T-bet deficiency attenuates renal injury in experimental crescentic glomerulonephritis

A case of anti-GBM nephritis following centipede bites and COVID-19 vaccination

A case of newly developed anti-glomerular basement membrane (GBM) glomerulonephritis (GN) following centipede bites and COVID-19 vaccination is presented. A 70-year-old woman presented for investigation of mild fever, generalized fatigue, and macroscopic hematuria with no past history of renal disease. One year earlier, she had been bitten by a centipede. Based on the governmental policy, she was given the first COVID-19 vaccination, and the second injection was planned 3 weeks later. Accidentally, she was again bitten by a centipede, and the injured site had swollen severely. Based on a physician's judgment, the interval between vaccinations was extended to 8 weeks. One week after the second vaccination, macroscopic hematuria occurred suddenly, coincident with mild fever. Her serum anti-GBM titer was above the upper limit. There was no pulmonary involvement. Renal pathology showed anti-GBM GN, and she was treated with corticosteroid pulse therapy followed by sequential plasmapheresis. She had advanced renal dysfunction, but was independent of dialysis therapy during the one month of the remission induction therapy phase, and she is being treated with immunosuppressant therapy. Both vaccination and animal bites skew towards Th1 immunity, a key mechanism involved in the development of necrotizing GN evoked by anti-GBM antibody. Though there is no direct evidence for causality linking centipede bites, vaccination, and anti-GBM GN, the risk of anti-GBM GN appears to be increased by excessively induced Th1 immunity.

Splicing factor SRSF1 limits IFN-γ production via RhoH and ameliorates experimental nephritis

OBJECTIVE

CD4 T helper 1 (Th1) cells producing IFN-γ contribute to inflammatory responses in the pathogenesis of SLE and lupus nephritis. Moreover, elevated serum type II IFN levels precede the appearance of type I IFNs and autoantibodies in patient years before clinical diagnosis. However, the molecules and mechanisms that control this inflammatory response in SLE remain unclear. Serine/arginine-rich splicing factor 1 (SRSF1) is decreased in T cells from SLE patients, and restrains T cell hyperactivity and systemic autoimmunity. Our objective here was to evaluate the role of SRSF1 in IFN-γ production, Th1 differentiation and experimental nephritis.

METHODS

T cell-conditional Srsf1-knockout mice were used to study nephrotoxic serum-induced nephritis and evaluate IFN-γ production and Th1 differentiation by flow cytometry. RNA sequencing was used to assess transcriptomics profiles. RhoH was silenced by siRNA transfections in human T cells by electroporation. RhoH and SRSF1 protein levels were assessed by immunoblots.

RESULTS

Deletion of Srsf1 in T cells led to increased Th1 differentiation and exacerbated nephrotoxic serum nephritis. The expression levels of RhoH are decreased in Srsf1-deficient T cells, and silencing RhoH in human T cells leads to increased production of IFN-γ. Furthermore, RhoH expression was decreased and directly correlated with SRSF1 in T cells from SLE patients.

CONCLUSION

Our study uncovers a previously unrecognized role of SRSF1 in restraining IFN-γ production and Th1 differentiation through the control of RhoH. Reduced expression of SRSF1 may contribute to pathogenesis of autoimmune-related nephritis through these molecular mechanisms.

T helper cell trafficking in autoimmune kidney diseases

CD4⁺ T cells are key drivers of autoimmune diseases, including crescentic GN. Many effector mechanisms employed by T cells to mediate renal damage and repair, such as local cytokine production, depend on their presence at the site of inflammation. Therefore, the mechanisms regulating the renal CD4⁺ T cell infiltrate are of central importance. From a conceptual point of view, there are four distinct factors that can regulate the abundance of T cells in the kidney: (1) T cell infiltration, (2) T cell proliferation, (3) T cell death and (4) T cell retention/egress. While a substantial amount of data on the recruitment of T cells to the kidneys in crescentic GN have accumulated over the last decade, the roles of T cell proliferation and death in the kidney in crescentic GN is less well characterized. However, the findings from the data available so far do not indicate a major role of these processes. More importantly, the molecular mechanisms underlying both egress and retention of T cells from/in peripheral tissues, such as the kidney, are unknown. Here, we review the current knowledge of mechanisms and functions of T cell migration in renal autoimmune diseases with a special focus on chemokines and their receptors.

Hypertension and endothelial dysfunction in the pristane model of systemic lupus erythematosus

Autoimmune diseases such as psoriasis, rheumatoid arthritis, and systemic lupus erythematosus (SLE) have high rates of hypertension and cardiovascular disease. Systemic lupus erythematosus is a prototypic autoimmune disorder that primarily affects women of childbearing age and is associated with a loss of self-tolerance, autoreactive B and T lymphocytes, and the production of autoantibodies, especially to nuclear components. In this study, we hypothesized that the pristane-inducible model of SLE would develop hypertension and vascular dysfunction as the disease progressed. To test this hypothesis, female C57BL/6 mice were administered PBS or pristane. Seven months after pristane administration, mice developed various autoantibodies, including anti-dsDNA IgG, anti-ssDNA IgG, and anti-nRNP IgG, as well as hypergammaglobulinemia. Several other immunological changes, including increased circulating neutrophils and increased CD4- CD8- (double negative) thymocytes were also detected. Mean arterial pressure (MAP) was elevated in pristane-treated mice when compared to PBS-treated mice. In addition, second-order mesenteric arteries from pristine-treated mice had impaired relaxation to the endothelium-dependent vasodilator acetylcholine compared to PBS-treated mice. These data suggest that the immune system dysfunction present in the pristane model of lupus contributes to the development of hypertension and vascular dysfunction.

Immune regulation in renal inflammation

Renal inflammation, induced by autoantigen recognition or toxic drugs, leads to renal tissue injury and decline in kidney function. Recent studies have demonstrated the crucial role for regulatory T cells in suppressing pathogenic adaptive but also innate immune responses in the inflamed kidney. However, there is also evidence for other immune cell populations with immunosuppressive function in renal inflammation. This review summarizes mechanisms of immune cell regulation in immune-mediated glomerulonephritis and acute and chronic nephrotoxicity.

The role of Treg subtypes in glomerulonephritis

While Th1 and Th17 T effector cells are pathogenic drivers of glomerulonephritis (GN), regulatory T cells (Tregs) potently protect from renal tissue injury. Recently, it has become evident that different Treg subtypes exist. Among these are lineage specific Treg1 and Treg17 cells, which are specialized to down regulate either Th1 or Th17 T effector cell responses. Interestingly, programming of specialized Tregs and the corresponding T helper effector cells depend on the same lineage specific master transcription factors Tbet (Th1/Treg1) and STAT3 (Th17/Treg17). Furthermore, early control of T effector cell priming in secondary lymphoid organs by specialized Tregs was described. One central mechanism of T effector cell control by the corresponding Treg subtype seems to be expression of the same chemokine receptor repertoire, which facilitates their co-localization. More recently, another intriguing Treg subset was identified, which expresses Foxp3 together with the Th17 characteristic transcription factor RORγt. While these Foxp3⁺RORγt⁺ Tregs were shown to be highly immunosuppressive, studies in GN also identified pro-inflammatory potential via secretion of IL-17. Many questions regarding this unusual Treg subset remain, including their origin, stability, and mechanisms of action. Further characterization of the renal Treg landscape during GN will help to identify novel immunosuppressive mechanisms and develop successful Treg-directed therapies. In this review, we summarize the currently available data about specialized Treg subsets and discuss their role in GN.

Tocilizumab monotherapy uncovered the role of the CCL22/17-CCR4+ Treg axis during remission of crescentic glomerulonephritis

Objectives

Tocilizumab (TCZ) is a humanised anti‐interleukin (IL)‐6 receptor (IL‐6R) monoclonal antibody that is a promising agent to treat various autoimmune diseases. However, the mechanism of TCZ efficacy is unclear. This study aims to elucidate the relationship between Tregs and IL‐6R blockade in autoimmunity‐mediated renal disease based on a TCZ‐treated cohort of patients with anti‐neutrophil cytoplasmic antibody (ANCA)‐associated vasculitis (AAV) and in an experimental model of crescentic glomerulonephritis (cGN).

Methods

We examined multiple serum levels of cytokines and chemokines and peripheral blood mononuclear cells in patients with AAV who received TCZ monotherapy and achieved drug‐free remission. Moreover, we investigated the mechanistic role of IL‐6R blockade in accelerated cGN model to analyse the local sites of inflammation.

Results

Serum chemokines CCL22 and CCL17, in addition to the CCR4⁺Foxp3⁺ Treg population, increased in patients who demonstrated drug‐free remission after the cessation of TCZ. In the cGN model, IL‐6R blockade ameliorated the disease, elevated CCL22/17 in CD206⁺CD11b⁺CD11c⁺ kidney M2‐like type macrophages, and increased the migration of Tregs into the kidney and regional lymph nodes. The local administration of CCL22 in the kidney facilitated Treg accumulation and reduced glomerular crescent formation.

Conclusions

This study revealed a new mechanism whereby effector Tregs migrate into the inflammatory kidney via the CCL22/17–CCR4 axis that is facilitated by M2‐like type macrophages that are induced by IL‐6R blockade.

IL-17 in Renal Immunity and Autoimmunity

The kidney is an organ particularly susceptible to damage caused by infections and autoimmune conditions. Renal inflammation confers protection against microbial infections. However, if unchecked, unresolved inflammation may lead to kidney damage. Although proinflammatory cytokine IL-17 is required for immunity against extracellular pathogens, dysregulated IL-17 response is also linked to autoimmunity. In this review, we will discuss the current knowledge of IL-17 activity in the kidney in context to renal immunity and autoimmunity and raise the intriguing question to what extent neutralization of IL-17 is beneficial or harmful to renal inflammation.

Group 1 innate lymphoid cells are involved in the progression of experimental anti-glomerular basement membrane glomerulonephritis and are regulated by peroxisome proliferator-activated receptor α

Innate lymphoid cells play an important role in the early effector cytokine-mediated response. In Wistar Kyoto rats, CD8⁺ non-T lymphocytes (CD8⁺Lym) infiltrate into glomeruli during the development of anti-glomerular basement membrane (anti-GBM) glomerulonephritis. Here, we examined the profiles and roles of CD8⁺Lym in anti-GBM glomerulonephritis. The regulation of CD8⁺Lym by peroxisome proliferator-activated receptor (PPAR)-α in anti-GBM glomerulonephritis was also evaluated. Glomerular infiltrating CD8⁺Lym were lineage-negative cells that showed markedly high expression of IFN-γ and T-bet mRNAs but not Eomes, indicating these cells are group 1 innate lymphoid cells. In anti-GBM glomerulonephritis, the glomerular mRNAs of innate lymphoid cell-related cytokines (IFN-γ and TNF-α) and chemokines (CXCL9, CXCL10, and CXCL11) are significantly increased. Treatment with a PPARα agonist ameliorated renal injury, with reduced expression of these mRNAs. In vitro, enhanced IFN-γ production from innate lymphoid cells upon IL-12 and IL-18 stimulation was reduced by the PPARα agonist. Moreover, CXCL9 mRNA in glomerular endothelial cells and CXCL9, CXCL10, and CXCL11 mRNAs in podocytes and macrophages were upregulated by IFN-γ, whereas the PPARα agonist downregulated their expression. We also detected the infiltration of innate lymphoid cells into glomeruli in human anti-GBM glomerulonephritis. Thus, innate lymphoid cells are involved in the progression of anti-GBM glomerulonephritis and regulated directly or indirectly by PPARα. Our findings suggest that innate lymphoid cells could serve as novel therapeutic targets for anti-GBM glomerulonephritis.

The co-inhibitory molecule PD-L1 contributes to regulatory T cell-mediated protection in murine crescentic glomerulonephritis

Immune-mediated glomerular diseases like crescentic glomerulonephritis (cGN) are driven by inappropriately regulated cellular and humoral immune responses subsequently leading to renal tissue injury. Recent studies demonstrated the crucial role for regulatory T cells (Tregs) in suppressing pathogenic T-cell responses during nephrotoxic nephritis (NTN), a murine model of cGN. However, mechanisms of immune regulation in cGN are less clear. Here, we aim at investigating the role of the co-inhibitory PD-1/PD-L1 pathway in Treg-mediated suppression of renal inflammation. We demonstrated that Foxp3⁺ Tregs expressing PD-L1 infiltrate the kidney during NTN. Inhibition of PD-L1 signalling by using PD-L1^−/− mice or by blockage of PD-L1 in wildtype mice resulted in an increased Treg frequency in the inflamed kidney. However, mice lacking PD-L1 developed more severe NTN associated with an elevated pathogenic renal Th1 immune response, which was reversed by blockage of IFNγ in these mice. Interestingly, lack of PD-L1 altered the gene expression profile of Tregs in homeostasis and kidney inflammation. Functionally, Tregs from nephritic PD-L1^−/− mice had impaired suppressive capacity in vitro and failed to protect from NTN in vivo. Thus, PD-L1 displays a protective role in NTN, which is related to Treg-mediated suppression of the Th1 immune response.

Plasticity and heterogeneity of Th17 in immune-mediated kidney diseases

Anti-neutrophil cytoplasmatic antibody (ANCA)-associated glomerulonephritis, anti-glomerular basement membrane (GBM) glomerulonephritis and lupus nephritis are the most common causes of rapid progressive glomerulonephritis (RPGN) in the Western world. These aggressive forms of autoimmune kidney diseases significantly contribute to end-stage renal disease and are associated with high morbidity and mortality. Moreover, patients show significant heterogeneity with respect to clinical outcome and response to therapy. T cell infiltration is a morphological hallmark of RPGN and it is a critical driver of kidney injury. Different CD4⁺ T cell subsets that are endowed with distinct regulatory and effector functions are involved in this detrimental inflammatory process. In particular, the identification and functional characterization of IL-17-expressing CD4⁺ Th17 cells have substantially advanced our understanding of organ-specific autoimmunity. In experimental models of crescentic and proliferative GN, including ANCA-associated GN, anti-GBM-GN and lupus nephritis, the Th17/IL-17 axis significantly contributes to renal tissue damage. In patients with ANCA-associated GN or lupus nephritis, IL-17 serum levels correlated with disease activity. Moreover, Th17 cells are present in the kidneys of these patients and represents a topic of intense ongoing clinical and basic research. Importantly, recent studies have challenged the view of CD4⁺ T cells subsets as terminally differentiated homogenous cells, showing that T cells, in particular Th17 cells, are much more flexible and heterogeneous than previously thought. However, analysis of Th17 cell fate in mouse models of autoimmune kidney disease revealed a high degree of stability within these cells, an observation that is in contrast to Th17 cells in other models of autoimmune diseases including experimental autoimmune encephalomyelitis. Interestingly, anti-CD3 treatment interferes with stable Th17 cells and induces a potential regulatory phenotype in Th17 cells, highlighting the therapeutic potential of targeting pathogenic Th17 cells in autoimmunity. In this review, we discuss the current knowledge of Th17 cell plasticity and heterogeneity in autoimmune kidney diseases with a special focus on the underlying mechanisms of this process and debate if Th17 cell plasticity is beneficial or harmful to renal inflammation.

Role of immune cells in crystal-induced kidney fibrosis

Chronic kidney diseases can lead to kidney fibrosis, which can be considered a futile attempt of tissue healing to replaces functional kidney tissue with connective tissue, basically forming a scar. Chronic inflammation is a frequent cause of kidney fibrosis. Classical as well as recently discovered immune cell subsets and their molecular mediators have been intensively investigated for their contribution to kidney fibrosis and their potential as therapeutic targets. Here we review the current knowledge about the role of immune cells in crystal-induced renal fibrosis.

ID3 may protect mice from anti‑GBM glomerulonephritis by regulating the differentiation of Th17 and Treg cells

Anti‑glomerular basement membrane glomerulonephritis (anti‑GBM GN) is an autoimmune disease that leads to severe and rapidly progressive renal injury. Inhibition of DNA‑binding factor 3 (ID3) serves a key role in autoimmune diseases, such as asthma and Sjögren's syndrome, and in experimental allergic encephalitis models. However, the role of ID3 in the progression of anti‑GBM GN remains unknown. In the present study, ID3 mRNA expression increased between 3‑ and 20‑fold in the renal tissues of anti‑GBM GN mice compared with the Control group, with a peak at day 14 post‑induction. In addition, ID3 protein expression was upregulated from day 7 onwards. The expression of ID3 was also examined in the spleen, and was demonstrated to be increased in the spleen of nephritic mice. T helper 17 (Th17) cells and regulatory T (Treg) cells were present throughout the entire period of observation (from day 7 to day 28) in anti‑GBM GN mice, which may vary at different time points, accompanied with the expression of ID3. In vitro, ID3 expression was increased when CD4+ T cells differentiated into Tregs; however, expression was lower in Th17 cells. Following treatment with ID3 small interfering RNA, RAR‑related orphan receptor γt, but not forkhead box P3, expression increased. Furthermore, increased expression of interleukin‑17A was also observed when ID3 was blocked. In addition, ID3 was able to interact with transcription factor E2A. A significant increase in binding between ID3 and E2A was observed in anti‑GBM GN from day 7 onwards, with a peak at day 14 in both renal tissue and spleen. In conclusion, ID3 may be involved in the differentiation of Th17 and Tregs by downregulating Th17 cells, which is probably associated with binding to E2A. The present results suggested that ID3 may offer protection against anti‑GBM GN in mice.

Early life stress induces immune priming in kidneys of adult male rats

Early life stress (ELS) in humans is associated with elevated proinflammatory markers. We hypothesized that ELS induces activation of the immune response in a rat model of ELS, maternal separation (MatSep), in adulthood. MatSep involves separating pups from the dam from postnatal day 2 to postnatal day 14 for 3 h/day. Control rats are nonseparated littermates. We determined circulating and renal immune cell numbers, renal immune cell activation markers, renal cytokine levels, and the renal inflammatory gene expression response to low-dose lipopolysaccharide (LPS) in male MatSep and control rats. We observed that MatSep did not change the percentage of gated events for circulating CD3⁺, CD4⁺, CD8⁺, and CD4⁺/Foxp3⁺ cells or absolute numbers of mononuclear and T cells in the circulation and kidneys; however, MatSep led to an increase in activation of renal neutrophils as well as CD44⁺ cells. Renal toll-like receptor 4 (TLR4) and interleukin 1 beta (IL-1β) was significantly increased in MatSep rats, specifically in the outer and inner medulla and distal nephron, respectively. Evaluation of renal inflammatory genes showed that in response to a low-dose LPS challenge (2 mg/kg iv) a total of 20 genes were significantly altered in kidneys from MatSep rats (17 genes were upregulated and 3 were downregulated), as opposed to no significant differences in gene expression in control vs. control + LPS groups. Taken together, these findings indicate that MatSep induces priming of the immune response in the kidney.

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.

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 Foxp3^CrexT-bet^fl/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 Foxp3^CrexT-bet^fl/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.

IL-17 Expression in the Time Course of Acute Anti-Thy1 Glomerulonephritis

BACKGROUND

Interleukin-17 (IL-17) is a new pro-inflammatory cytokine involved in immune response and inflammatory disease. The main source of IL-17 is a subset of CD4+ T-helper cells, but is also secreted by non-immune cells. The present study analyzes expression of IL-17 in the time course of acute anti-thy1 glomerulonephritis and the role of IL-17 as a potential link between inflammation and fibrosis.

METHODS

Anti-thy1 glomerulonephritis was induced into male Wistar rats by OX-7 antibody injection. After that, samples were taken on days 1, 5, 10 (matrix expansion phase), 15 and 20 (resolution phase). PBS-injected animals served as controls. Proteinuria and histological matrixes score served as the main markers for disease severity. In in vitro experiments, NRK-52E cells were used. For cytokine expressions, mRNA and protein levels were analyzed by utilizing RT-PCR, in situ hybridization and immunofluorescence.

RESULTS

Highest IL-17 mRNA-expression (6.50-fold vs. con; p<0.05) was found on day 5 after induction of anti-thy1 glomerulonephritis along the maximum levels of proteinuria (113 ± 13 mg/d; p<0.001), histological glomerular-matrix accumulation (82%; p<0.001) and TGF-β1 (2.2-fold; p<0.05), IL-6 mRNA expression (36-fold; p<0.05). IL-17 protein expression co-localized with the endothelial cell marker PECAM in immunofluorescence. In NRK-52E cells, co-administration of TGF-β1 and IL-6 synergistically up-regulated IL-17 mRNA 4986-fold (p<0.001).

CONCLUSIONS

The pro-inflammatory cytokine IL-17 is up-regulated in endothelial cells during the time course of acute anti-thy1 glomerulonephritis. In vitro, NRK-52E cells secrete IL-17 under pro-fibrotic and pro-inflammatory conditions.

AKAP9 regulates activation-induced retention of T lymphocytes at sites of inflammation

The mechanisms driving T cell homing to lymph nodes and migration to tissue are well described but little is known about factors that affect T cell egress from tissues. Here, we generate mice with a T cell-specific deletion of the scaffold protein A kinase anchoring protein 9 (AKAP9) and use models of inflammatory disease to demonstrate that AKAP9 is dispensable for T cell priming and migration into tissues and lymph nodes, but is required for T cell retention in tissues. AKAP9 deficiency results in increased T cell egress to draining lymph nodes, which is associated with impaired T cell re-activation in tissues and protection from organ damage. AKAP9-deficient T cells exhibit reduced microtubule-dependent recycling of TCRs back to the cell surface and this affects antigen-dependent activation, primarily by non-classical antigen-presenting cells. Thus, AKAP9-dependent TCR trafficking drives efficient T cell re-activation and extends their retention at sites of inflammation with implications for disease pathogenesis.

A-kinase anchoring protein 9 (AKAP9) is a scaffold protein that binds signalling proteins and regulates microtubules. Here the authors show that during inflammation AKAP9 in T cells is required for their reactivation and retention at the inflammation site and that its deletion protects from inflammation-induced organ damage.

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.

Local IL-17 Production Exerts a Protective Role in Murine Experimental Glomerulonephritis

IL-17 is a pro-inflammatory cytokine implicated in the pathogenesis of glomerulonephritis and IL-17 deficient mice are protected from nephrotoxic nephritis. However, a regulatory role for IL-17 has recently emerged. We describe a novel protective function for IL-17 in the kidney. Bone marrow chimeras were created using wild-type and IL-17 deficient mice and nephrotoxic nephritis was induced. IL-17 deficient hosts transplanted with wild-type bone marrow had worse disease by all indices compared to wild-type to wild-type bone marrow transplants (serum urea p<0.05; glomerular thrombosis p<0.05; tubular damage p<0.01), suggesting that in wild-type mice, IL-17 production by renal cells resistant to radiation is protective. IL-17 deficient mice transplanted with wild-type bone marrow also had a comparatively altered renal phenotype, with significant differences in renal cytokines (IL-10 p<0.01; IL-1β p<0.001; IL-23 p<0.01), and macrophage phenotype (expression of mannose receptor p<0.05; inducible nitric oxide synthase p<0.001). Finally we show that renal mast cells are resistant to radiation and produce IL-17, suggesting they are potential local mediators of disease protection. This is a novel role for intrinsic cells in the kidney that are radio-resistant and produce IL-17 to mediate protection in nephrotoxic nephritis. This has clinical significance as IL-17 blockade is being trialled as a therapeutic strategy in some autoimmune diseases.

Cytokines: Names and Numbers You Should Care About

Cytokines play an important role in host defense against microorganisms. They orchestrate innate immunity by inducing protective local inflammation and systemic acute phase responses. Cytokines are important in initiating, amplifying, directing, mediating, and regulating adaptive immunity. Unfortunately, they may also direct tissue damage if excessive responses occur or if they are involved in directing and mediating autoimmunity. Under these circumstances, cytokines are potential therapeutic targets. Over the last 20 years, we have seen the successful development and clinical implementation of biologic strategies that target key cytokines in specific inflammatory diseases with efficacy, specificity, and toxicity profiles challenging conventional drug therapies. These therapies are finding new applications and many new agents show promise. Unfortunately, these new cytokine-based therapies have had little effect on renal disease. This review provides evidence that common renal diseases, including those causing AKI and the autoimmune proliferative and crescentic forms of GN, have cytokine mediation profiles that suggest they would be susceptible to cytokine-targeting therapeutic strategies.

Association between the IL17RA rs4819554 polymorphism and reduced renal filtration rate in the Spanish RENASTUR cohort

DNA variants at the genes that encode components of the IL17-pathway may contribute to the risk of impaired renal function/chronic kidney disease. Our aim was to determine whether common IL17RA single nucleotide polymorphisms (SNPs) were associated with a reduced estimated glomerular filtration rate (eGFR) in a cohort of healthy elderly individuals (n=650). We found a significantly higher frequency of SNP rs4819554 AA homozygotes among individuals with eGFR<60 ml/min/1.73 m(2) (n=90) (p=0.005, OR=2.11; 1.26-3.54), an effect that was independent of the presence of type 2 diabetes. Allele rs4819554 A had been associated to the risk of developing end stage renal disease, and was also linked to an increased expression of the IL17RA protein and higher levels of Th17 cell subsets. A scenario in which the pro-inflammatory role of the IL17-pathway contributes to kidney damage might explain the association between Il17RA polymorphisms and an impaired renal function.

The pathological role of IL-18Rα in renal ischemia/reperfusion injury

Interleukin (IL)-18 is a proinflammatory cytokine produced by leukocytes and parenchymal cells (eg, tubular epithelial cells (TECs), mesangial cells, and podocytes). IL-18 receptor (IL-18R) is expressed on these cells in the kidney during ischemia/reperfusion injury (IRI), but its role in this injury is unknown. Fas/Fas ligand (FasL) is also involved in the pathogenesis of renal IRI via tubular apoptosis. In addition, IL-18 enhances the expression of FasL on TECs, but the mechanism underlying this enhancement is not known. Here we used IL-18Rα-deficient mice to explore the pathological role of IL-18Rα in renal IRI. We found that compared to wild-type (WT) mice with renal IRI as an acute kidney injury (AKI), the IL-18Rα-deficient mice demonstrated decreased renal function (as represented by blood urea nitrogen), tubular damage, an increased accumulation of leukocytes (CD4+ T cells, neutrophils, and macrophages), upregulated early AKI biomarkers (ie, urinary kidney injury molecule-1 levels), and increased mRNA expressions of proinflammatory cytokines (IL-1β, IL-12p40, and IL-18) and chemokines (intercellular adhesion molecule-1 and CCL2/monocyte chemoattractant protein-1). The mRNA expression of FasL in the kidney was increased in the IL-18Rα-deficient mice compared to the WT mice. The adoptive transfer of splenocytes by WT mice led to decreased renal IRI compared to the IL-18Rα-deficient mice. In vitro, the mRNA expression of FasL on TECs was promoted in the presence of recombinant IL-18. These data reveal that IL-18Rα has an anti-inflammatory effect in IRI-induced AKI. Above all, IL-18 enhanced the inflammatory mechanisms and the apoptosis of TECs through the Fas/FasL pathway by blocking IL-18Rα.

Update on crescentic glomerulonephritis

The recent years have seen a number of major progresses in the field of extracapillary glomerulonephritis. This entity is the final damage caused by unrelated immunological disorders such as immune complexes glomerular deposits or microvascular injury caused by proinflammatory cytokines, neutrophil extracellular traps (NET), and cell adhesion molecules in the context of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). This review provides a summary of recent advances in the understanding of crescentic glomerulonephritis, focusing on interplays of local immune cells and on local mediators participating to crescent formation especially in anti-glomerular basement membrane (anti-GBM) antibody disease. The recent advances about AAV and lupus nephritis are covered by other chapters of this issue. Nevertheless, these considerations may apply to the general case of crescentic glomerulonephritis of all causes.

Galectin-9 ameliorates anti-GBM glomerulonephritis by inhibiting Th1 and Th17 immune responses in mice

Antiglomerular basement membrane glomerulonephritis (anti-GBM GN) is a Th1- and Th17-predominant autoimmune disease. Galectin-9 (Gal-9), identified as the ligand of Tim-3, functions in diverse biological processes and leads to the apoptosis of CD4(+)Tim-3(+) T cells. It is still unclear how Gal-9 regulates the functions of Th1 and Th17 cells and prevents renal injury in anti-GBM GN. In this study, Gal-9 was administered to anti-GBM GN mice for 7 days. We found that Gal-9 retarded the increase of Scr, ameliorated renal tubular injury, and reduced the formation of crescents. The infiltration of Th1 and Th17 cells into the spleen and kidneys significantly decreased in Gal-9-treated nephritic mice. The reduced infiltration of Th1 and Th17 cells might be associated with the downregulation of CCL-20, CXCL-9, and CXCL-10 mRNAs in the kidney. In parallel, the blood levels of IFN-γ and IL-17A declined in Gal-9-treated nephritic mice at days 21 and 28. In addition, an enhanced Th2 cell-mediated immune response was observed in the kidneys of nephritic mice after a 7-day injection of Gal-9. In conclusion, the protective role of Gal-9 in anti-GBM GN is associated with the inhibition of Th1 and Th17 cell-mediated immune responses and enhanced Th2 immunity in the kidney.

MicroRNA-155 drives TH17 immune response and tissue injury in experimental crescentic GN

CD4(+) T cells play a pivotal role in the pathogenesis of autoimmune disease, including human and experimental crescentic GN. Micro-RNAs (miRs) have emerged as important regulators of immune cell development, but the impact of miRs on the regulation of the CD4(+) T cell immune response remains to be fully clarified. Here, we report that miR-155 expression is upregulated in the kidneys of patients with ANCA-associated crescentic GN and a murine model of crescentic GN (nephrotoxic nephritis). To elucidate the potential role of miR-155 in T cell-mediated inflammation, nephritis was induced in miR-155(-/-) and wild-type mice. The systemic and renal nephritogenic TH17 immune response decreased markedly in nephritic miR-155(-/-) mice. Consistent with this finding, miR-155-deficient mice developed less severe nephritis, with reduced histologic and functional injury. Adoptive transfer of miR-155(-/-) and wild-type CD4(+) T cells into nephritic recombination activating gene 1-deficient (Rag-1(-/-)) mice showed the T cell-intrinsic importance of miR-155 for the stability of pathogenic TH17 immunity. These findings indicate that miR-155 drives the TH17 immune response and tissue injury in experimental crescentic GN and show that miR-155 is a potential therapeutic target in TH17-mediated diseases.

Regulation of pathogenic Th17 cell differentiation by IL-10 in the development of glomerulonephritis

Although it is clear that T helper (Th)17 cells play a pathologic role in the pathogenesis of several inflammatory diseases, the contribution and regulation of pathogenic Th17 cells in the development of glomerulonephritis are still not fully understood. Herein, we show that IL-10-deficient mice exhibit exacerbation of glomerulonephritis after induction with anti-glomerular basement membrane globulin, with enhanced pathogenic Th17 immune responses. We further demonstrate that Rag1(-/-) mice reconstituted with IL-10(-/-) CD4(+) T cells develop more severe glomerulonephritis after induction of anti-glomerular basement membrane disease, with more infiltration of inflammatory cells into the kidneys. Finally, IL-17 and interferon γ double-positive cells were significantly increased in IL-10(-/-) CD4(+) T-cell cultures under pathogenic Th17 conditions compared with wild-type cell cultures. These findings suggest that T-cell-derived IL-10 plays a critical suppressive role in the control of pathogenic Th17 cell differentiation and highlights the importance of IL-10 as protection against glomerulonephritis development.

Deficiency of annexin A1 in CD4+ T cells exacerbates T cell-dependent inflammation

Annexin A1 (AnxA1) is recognized as an endogenous anti-inflammatory molecule. However, its effects on the adaptive immune response and, in particular, on T cells remain unclear. In this study, we investigated the actions of AnxA1 in three distinct models of T cell-mediated inflammation. In contact hypersensitivity, collagen-induced arthritis, and inflammation induced by OT-II TCR transgenic T cells responding to OVA, AnxA1 deficiency significantly increased Ag-induced T cell proliferation and the resultant level of inflammation. In the contact hypersensitivity model, this was associated with increased adhesion of CD4(+) T cells, CD8(+) T cells, and neutrophils in the dermal microvasculature, as well as increased T cell expression of RORγt and IL-17A. In collagen-induced arthritis, deficiency of endogenous AnxA1 increased susceptibility to arthritis and Ag-specific T cell activation. Deficiency of AnxA1 also increased OVA-induced cutaneous delayed-type hypersensitivity and IFN-γ and IL-17 release. Transfer experiments using CD4(+) T cells from AnxA1(-/-) mice demonstrated that the absence of AnxA1 solely in T cells resulted in increased inflammatory responses in wild-type recipients. Similarly, experiments using AnxA1(-/-) OT-II CD4(+) T cells demonstrated that the absence of AnxA1 in T cells was sufficient to induce increased Ag-specific CD4(+) T cell proliferation in vivo, augment T cell production of IFN-γ, IL-17, TNF, and IL-6, and increase Akt, ERK, and p38 activation. Together, these findings indicate that T cell-expressed AnxA1 functions to attenuate T cell-driven inflammatory responses via T cell-intrinsic effects on intracellular signaling, proliferation, and Th1/Th17 cytokine release.

Gene polymorphisms of interleukin-17 and interleukin-17 receptor are associated with end-stage kidney disease

BACKGROUND

Inflammation could be a causal factor in progression of chronic kidney disease. To date, there is convincing experimental and clinical evidence to support the notion that interleukin (IL)-17-producing T cells contribute to kidney injury in renal diseases. However, the genetic relationship between end-stage renal disease (ESRD) and the T-helper 17 pathway has never been studied. In this study, we hypothesized that polymorphisms of IL-17 or their receptors may be associated with ESRD.

METHODS

A total of 290 nondiabetic ESRD patients and 289 normal controls were included. We analyzed 13 single nucleotide polymorphisms located within the four genes of IL17A, IL17E, IL17RA and IL17RB.

RESULTS

The ESRD patients had a significantly higher allele frequency compared to control subjects for the IL17E rs10137082*C and IL17RA rs4819554*A alleles. Genotyping analysis demonstrated that 2 SNPs among 13 were significantly associated with ESRD after adjusting for age and sex, which were shown by IL17E rs10137082 (odds ratio (OR) 1.48 in codominant 1, OR 1.54 in dominant, OR 1.47 in log-additive) and IL17RA rs4819554 (OR 1.46 in codominant 1, OR 1.79 in codominant 2, OR 1.54 in dominant, OR 1.39 in log-additive).

CONCLUSIONS

Two polymorphisms within the IL17E and IL17RA genes are associated with ESRD independent of age and sex. This is the first finding to suggest that genetic variations of IL17 genes affect the risk of development of ESRD.

Signaling through the interleukin-18 receptor α attenuates inflammation in cisplatin-induced acute kidney injury

Interleukin (IL)-18 is produced by leukocytes and renal parenchymal cells (tubular epithelial cells, podocytes, and mesangial cells). The IL-18 receptor (IL-18R) is expressed on these cells in cisplatin-induced acute kidney injury, but the role of IL-18R is unknown. To help define this, we compared IL-18Rα knockout with wild-type mice in cisplatin-induced acute kidney injury and found deteriorated kidney function, tubular damage, increased accumulation of leukocytes (CD4(+) and CD8(+) T-cells, macrophages, and neutrophils), upregulation of early kidney injury biomarkers (serum TNF, urinary IL-18, and KIM-1 levels), and increased expression of pro-inflammatory molecules downstream of IL-18. In vitro, leukocytes from the spleen and kidneys of the knockout mice produced greater amounts of pro-inflammatory cytokines upon stimulation with concanavalin A compared to that in wild-type mice. Levels of the suppressor of cytokine signaling 1 and 3 (negative regulators of cytokine signaling) were reduced in the spleen and kidneys of IL-18Rα-deficient compared to wild-type mice. Adoptive transfer of wild-type splenocytes by IL-18Rα-deficient mice led to decreased cisplatin nephrotoxicity compared to control IL-18Rα-deficient mice. In contrast, anti-IL-18Rα and anti-IL-18Rβ antibody treatment tended to increase cisplatin nephrotoxicity in wild-type mice. Thus, signaling through IL-18Rα activates both inflammation-suppressing and pro-injury pathways in cisplatin-induced acute kidney injury.

A novel role for type 1 angiotensin receptors on T lymphocytes to limit target organ damage in hypertension

RATIONALE

Human clinical trials using type 1 angiotensin (AT(1)) receptor antagonists indicate that angiotensin II is a critical mediator of cardiovascular and renal disease. However, recent studies have suggested that individual tissue pools of AT(1) receptors may have divergent effects on target organ damage in hypertension.

OBJECTIVE

We examined the role of AT(1) receptors on T lymphocytes in the pathogenesis of hypertension and its complications.

METHODS AND RESULTS

Deficiency of AT(1) receptors on T cells potentiated kidney injury during hypertension with exaggerated renal expression of chemokines and enhanced accumulation of T cells in the kidney. Kidneys and purified CD4(+) T cells from "T cell knockout" mice lacking AT(1) receptors on T lymphocytes had augmented expression of Th1-associated cytokines including interferon-γ and tumor necrosis factor-α. Within T lymphocytes, the transcription factors T-bet and GATA-3 promote differentiation toward the Th1 and Th2 lineages, respectively, and AT(1) receptor-deficient CD4(+) T cells had enhanced T-bet/GATA-3 expression ratios favoring induction of the Th1 response. Inversely, mice that were unable to mount a Th1 response due to T-bet deficiency were protected from kidney injury in our hypertension model.

CONCLUSIONS

The current studies identify an unexpected role for AT(1) receptors on T lymphocytes to protect the kidney in the setting of hypertension by favorably modulating CD4(+) T helper cell differentiation.

Chemokines play a critical role in the cross-regulation of Th1 and Th17 immune responses in murine crescentic glomerulonephritis

Th1 and Th17 subtype effector CD4(+) T cells are thought to play a critical role in the pathogenesis of human and experimental crescentic glomerulonephritis. The time course, mechanism, and functions of Th1 and Th17 cell recruitment, and their potential interaction in glomerulonephritis, however, remain to be elucidated. We performed interventional studies using IL-17- and IFN-γ-gene-deficient mice, as well as neutralizing antibodies that demonstrated the importance of the Th17-mediated immune response during the early phase of the disease. At a later stage, we found that Th1 cells were critical mediators of renal tissue injury. Early recruitment of IL-17-producing Th17 cells triggered expression of the chemokine CXCL9 in the kidney that drove the infiltration of Th1 cells bearing its receptor CXCR3. At a later stage, Th1 cell-derived IFN-γ was found to inhibit local chemokine CCL20 expression, acting through its receptor CCR6 on Th17 cells, thereby limiting the renal Th17 immune response. Thus, our findings provide mechanistic evidence for a cytokine-chemokine-driven feedback loop that orchestrates the observed differential Th1 and Th17 cell infiltration into the inflamed kidney. This contributes to the observed time-dependent function of these two major pathogenic effector CD4(+) T cell subsets in crescentic glomerulonephritis.

Endogenous Tim-1 (Kim-1) promotes T-cell responses and cell-mediated injury in experimental crescentic glomerulonephritis

The T-cell immunoglobulin mucin 1 (Tim-1) modulates CD4(+) T-cell responses and is also expressed by damaged proximal tubules in the kidney where it is known as kidney injury molecule-1 (Kim-1). We sought to define the role of endogenous Tim-1 in experimental T-cell-mediated glomerulonephritis induced by sheep anti-mouse glomerular basement membrane globulin acting as a planted foreign antigen. Tim-1 is expressed by infiltrating activated CD4(+) cells in this model, and we studied the effects of an inhibitory anti-Tim-1 antibody (RMT1-10) on immune responses and glomerular disease. Crescentic glomerulonephritis, proliferative injury, and leukocyte accumulation were attenuated following treatment with anti-Tim-1 antibodies, but interstitial foxp3(+) cell accumulation and interleukin-10 mRNA were increased. T-cell proliferation and apoptosis decreased in the immune system along with a selective reduction in Th1 and Th17 cellular responses both in the immune system and within the kidney. The urinary excretion and renal expression of Kim-1 was reduced by anti-Tim-1 antibodies reflecting diminished interstitial injury. The effects of anti-Tim-1 antibodies were not apparent in the early phase of renal injury, when the immune response to sheep globulin was developing. Thus, endogenous Tim-1 promotes Th1 and Th17 nephritogenic immune responses and its neutralization reduces renal injury while limiting inflammation in cell-mediated glomerulonephritis.

Search for genetic association between IgA nephropathy and candidate genes selected by function or by gene mapping at loci IGAN2 and IGAN3

BACKGROUND

IgA nephropathy (IgAN) is not generally considered a hereditary disease, even though extensive evidence suggests an undefined genetic influence. Linkage analysis identified a number of genome regions that could contain variations linked to IgAN.

METHODS

In this case-control association study, genes possibly involved in the development of IgAN were investigated. DNA samples from 460 North Italian patients with IgAN and 444 controls were collected. Candidate genes were selected based on their possible functional involvement (6 genes) or because of their location within linkage-identified genomic regions IGAN2 and IGAN3 (5 and 13 genes within chromosome 4q26-31 and 17q12-22, respectively). One hundred and ninety-two tag and functional single-nucleotide polymorphisms (SNPs) were typed with Veracode GoldenGate technology (Illumina).

RESULTS

C1GALT1 showed an association with IgAN (rs1008898: P = 0.0019 and rs7790522: P = 0.0049). Associations were found when the population was stratified by gender (C1GALT1, CD300LG, GRN, ITGA2B, ITGB3 in males and C1GALT1, TRPC3, B4GALNT2 in females) and by age (TLR4, ITGB3 in patients aged <27 years). Furthermore, rs7873784 in TLR4 showed an association with proteinuria (G allele: P = 0.0091; GG genotype: P = 0.0077).

CONCLUSIONS

Age and gender are likely to evidence distinct immunological and inflammatory reactions leading to individual susceptibility to IgAN. Overall, a genetic predisposition to sporadic IgAN was found. We might hypothesize that C1GALT1 and TLR4 polymorphisms influence the risk to develop IgAN and proteinuria, respectively.

Signal transducer and activation of transcription 6 (STAT6) regulates T helper type 1 (Th1) and Th17 nephritogenic immunity in experimental crescentic glomerulonephritis

Experimental crescentic glomerulonephritis is driven by systemic cellular immune responses. A pathogenic role for T helper type 1 (Th1) and Th17 cells is well established. T-bet, a key transcription factor required for Th1 lineage commitment, and retinoic acid-related orphan receptor-γt (Rorγt), a key Th17 transcription factor, are required for full expression of disease. Similarly, several Th1- and Th17-associated cytokines have been implicated in disease augmentation. The role of Th2 cells in the disease is less clear, although Th2-associated cytokines, interleukin (IL)-4 and IL-10, are protective. We sought to determine the role of signal transducer and activation of transcription 6 (STAT6), a key regulator of Th2 responses, in experimental crescentic glomerulonephritis. Compared to wild-type mice, histological and functional renal injury was enhanced significantly in STAT6(-/-) mice 21 days after administration of sheep anti-mouse glomerular basement membrane globulin. Consistent with the enhanced renal injury, both Th1 and Th17 nephritogenic immune responses were increased in STAT6(-/-) mice. Conversely, production of IL-5, a key Th2-associated cytokine, was decreased significantly in STAT6(-/-) mice. Early in the disease process systemic mRNA expression of T-bet and Rorγ was increased in STAT6(-/-) mice. We conclude that STAT6 is required for attenuation of Th1 and Th17 nephritogenic immune responses and protection from crescentic glomerulonephritis.

Tim-1 promotes cisplatin nephrotoxicity

Nephrotoxicity is a frequent complication of cisplatin-based chemotherapy, in which T cells are known to promote acute kidney injury. In this study, we examined the role of T cell immunoglobulin mucin 1 (Tim-1) in cisplatin-induced acute kidney injury using an inhibitory anti-Tim-1 antibody. Tim-1 acts to modulate T cell responses, but it is also expressed by damaged proximal tubules in the kidney, where it is known as kidney injury molecule-1 (Kim-1). Anti-Tim-1 antibodies attenuated cisplatin nephrotocity, with less histologic damage, improved renal function, and fewer leukocytes infiltrating the kidney compared with control antibody-treated mice. Renal NF-κB activation and apoptosis were reduced, and proinflammatory renal cytokine and chemokine mRNA expression was decreased. Renal Kim-1 expression was reduced, consistent with the diminished kidney injury after anti-Tim-1 antibody treatment. Furthermore, anti-Tim-1 antibodies reduced early systemic CD4+ and CD8+ T cell activation, apoptosis, and cytokine production. To determine whether the protective actions of anti-Tim-1 antibodies were due to effects on renal tubular cells, cisplatin nephrotoxicity was studied in Rag1(-/-) mice. Anti-Tim-1 antibodies did not affect renal dysfunction or histologic damage in Rag1(-/-) mice, showing that the benefits of inhibiting Tim-1 come from T cell effects. As Tim-1 plays an important role in promoting cisplatin nephrotoxicity, inhibiting Tim-1 may be a therapeutic strategy to prevent cisplatin-induced acute kidney injury.

Interleukin-17A promotes early but attenuates established disease in crescentic glomerulonephritis in mice

T helper (Th)17 cells might contribute to immune-mediated renal injury. Thus, we sought to define the time course of IL-17A-induced kidney damage and examined the relation between Th17 and Th1 cells in a model of crescentic anti-glomerular basement membrane glomerulonephritis. Renal injury and immune responses were assessed in wild-type and in IL-17A-deficient mice on days 6, 14, and 21 of disease development. On day 6, when mild glomerulonephritis developed, IL-17A-deficient mice were protected from renal injury. On day 14, when more severe disease developed, protection from renal injury due to IL-17A deficiency was less evident. On day 21, when crescentic glomerulonephritis was fully established, disease was enhanced in IL-17A(-/-) mice, with increased glomerular T-cell accumulation and fibrin deposition, and augmented Th1 responses. Mice lacking the Th17-promoting cytokine, IL-23 (p19), also developed more severe disease than wild-type animals on day 21. In contrast, mice deficient in the key Th1-promoting cytokine, IL-12 (p35), had decreased Th1 and increased Th17 responses and developed less severe crescentic glomerulonephritis than wild-type animals. These studies show that IL-17A contributes to early glomerular injury, but it attenuates established crescentic glomerulonephritis by suppressing Th1 responses. They provide further evidence that Th1 cells mediate crescentic injury in this model and that Th1 and Th17 cells counterregulate each other during disease development.

The IL-27 receptor has biphasic effects in crescentic glomerulonephritis mediated through Th1 responses

Despite its initially defined role as a T-helper type 1 cell (Th1)-inducing cytokine, interleukin-27 (IL-27) has complex roles in vivo. The role of IL-27 receptor (IL-27R) was defined in experimental crescentic glomerulonephritis induced by a foreign antigen, sheep globulin, which is planted in glomeruli. This lesion is dependent on a Th1 effector cellular response. Twenty-one days after the administration of sheep anti-mouse glomerular basement membrane antibody, wild-type mice developed histologic and functional inflammatory renal injury. Injury was attenuated in the absence of IL-27R α chain (IL-27Rα), the unique component of the IL-27R complex. In contrast to the attenuated renal injury on day 21, Il27ra(-/-) mice exhibited enhanced systemic immune responses, including Th1 responses, with increased IL-2-dependent interferon-γ (IFN-γ) production. However, earlier in the development of the nephritogenic immune response, IFN-γ production was decreased, with reduced early immune responses translating into attenuated renal injury. Having demonstrated decreased early Th1 systemic immune responses, followed by enhanced nephritogenic Th1 immune responses, renal injury was studied at later time points. On days 28 and 35 after injection of the nephritogenic antigen, renal injury was enhanced in Il27ra(-/-) mice compared with wild-type mice in an at least partially IFN-γ-dependent manner. In Th1-dependent autoinflammatory lesions, IL-27Rα has a biphasic role in vivo, initially pathogenic, but ultimately playing a protective role by regulating immune responses and attenuating disease.

Chemokines in renal injury

The main function of chemokines is to guide inflammatory cells in their migration to sites of inflammation. During the last 2 decades, an expanding number of chemokines and their receptors have driven broad inquiry into how inflammatory cells are recruited in a variety of diseases. Although this review focuses on chemokines and their receptors in renal injury, proinflammatory IL-17, TGFβ, and TWEAK signaling pathways also play a critical role in their expression. Recent studies in transgenic mice as well as blockade of chemokine signaling by neutralizing ligands or receptor antagonists now allow direct interrogation of chemokine action. The emerging role of regulatory T cells and Th17 cells during renal injury also forges tight relationships between chemokines and T cell infiltration in the development of kidney disease. As chemokine receptor blockade inches toward clinical use, the field remains an attractive area with potential for unexpected opportunity in the future.

Endogenous foxp3(+) T-regulatory cells suppress anti-glomerular basement membrane nephritis

Foxp3(+) T-regulatory cells (Tregs) may suppress pathogenic inflammation; however, although transferred Tregs lessen glomerulonephritis in mice, the role of endogenous foxp3(+) cells is not known. To study this, we characterized endogenous foxp3(+) cells in accelerated anti-glomerular basement membrane (GBM) nephritis by using foxp3(GFP) reporter mice to track their responses in early and established disease. Further, diphtheria toxin was used to ablate foxp3(+) Tregs in foxp3(DTR) mice after establishing an immune response. In this model, mice were immunized with sheep globulin in adjuvant, and sheep anti-mouse GBM globulin was injected after 4 days to initiate progressive histological and functional injury. Intrarenal leukocytic infiltrates were increased by day 3 but intrarenal foxp3(+) Tregs, present in interstitial and periglomerular areas, were only increased at day 7. Ablation of foxp3(+) Tregs after injection of anti-GBM globulin increased renal injury and systemic T-cell responses, including increased interferon-γ and interleukin-17A (IL-17A) production, but no change in antibody titers. Compared with foxp3(+) Tregs isolated from naive mice, those from immunized mice produced more IL-10 and more effectively regulated CD4(+)foxp3(-) responder T cells. Thus, endogenous foxp3(+) Tregs infiltrate the kidney in glomerulonephritis, and deleting foxp3(+) cells after the induction of immune responses upregulated T-cell reactions and enhanced disease. Hence, endogenous foxp3(+) cells have increased suppressive capacity after immune stimuli.

The Th17-defining transcription factor RORγt promotes glomerulonephritis

Although Th17 responses may contribute to the pathogenesis of glomerulonephritis, whether the key transcription factor in Th17 cell development, RORγt, also promotes glomerulonephritis is unknown. Here, we induced crescentic glomerulonephritis in wild-type and RORγt-deficient (RORγt(-/-)) mice. RORγt(-/-) mice were protected from disease, with reduced histologic and functional injury and decreased leukocyte infiltration. Because RORγt(-/-) mice lack lymph nodes, which may influence the development of nephritis, we performed cell-transfer studies. We reconstituted Rag1(-/-) mice, which lack adaptive immunity but otherwise have normal architecture of the lymphatic system, with splenocytes from naïve wild-type or RORγt(-/-) mice. Mice receiving wild-type splenocytes exhibited high mortality from renal failure after induction of nephritis whereas mice receiving RORγt(-/-) cells were protected. To determine the effect of RORγt deficiency specifically in T helper cells, we isolated naïve CD4(+) T cells from wild-type and RORγt(-/-) mice and transferred them into Rag1(-/-) animals. Recipients of wild-type CD4(+) T cells developed severe glomerulonephritis whereas recipients of RORγt(-/-) cells developed less severe disease. To exclude effects of altered regulatory T cell (Treg) development caused by RORγt deficiency, we transferred naïve CD4(+) T cells depleted of Tregs into Rag1(-/-) mice. Recipients of wild-type, Treg-depleted, CD4(+) T cells developed severe glomerulonephritis whereas recipients of RORγt(-/-), Treg-depleted CD4(+) T cells did not. Taken together, this study demonstrates that RORγt promotes the development of crescentic glomerulonephritis by directing nephritogenic Th17 responses.

Toll-like receptor 9 enhances nephritogenic immunity and glomerular leukocyte recruitment, exacerbating experimental crescentic glomerulonephritis

Glomerular disease can be triggered or exacerbated by microbes that activate the immune system by Toll-like receptor (TLR) ligation. TLR9 activation promotes host defenses through the enhancement of innate and adaptive immune responses that facilitate the recruitment of leukocytes to areas of inflammation. We defined the role of TLR9 in experimental crescentic glomerulonephritis. Wild-type mice administered a TLR9 ligand and sheep anti-mouse glomerular basement membrane antibody developed histological injury with impaired renal function, which was attenuated in TLR9 knockout mice. Consistent with enhanced renal injury, wild-type mice exhibited enhanced T helper 1 and T helper 17 cellular immune responses. Kidney mRNA expression of inflammatory cytokines and chemokines as well as leukocyte recruitment were increased in wild-type mice. The use of bone marrow chimeric mice demonstrated that while both bone marrow and tissue cell TLR9 are required for maximal injury, bone marrow TLR9 is more important. Administration of a TLR9 inhibitor before sheep anti-mouse glomerular basement membrane globulin in wild-type mice attenuated cellular nephritogenic immunity that resulted in decreased renal injury. Administration of the inhibitor 7 days after disease initiation decreased glomerular leukocyte recruitment as well as renal injury. These results define the role of TLR9 in experimental crescentic glomerulonephritis and identify therapeutic potential for TLR9 inhibitors in attenuating renal injury, decreasing cellular nephritogenic immunity early in disease, and decreasing kidney effector responses later.

Tim3 is upregulated and protective in nephrotoxic serum nephritis

T cell immunoglobulin and mucin protein-3 (Tim3) is mainly expressed on the cell surface of T-helper lymphocytes (T(H)) that negatively regulates T(H)-type 1 (T(H)-1) responses. Because blockade of Tim3 aggravates disease activity in T(H)-1-dependent diseases, we investigated whether Tim3 is involved in the pathogenesis of the T(H)-1-dependent nephrotoxic nephritis (NTS). We first evaluated Tim3 expression in mice after induction of nephrotoxic serum nephritis (NTS) and then studied the effects of anti-Tim3 treatment toward the course of NTS for up to seven days. Whereas Tim3 expression was undetectable in control mice, we found significantly increased Tim3 expression in kidneys, but not in draining lymph nodes, at one, four, and eight weeks after induction of NTS. Tim3-expressing cells that infiltrated kidneys of mice subjected to NTS turned out to be CD4(+) T cells rather than CD8(+) cytotoxic T cells and dendritic cells. Administration of a blocking anti-Tim3 antibody aggravated nephritis as shown by significantly increased albuminuria, respective histological changes, and increased expression of the kidney injury molecule lipocalin-2. In parallel, an increase of infiltrating T cells, macrophages, and macrophage pro-inflammatory cytokine formation as well as increased proliferation and apoptosis in kidneys of anti-Tim3-treated mice was detected. Together, we provide the first evidence that Tim3 is up-regulated in kidneys in NTS and that Tim3 exerts protective roles in the course of disease.

The role of the Th1 transcription factor T-bet in a mouse model of immune-mediated bone-marrow failure

The transcription factor T-bet is a key regulator of type 1 immune responses. We examined the role of T-bet in an animal model of immune-mediated bone marrow (BM) failure using mice carrying a germline T-bet gene deletion (T-bet(-/-)). In comparison with normal C57BL6 (B6) control mice, T-bet(-/-) mice had normal cellular composition in lymphohematopoietic tissues, but T-bet(-/-) lymphocytes were functionally defective. Infusion of 5 x 10(6) T-bet(-/-) lymph node (LN) cells into sublethally irradiated, major histocompatibility complex-mismatched CByB6F1 (F1) recipients failed to induce the severe marrow hypoplasia and fatal pancytopenia that is produced by injection of similar numbers of B6 LN cells. Increasing T-bet(-/-) LN-cell dose to 10 to 23 x 10(6) per recipient led to only mild hematopoietic deficiency. Recipients of T-bet(-/-) LN cells had no expansion in T cells or interferon-gamma-producing T cells but showed a significant increase in Lin(-)Sca1(+)CD117(+)CD34(-) BM cells. Plasma transforming growth factor-beta and interleukin-17 concentrations were increased in T-bet(-/-) LN-cell recipients, possibly a compensatory up-regulation of the Th17 immune response. Continuous infusion of interferon-gamma resulted in hematopoietic suppression but did not cause T-bet(-/-) LN-cell expansion or BM destruction. Our data provided fresh evidence demonstrating a critical role of T-bet in immune-mediated BM failure.

Th1 and Th17 cells induce proliferative glomerulonephritis

Th1 effector CD4+ cells contribute to the pathogenesis of proliferative and crescentic glomerulonephritis, but whether effector Th17 cells also contribute is unknown. We compared the involvement of Th1 and Th17 cells in a mouse model of antigen-specific glomerulonephritis in which effector CD4+ cells are the only components of adaptive immunity that induce injury. We planted the antigen ovalbumin on the glomerular basement membrane of Rag1(-/-) mice using an ovalbumin-conjugated non-nephritogenic IgG1 monoclonal antibody against alpha3(IV) collagen. Subsequent injection of either Th1- or Th17-polarized ovalbumin-specific CD4+ effector cells induced proliferative glomerulonephritis. Mice injected with Th1 cells developed progressive albuminuria over 21 d, histologic injury including 5.5 +/- 0.9% crescent formation/segmental necrosis, elevated urinary nitrate, and increased renal NOS2, CCL2, and CCL5 mRNA. Mice injected with Th17 cells developed albuminuria by 3 d; compared with Th1-injected mice, their glomeruli contained more neutrophils and greater expression of renal CXCL1 mRNA. In conclusion, Th1 and Th17 effector cells can induce glomerular injury. Understanding how these two subsets mediate proliferative forms of glomerulonephritis may lead to targeted therapies.