Plasticity of Th17 cells in Peyer's patches is responsible for the induction of T cell-dependent IgA responses.

Intestinal Peyer's patches are essential lymphoid organs for the generation of T cell-dependent immunoglobulin A (IgA) for gut homeostasis. Through the use of interleukin 17 (IL-17) fate-reporter mice, we found here that endogenous cells of the TH17 subset of helper T cells in lymphoid organs of naive mice 'preferentially' homed to the intestines and were maintained independently of IL-23. In Peyer's patches, such TH17 cells acquired a follicular helper T cell (TFH cell) phenotype and induced the development of IgA-producing germinal center B cells. Mice deficient in TH17 cells failed to generate antigen-specific IgA responses, which provides evidence that TH17 cells are the crucial subset required for the production of high-affinity T cell-dependent IgA.

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.

The CCR6/CCL20 axis expands RORγt+ Tregs to protect from glomerulonephritis.

Previous studies have identified a unique Treg population, which expresses the Th17 characteristic transcription factor RORγt. These RORγt+ Tregs possess enhanced immunosuppressive capacity, which endows them with great therapeutic potential. However, as a caveat, they are also capable of secreting pro-inflammatory IL-17A. Since the sum function of RORγt+ Tregs in glomerulonephritis (GN) remains unknown, we studied the effects of their absence. Purified CD4+ T cell populations, containing or lacking RORγt+ Tregs, were transferred into immunocompromised RAG1 knockout mice and the nephrotoxic nephritis model of GN was induced. Absence of RORγt+ Tregs significantly aggravated kidney injury, demonstrating overall kidney-protective properties. Analyses of immune responses showed that RORγt+ Tregs were broadly immunosuppressive with no preference for a particular type of T cell response. Further characterization revealed a distinct functional and transcriptional profile, including enhanced production of IL-10. Expression of the chemokine receptor CCR6 marked a particularly potent subset, whose absence significantly worsened GN. As an underlying mechanism, we found that chemokine CCL20 acting through receptor CCR6 signaling mediated expansion and activation of RORγt+ Tregs. Finally, we also detected an increase of CCR6+ Tregs in kidney biopsies, as well as enhanced secretion of chemokine CCL20 in 21 patients with anti-neutrophil cytoplasmic antibody associated GN compared to that of 31 healthy living donors, indicating clinical relevance. Thus, our data characterize RORγt+ Tregs as anti-inflammatory mediators of GN and identify them as promising target for Treg directed therapies.

The Amphiregulin/EGFR axis protects from lupus nephritis via downregulation of pathogenic CD4+ T helper cell responses.

Systemic lupus erythematosus (SLE) is a common autoimmune disorder with a complex and poorly understood immuno-pathogenesis. Lupus nephritis (LN) is a frequent and difficult to treat complication, which causes high morbidity and mortality. The multifunctional cytokine amphiregulin (AREG) has been implicated in SLE pathogenesis, but its function in LN currently remains unknown. We thus studied the model of pristane-induced LN and found increasing renal and systemic AREG expression during the course of disease. Importantly, renal injury was significantly aggravated in the absence of AREG, revealing a net anti-inflammatory role. Analyses of immune responses showed dual effects. On the one hand, AREG enhanced activation of pro-inflammatory myeloid cells, which however did not play a major role for the course of LN. More importantly, on the other hand, AREG strongly suppressed pathogenic cytokine production by T helper effector cells. This effect was more general in nature and could be reproduced in response to antigen immunization. Since AREG has been postulated to downregulate T cell responses via enhancing Treg suppressive capacity, we followed up on this aspect. Interestingly, however, in vitro studies revealed potential direct and Treg independent effects of AREG on T helper effector cells. In favor of this notion, we found significantly enhanced T cell responses and consecutive aggravation of LN, only if epidermal growth factor receptor (EGFR) signaling was abrogated in total T cells, but not if the EGFR was absent on Tregs alone. Finally, we also found enhanced AREG expression in plasma and renal biopsies of patients with LN, supporting the relevance of our findings for human disease. In summary, our data identify AREG as an anti-inflammatory mediator of LN via broad downregulation of pathogenic T cell immunity. These findings further highlight the AREG/EGFR axis as a potential therapeutic target.

[Renal manifestations in connective tissue diseases]. / Nierenbeteiligung bei Kollagenosen.

Connective tissue diseases (CTD) comprise a group of inflammatory systemic diseases that can affect various organs. Kidney involvement is frequently associated with significant irreversible damage and often before patients become symptomatic. Screening tests of blood and urine as well as clinical vigilance are therefore essential for all CTDs with possible renal involvement. A kidney biopsy is the gold standard for the diagnosis, prognosis and treatment decisions. A common and severe organ involvement in systemic lupus erythematosus (SLE) is glomerulonephritis (GN), also collectively referred to as lupus nephritis (LN). If left untreated LN often leads to end-stage renal failure. The treatment depends on the clinical parameters and histopathology of the renal involvement. Mycophenolate mofetil and cyclophosphamide are potent but nonspecific immunosuppressants which have been available for many years. Recently, new substances specific for LN have also been approved for the first time. Kidney involvement in Sjogren's syndrome has been far less studied. In studies the frequency of renal involvement is still unclear and ranges from 5% to 33%. Tubulointerstitial nephritis (IN) is the typical form of renal involvement which clearly differs from GN in its clinical presentation. Recommendations for treatment are based exclusively on retrospective studies. A renal crisis in systemic scleroderma (SSc) is a rare but feared complication with a high mortality. An antiphospholipid syndrome (APS) nephropathy (APSN) can occur during CTD. These entities are vasculopathies and often thrombotic microangiopathies, which clearly differ from GN and IN in terms of pathophysiology, clinical features and treatment. This article provides an overview of the diversity of the most important renal manifestations of CTDs.

[Sarcoidosis as prime example of a granulomatous disease]. / Sarkoidose als Paradebeispiel einer granulomatösen Erkrankung.

Sarcoidosis is the most frequent immunologically related granulomatous disease and can serve as a model for understanding diseases within this category. The evidence on the diagnostics and treatment is so far limited. It is therefore all the more important that two new and significant guidelines on diagnosis and treatment of sarcoidosis were published during the last 2 years. Additionally, there were more new publications, which were considered for this review article. In this context, this review article provides a current update and overview of sarcoidosis. Pathophysiologically, there is an increasing understanding of the complex processes and interactions involved in the inflammatory processes and granuloma formation. The probability of a diagnosis of sarcoidosis is determined by compatible histology, the exclusion of differential diagnoses and if possible evidence of a multiorgan manifestation. The clinical course is variable and ranges from an asymptomatic manifestation to severe life-threatening organ failure. The most frequently affected organ are the lungs. Pulmonary fibrosis is the most severe form and is also decisive for mortality. An increasing focus is on the extrapulmonary organ manifestations, in particular, cardiac, hepatosplenic, gastrointestinal, renal, ocular and neurological involvement. Treatment, which consists primarily of immunosuppression, should be initiated in cases of organ-threatening or quality of life-impairing activity of the disease. Additional organ-specific management must also be evaluated. In cases of organ failure transplantation should be considered. Due to the limited evidence especially for the treatment of multiorgan sarcoidosis, when possible, patients with this disease should be included in clinical trials.

Amphiregulin Aggravates Glomerulonephritis via Recruitment and Activation of Myeloid Cells.

BACKGROUND: Recent studies have identified the EGF receptor (EGFR) ligand amphiregulin (AREG) as an important mediator of inflammatory diseases. Both pro- and anti-inflammatory functions have been described, but the role of AREG in GN remains unknown. METHODS: The nephrotoxic nephritis model of GN was studied in AREG-/- mice after bone marrow transplantation, and in mice with myeloid cell-specific EGFR deficiency. Therapeutic utility of AREG neutralization was assessed. Furthermore, AREG's effects on renal cells and monocytes/macrophages (M/M) were analyzed. Finally, we evaluated AREG expression in human renal biopsies. RESULTS: Renal AREG mRNA was strongly upregulated in murine GN. Renal resident cells were the most functionally relevant source of AREG. Importantly, the observation that knockout mice showed significant amelioration of disease indicates that AREG is pathogenic in GN. AREG enhanced myeloid cell responses via inducing chemokine and colony stimulating factor 2 (CSF2) expression in kidney resident cells. Furthermore, AREG directly skewed M/M to a proinflammatory M1 phenotype and protected them from apoptosis. Consequently, anti-AREG antibody treatment dose-dependently ameliorated GN. Notably, selective abrogation of EGFR signaling in myeloid cells was sufficient to protect against nephritis. Finally, strong upregulation of AREG expression was also detected in kidneys of patients with two forms of crescentic GN. CONCLUSIONS: AREG is a proinflammatory mediator of GN via (1) enhancing renal pathogenic myeloid cell infiltration and (2) direct effects on M/M polarization, proliferation, and cytokine secretion. The AREG/EGFR axis is a potential therapeutic target for acute GN.

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.

Bevacizumab-associated glomerular microangiopathy.

Bevacizumab is a humanized monoclonal IgG1 antibody, which neutralizes vascular endothelial growth factor and is used for treating multiple cancer types. As a known and frequent adverse event, this therapy can lead to renal damage including proteinuria and nephrotic syndrome. In a retrospective approach, we analyzed 17 renal biopsies from patients receiving bevacizumab treatment. We observed a distinctive histopathological pseudothrombotic pattern different from the previously reported thrombotic microangiopathy. Since this pattern includes some features similar to acute and chronic thrombotic microangiopathy, focal segmental glomerulosclerosis and cryoglobulinemic membranoproliferative glomerulonephritis, biopsies with these diagnoses were included for comparison. Clinical, laboratory, light microscopic, immunohistochemical (including a proximity ligation assay), proteomic and electron microscopic features were assessed. Nephrotic syndrome was present in 15 of the 17 bevacizumab-treated patients. All 17 displayed a patchy pattern of variably PAS-positive hyaline pseudothrombi occluding markedly dilated glomerular capillaries in their biopsies. Mass spectrometry-based proteome analysis revealed a special protein pattern demonstrating some features of thrombotic microangiopathy and some of cryoglobulinemic glomerulonephritis, including a strong accumulation of IgG in the pseudothrombi. Proximity ligation assay did not show interaction of IgG with C1q, arguing for accumulation without classic pathway complement activation. In contrast to thrombi in thrombotic microangiopathy cases, the hyaline pseudothrombi did not contain clusters of CD61-positive platelets. Electron microscopy of bevacizumab cases did not show fibrin polymers or extensive loss of podocyte foot processes. Even though cases of bevacizumab-associated microangiopathy share some features with thrombotic microangiopathy, its overall histopathological pattern is quite different from acute or chronic thrombotic microangiopathy cases. We conclude that bevacizumab therapy can lead to a unique hyaline occlusive glomerular microangiopathy, likely arising from endothelial leakage followed by subendothelial accumulation of serum proteins. It can be diagnosed by light microscopy and is an important differential diagnosis in cancer patients with nephrotic syndrome.

IL-10 Receptor Signaling Empowers Regulatory T Cells to Control Th17 Responses and Protect from GN.

Background Th17 cells are central pathogenic mediators of autoimmune disease, including many forms of GN. IL-10 receptor signaling (IL-10R) in regulatory T cells (Tregs) has been implicated in the downregulation of Th17 cells, but the underlying molecular mechanisms and functional relevance of this process remain unclear.Methods We generated mice with Treg-specific IL-10Ra deficiency and subjected these mice to nephrotoxic serum-induced nephritis as a model of crescentic GN. Immune responses and Treg phenotypes were extensively analyzed.Results Compared with controls, mice with IL-10Ra-/- Tregs showed a spontaneously overshooting Th17 immune response. This hyper-Th17 phenotype was further boosted during GN and associated with aggravated renal injury. Notably, abrogation of IL-10Ra signaling in Tregs increased dendritic cell activation and production of Th17-inducing cytokines. In contrast, Treg trafficking and expression of chemokine receptor CCR6 remained unaffected, indicating mechanisms of Th17 control, differing from those of previously identified CCR6+ Treg17 cells. Indeed, the capacity for direct in vitro suppression of Th17 responses by IL-10Ra-/- Tregs was significantly impaired. As underlying pathology, analyses conducted in vitro and in vivo using double-fluorescent reporter mice revealed strikingly decreased IL-10 production by IL-10Ra-/- Tregs. To assess, whether reduced IL-10 could explain the hyper Th17 phenotype, competitive cotransfer experiments were performed. Supporting our concept, IL-10Ra-/- T cells differentiated into Th17 cells at much higher frequencies than wild type T cells did during GN.Conclusions IL-10R engagement optimizes Treg-mediated suppression of Th17 immunity. We hypothesize a feed-forward loop, in which IL-10Ra signaling reinforces IL-10 secretion by Tregs which potently controls Th17 development via direct and indirect mechanisms. IL-10R thus may be a promising therapeutic target for the treatment of GN.

IL-17C/IL-17 Receptor E Signaling in CD4+ T Cells Promotes TH17 Cell-Driven Glomerular Inflammation.

The IL-17 cytokine family and the cognate receptors thereof have a unique role in organ-specific autoimmunity. Most studies have focused on the founding member of the IL-17 family, IL-17A, as the central mediator of diseases. Indeed, although pathogenic functions have been ascribed to IL-17A and IL-17F in the context of immune-mediated glomerular diseases, the specific functions of the other IL-17 family members in immunity and inflammatory kidney diseases is largely unknown. Here, we report that compared with healthy controls, patients with acute Anti-neutrophil cytoplasmatic antibody (ANCA)-associated crescentic glomerulonephritis (GN) had significantly elevated serum levels of IL-17C (but not IL-17A, F, or E). In mouse models of crescentic GN (nephrotoxic nephritis) and pristane-induced lupus nephritis, deficiency in IL-17C significantly ameliorated the course of GN in terms of renal tissue injury and kidney function. Deficiency of the unique IL-17C receptor IL-17 receptor E (IL-17RE) provided similar protection against crescentic GN. These protective effects associated with a reduced TH17 response. Bone marrow transplantation experiments revealed that IL-17C is produced by tissue-resident cells, but not by lymphocytes. Finally, IL-17RE was highly expressed by CD4+ TH17 cells, and loss of this expression prevented the TH17 responses and subsequent tissue injury in crescentic GN. Our findings indicate that IL-17C promotes TH17 cell responses and immune-mediated kidney disease via IL-17RE expressed on CD4+ TH17 cells. Targeting the IL-17C/IL-17RE pathway may present an intriguing therapeutic strategy for TH17-induced autoimmune disorders.

Organisation of lymphocytic infiltrates in ANCA-associated glomerulonephritis.

AIMS: Renal involvement in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis contributes to significant morbidity and mortality in patients. In chronic inflammation, B cells are recruited to the inflamed tissue and organised lymphoid structures have been described in several autoimmune diseases. The aim of this study was to correlate the lymphoid organisation in renal biopsies with renal outcome in ANCA-associated glomerulonephritis (GN). METHODS AND RESULTS: We investigated 112 renal biopsies from patients with newly diagnosed ANCA-associated necrotising GN. We identified four different levels of the intrarenal organisation of lymphocytes: T cells without B cells, scattered B and T cells, clustered lymphocytic infiltrates and nodular compartmentally arranged B and T cell aggregates. Almost half the patients showed clusters of B and T lymphocytes in their biopsies. In 15 of these biopsies, a higher degree of organisation with lymphocytic compartments was detected. Inflammatory cell organisation was associated with renal failure, but not with tubular atrophy and interstitial fibrosis. Patients with organised lymphocytic infiltrates in their biopsy had worse renal function during follow-up and were more likely to develop end stage renal disease. CONCLUSIONS: In the present study, we show that the renal lymphocytic organisation is associated with renal outcome in ANCA-associated GN. The organisation of the lymphocytic infiltrate may be a morphological correlate of a perpetual and exaggerated inflammation in renal ANCA disease. Classifying the lymphocytic infiltrate could help to predict renal outcome, and might therefore be used for individualised adjustments in the intensity and duration of immunosuppressive therapy.

Plasticity of Th17 Cells in Autoimmune Kidney Diseases.

The ability of CD4(+) T cells to differentiate into pathogenic Th1 and Th17 or protective T regulatory cells plays a pivotal role in the pathogenesis of autoimmune diseases. Recent data suggest that CD4(+) T cell subsets display a considerable plasticity. This plasticity seems to be a critical factor for their pathogenicity, but also for the potential transition of pathogenic effector T cells toward a more tolerogenic phenotype. The aim of the current study was to analyze the plasticity of Th17 cells in a mouse model of acute crescentic glomerulonephritis and in a mouse chronic model of lupus nephritis. By transferring in vitro generated, highly purified Th17 cells and by using IL-17A fate reporter mice, we demonstrate that Th17 cells fail to acquire substantial expression of the Th1 and Th2 signature cytokines IFN-γ and IL-13, respectively, or the T regulatory transcription factor Foxp3 throughout the course of renal inflammation. In an attempt to therapeutically break the stability of the Th17 phenotype in acute glomerulonephritis, we subjected nephritic mice to CD3-specific Ab treatment. Indeed, this treatment induced an immunoregulatory phenotype in Th17 cells, which was marked by high expression of IL-10 and attenuated renal tissue damage in acute glomerulonephritis. In summary, we show that Th17 cells display a minimum of plasticity in acute and chronic experimental glomerulonephritis and introduce anti-CD3 treatment as a tool to induce a regulatory phenotype in Th17 cells in the kidney that may be therapeutically exploited.

T-Bet Enhances Regulatory T Cell Fitness and Directs Control of Th1 Responses in Crescentic GN.

Th1 cells are central pathogenic mediators of crescentic GN (cGN). Mechanisms responsible for Th1 cell downregulation, however, remain widely unknown. Recently, it was proposed that activation of the Th1-characteristic transcription factor T-bet optimizes Foxp3+ regulatory T (Treg) cells to counteract Th1-type inflammation. Because very little is known about the role of T-bet+ Treg1 cells in inflammatory diseases, we studied the function of these cells in the nephrotoxic nephritis (NTN) model of cGN. The percentage of Treg1 cells progressively increased in kidneys of nephritic wild-type mice during the course of NTN, indicating their functional importance. Notably, naïve Foxp3CrexT-betfl/fl mice, lacking Treg1 cells, showed spontaneous skewing toward Th1 immunity. Furthermore, absence of Treg1 cells resulted in aggravated NTN with selectively dysregulated renal and systemic Th1 responses. Detailed analyses of Treg cells from Foxp3CrexT-betfl/fl mice revealed unaltered cytokine production and suppressive capacity. However, in competitive cotransfer experiments, wild-type Treg cells outcompeted T-bet-deficient Treg cells in terms of population expansion and expression levels of Foxp3, indicating that T-bet expression is crucial for general Treg fitness. Additionally, T-bet-deficient Treg cells lacked expression of the Th1-characteristic trafficking receptor CXCR3, which correlated with significant impairment of renal Treg infiltration. In summary, our data indicate a new subtype of Treg cells in cGN. These Treg1 cells are characterized by activation of the transcription factor T-bet, which enhances the overall fitness of these cells and optimizes their capacity to downregulate Th1 responses by inducing chemokine receptor CXCR3 expression.

Population pharmacokinetics and dosing simulations of ceftazidime in critically ill patients receiving sustained low-efficiency dialysis.

Objectives: To describe the population PKs of ceftazidime in critically ill patients receiving sustained low-efficiency dialysis (SLED). Patients and methods: This study was performed in ICUs of a university hospital. We collected blood samples during three consecutive days of SLED sessions in patients receiving ceftazidime. Concentration versus time curves were analysed using a population PKs approach with Pmetrics ® . Monte Carlo simulation for the first 24 h including a 6 h SLED session was performed with the final model. The fractional target attainment against the MIC of Pseudomonas aeruginosa was executed using targets of 50 and 100% fT > MIC . Results: In total, 211 blood samples of 16 critically ill patients under SLED were collected. SLED treatments were 299.3 (68.4) min in duration. A two-compartment linear population PK model was most appropriate. The mean (SD) CL of ceftazidime on SLED, and off SLED were 5.32 (3.2), 1.06 (1.0) L/h respectively. The PTA for 50% fT > MIC for a dose of 1 g intravenously every 8 h was 98%. Assuming a target of 100% fT > MIC a dose of 2 g every 12 h covers isolates with MIC ≤8 mg/L with a PTA of 96%. Conclusion: In critically ill patients receiving SLED, ceftazidime 1 g every 8 h and ceftazidime 2 g every 12 h appear to be sufficient for achieving traditional (50% fT > MIC ) and aggressive PD targets (100% fT > MIC ) for susceptible isolates (MIC ≤8 mg/L), respectively.

IL-17F Promotes Tissue Injury in Autoimmune Kidney Diseases.

The TH17 immune response has a central role in the pathogenesis of autoimmune diseases, implicating the TH17 master cytokine, IL-17A, as the critical mediator of diseases such as human and experimental crescentic GN. However, the relative importance of additional TH17 effector cytokines, including IL-17F, in immune-mediated tissue injury remains to be fully elucidated. Here, using a mouse model of acute crescentic GN (nephrotoxic nephritis), we identified CD4+ T cells and γδ T cells as the major cellular source of IL-17F in the inflamed kidney. Interventional studies using IL-17F gene-deficient mice, IL-17F-neutralizing antibodies, and adoptive transfer experiments into Rag1-/- mice demonstrated that CD4+ T cell-derived IL-17F drives renal tissue injury in acute crescentic GN. Notably, IL-17F-deficient nephritic mice had fewer renal infiltrating neutrophils than wild-type nephritic mice, and neutrophil depletion did not affect the course of GN in IL-17F-deficient mice. Moreover, in the chronic model of pristane-induced SLE, IL-17F-deficient mice developed less severe disease than wild-type mice, with respect to survival and renal injury. Finally, we show that IL-17F induced expression of the neutrophil-attracting chemokines CXCL1 and CXCL5 in kidney cells. The finding that IL-17F has a nonredundant function in the development of renal tissue injury in experimental GN might be of great importance for the development of anti-IL-17 cytokine therapies in TH17-mediated human autoimmune diseases.

RORγt(+)Foxp3(+) Cells are an Independent Bifunctional Regulatory T Cell Lineage and Mediate Crescentic GN.

Cells expressing both the regulatory T cell (Treg)-inducing transcription factor Foxp3 and the Th17 transcription factor RORγt have been identified (biTregs). It is unclear whether RORγt(+)Foxp3(+) biTregs belong to the Th17-specific Treg17 cells, represent intermediates during Treg/Th17 transdifferentiation, or constitute a distinct cell lineage. Because the role of biTregs in inflammatory renal disease is also unknown, we studied these cells in the nephrotoxic nephritis (NTN) model of acute crescentic GN. Induction of NTN resulted in rapid renal and systemic expansion of biTregs. Notably, analyses of the biTreg expression profile revealed production of both anti-inflammatory (IL-10, IL-35) and proinflammatory (IL-17) cytokines. Additionally, biTregs expressed a signature of surface molecules and transcription factors distinct from those of Th17 cells and conventional Tregs (cTregs), and biTregs were identified in Treg17-deficient mice. Finally, fate reporter and cell transfer studies confirmed that biTregs are not Treg/Th17 transdifferentiating cells. Therapeutic transfer of biTregs suppressed the development of nephritis to an extent similar to that observed with transferred cTregs, but in vitro studies indicated different mechanisms of immunosuppression for biTregs and cTregs. Intriguingely, as predicted from their cytokine profile, endogenous biTregs displayed additional proinflammatory functions in NTN that were abrogated by cell-specific deletion of RORγt. In summary, we provide evidence that RORγt(+)Foxp3(+) biTregs are a novel and independent bifunctional regulatory T cell lineage distinct from cTregs, Treg17 cells, and Th17 cells. Furthermore, biTregs appear to contribute to crescentic GN and hence may be novel therapeutic targets.

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.

Treg17 cells are programmed by Stat3 to suppress Th17 responses in systemic lupus.

Systemic lupus erythematosus (SLE) is a complex and potentially fatal autoimmune disorder. Although Th17 cells are thought to be central mediators of SLE, mechanisms underlying their counter regulation remain largely unknown. To help define this, we studied the function of the newly defined Stat3-dependent Th17-specific regulatory T cells (Treg17). Treg-specific deletion of Stat3 was achieved by generating Foxp3(Cre) × Stat3(fl/fl) mice and SLE was induced by intraperitoneal injection of pristane. Lack of Treg17 cells in these mice caused selectively enhanced peritoneal Th17 inflammation. Importantly, Treg17 deficiency also resulted in aggravated pulmonary vasculitis with increased percentages of Th17 cells and significantly higher mortality. Similarly, 4 and 9 months after pristane injection, analysis of renal and systemic immunity showed overshooting Th17 responses in the absence of Treg17 cells, associated with the aggravation of lupus nephritis. Expression of the Th17 characteristic trafficking receptor CCR6 was strikingly reduced on Tregs of Foxp3(Cre) × Stat3(fl/fl) mice, resulting in impaired renal Treg infiltration. Thus, Stat3-induced Treg17 cells are novel antiinflammatory mediators of SLE. One mechanism enabling Treg17 cells to target pathogenic Th17 responses is shared expression of the chemokine receptor CCR6.

CD4+ T Cell Fate in Glomerulonephritis: A Tale of Th1, Th17, and Novel Treg Subtypes.

Multiple studies have identified CD4+ T cells as central players of glomerulonephritis (GN). Cells of the Th1 and Th17 responses cause renal tissue damage, while Tregs mediate protection. Recently, a high degree of plasticity among these T cell lineages was proposed. During inflammation, Th17 cells were shown to have the potential of transdifferentiation into Th1, Th2, or alternatively anti-inflammatory Tr1 cells. Currently available data from studies in GN, however, do not indicate relevant Th17 to Th1 or Th2 conversion, leaving the Th17 cell fate enigmatic. Tregs, on the other hand, were speculated to transdifferentiate into Th17 cells. Again, data from GN do not support this concept. Rather, it seems that previously unrecognized subspecialized effector Treg lineages exist. These include Th1 specific Treg1 as well as Th17 directed Treg17 cells. Furthermore, a bifunctional Treg subpopulation was recently identified in GN, which secrets IL-17 and coexpresses Foxp3 together with the Th17 characteristic transcription factor RORγt. Similarities between these different and highly specialized effector Treg subpopulations with the corresponding T helper effector cell lineages might have resulted in previous misinterpretation as Treg transdifferentiation. In summary, Th17 cells have a relatively stable phenotype during GN, while, in the case of Tregs, currently available data suggest lineage heterogeneity rather than plasticity.