy imply a role in the prevention of intrauterine infection or quality control of fetal development. These data suggest the need for a more rigorous evaluation of the role of IL-17 in sustaining normal pregnancy, particularly as emerging data points to a pathogenic role for IL-17 in pre-eclampsia, pre-term birth, miscarriage and maternal immune activation-induced behavioral abnormalities in offspring.

Injection of Interleukin-2 (IL-2) complexed with a particular anti–IL-2 monoclonal antibody (mab) JES6-1 has been shown to selectively expand CD4+Foxp3+ T regulatory T cells (Tregs) in vivo. Although the potency of this approach with regard to transplantation has already been proven in an islet transplantation model, skin graft survival could not be prolonged. Since the latter is relevant to human allograft survival, we sought to improve the efficiency of IL-2 complex (cplx) treatment for skin allograft survival in a stringent murine skin graft model. Here, we show that combining low doses of IL-2 cplxs with rapamycin and blockade of the inflammatory cytokine IL-6 leads to long-term (>75 d) survival of major histocompatibility complex-different skin allografts without the need for immunosuppression. Allograft survival was critically dependent on CD25+FoxP3+ Tregs and was not accompanied by impaired responsiveness toward donor alloantigens in vitro after IL-2 cplx treatment was stopped. Furthermore, second donor-type skin grafts were rejected and provoked rejection of the primary graft, suggesting that operational tolerance is not systemic but restricted to the graft. These findings plus the lack of donor-specific antibody formation imply that prolonged graft survival was largely a reflection of immunological ignorance. The results may represent a potentially clinically translatable strategy for the development of protocols for tolerance induction.