Infections and TLR signals at the time of transplantation have been shown to prevent the induction of tolerance, but their effect on allografts after tolerance has been established is unclear. We here report that infection with Listeria monocytogenes precipitated the loss of tolerance and the MyD88- and T cell-dependent rejection of accepted cardiac allografts in mice. This loss of tolerance was associated with increases in the numbers of graft-infiltrating macrophages and dendritic cells, as well as CD4+FoxP3− and CD8+ T cells. Rejection was also associated with increased numbers of graft-infiltrating alloreactive as well as Listeria-reactive IFNγ-producing T cells. Rejection of the established grafts required both IL-6 and IFNβ, cytokines produced during acute Listeria infection. However, IL-6 and IFNβ alone, even when present at higher concentrations than during Listeria infection, were insufficient to break tolerance, while the combination of IL-6 and IFNβ was able to break tolerance. These and in vitro observations that IL-6 but not IFNβ enhanced T cell proliferation while IFNβ but not IL-6 enhanced IFNγ production support a hypothesis that these cytokines play non-redundant roles. In conclusion, these studies demonstrate that the pro-inflammatory effects of infections can induce the loss of tolerance and acute rejection of accepted allografts.

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Exposure to certain viruses and parasites has been shown to prevent the induction of transplantation tolerance in mice via the generation of cross-reactive memory T cell responses or the induction of bystander activation. Bacterial infections are common in the perioperative period of solid organ allograft recipients in the clinic, and correlations between bacterial infections and acute allograft rejection have been reported. However, whether bacterial infections at the time of transplantation have any effect on the generation of transplantation tolerance remains to be established. We used the Gram-positive intracellular bacterium Listeria monocytogenes (LM) as a model pathogen because its effects on immune responses are well described. Perioperative LM infection prevented cardiac and skin allograft acceptance induced by anti-CD154 and donor-specific transfusion in mice. LM-mediated rejection was not due to the generation of cross-reactive T cells and was largely independent of signaling via MyD88, an adaptor for most TLRs, IL-1, and IL-18. Instead, transplant rejection following LM infection was dependent on the expression of the phagosome-lysing pore former listeriolysin O and on type I IFN receptor signaling. Our results indicate that bacterial exposure at the time of transplantation can antagonize tolerogenic regimens by enhancing alloantigen-specific immune responses independently of the generation of cross-reactive memory T cells.

Acute allograft rejection has often been correlated with Th1 differentiation, whereas transplantation tolerance is frequently associated with induction of regulation. The discovery of the Th17 phenotype has prompted its scrutiny in transplant rejection. Although IL-17 has recently been observed in settings of acute allograft rejection and drives rejection in T-bet-deficient mice that have impaired type 1 T cell responses, there is little evidence of its requirement during acute rejection in wild-type animals. We and others have previously shown that TLR9 signaling by exogenous CpG at the time of transplantation is sufficient to abrogate anti-CD154-mediated acceptance of fully mismatched cardiac allografts. In this study, we investigated the mechanism by which acute rejection occurs in this inflammatory context. Our results indicate that CpG targets recipient hemopoietic cells and that its pro-rejection effects correlate both with prevention of anti-CD154-mediated conversion of conventional CD4+ T cells into induced regulatory T cells and with the expression of IFN-γ and IL-17 by intragraft CD4+ T cells. Moreover, the combined elimination of IL-6 and IL-17 signaling abrogated the ability of CpG to promote acute cardiac allograft rejection. Thus, proinflammatory signals at the time of transplantation can change the quality of the effector immune response and reveal a pathogenic function for IL-6 and IL-17 in wild-type recipients.

Innate effector cells that produce Th2-type cytokines are critical in Th2 cell-mediated immune responses. However, it is not known how these cells acquire the ability to produce Th2 cytokines. IL-4 is a potent inducer that directs differentiation of naive CD4+ T cells into CD4+ Th2 effector cells. To determine whether IL-4 can induce differentiation and expansion of Th2 cytokine-producing innate cells, we used mice whose il-4 gene was replaced by a knock-in green fluorescence protein (gfp) gene. We found that, directly ex vivo, IL-4 increased the number of GFP+ cells in the airway and the lung tissue in an Ag-specific manner. The majority of GFP+ cells were eosinophils, suggesting that IL-4 plays a pivotal role in expanding IL-4-producing eosinophils in vivo. IL-4-producing eosinophils showed some unique features compared with IL-4-producing CD4+ T cells. They exhibited biallelic expression of the il-4 gene when stimulated and were more dominant IL-4- and IL-5-producing cells. Furthermore, we show that IL-4 drove bone marrow progenitor cells to differentiate into Th2 cytokine-producing eosinophils in vitro. These results strongly suggest IL-4 is a potent factor in directing bone marrow progenitor cells to differentiate into Th2 cytokine-producing eosinophils.

BackgroundT cells have the capacity to eliminate tumors but the signaling pathways by which they do so are incompletely understood. T cell priming requires activation of the transcription factors AP-1, NFAT and NF-κB downstream of the TCR, but whether activation of T cell-NF-κB in vivo is required for tumor control has not been addressed. In humans and mice with progressively growing tumors, the activity of T cell-intrinsic NF-κB is often reduced. However, it is not clear if this is causal for an inability to reject transformed cells, or if it is a consequence of tumor growth. T cell-NF-κB is important for T cell survival and effector differentiation and plays an important role in enabling T cells to reject cardiac and islet allografts, suggesting the possibility that it may also be required for tumor elimination. In this study, we tested whether normal T cell-NF-κB activation is necessary for the rejection of tumors whose growth is normally controlled by the immune system.MethodsMice with genetically impaired T cell-NF-κB activity were subcutaneously injected with MC57-SIY tumor cells. Tumor growth was measured over time, and the anti-tumor immune response was evaluated using flow cytometry and cytokine detection assays.ResultsMice with impaired T cell-NF-κB activity were unable to reject tumors that were otherwise eliminated by wildtype mice, despite equal accumulation of tumor-reactive T cells. In addition, specific impairment of NF-κB signaling downstream of the TCR was sufficient to prevent tumor rejection. Tumor antigen-specific T cell-IFN-γ and TNF-α production, as well as cytotoxic ability, were all reduced in mice with impaired T cell-NF-κB, suggesting an important role for this transcription factor in the effector differentiation of tumor-specific effector T cells.ConclusionsOur results have identified the NF-κB pathway as an important signaling axis in T cells, required for the elimination of growing tumors in vivo. Maintaining or enhancing T cell-NF-κB activity may be a promising avenue for anti-tumor immunotherapy.Electronic supplementary materialThe online version of this article (doi:10.1186/s40425-014-0045-x) contains supplementary material, which is available to authorized users.

We analyzed the responses of several T cell fractions reactive with superantigenic toxins (SAGTs), staphylococcal enterotoxin A (SEA), or Yersinia pseudotuberculosis-derived mitogen (YPM) in mice implanted with mini-osmotic pumps filled with SEA or YPM. In mice implanted with the SEA pump, SEA-reactive Vβ3+CD4+ T cells exhibited a high-level protracted expansion for 30 days, and SEA-reactive Vβ11+CD4+ T cells exhibited a low-level protracted expansion. SEA-reactive CD8+ counterparts exhibited only a transient expansion. A similar difference in T cell expansion was also observed in YPM-reactive T cell fractions in mice implanted with the YPM pump. Vβ3+CD4+ and Vβ11+CD4+ T cells from mice implanted with the SEA pump exhibited cell divisions upon in vitro restimulation with SEA and expressed surface phenotypes as memory T cells. CD4+ T cells from mice implanted with the SEA pump exhibited high IL-4 production upon in vitro restimulation with SEA, which was due to the enhanced capacity of the SEA-reactive CD4+ T cells to produce IL-4. The findings in the present study indicate that, in mice implanted with a specific SAGT, the level of expansion of the SAGT-reactive CD4+ T cell fractions varies widely depending on the TCR Vβ elements expressed and that the reactive CD4+ T cells acquire a capacity to raise a memory response. CD8+ T cells are low responders to SAGTs.

T cells are essential for immune defenses against pathogens, such that viability of naïve T cells before antigen encounter is critical to preserve a polyclonal repertoire and prevent immunodeficiencies. The viability of naïve T cells before antigen recognition is ensured by IL-7, which drives expression of the prosurvival factor Bcl-2. Quiescent naïve T cells have low basal activity of the transcription factor NF-κB, which was assumed to have no functional consequences. In contrast to this postulate, our data show that basal nuclear NF-κB activity plays an important role in the transcription of IL-7 receptor α-subunit (CD127), enabling responsiveness of naïve T cells to the prosurvival effects of IL-7 and allowing T-cell persistence in vivo. Moreover, we show that this property of basal NF-κB activity is shared by mouse and human naïve T cells. Thus, NF-κB drives a distinct transcriptional program in T cells before antigen encounter by controlling susceptibility to IL-7. Our results reveal an evolutionarily conserved role of NF-κB in T cells before antigenic stimulation and identify a novel molecular pathway that controls T-cell homeostasis.urvival of naïve quiescent T cells is essential to maintain a pool of polyclonal T cells ready for activation by their cognate antigen. On egress from the thymus, survival of peripheral naïve T cells (CD4 + CD44 lo and CD8 + CD44 lo ) depends on intermittent tonic engagement of the T-cell receptor (TCR) and signaling by the cytokine IL-7 (1, 2). Tonic TCR engagement is generated by the interaction of the TCR with weakly reactive self-peptides (3). Survival of quiescent CD8 T cells requires MHC class I-TCR engagement, which is indicated by dwindling numbers of naïve CD8 T cells after transfer into MHC class I-deficient mice (4, 5). In addition, long-term (but not short-term) survival of CD4 T cells requires the presence of MHC class II (6).IL-7 is important for survival and homeostatic proliferation of naïve T cells, which is shown by reduced recovery of naïve T cells transferred into IL-7 −/− mice (7, 8) and impaired survival and homeostatic proliferation of T cells from IL-7 receptor α-subunit (IL-7Rα) -deficient mice (9, 10). The receptor for IL-7 is a heterodimer consisting of the IL-7Rα (CD127) and common γ-chain receptor (γ c ; CD132) subunits. Triggering of IL-7R activates Stat5 through Jak1/Jak3 (11) and the PI3K/Akt/mTOR axis (12). IL-7-mediated survival involves up-regulation of the prosurvival factors Bcl-2 and Mcl-1 as well as reduction of proapoptotic molecules Bax, Bad, and Bim (13). Interestingly, IL-7 negatively regulates the expression of its receptor, promoting endocytosis, degradation, and the transcriptional inhibition of Il7r expression (11,14). This milieu enables a pool of T cells that have not yet encountered IL-7 to be preferentially responsive to limiting concentrations of this cytokine. Several transcription factors are involved in the control of Il7r expression in T cells, including positive regulation by GA binding protein, glucocorticoid receptor,...