Short-term dietary changes can result in mucosal and systemic immune depression.

Omnivorous animals, including mice and humans, tend to prefer energy-dense nutrients rich in fat over plant-based diets, especially for short periods of time, but the health consequences of this short-term consumption of energy-dense nutrients are unclear. Here, we show that short-term reiterative switching to 'feast diets', mimicking our social eating behavior, breaches the potential buffering effect of the intestinal microbiota and reorganizes the immunological architecture of mucosa-associated lymphoid tissues. The first dietary switch was sufficient to induce transient mucosal immune depression and suppress systemic immunity, leading to higher susceptibility to Salmonella enterica serovar Typhimurium and Listeria monocytogenes infections. The ability to respond to antigenic challenges with a model antigen was also impaired. These observations could be explained by a reduction of CD4+ T cell metabolic fitness and cytokine production due to impaired mTOR activity in response to reduced microbial provision of fiber metabolites. Reintroducing dietary fiber rewired T cell metabolism and restored mucosal and systemic CD4+ T cell functions and immunity. Finally, dietary intervention with human volunteers confirmed the effect of short-term dietary switches on human CD4+ T cell functionality. Therefore, short-term nutritional changes cause a transient depression of mucosal and systemic immunity, creating a window of opportunity for pathogenic infection.

Kidney-resident innate-like memory γδ T cells control chronic Staphylococcus aureus infection of mice.

γδ T cells are involved in the control of Staphylococcus aureus infection, but their importance in protection compared to other T cells is unclear. We used a mouse model of systemic S. aureus infection associated with high bacterial load and persistence in the kidney. Infection caused fulminant accumulation of γδ T cells in the kidney. Renal γδ T cells acquired tissue residency and were maintained in high numbers during chronic infection. At day 7, up to 50% of renal γδ T cells produced IL-17A in situ and a large fraction of renal γδ T cells remained IL-17A+ during chronic infection. Controlled depletion revealed that γδ T cells restricted renal S. aureus replication in the acute infection and provided protection during chronic renal infection and upon reinfection. Our results demonstrate that kidney-resident γδ T cells are nonredundant in limiting local S. aureus growth during chronic infection and provide enhanced protection against reinfection.

Autoimmune Renal Disease Is Exacerbated by S1P-Receptor-1-Dependent Intestinal Th17 Cell Migration to the Kidney.

Th17 cells are most abundant in the gut, where their presence depends on the intestinal microbiota. Here, we examined whether intestinal Th17 cells contribute to extra-intestinal Th17 responses in autoimmune kidney disease. We found high frequencies of Th17 cells in the kidneys of patients with antineutrophil cytoplasmatic antibody (ANCA)-associated glomerulonephritis. We utilized photoconversion of intestinal cells in Kaede mice to track intestinal T cell mobilization upon glomerulonephritis induction, and we found that Th17 cells egress from the gut in a S1P-receptor-1-dependent fashion and subsequently migrate to the kidney via the CCL20/CCR6 axis. Depletion of intestinal Th17 cells in germ-free and antibiotic-treated mice ameliorated renal disease, whereas expansion of these cells upon Citrobacter rodentium infection exacerbated pathology. Thus, in some autoimmune settings, intestinal Th17 cells migrate into target organs, where they contribute to pathology. Targeting the intestinal Th17 cell "reservoir" may present a therapeutic strategy for these autoimmune disorders.

Pregnancy-induced transfer of pathogen-specific T cells from mother to fetus in mice.

Neonatal health is determined by the transfer of maternal antibodies from the mother to the fetus. Besides antibodies, maternal cells cross the placental barrier and seed into fetal organs. Contrary to maternal antibodies, maternal microchimeric cells (MMc) show a high longevity, as they can persist in the offspring until adulthood. Recent evidence highlights that MMc leukocytes promote neonatal immunity against early-life infections in mice and humans. As shown in mice, this promotion of immunity was attributable to an improved fetal immune development. Besides this indirect effect, MMc may be pathogen-specific and thus, directly clear pathogen threats in the offspring postnatally. By using ovalbumin recombinant Listeria monocytogenes (LmOVA), we here provide evidence that OVA-specific T cells are transferred from the mother to the fetus, which is associated with increased activation of T cells and a milder course of postnatal infection in the offspring. Our data highlight that maternally-derived passive immunity of the neonate is not limited to antibodies, as MMc have the potential to transfer immune memory between generations.

Cell-Autonomous Constitutive gp130 Signaling in T Cells Amplifies TH17 Cell Responses and Causes Severe Lung Inflammation.

IL-6 plays a fundamental role in T cell differentiation and is strictly controlled by surface expression and shedding of IL-6R. IL-6 also acts on other cells that might affect T cell maturation. To study the impact of cell-autonomous and uncontrolled IL-6 signaling in T cells, we generated mice with a constitutively active IL-6R gp130 chain (Lgp130) expressed either in all T cells (Lgp130 × CD4Cre mice) or inducible in CD4+ T cells (Lgp130 × CD4CreERT2 mice). Lgp130 × CD4Cre mice accumulated activated T cells, including TH17 cells, in the lung, resulting in severe inflammation. Tamoxifen treatment of Lgp130 × CD4CreERT2 mice caused Lgp130 expression in 40-50% of CD4+ T cells, but mice developed lung disease only after several months. Lgp130+ CD4+ T cells were also enriched for TH17 cells; however, there was concomitant expansion of Lgp130- regulatory T cells, which likely restricted pathologic Lgp130+ T cells. In vitro, constitutive gp130 signaling in T cells enhanced but was not sufficient for TH17 cell differentiation. Augmented TH17 cell development of Lgp130+ T cells was also observed in Lgp130 × CD4CreERT2 mice infected with Staphylococcus aureus, but gp130 activation did not interfere with formation of TH1 cells against Listeria monocytogenes. Lgp130+ CD4+ T cells acquired a memory T cell phenotype and persisted in high numbers as a polyclonal T cell population in lymphoid and peripheral tissues, but we did not observe T cell lymphoma formation. In conclusion, cell-autonomous gp130 signaling alters T cell differentiation. Although gp130 signaling is not sufficient for TH17 cell differentiation, it still promotes accumulation of activated T cells in the lung that cause tissue inflammation.

Th17 cell plasticity towards a T-bet-dependent Th1 phenotype is required for bacterial control in Staphylococcus aureus infection.

Staphylococcus aureus is frequently detected in patients with sepsis and thus represents a major health burden worldwide. CD4+ T helper cells are involved in the immune response to S. aureus by supporting antibody production and phagocytosis. In particular, Th1 and Th17 cells secreting IFN-γ and IL-17A, are involved in the control of systemic S. aureus infections in humans and mice. To investigate the role of T cells in severe S. aureus infections, we established a mouse sepsis model in which the kidney was identified to be the organ with the highest bacterial load and abundance of Th17 cells. In this model, IL-17A but not IFN-γ was required for bacterial control. Using Il17aCre × R26YFP mice we could show that Th17 fate cells produce Th17 and Th1 cytokines, indicating a high degree of Th17 cell plasticity. Single cell RNA-sequencing of renal Th17 fate cells uncovered their heterogeneity and identified a cluster with a Th1 expression profile within the Th17 cell population, which was absent in mice with T-bet/Tbx21-deficiency in Th17 cells (Il17aCre x R26eYFP x Tbx21-flox). Blocking Th17 to Th1 transdifferentiation in Th17 fate cells in these mice resulted in increased S. aureus tissue loads. In summary, we highlight the impact of Th17 cells in controlling systemic S. aureus infections and show that T-bet expression by Th17 cells is required for bacterial clearance. While targeting the Th17 cell immune response is an important therapeutic option in autoimmunity, silencing Th17 cells might have detrimental effects in bacterial infections.

Interferon regulatory factor 4 controls effector functions of CD8+ memory T cells.

The transcription factor IRF4 is required for CD8+ T cell activation, proliferation, and differentiation to effector cells and thus is essential for robust CD8+ T cell responses. The function of IRF4 in memory CD8+ T cells yet needs to be explored. To investigate the role of IRF4 for maintaining differentiation state and survival of CD8+ memory T cells, we used a mouse model with tamoxifen-inducible Irf4 knockout to preclude effects due to inefficient memory cell differentiation in absence of IRF4. We infected mice with ovalbumin-recombinant listeria and induced Irf4 knockout after clearance of the pathogen. Loss of IRF4 resulted in phenotypical changes of CD8+ memory T cells but did not cause a reduction of the total memory T cell population. However, upon reencounter of the pathogen, CD8+ memory T cells showed impaired expansion and acquisition of effector functions. When compared to CD8+ effector memory T cells, CD8+ tissue-resident memory T cells (TRM cells) expressed higher IRF4 levels. Mice with constitutive Irf4 knockout had diminished CD8+ TRM-cell populations, and tamoxifen-induced Irf4 deletion caused a reduction of this cell population. In conclusion, our results demonstrate that IRF4 is required for effective reactivation but not for general survival of CD8+ memory T cells. Formation and maintenance of CD8+ TRM cells, in contrast, appear to depend on IRF4.

Cell-autonomous hepatocyte-specific GP130 signaling is sufficient to trigger a robust innate immune response in mice.

BACKGROUND & AIMS: Interleukin (IL)-6 cytokine family members contribute to inflammatory and regenerative processes. Engagement of the signaling receptor subunit gp130 is common to almost all members of the family. In the liver, all major cell types respond to IL-6-type cytokines, making it difficult to delineate cell type-specific effects. We therefore generated mouse models for liver cell type-specific analysis of IL-6 signaling. METHODS: We produced mice with a Cre-inducible expression cassette encoding a designed pre-dimerized constitutive active gp130 variant. We bred these mice to different Cre-drivers to induce transgenic gp130 signaling in distinct liver cell types: hepatic stellate cells, cholangiocytes/liver progenitor cells or hepatocytes. We phenotyped these mice using multi-omics approaches, immunophenotyping and a bacterial infection model. RESULTS: Hepatocyte-specific gp130 activation led to the upregulation of innate immune system components, including acute-phase proteins. Consequently, we observed peripheral mobilization and recruitment of myeloid cells to the liver. Hepatic myeloid cells, including liver-resident Kupffer cells were instructed to adopt a bactericidal phenotype which ultimately conferred enhanced resistance to bacterial infection in these mice. We demonstrate that persistent hepatocyte-specific gp130 activation resulted in amyloid A amyloidosis in aged mice. In contrast, we did not observe overt effects of hepatic stellate cell- or cholangiocyte/liver progenitor cell-specific transgenic gp130 signaling. CONCLUSIONS: Hepatocyte-specific gp130 activation alone is sufficient to trigger a robust innate immune response in the absence of NF-κB activation. We therefore conclude that gp130 engagement, e.g. by IL-6 trans-signaling, represents a safe-guard mechanism in innate immunity. LAY SUMMARY: Members of the interleukin-6 cytokine family signal via the receptor subunit gp130 and are involved in multiple processes in the liver. However, as several liver cell types respond to interleukin-6 family cytokines, it is difficult to delineate cell type-specific effects. Using a novel mouse model, we provide evidence that hepatocyte-specific gp130 activation is sufficient to trigger a robust systemic innate immune response.

The sorting receptor Sortilin exhibits a dual function in exocytic trafficking of interferon-γ and granzyme A in T cells.

Immunological control of infections or tumors depends on the release of effector cytokines and polarized secretion of cytotoxic granules from T cells and natural killer cells. Here we show that the sorting receptor Sortilin controlled both processes. In murine Sortilin-deficient cytotoxic T lymphocytes, regulated secretion of granzyme A and cytotoxic killing was enhanced and correlated with increased vesicle-associated membrane protein 7 availability. In contrast, loss of Sortilin reduced the release of interferon-γ upon infections and in autoimmune colitis. Exit of interferon-γ from the Golgi apparatus required the presence of Sortilin. Furthermore, we tracked the transport route of interferon-γ beyond this Sortilin-dependent Golgi to early endosome step. In wild-type T cells, trafficking of interferon-γ from the endosomal sorting platform to the plasma membrane proceeded independently of recycling endosomes, and interferon-γ remained excluded from late endosomes. Our results suggest that Sortilin modulates systemic immune responses through exocytic sorting of immunological effector molecules.

Deubiquitinating Enzyme UCH-L1 Promotes Dendritic Cell Antigen Cross-Presentation by Favoring Recycling of MHC Class I Molecules.

The deubiquitinating enzyme ubiquitin C-terminal hydrolase-L1 (UCH-L1) is required for the maintenance of axonal integrity in neurons and is thought to regulate the intracellular pool of ubiquitin in the brain. In this study, we show that UCH-L1 has an immunological function in dendritic cell (DC) Ag cross-presentation. UCH-L1 is expressed in mouse kidney, spleen, and bone marrow-derived DCs, and its expression and activity are regulated by the immune stimuli LPS and IFN-γ. UCH-L1-deficient mice have significantly reduced ability to cross-prime CD8 T cells in vivo and in vitro because of a reduced ability of DCs to generate MHC class I (MHC I) peptide complexes for cross-presented Ags. Mechanistically, Ag uptake by phagocytosis and receptor-mediated endocytosis as well as phagosome maturation are unaffected by loss of UCH-L1 in DCs. Rather, MHC I recycling is reduced by loss of UCH-L1, which affects the colocalization of intracellular MHC I with late endosomal/lysosomal compartments necessary for cross-presentation of Ag. These results demonstrate a hitherto unrecognized role of the deubiquitinating enzyme UCH-L1 in DC Ag processing.

Arc/Arg3.1 defines dendritic cells and Langerhans cells with superior migratory ability independent of phenotype and ontogeny in mice.

The key function of migratory dendritic cells (migDCs) is to take up antigens in peripheral tissues and migrate to draining lymph nodes (dLN) to initiate immune responses. Recently, we discovered that in the mouse immune system activity-regulated cytoskeleton associated protein/activity-regulated gene 3.1 (Arc/Arg3.1) is exclusively expressed by migDCs and is a central driver of fast inflammatory migration. However, the frequency of Arc/Arg3.1-expressing cells in different migDC subsets and Langerhans cells (LCs), their phylogenetic origin, transcription factor dependency, and functional role remain unclear. Here, we found that Arc/Arg3.1+ migDCs derived from common DC precursors and radio-resistant LCs. We detected Arc/Arg3.1+ migDCs in varying frequencies within each migDC subset and LCs. Consistently, they showed superiority in inflammatory migration. Arc/Arg3.1 expression was independent of the transcription factors Irf4 or Batf3 in vivo. In intradermal Staphylococcus aureus infection that relies on inflammatory antigen transport, Arc/Arg3.1 deletion reduced T-cell responses. By contrast, Arc/Arg3.1 deficiency did not hamper the immune response to systemic Listeria monocytogenes infection, which does not require antigen transport. Thus, Arc/Arg3.1 expression is independent of ontogeny and phenotype and although it is restricted to a small fraction within each migDC subset and LCs, Arc/Arg3.1+ migDCs are important to facilitate infectious migration.

A Novel Role for IL-6 Receptor Classic Signaling: Induction of RORγt+Foxp3+ Tregs with Enhanced Suppressive Capacity.

BACKGROUND: New therapies blocking the IL-6 receptor (IL-6R) have recently become available and are successfully being used to treat inflammatory diseases like arthritis. Whether IL-6 blockers may help patients with kidney inflammation currently remains unknown. METHODS: To learn more about the complex role of CD4+ T cell-intrinsic IL-6R signaling, we induced nephrotoxic nephritis, a mouse model for crescentic GN, in mice lacking T cell-specific IL-6Ra. We used adoptive transfer experiments and studies in reporter mice to analyze immune responses and Treg subpopulations. RESULTS: Lack of IL-6Ra signaling in mouse CD4+ T cells impaired the generation of proinflammatory Th17 cells, but surprisingly did not ameliorate the course of GN. In contrast, renal damage was significantly reduced by restricting IL-6Ra deficiency to T effector cells and excluding Tregs. Detailed studies of Tregs revealed unaltered IL-10 production despite IL-6Ra deficiency. However, in vivo and in vitro, IL-6Ra classic signaling induced RORγt+Foxp3+ double-positive Tregs (biTregs), which carry the trafficking receptor CCR6 and have potent immunoregulatory properties. Indeed, lack of IL-6Ra significantly reduced Treg in vitro suppressive capacity. Finally, adoptive transfer of T cells containing IL-6Ra-/- Tregs resulted in severe aggravation of GN in mice. CONCLUSIONS: Our data refine the old paradigm, that IL-6 enhances Th17 responses and suppresses Tregs. We here provide evidence that T cell-intrinsic IL-6Ra classic signaling indeed induces the generation of Th17 cells but at the same time highly immunosuppressive RORγt+ biTregs. These results advocate caution and indicate that IL-6-directed therapies for GN need to be cell-type specific.

Role of regulatory T cells in experimental autoimmune glomerulonephritis.

Anti-glomerular basement membrane (anti-GBM) disease is characterized by antibodies and T cells directed against the Goodpasture antigen, the noncollagenous domain of the α3-chain of type IV collagen [α3(IV)NC1] of the GBM. Consequences are the deposition of autoantibodies along the GBM and the development of crescentic glomerulonephritis (GN) with rapid loss of renal function. Forkhead box protein P3 (Foxp3)+ regulatory T (Treg) cells are crucial for the maintenance of peripheral tolerance to self-antigens and the prevention of immunopathology. Here, we use the mouse model of experimental autoimmune GN to characterize the role of Treg cells in anti-GBM disease. Immunization of DBA/1 mice with α3(IV)NC1 induced the formation of α3(IV)NC1-specific T cells and antibodies and, after 8-10 wk, the development of crescentic GN. Immunization resulted in increased frequencies of peripheral Treg cells and renal accumulation of these cells in the stage of acute GN. Depletion of Treg cells during immunization led to enhanced generation of α3(IV)NC1-specific antibodies and T cells and to aggravated GN. In contrast, depletion or expansion of the Treg cell population in mice with established autoimmunity had only minor consequences for renal inflammation and did not alter the severity of GN. In conclusion, our results indicate that in anti-GBM disease, Treg cells restrict the induction of autoimmunity against α3(IV)NC1. However, Treg cells are inefficient in preventing crescentic GN after autoimmunity has been established.

Tissue-Resident Lymphocytes in the Kidney.

It has become evident that nonlymphoid tissues are populated by distinct subsets of innate and adaptive lymphocytes that are characterized by minimal exchange with recirculating counterparts. Especially at barrier sites, such as the skin, gut, and lung, these tissue-resident lymphocyte populations are ideally positioned to quickly respond to pathogens and other environmental stimuli. The kidney harbors several classes of innate and innate-like lymphocytes that have been described to contribute to this tissue-resident population in other organs, including innate lymphoid cells, natural killer cells, natural killer T cells, mucosal-associated invariant T cells, and γδ T cells. Additionally, a substantial proportion of the adaptive lymphocytes that are found in the kidney displays a surface phenotype suggestive of tissue residency, such as CD69+CD4+ T cells. In this review, we summarize recent advances in the understanding of tissue-resident lymphocyte populations, review the available evidence for the existence of these populations in the kidney, and discuss the potential physiologic and pathophysiologic roles thereof in kidney.

IL-6 trans-signaling is essential for the development of hepatocellular carcinoma in mice.

Hepatocellular carcinoma (HCC) is one of the most frequent tumors worldwide with rising incidence. The inflammatory cytokine, interleukin-6 (IL-6), is a critical mediator of HCC development. It can signal through two distinct pathways: the IL-6 classic and the IL-6 trans-signaling pathway. Whereas IL-6 classic signaling is important for innate and acquired immunity, IL-6 trans-signaling has been linked to accelerated liver regeneration and several chronic inflammatory pathologies. However, its implication in liver tumorigenesis has not been addressed yet. Here, we show that IL-6 trans-signaling, but not IL-6 classic signaling, is essential to promote hepatocellular carcinogenesis by two mechanisms: First, it prevents DNA-damage-induced hepatocyte apoptosis through suppression of p53 and enhances ß-catenin activation and tumor proliferation. Second, IL-6 trans-signaling directly induces endothelial cell proliferation to promote tumor angiogenesis. Consequently, soluble gp130 fused to Fc transgenic mice lacking IL-6 trans-signaling are largely protected from tumor formation in a diethylnitrosamine/3,3',5,5'-tetrachloro-1,4-bis(pyridyloxy)benzene model of HCC. CONCLUSION: IL-6 trans-signaling, and not IL-6 classic signaling, is mandatory for development of hepatocellular carcinogenesis. Therefore, specific inhibition of IL-6 trans-signaling, rather than total inhibition of IL-6 signaling, is sufficient to blunt tumor initiation and impair tumor progression without compromising IL-6 classic signaling-driven protective immune responses. (Hepatology 2017;65:89-103).

Mast cell-mediated antigen presentation regulates CD8+ T cell effector functions.

The characteristics, importance, and molecular requirements for interactions between mast cells (MCs) and CD8(+) T cells have not been elucidated. Here, we demonstrated that MCs induced antigen-specific CD8(+) T cell activation and proliferation. This process required direct cell contact and MHC class I-dependent antigen cross-presentation by MCs and induced the secretion of interleukin-2, interferon-gamma, and macrophage inflammatory protein-1alpha by CD8(+) T cells. MCs regulated antigen-specific CD8(+) T cell cytotoxicity by increasing granzyme B expression and by promoting CD8(+) T cell degranulation. Because MCs also upregulated their expression of costimulatory molecules (4-1BB) and released osteopontin upon direct T cell contact, MC-T cell interactions probably are bidirectional. In vivo, adoptive transfer of antigen-pulsed MCs induced MHC class I-dependent, antigen-specific CD8(+) T cell proliferation, and MCs regulated CD8(+) T cell-specific priming in experimental autoimmune encephalomyelitis. Thus, MCs are important players in antigen-specific regulation of CD8(+) T cells.

Opposing role of tumor necrosis factor receptor 1 signaling in T cell-mediated hepatitis and bacterial infection in mice.

UNLABELLED: Death receptor (DR) ligands such as tumor necrosis factor (TNF) have been identified as fundamental mediators of liver damage both in mouse models and in humans. While the essential site of function of DR signaling is conceivably the hepatocyte, a systematic analysis is missing. Using mice with conditional gene ablation, we analyzed the tissue-specific function of DR signaling in T cell-dependent (concanavalin A) and independent (lipopolysaccharide/galactosamine) hepatitis and in models of bacterial infection (Listeria monocytogenes, lipopolysaccharide). We report that lipopolysaccharide/galactosamine-induced liver injury depends on hepatocyte-intrinsic TNF receptor 1 (p55, TNFR1). In contrast, we show that T cell-induced hepatitis was independent of TNFR1 signaling in hepatocytes, T cells, or endothelial cells. Moreover, T cell-induced hepatitis was independent of hepatocyte-intrinsic Fas-associated protein with death domain, TNF-related apoptosis-inducing ligand receptor, or Fas signaling. Instead, concanavalin A-induced hepatitis was completely prevented in mice with myeloid-derived cell (MDC)-specific deletion of TNFR1. Significantly, however, mice lacking TNFR1 in MDCs succumbed to listeria infection, although they displayed similar sensitivity toward endotoxin-induced septic shock when compared to control mice. These results suggest that TNFR1 signaling in MDCs is a critical mediator of both the detrimental and the protective functions of TNF in T cell-induced hepatitis and bacterial infection, respectively. CONCLUSION: The critical site of action of DRs is completely dependent on the nature of hepatitis; the data specify MDCs as the essential cell type of TNFR1 function in T cell-mediated hepatitis and in the response to listeria, thereby identifying the opposing role of MDC TNFR1 in autoimmunity and bacterial infection. (Hepatology 2016;64:508-521).

Glomerulopathy induced by immunization with a peptide derived from the goodpasture antigen α3IV-NC1.

Mouse experimental autoimmune glomerulonephritis, a model of human antiglomerular basement membrane disease, depends on both Ab and T cell responses to the Goodpasture Ag noncollagenous domain 1 of the α3-chain of type IV collagen (α3IV-NC1). The aim of our study was to further characterize the T cell-mediated immune response. Repeated immunization with mouse α3IV-NC1 caused fatal glomerulonephritis in DBA/1 mice. Although two immunizations were sufficient to generate high α3IV-NC1-specific IgG titers, Ab and complement deposition along the glomerular basement membranes, and a nephrotic syndrome, two additional immunizations were needed to induce a necrotizing/crescentic glomerulonephritis. Ten days after the first immunization, α3IV-NC1-specific CD4(+) cells producing TNF-α, IFN-γ, or IL-17A were detected in the spleen. With the emergence of necrotizing/crescentic glomerulonephritis, ∼0.15% of renal CD4(+) cells were specific for α3IV-NC1. Using peptides spanning the whole α3IV-NC1 domain, three immunodominant T cell epitopes were identified. Immunization with these peptides did not lead to clinical signs of experimental autoimmune glomerulonephritis or necrotizing/crescentic glomerulonephritis. However, mice immunized with one of the peptides (STVKAGDLEKIISRC) developed circulating Abs against mouse α3IV-NC1 first detected at 8 wk, and 50% of the mice showed mild proteinuria at 18-24 wk due to membranous glomerulopathy. Taken together, our results suggest that autoreactive T cells are able to induce the formation of pathologic autoantibodies. The quality and quantity of α3IV-NC1-specific Ab and T cell responses are critical for the phenotype of the glomerulonephritis.

CXCR3+ Regulatory T Cells Control TH1 Responses in Crescentic GN.

Chemokines and chemokine receptors are implicated in regulatory T cell (Treg) trafficking to sites of inflammation and suppression of excessive immune responses in inflammatory and autoimmune diseases; however, the specific requirements for Treg migration into the inflamed organs and the positioning of these cells within the tissue are incompletely understood. Here, we report that Tregs expressing the TH1-associated chemokine receptor CXCR3 are enriched in the kidneys of patients with ANCA-associated crescentic GN and colocalize with CXCR3(+) effector T cells. To investigate the functional role of CXCR3(+) Tregs, we generated mice that lack CXCR3 in Tregs specifically (Foxp3(eGFP-Cre) × Cxcr3(fl/fl)) and induced experimental crescentic GN. Treg-specific deletion of CXCR3 resulted in reduced Treg recruitment to the kidney and an overwhelming TH1 immune response, with an aggravated course of the nephritis that was reversible on anti-IFNγ treatment. Together, these findings show that a subset of Tregs expresses CXCR3 and thereby, acquires trafficking properties of pathogenic CXCR3(+) TH1 cells, allowing Treg localization and control of excessive TH1 responses at sites of inflammation.