Mechanisms of T cell-induced glomerular injury in anti-glomerular basement membrane (GBM) glomerulonephritis in rats

Prognostic value of complement serum C3 level and glomerular C3 deposits in anti-glomerular basement membrane disease

Background and objectives

Activation of the complement system is involved in the pathogenesis of anti-glomerular basement membrane (anti-GBM) disease. Glomerular deposits of complement 3 (C3) are often detected on kidney biopsies. The primary objective of this study was to analyze the prognostic value of the serum C3 level and the presence of C3 glomerular deposits in patients with anti-GBM disease.

Methods

We conducted a retrospective cohort study of 150 single-positive patients with anti-GBM disease diagnosed between 1997 and 2017. Patients were categorized according to the serum C3 level (forming a low C3 (C3<1.23 g/L) and a high C3 (C3≥1.23 g/L) groups) and positivity for C3 glomerular staining (forming the C3+ and C3- groups). The main outcomes were kidney survival and patient survival.

Results

Of the 150 patients included, 89 (65%) were men. The median [interquartile range (IQR)] age was 45 [26-64]. At diagnosis, kidney involvement was characterized by a median [IQR] peak serum creatinine (SCr) level of 578 [298-977] µmol/L, and 106 (71%) patients required dialysis. Patients in the low C3 group (72 patients) had more severe kidney disease at presentation, as characterized by higher prevalences of oligoanuria, peak SCr ≥500 µmol/L (69%, vs. 53% in the high C3 group; p=0.03), nephrotic syndrome (42%, vs. 24%, respectively; p=0.02) and fibrous forms on the kidney biopsy (21%, vs. 8%, respectively; p=0.04). Similarly, we observed a negative association between the presence of C3 glomerular deposits (in 52 (41%) patients) and the prevalence of cellular forms (83%, vs. 58% in the C3- group; p=0.003) and acute tubulo-interstitial lesions (60%, vs. 36% in the C3- group; p=0.007). When considering patients not on dialysis at diagnosis, the kidney survival rate at 12 months was poorer in the C3+ group (50% [25-76], vs. 91% [78-100] in the C3- group; p=0.01), with a hazard ratio [95% confidence interval] of 5.71 [1.13-28.85] (p=0.04, after adjusting for SCr).

Conclusion

In patients with anti-GBM disease, a low serum C3 level and the presence of C3 glomerular deposits were associated with more severe disease and histological kidney involvement at diagnosis. In patients not on dialysis at diagnosis, the presence of C3 deposits was associated with worse kidney survival.

Metalloporphyrins as Tools for Deciphering the Role of Heme Oxygenase in Renal Immune Injury

Renal immune injury is a frequent cause of end-stage renal disease, and, despite the progress made in understanding underlying pathogenetic mechanisms, current treatments to preserve renal function continue to be based mainly on systemic immunosuppression. Small molecules, naturally occurring biologic agents, show considerable promise in acting as disease modifiers and may provide novel therapeutic leads. Certain naturally occurring or synthetic Metalloporphyrins (Mps) can act as disease modifiers by increasing heme oxygenase (HO) enzymatic activity and/or synthesis of the inducible HO isoform (HO-1). Depending on the metal moiety of the Mp employed, these effects may occur in tandem or can be discordant (increased HO-1 synthesis but inhibition of enzyme activity). This review discusses effects of Mps, with varying redox-active transitional metals and cyclic porphyrin cores, on mechanisms underlying pathogenesis and outcomes of renal immune injury.

Anti-glomerular basement membrane glomerulonephritis concurrent with membranous nephropathy and acute tubular interstitial nephritis in a lung cancer patient treated with pembrolizumab

Immune checkpoint inhibitors (ICIs) have become the standard treatment for many types of cancer and have improved patient prognosis. However, ICIs upregulate the immune system against tumors, leading to immune-related adverse events (irAEs). Kidney irAEs are less common, and most of them are acute tubulointerstitial nephritis (ATIN). However, there has been a recent increase in recognition of glomerular disease related to ICI therapies. We report the case of a 65-year-old man with lung adenocarcinoma who was treated with pembrolizumab (a monoclonal antibody targeting programmed cell death protein-1 [PD-1]). Pembrolizumab was discontinued after seven cycles due to the development of destructive thyroiditis. Within three months of discontinuing the pembrolizumab treatment, the patient developed rapid progressive glomerulonephritis (RPGN), liver dysfunction, and dysgeusia. The patient underwent renal biopsy and was diagnosed with crescentic glomerulonephritis due to anti-glomerular basement membrane (GBM) antibodies complicated with membranous nephropathy (MN) and ATIN. Treatment with systemic corticosteroids resulted in a favorable clinical response. Various ICI-associated glomerular diseases have been described; however, this is the first reported case of anti-GBM glomerulonephritis associated with MN and ATIN following ICI treatment.

Cell-Mediated Glomerulonephritis Without Immune Complexes in Native Kidney Biopsies: A Report of 7 Cases

We report 7 native kidney biopsies with diffuse endocapillary hypercellularity without immune deposits, affecting 5 women and 2 men aged 52-85 years. All patients had acute kidney injury, and 4 had nephrotic-range proteinuria. Comorbidities included breast cancer in 2, pancreatitis in 1, and para-aortic lymphadenopathy and bilateral carpal tunnel syndrome in 1. Kidney biopsies were characterized by predominant T-cell and CD68-positive macrophage infiltration in glomerular capillaries without deposits. Coexisting lesions included small cellular crescents in 5, mild peritubular capillaritis in 1, mononuclear cell intimal arteritis in 1, acute tubulointerstitial nephritis in 4, and mild arteriolosclerosis in 1. During the mean follow-up duration of 24.8 months, 4 patients showed partial or complete initial remission in response to immunosuppression. However, 2 deteriorated when prednisone was rapidly tapered (1 of them achieved subsequent remission with increased prednisone). Three patients developed kidney failure. We propose that this unusual pattern of injury is mediated by abnormal cell-mediated immune response. The underlying causes and pathogenesis of this cell-mediated glomerulonephritis will require further study.

Conventional NK Cells and Type 1 Innate Lymphoid Cells Do Not Influence Pathogenesis of Experimental Glomerulonephritis

Innate lymphoid cells (ILCs) that express NK cell receptors (NCRs) and the transcription factor T-bet populate nonlymphoid tissues and are crucial in immune responses against viral infections and malignancies. Recent studies highlighted the heterogeneity of this ILC population and extended their functional spectrum to include important roles in tissue homeostasis and autoimmunity. In this article, we provide detailed profiling of NCR+T-bet+ ILC populations in the murine kidney, identifying conventional NK (cNK) cells and type 1 ILCs (ILC1s) as the two major subsets. Induction of renal inflammation in a mouse model of glomerulonephritis did not substantially influence abundance or phenotype of cNK cells or ILC1s in the kidney. For functional analyses in this model, widely used depletion strategies for total NCR+ ILCs (anti-NK1.1 Ab application) and cNK cells (anti-asialoGM1 serum application) were unreliable tools, because they were accompanied by significant off-target depletion of kidney NKT cells and CD8+ T cells, respectively. However, neither depletion of cNK cells and ILC1s in NKT cell–deficient mice nor specific genetic deletion of cNK cells in Ncr1Cre/wt × Eomesfl/fl mice altered the clinical course of experimental glomerulonephritis. In summary, we show in this article that cNK cells and ILC1s are dispensable for initiation and progression of immune-mediated glomerular disease and advise caution in the use of standard Ab depletion methods to study NCR+ ILC function in mouse models.

Crescentic Glomerulonephritis: Pathogenesis and Therapeutic Potential of Human Amniotic Stem Cells

Chronic kidney disease (CKD) leads to significant morbidity and mortality worldwide. Glomerulonephritis (GN) is the second leading cause of CKD resulting in end stage renal failure. The most severe and rapidly progressive type of GN is characterized by glomerular crescent formation. The current therapies for crescentic GN, which consist of broad immunosuppressive drugs, are partially effective, non-specific, toxic and cause many serious side effects including infections, cancer, and cardiovascular problems. Therefore, new and safer therapies are needed. Human amniotic epithelial cells (hAECs) are a type of stem cell which are isolated from the placenta after birth. They represent an attractive and novel therapeutic option for the treatment of various inflammatory conditions owing to their unique and selective immunosuppressive ability, as well as their excellent safety profile and clinical applicability. In this review, we will discuss the immunopathogenesis of crescentic GN, issues with currently available treatments and how hAECs offer potential to become a new and harmless treatment option for this condition.

Disease activity prediction and prognosis of anti-GBM nephritis based on T lymphocyte subset ratios

Introduction

Cell-mediated autoimmunity, especially the autoreactivity of T cells, is known to underlie the initiation of anti-glomerular basement membrane disease. However, the T lymphocyte subsets that determine the disease activity, renal fibrosis, and prognosis of anti-GBM disease have not been clearly elucidated.

Methods

The T lymphocyte subsets (CD4+ and CD8+) were examined on peripheral blood and renal biopsy tissues from 65 patients with biopsy proven anti-GBM disease. Patients were divided into the high ratio group and low ratio group according to the cutoff values in the receiver operating characteristic curve analysis. The correlations of T lymphocyte subsets with clinical, pathological data, and renal outcome were analyzed.

Results

By the end of follow-up, 45 patients (69.2%) developed end-stage renal disease (ESRD). In peripheral blood, the CD4+/CD8+ ratio showed a predictive ability with a sensitivity and specificity of 91.3% and 52.9%, respectively, which gave rise to a cutoff value of 0.89. There was a significant difference in the activity index between these two groups (3.91 ± 1.38 vs. 2.89 ± 1.13, p = 0.007). In the renal tissues, the CD4+/CD8+ ratio had the optimal cutoff point of 0.82 with a sensitivity of 57.8% and specificity of 85%. The renal activity index was higher for the renal tissues with high CD4+/CD8+ ratios than that of tissues with low CD4+/CD8+ ratios (4.32 ± 1.55 vs. 3.37 ± 1.41, p = 0.016). Peripheral blood CD4+/CD8+ ratios of ≥0.89 or renal tissue CD4+/CD8+ ratios of < 0.82 positively correlated with poor renal prognosis in patients with anti-GBM nephritis.

Conclusions

The CD4+/CD8+ ratio was associated with renal activity index both in peripheral blood and renal tissue and predicts the renal prognosis of patients with anti-GBM nephritis.

Evaluation of Inflammasome Activation in Peripheral Blood Mononuclear Cells of Hemodialysis Treated Patients with Glomerulonephritis

Recently, it has been found that abnormal activation of inflammasomes, the intracellular multiprotein complexes, plays an important role in the pathogenesis and the development of inflammatory diseases. To determine whether the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is involved in chronic inflammatory condition reported in glomerulonephritic- hemodialysis (HD) patients, we investigated the mRNA levels of NLRP3, CASP-1, ASC, IL-1β, IL-18, NLRC4, and P2X7 in human peripheral blood mononuclear cells (PBMCs) collected from 28 glomerulonephritic-HD patients. To confirm the mRNA quantification results, we investigated the IL-1ß content and Caspase 1 activity in serum and PBMC lysates, respectively. Compared with PBMCs derived from healthy subjects, genes encoding proinflammatory cytokines such as IL-1β and IL-18 as well as NLRP3, ASC, CASP-1 were markedly overexpressed in those derived from patients. Moreover, there was no significant difference between the expression level of P2X 7 mRNA in PBMCs isolated from glomerulonephritis-HD patients and controls. The serum level of active IL1-β and cell lysate CASP-1 activity were up-regulated in patients compared to controls. We also revealed that PBMCs isolated from glomerulonephritis-HD patients had elevated mRNA levels of NLRC4 compared to controls, suggesting the priming of NLRC4 inflammasome. These results revealed that the NLRP3-ASC-caspase-1 axis might have a role in increased inflammation severity reported in glomerulonephritic patients undergoing hemodialysis. These findings provide new insights into molecular mechanisms underlying chronic inflammation in HD- glomerulonephritic patients. Additionally, the NLRP3 inflammasome pathway can be attractive as a potential therapeutic target for complication avoidance in HD- glomerulonephritic patients.

Growth Differentiation Factor 15 Ameliorates Anti-Glomerular Basement Membrane Glomerulonephritis in Mice

Growth differentiation factor 15 (GDF15) is a member of the transforming growth factor-β (TGF-β) cytokine family and an inflammation-associated protein. Here, we investigated the role of GDF15 in murine anti-glomerular basement membrane (GBM) glomerulonephritis. Glomerulonephritis induction in mice induced systemic expression of GDF15. Moreover, we demonstrate the protective effects for GDF15, as GDF15-deficient mice exhibited increased proteinuria with an aggravated crescent formation and mesangial expansion in anti-GBM nephritis. Herein, GDF15 was required for the regulation of T-cell chemotactic chemokines in the kidney. In addition, we found the upregulation of the CXCR3 receptor in activated T-cells in GDF15-deficient mice. These data indicate that CXCL10/CXCR3-dependent-signaling promotes the infiltration of T cells into the organ during acute inflammation controlled by GDF15. Together, these results reveal a novel mechanism limiting the migration of lymphocytes to the site of inflammation during glomerulonephritis.

TNF-α in T lymphocytes attenuates renal injury and fibrosis during nephrotoxic nephritis

Nephrotoxic serum nephritis (NTN) models immune-mediated human glomerulonephritis and culminates in kidney inflammation and fibrosis, a process regulated by T lymphocytes. TNF-α is a key proinflammatory cytokine that contributes to diverse forms of renal injury. Therefore, we posited that TNF-α from T lymphocytes may contribute to NTN pathogenesis. Here, mice with T cell-specific deletion of TNF-α (TNF TKO) and wild-type (WT) control mice were subjected to the NTN model. At 14 days after NTN, kidney injury and fibrosis were increased in kidneys from TNF TKO mice compared with WT mice. PD1+CD4+ T cell numbers and mRNA levels of IL-17A were elevated in NTN kidneys of TNF TKO mice, suggesting that augmented local T helper 17 lymphocyte responses in the TNF TKO kidney may exaggerate renal injury and fibrosis. In turn, we found increased accumulation of neutrophils in TNF TKO kidneys during NTN. We conclude that TNF-α production in T lymphocytes mitigates NTN-induced kidney injury and fibrosis by inhibiting renal T helper 17 lymphocyte responses and infiltration of neutrophils.

OX40 ligand is inhibitory during the effector phase of crescentic glomerulonephritis

BACKGROUND

The functional relevance of OX40 ligand (OX40L) in the effector phase of crescentic glomerulonephritis (GN) is unknown. These studies defined the role of endogenous OX40L during the effector stage of murine crescentic GN.

METHODS

GN was induced by immunization with sheep globulin/adjuvant on Day 0 and injection of sheep anti-mouse glomerular basement membrane immunoglobulin (Ig) on Day 10. Rat IgG or neutralizing anti-OX40L antibody was administered on Days 10-18 and immune responses and renal injury assessed on Day 20.

RESULTS

Compared with naïve animals, OX40L was upregulated in the lymph nodes (LNs) and on leucocytes and resident non-immune cells in the kidneys of mice with GN. Inhibition of OX40L in GN augmented renal injury, as indicated by increased crescent formation, proteinuria and glomerular leucocyte accumulation. In line with increased injury, anti-OX40L treatment increased proliferation and decreased apoptosis of CD4 T cells in the LNs, without affecting LN CD4 cytokine production and CD8 T-cell responses. Blockade of OX40L decreased LN regulatory T-cell (Treg) proliferation, transforming growth factor β production and foxp3 expression. OX40L inhibition did not affect B cell expansion or circulating antibody levels. In the kidney, neutralization of OX40L augmented interferon γ (IFNγ) expression by CD4 and CD8 T cells and shifted macrophage polarization towards the pro-inflammatory M1 phenotype.

CONCLUSIONS

OX40L is protective during the effector phase of murine crescentic GN by reducing the expansion of CD4 T cells and enhancing Treg responses in the LNs, and by locally inhibiting T-cell IFNγ production and pro-inflammatory macrophage phenotype in the kidney.

Natural Killer Cells in Kidney Health and Disease

Natural killer (NK) cells are a specialized population of innate lymphocytes that have a major effector function in local immune responses. While their immunological functions in many inflammatory diseases are well established, comparatively little is still known about their roles in kidney homeostasis and disease. Our understanding of kidney NK cells is rapidly evolving, with murine studies highlighting the functional significance of NK cells in acute and chronic forms of renal disease. Recent progress has been made in translating these murine findings to human kidneys, with indications of NK cell subset-specific roles in disease progression in both native and allograft kidneys. Clearly, a better understanding of the molecular mechanisms driving NK cell activation and importantly, their downstream interactions with intrinsic renal cells and infiltrating immune cells is necessary for the development of targeted therapeutics to halt disease progression. In this review, we discuss the properties and potential functions of kidney NK cells.

Loss of endogenous thymosin β4 accelerates glomerular disease

Glomerular disease is characterized by morphologic changes in podocyte cells accompanied by inflammation and fibrosis. Thymosin β₄ regulates cell morphology, inflammation, and fibrosis in several organs and administration of exogenous thymosin β₄ improves animal models of unilateral ureteral obstruction and diabetic nephropathy. However, the role of endogenous thymosin β₄ in the kidney is unknown. We demonstrate that thymosin β₄ is expressed prominently in podocytes of developing and adult mouse glomeruli. Global loss of thymosin β₄ did not affect healthy glomeruli, but accelerated the severity of immune-mediated nephrotoxic nephritis with worse renal function, periglomerular inflammation, and fibrosis. Lack of thymosin β₄ in nephrotoxic nephritis led to the redistribution of podocytes from the glomerular tuft toward the Bowman capsule suggesting a role for thymosin β₄ in the migration of these cells. Thymosin β₄ knockdown in cultured podocytes also increased migration in a wound-healing assay, accompanied by F-actin rearrangement and increased RhoA activity. We propose that endogenous thymosin β₄ is a modifier of glomerular injury, likely having a protective role acting as a brake to slow disease progression.

Severe Nephrotoxic Nephritis following Conditional and Kidney-Specific Knockdown of Stanniocalcin-1

BACKGROUND

Inflammation is the hallmark of nephrotoxic nephritis. Stanniocalcin-1 (STC1), a pro-survival factor, inhibits macrophages, stabilizes endothelial barrier function, and diminishes trans-endothelial migration of leukocytes; consistently, transgenic (Tg) overexpression of STC1 protects from nephrotoxic nephritis. Herein, we sought to determine the phenotype of nephrotoxic nephritis after conditional and kidney-specific knockdown of STC1.

METHODS

We used Tg mice that, express either STC1 shRNA (70% knockdown of STC1 within 4d) or scrambled shRNA (control) upon delivery of Cre-expressing plasmid to the kidney using ultrasound microbubble technique. Sheep anti-mouse GBM antibody was administered 4d after shRNA activation; and mice were euthanized 10 days later for analysis.

RESULTS

Serum creatinine, proteinuria, albuminuria and urine output were similar 10 days after anti-GBM delivery in both groups; however, anti-GBM antibody delivery to mice with kidney-specific knockdown of STC1 produced severe nephrotoxic nephritis, characterized by severe tubular necrosis, glomerular hyalinosis/necrosis and massive cast formation, while control mice manifested mild tubular injury and crescentic glomerulonephritis. Surprisingly, the expression of cytokines/chemokines and infiltration with T-cells and macrophages were also diminished in STC1 knockdown kidneys. Staining for sheep anti-mouse GBM antibody, deposition of mouse C3 and IgG in the kidney, and antibody response to sheep IgG were equal.

CONCLUSIONS

nephrotoxic nephritis after kidney-specific knockdown of STC1 is characterized by severe tubular and glomerular necrosis, possibly due to loss of STC1-mediated pro-survival factors, and we attribute the paucity of inflammation to diminished release of cytokines/chemokines/growth factors from the necrotic epithelium.

Macrophages in vascular inflammation--From atherosclerosis to vasculitis

The spectrum of vascular inflammatory disease ranges from atherosclerosis and hypertension, widespread conditions affecting large proportions of the population, to the vasculitides, rare syndromes leading to fast and irreversible organ failure. Atherosclerosis progresses over decades, inevitably proceeding through multiple phases of disease and causes its major complications when the vessel wall lesion ruptures, giving rise to lumen-occlusive atherothrombosis. Vasculitides of medium and large arteries progress rapidly, causing tissue ischemia through lumen-occlusive intimal hyperplasia. In both disease entities, macrophages play a decisive role in pathogenesis, but function in the context of other immune cells that direct their differentiation and their functional commitments. In atherosclerosis, macrophages are involved in the removal of lipids and tissue debris and make a critical contribution to tissue damage and wall remodeling. In several of the vasculitides, macrophages contribute to granuloma formation, a microstructural platform optimizing macrophage-T-cell interactions, antigen containment and inflammatory amplification. By virtue of their versatility and plasticity, macrophages are able to promote a series of pathogenic functions, ranging from the release of cytokines and enzymes, the production of reactive oxygen species, presentation of antigen and secretion of tissue remodeling factors. However, as short-lived cells that lack memory, macrophages are also amendable to reprogramming, making them promising targets for anti-inflammatory interventions.

Glomerulonephritis-Induced Changes in Urinary and Kidney MicroRNA Profiles in Rats

MicroRNAs (miRNAs) regulate gene expression post-transcriptionally and thus are involved in various physiological and pathological states. Due to their stability in biofluids miRNAs have also been proposed as biomarkers (BMs) for tissue injury. We investigated the usefulness of urinary miRNAs for detection of site-specific renal damage in an antiglomerular basement membrane glomerulonephritis (GN) model in rats by comparing GN-induced urinary miRNAs profiles to traditional and newer protein BMs, and to proximal tubular injury-induced urinary miRNA profiles observed previously after cisplatin (Cp) treatment. Male Wistar Kyoto and Sprague Dawley rats were dosed once with 1, 2.5, and 5 ml/kg nephrotoxic serum (NTS) or 1.5 and 5 ml/kg NTS, respectively. GN and tubular damage were observed histopathologically in all treated rats after 14 days. Although serum creatinine and BUN were not changed, several protein BMs and 74 urinary miRNAs were found to be increased 8 and 14 days after NTS administration. Of these 74 miRNAs, 5 were identified as increased after NTS but not after Cp treatment. Using in situ hybridization two of them, miR-10 b and -100, were found to be localized in distal segments of the nephron, potentially reflecting the tubular injury in those regions. Furthermore, evaluation of both miRNA and mRNA expression in the kidney revealed possible miRNA-mRNA interactions mostly associated with fibrotic and transforming growth factor β signaling. In conclusion, our investigations support the potential of urinary miRNAs as specific BMs for kidney injury, and suggest a role of miRNAs in pathological processes during GN in the kidney.

S100A8/A9 (calprotectin) is critical for development of glomerulonephritis and promotes inflammatory leukocyte-renal cell interactions

Glomerulonephritis is a common cause of end-stage renal disease. Infiltrating leukocytes interacting with renal cells play a critical role during the initiation and progression of glomerulonephritis, but the exact mechanisms are not clearly defined. By using the murine model of nephrotoxic nephritis, we investigated the role of S100A8/A9 [myeloid-related protein (MRP) 8/14, calprotectin] in promoting glomerulonephritis. In nephrotoxic nephritis, wild-type (WT) mice with glomerulonephritis have elevated serum levels of S100A8/A9, whereas mice deficient in MRP14 (S100a9(-/-)), and hence S100A8/A9, are significantly protected from disease. By using bone marrow transplants, we showed that MRP14 deficiency is required in both the hemopoietic and intrinsic cells for the protective effect. In vitro, both the WT bone marrow-derived macrophages and renal mesangial cells stimulated with S100A8/A9 secrete IL-6, CXCL1, and tumor necrosis factor α; however, Mrp14(-/-) cells exhibit significantly blunted proinflammatory responses. The interaction of WT bone marrow-derived macrophages with renal microvascular endothelial cells results in increased levels of monocyte chemotactic protein 1, IL-8, and IL-6 cytokines, which is attenuated in Mrp14(-/-) bone marrow-derived macrophages. Data shows that S100A8/A9 plays a critical role during glomerulonephritis, exerting and amplifying autocrine and paracrine proinflammatory effects on bone marrow-derived macrophages, renal endothelial cells, and mesangial cells. Therefore, complete S100A8/A9 blockade may be a new therapeutic target in glomerulonephritis.

Dendritic cells and macrophages in the kidney: a spectrum of good and evil

Renal dendritic cells (DCs) and macrophages represent a constitutive, extensive and contiguous network of innate immune cells that provide sentinel and immune-intelligence activity; they induce and regulate inflammatory responses to freely filtered antigenic material and protect the kidney from infection. Tissue-resident or infiltrating DCs and macrophages are key factors in the initiation and propagation of renal disease, as well as essential contributors to subsequent tissue regeneration, regardless of the aetiological and pathogenetic mechanisms. The identification, and functional and phenotypic distinction of these cell types is complex and incompletely understood, and the same is true of their interplay and relationships with effector and regulatory cells of the adaptive immune system. In this Review, we discuss the common and distinct characteristics of DCs and macrophages, as well as key advances that have identified the renal-specific functions of these important phagocytic, antigen-presenting cells, and their roles in potentiating or mitigating intrinsic kidney disease. We also identify remaining issues that are of priority for further investigation, and highlight the prospects for translational and therapeutic application of the knowledge acquired.

Absence of the lysosomal protein Limp-2 attenuates renal injury in crescentic glomerulonephritis

In humans, mutations of the intrinsic lysosomal protein SCARB2 are associated with myoclonic epilepsy, collapsing focal and segmental glomerulosclerosis, and tubular proteinuria. Mice with deficiency of Limp-2 (the murine homologue) develop tubular proteinuria but not focal and segmental glomerulosclerosis and they have a defect in macrophage function. To further elucidate the role of Limp-2 in immune function, we induced anti-glomerular basement membrane (GBM) model of crescentic glomerulonephritis in wild-type (WT) and Limp-2(-/-) littermates by intraperitoneal injections of nephrotoxic sheep serum. Renal injury and immune responses were assessed on day 14. Compared with WT, Limp-2(-/-) mice had significantly reduced crescent formation, interstitial inflammation and a trend to reduced tubulointerstitial injury. On day 1 during the heterologous phase of the disease, albuminuria was significantly increased in WT but not in Limp-2(-/-) mice. On day 14, albuminuria and renal function were similar in the two groups. There was, however, a significant reduction in the influx of glomerular macrophages and CD4(+) T cells in Limp-2(-/-) mice. Interleukin (IL)-4 and macrophage chemoattractant protein-1 (MCP-1) mRNA expression levels were significantly reduced. Despite the reduction in numbers of infiltrating cells, flow cytometry showed no difference in macrophage or T-cell numbers in the peripheral blood from untreated mice. The systemic humoral immune response, determined by glomerular mouse immunoglobulin G (IgG) deposition and mouse anti-sheep IgG subclass production, was similar in both groups. These data suggest that absence of Limp-2 reduces inflammation in experimental crescentic glomerulonephritis with decreased macrophage and T-cell infiltration in the kidney. It suggests an important role for Limp-2 in mediating the inflammatory response.

Lutheran/basal cell adhesion molecule accelerates progression of crescentic glomerulonephritis in mice

Migration of circulating leukocytes from the vasculature into the surrounding tissue is an important component of the inflammatory response. Among the cell surface molecules identified as contributing to leukocyte extravasation is VCAM-1, expressed on activated vascular endothelium, which participates in all stages of leukocyte–endothelial interaction by binding to leukocyte surface expressed integrin VLA-4. However, not all VLA-4-mediated events can be linked to VCAM-1. A novel interaction between VLA-4 and endothelial Lutheran (Lu) blood group antigens and basal cell adhesion molecule (BCAM) proteins has been recently shown, suggesting that Lu/BCAM may have a role in leukocyte recruitments in inflamed tissues. Here, we assessed the participation of Lu/BCAM in the immunopathogenesis of crescentic glomerulonephritis. High expression of Lu/BCAM in glomeruli of mice with rapidly progressive glomerulonephritis suggests a potential role for the local expression of Lu/BCAM in nephritogenic recruitment of leukocytes. Genetic deficiency of Lu/BCAM attenuated glomerular accumulation of T cells and macrophages, crescent formation, and proteinuria, correlating with reduced fibrin and platelet deposition in glomeruli. Furthermore, we found a pro-adhesive interaction between human monocyte α4β1 integrin and Lu/BCAM proteins. Thus, Lu/BCAM may have a critical role in facilitating the accumulation of monocytes and macrophages, thereby exacerbating renal injury.

Thymic deletion and regulatory T cells prevent antimyeloperoxidase GN

Loss of tolerance to neutrophil myeloperoxidase (MPO) underlies the development of ANCA-associated vasculitis and GN, but the mechanisms underlying this loss of tolerance are poorly understood. Here, we assessed the role of the thymus in deletion of autoreactive anti-MPO T cells and the importance of peripheral regulatory T cells in maintaining tolerance to MPO and protecting from GN. Thymic expression of MPO mRNA predominantly localized to medullary thymic epithelial cells. To assess the role of MPO in forming the T cell repertoire and the role of the autoimmune regulator Aire in thymic MPO expression, we compared the effects of immunizing Mpo(-/-) mice, Aire(-/-) mice, and control littermates with MPO. Immunized Mpo(-/-) and Aire(-/-) mice developed significantly more proinflammatory cytokine-producing anti-MPO T cells and higher ANCA titers than control mice. When we triggered GN with a subnephritogenic dose of anti-glomerular basement membrane antibody, Aire(-/-) mice had more severe renal disease than Aire(+/+) mice, consistent with a role for Aire-dependent central deletion in establishing tolerance to MPO. Furthermore, depleting peripheral regulatory T cells in wild-type mice also led to more anti-MPO T cells, higher ANCA titers, and more severe GN after immunization with MPO. Taken together, these results suggest that Aire-dependent central deletion and regulatory T cell-mediated peripheral tolerance both play major roles in establishing and maintaining tolerance to MPO, thereby protecting against the development of anti-MPO GN.

Mast cells contribute to peripheral tolerance and attenuate autoimmune vasculitis

Mast cells contribute to the modulation of the immune response, but their role in autoimmune renal disease is not well understood. Here, we induced autoimmunity resulting in focal necrotizing GN by immunizing wild-type or mast cell-deficient (Kit(W-sh/W-sh)) mice with myeloperoxidase. Mast cell-deficient mice exhibited more antimyeloperoxidase CD4+ T cells, enhanced dermal delayed-type hypersensitivity responses to myeloperoxidase, and more severe focal necrotizing GN. Furthermore, the lymph nodes draining the sites of immunization had fewer Tregs and reduced production of IL-10 in mice lacking mast cells. Reconstituting these mice with mast cells significantly increased the numbers of Tregs in the lymph nodes and attenuated both autoimmunity and severity of disease. After immunization with myeloperoxidase, mast cells migrated from the skin to the lymph nodes to contact Tregs. In an ex vivo assay, mast cells enhanced Treg suppression through IL-10. Reconstitution of mast cell-deficient mice with IL-10-deficient mast cells led to enhanced autoimmunity to myeloperoxidase and greater disease severity compared with reconstitution with IL-10-intact mast cells. Taken together, these studies establish a role for mast cells in mediating peripheral tolerance to myeloperoxidase, protecting them from the development of focal necrotizing GN in ANCA-associated vasculitis.

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.

Natural recovery from antiglomerular basement membrane glomerulonephritis is associated with glomeruli-infiltrating CD8α+CD11c+MHC class II+ cells

BACKGROUND/AIMS

In an antiglomerular basement membrane glomerulonephritis (GN) model, GN-resistant Lewis (LEW) rats naturally recover from early glomerular inflammation (days 21-23). We have previously identified a glomeruli-infiltrating CD8α(+)CD11(high)MHC II(+) cell (GIL CD8α(+) cell) in GN-prone Wistar Kyoto (WKY) rats, which terminates glomerular inflammation through inducing T cell apoptosis prior to glomerular fibrosis at days 35-40. We investigated if GIL CD8α(+) cells were also associated with the recovery in LEW rats.

METHODS

GIL CD8α(+) cells in LEW rats were characterized; their infiltration was observed in connection with T cell apoptosis in glomeruli.

RESULTS

An influx of GIL CD8α(+) cells into inflamed glomeruli was confirmed in the immunized LEW rats at days 17-22, which was much earlier than days 28-35 in WKY rats. Notably, LEW rats had a GIL CD8α(+)CD11(high) subpopulation after day 17, while WKY rats lacked this population until after day 30. Analyses further revealed a large number of clustered apoptotic CD4(+) or CD3(+) T cells in the glomeruli during recovery (day 23) in LEW rats, as compared to day 35 (transition to fibrosis) in WKY rats. Thus, infiltration of GIL CD8α(+) cells coincided with decline of glomerular inflammation and T cell apoptosis during recovery in LEW rats. Isolated GIL CD8α(+) cells were able to infiltrate glomeruli in both WKY and LEW rats at day 20.

CONCLUSION

Our data revealed a strong association between GIL CD8a+ cells and recovery from early glomerular inflammation. It raises a possibility of involvement of GIL CD8a+ cells in the recovery.

The sphingosine-1-phosphate receptor agonist FTY720 prevents the development of anti-glomerular basement membrane glomerulonephritis

The sphingosine-1-phosphate (S1P) agonist FTY720 prolongs the survival of organ allograft and attenuates autoimmune-mediated injury in experimental models. Most cases of glomerulonephritis (GN) in human appear to be immunologically initiated. In this study, we evaluated the potential therapeutic role of FTY720 in GN via a mouse anti-glomerular basement membrane (GBM) model. Mice were immunized with rabbit IgG in complete Freund's adjuvant (CFA) followed by an intravenous injection of a rabbit anti-mouse GBM serum. Disease and immune responses were assessed on day 14. Mice were treated with FTY720 (0.3 or 3 mg/kg) and prednisone (10 mg/kg) from days 0 to 14. The S1P modulator reduced proteinuria, serum creatinine, crescent formation and serum IgG level. The expressions of splenic S1P receptor and renal Th-1 cytokine were also inhibited at the transcription stage. Treatment with FTY720 increased splenocyte production of protective Th2 cytokine IL-4 and promoted the apoptosis of splenic CD4+ T cells in the animal models, which suggests that FTY720 played a protective role at the induction stage of GN by inhibiting mRNA expressions of splenic S1P receptor 1, S1P receptor 2, and S1P receptor 5.

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.

Macrophages in renal development, injury, and repair

Macrophages have long been regarded as classic mediators of innate immunity because of their production of proinflammatory cytokines and their ability to induce apoptotic cell death. As a result of such activities and the detrimental long-term effect of kidney inflammation, macrophages principally have been regarded as mediators of glomerular damage, tubular cell death, and the downstream fibrotic events leading to chronic kidney disease. Although this has been the accepted consequence of macrophage infiltration in kidney disease, macrophages also play a critical role in normal organ development, cell turnover, and recovery from injury in many organs, including the kidney. There is also a growing awareness that there is considerable heterogeneity of phenotype and function within the macrophage population and that a greater understanding of these different states of activation may result in the development of therapies specifically designed to capitalize on this variation in phenotype and cellular responses. In this review, we discuss the current understanding of induction and consequences of classic versus alternative macrophage activation and highlight what additional therapeutic options this may provide for the management of both acute and chronic kidney disease as well as renal cancer.

Voltage-gated potassium channel Kv1.3 blocker as a potential treatment for rat anti-glomerular basement membrane glomerulonephritis

The voltage-gated potassium channel Kv1.3 has been recently identified as a molecular target that allows the selective pharmacological suppression of effector memory T cells (T(EM)) without affecting the function of naïve T cells (T(N)) and central memory T cells (T(CM)). We found that Kv1.3 was expressed on glomeruli and some tubules in rats with anti-glomerular basement membrane glomerulonephritis (anti-GBM GN). A flow cytometry analysis using kidney cells revealed that most of the CD4(+) T cells and some of the CD8(+) T cells had the T(EM) phenotype (CD45RC(-)CD62L(-)). Double immunofluorescence staining using mononuclear cell suspensions isolated from anti-GBM GN kidney showed that Kv1.3 was expressed on T cells and some macrophages. We therefore investigated whether the Kv1.3 blocker Psora-4 can be used to treat anti-GBM GN. Rats that had been given an injection of rabbit anti-rat GBM antibody were also injected with Psora-4 or the vehicle intraperitoneally. Rats given Psora-4 showed less proteinuria and fewer crescentic glomeruli than rats given the vehicle. These results suggest that T(EM) and some macrophages expressing Kv1.3 channels play a critical role in the pathogenesis of crescentic GN and that Psora-4 will be useful for the treatment of rapidly progressive glomerulonephritis.

Platelet recruitment to the inflamed glomerulus occurs via an alphaIIbbeta3/GPVI-dependent pathway

Recruitment of leukocytes to glomeruli is fundamental to the pathogenesis of many forms of glomerulonephritis. In a model of glomerulonephritis induced by in situ immune complex deposition, we previously observed that, in addition to leukocytes, platelets accumulate in glomerular capillaries, where they contribute to leukocyte recruitment. However, the mechanisms of platelet recruitment and the role of platelet-expressed P-selectin in leukocyte recruitment require further investigation. We used intravital microscopy to examine the mechanisms of platelet and leukocyte recruitment to glomeruli of mice following administration of an antibody against the glomerular basement membrane (anti-GBM antibody). Platelet recruitment was initiated within five minutes of administration of anti-GBM antibody. This was unaltered by inhibition of platelet GPIbalpha but was prevented by the absence of platelet GPVI. Fibrinogen was deposited in glomerular capillaries via a partially intercellular adhesion molecule 1 (ICAM-1)-dependent mechanism, and inhibition of alpha(IIb)beta(3), fibrinogen and ICAM-1 inhibited platelet recruitment. Notably, neutrophil depletion also reduced platelet accumulation, indicating a cooperative interaction underlying recruitment of platelets and neutrophils. Finally, using bone marrow chimeras to restrict expression of P-selectin to platelets or endothelial cells, platelet but not endothelial P-selectin was required for glomerular leukocyte recruitment. Together these data indicate that platelet recruitment in this model is dependent on the combined actions of GPVI and the alpha(IIb)beta(3)/fibrinogen/ICAM-1 pathway and that platelet P-selectin is crucial for subsequent leukocyte recruitment.

(S)-armepavine from Chinese medicine improves experimental autoimmune crescentic glomerulonephritis

OBJECTIVE

Intra-renal T cells and macrophages play a key pathogenic role in the development and progression of glomerular crescents. We aimed to establish (S)-armepavine [(S)-ARM], a major bioactive compound of a Chinese medicinal plant, Nelumbo nucifera, as a potential therapeutic agent in the treatment of autoimmune crescentic glomerulonephritis (ACGN).

METHODS

A mouse ACGN model associated with T-cell dysregulation, was used to evaluate the therapeutic effects of (S)-ARM on the rapidly progressive glomerular disorder.

RESULTS

The results showed that (S)-ARM administered in the established phase of ACGN is capable of dramatically decreasing glomerular crescents in the kidney and improving proteinuria and renal dysfunction. These effects were associated with greatly inhibited infiltration of T cells/macrophages and suppressed nuclear factor (NF)-κB activation in the kidney, lowered serum levels of autoantibodies and both serum and intra-renal levels of pro-inflammatory cytokines, suppressed T/B-cell activation and T-cell proliferation of the spleen, reduced glomerular immune deposits and apoptosis in both the spleen and kidney in (S)-ARM-treated ACGN mice, compared with the vehicle-treated (disease control) group of ACGN mice.

CONCLUSION

We demonstrated therapeutic effects of (S)-ARM on ACGN as a result of: (i) early systemic negative modulation of T/B cells; (ii) intra-renal regulation of combined NF-κB activation and mononuclear leucocytic infiltration, thereby preventing glomerular crescent formation; and (iii) protection from apoptosis in both the spleen and kidney.

Macrophages and immunologic inflammation of the kidney

Monocyte-derived tissue effector cells, macrophages, are present in large numbers in all forms of kidney disease with inflammation. Their roles in inflammation and the molecular effectors of macrophage function have been difficult to decipher. With the advent of modern genetic tools and mouse models of human disease, great insight into monocyte/macrophage biology has been forthcoming. This review places macrophage study in its historical context, defines immunologic diseases of the kidney, broadens its definition to encompass current thinking of the immune response to kidney injury, highlights key advances of the study of monocyte/macrophages in kidney diseases, and identifies new therapeutic pathways and targets that hinge around macrophage function. This article advances the case that targeting macrophage activation and phenotype is leading to new therapies in the treatment of many acute and chronic kidney diseases.

Endogenous CD100 promotes glomerular injury and macrophage recruitment in experimental crescentic glomerulonephritis

CD100 participates in adaptive immune responses and is important in neural cell migration. To determine the role of endogenous CD100 in severe glomerular inflammation, we induced experimental crescentic glomerulonephritis by planting a foreign antigen in glomeruli of sensitized normal and CD100-deficient (CD100(-/-)) mice. Fewer CD100(-/-) glomeruli exhibited crescent formation or severe histological changes. Antigen-specific immune responses were reduced in CD100(-/-) mice. There was less interferon (IFN)-gamma and interleukin (IL)-4 production by splenocytes and fewer activated T and B cells were present in lymph nodes of immunized CD100(-/-) mice. Serum antigen-specific immunoglobulin (IgG) levels were also decreased. Glomerular macrophage and CD4(+) cell infiltration, and IgG and C3 deposition were attenuated. Normal kidneys expressed mRNA for CD100 and plexin-B1 (the tissue receptor of CD100). Direct immunofluorescence showed that renal-CD100 protein was predominantly in tubules, while plexin-B1 was present in both glomeruli and tubules. To determine whether glomerular plexin-B1 mediates leucocyte recruitment via leucocyte CD100, recruitment was studied after passive transfer of heterologous antibody (attracting neutrophils) or isologous antibody (attracting macrophages). Glomerular macrophages were reduced in CD100(-/-) mice, but neutrophil recruitment was equivalent, consistent with CD100 expression on macrophages, but not neutrophils. CD100 promotes severe nephritogenic immune responses and leucocyte CD100-glomerular plexin-B1 interactions enhance macrophage recruitment to glomeruli.

Atorvastatin enhances humoral immune responses but does not alter renal injury in experimental crescentic glomerulonephritis

AIM

Statins are widely used for their cholesterol-lowering effects and for prevention of cardiovascular disease. Evidence indicates that these drugs also have immunomodulatory and other non-lipid lowering effects, with studies suggesting benefit in some animal models of immune (particularly T helper (Th)1)-mediated inflammatory disease and their corresponding human disease counterparts. We sought to evaluate the immunomodulatory effects and therapeutic potential of atorvastatin in experimental crescentic glomerulonephritis, a Th1-predominant animal model of glomerulonephritis.

METHODS

Autologous phase, anti-glomerular basement membrane glomerulonephritis was induced in C57BL/6 mice by intravenous injection of sheep anti-mouse glomerular basement membrane globulin. Mice were administered atorvastatin (10 or 100 mg/kg) or control (phosphate-buffered saline) daily by oral gavage. Immune responses and renal injury were assessed after 21 days.

RESULTS

Compared with control-treated mice, treatment with atorvastatin did not alter renal injury (serum creatinine, proteinuria, glomerular crescent formation) or glomerular leukocytic infiltration (CD4(+) T cells or macrophages). Atorvastatin resulted in a dose-related increase in circulating serum antibody to the disease-inducing antigen but no differences in antigen-stimulated splenocyte production of Th1/Th2 cytokines. At the higher dose, atorvastatin also led to a significant reduction in apoptosis of splenic CD4(+) T lymphocytes.

CONCLUSION

This study demonstrates that statins modulate humoral responses and alter splenic CD4(+) T cell apoptosis. However, atorvastatin does not lead to significant changes in T helper cell polarization or renal injury in experimental crescentic glomerulonephritis.

Mammalian stanniocalcin-1 activates mitochondrial antioxidant pathways: new paradigms for regulation of macrophages and endothelium

The mammalian homolog of the fish calcium regulatory hormone stanniocalcin-1 (STC1) is ubiquitously expressed and likely functions in an autocrine/paracrine fashion. Mammalian STC1 does not appear to exert significant effects on serum calcium, and its physiological role remains to be determined. In macrophages, STC1 decreases intracellular calcium and cell mobility; attenuates the response to chemoattractants; and diminishes superoxide generation through induction of uncoupling protein-2 (UCP2). In cytokine-treated endothelial cells, STC1 attenuates superoxide generation and the activation of inflammatory pathways [c-Jun NH(2)-terminal kinase (JNK) and NF-kappaB]; maintains the expression of tight junction proteins, preserving the endothelial monolayer seal; and decreases transendothelial migration of leukocytes. Combined, the effects of STC1 on endothelial cells and macrophages predict potent anti-inflammatory action. Indeed, application of the anti-glomerular basement membrane (GBM) glomerulonephritis model to STC1 transgenic mice that display increased expression of STC1 transgene in endothelial cells and macrophages yields renal protection. Our data suggest that STC1 activates antioxidant pathways in endothelial cells and macrophages and displays cytoprotective and anti-inflammatory actions.

Role of FTY720 on M1 and M2 macrophages, lymphocytes, and chemokines in 5/6 nephrectomized rats

Renal injury is accompanied by the presence of infiltrating inflammatory cells in the glomerulus and tubulointerstitium. FTY720 modifies lymphocyte migration into injured tissues by lymphocyte sequestration to secondary lymphoid organs. The purpose of this study was to examine the potential of FTY720 to influence the inflammatory response in a nonimmunological model of renal failure. Sham-operated and 5/6 nephrectomized (SNX) Sprague-Dawley rats received two different doses of FTY720 or vehicle orally for 14 wk. Treatment with FTY720 reduced glomerular and tubulointerstitial damage in SNX rats but failed to stabilize creatinine clearance. The increase in gene expression of chemokine receptors CCR1, CCR2, and CCR5 in kidneys of vehicle-treated SNX rats was significantly attenuated by high-dose FTY720. Treatment with high-dose FTY720 tended to normalize RANTES and MCP-1 renal gene expression. FTY720 affected not only glomerular and tubulointerstitial lymphocytes, but M1 and M2 phenotype macrophages were also reduced. FTY720 significantly reduced key mediators of renal inflammation and fibrosis. FTY720 also decreased immunoregulation of M2 macrophages, which are beneficial for tissue remodeling and repair.

P2X7 deficiency attenuates renal injury in experimental glomerulonephritis

The P2X7 receptor is a ligand-gated cation channel that is normally expressed by a variety of immune cells, including macrophages and lymphocytes. Because it leads to membrane blebbing, release of IL-1beta, and cell death by apoptosis or necrosis, it is a potential therapeutic target for a variety of inflammatory diseases. Although the P2X7 receptor is usually not detectable in normal renal tissue, we previously reported increased expression of both mRNA and protein in mesangial cells and macrophages infiltrating the glomeruli in animal models of antibody-mediated glomerulonephritis. In this study, we used P2X7-knockout mice in the same experimental model of glomerulonephritis and found that P2X7 deficiency was significantly renoprotective compared with wild-type controls, evidenced by better renal function, a striking reduction in proteinuria, and decreased histologic glomerular injury. In addition, the selective P2X7 antagonist A-438079 prevented the development of antibody-mediated glomerulonephritis in rats. These results support a proinflammatory role for P2X7 in immune-mediated renal injury and suggest that the P2X7 receptor is a potential therapeutic target.

Blockade of the c-Jun amino terminal kinase prevents crescent formation and halts established anti-GBM glomerulonephritis in the rat

Macrophages induce acute renal injury in anti-glomerular basement membrane (GBM) glomerulonephritis. This operates, in part, via activation of the c-Jun amino terminal kinase (JNK) signaling pathway. However, it is unknown whether inhibition of JNK signaling is effective once the proinflammatory response is established in the injured kidney. This study examined whether blockade of JNK signaling could halt disease progression, including crescent formation, in a model of severe crescentic anti-GBM glomerulonephritis. WKY rats were immunized with sheep IgG and then injected with sheep anti-GBM serum (day 0). Animals were treated with the JNK inhibitor, CC-401, vehicle alone, or no treatment from day 7 until being killed on day 24 of disease. Untreated animals at day 7 showed significant proteinuria, focal glomerular lesions, marked glomerular macrophage and T-cell accumulation, and upregulation of proinflammatory mediators (TNF-alpha, iNOS, MMP-12). Untreated and vehicle-treated groups displayed severe glomerulonephritis at day 24 with renal impairment and worsening proteinuria. These animals had severe glomerular lesions, with 60% of glomeruli exhibiting fibrocellular crescents, in association with increased macrophage and T-cell accumulation (including macrophage giant cells) and a further increase in mRNA levels of TNF-alpha, iNOS, MMP-12, and TGF-beta1. In contrast, CC-401 treatment prevented renal impairment, suppressed proteinuria, and prevented severe glomerular and tubulointerstitial lesions, including crescent formation and granulomatous-like lesions. These protective effects were independent of glomerular macrophage and T-cell accumulation, and of the humoral immune response. CC-401 treatment inhibited expression of both pro- and antiinflammatory molecules (interleukin-10 and heme oxygenase-1). In addition, IL-1 induced MMP-12 and IL-10 production by cultured macrophages was found to be JNK dependent. In conclusion, blockade of JNK signaling provides substantial protection against the progression of crescentic anti-GBM glomerulonephritis, which may be, in part, due to inhibition of the macrophage proinflammatory response.

Inhibition of indoleamine 2, 3-dioxygenase-mediated tryptophan catabolism accelerates crescentic glomerulonephritis

Immunomodulatory enzyme indoleamine 2, 3-dioxygenase (IDO) is one of the initial and rate-limiting enzymes involved in the catabolism of the essential amino acid tryptophan. Via catalysing tryptophan degradation, IDO suppresses adaptive T cell-mediated immunity and plays an important role in various forms of immune tolerance. Its role in T helper type 1 (Th1)-directed, cell-mediated crescentic glomerulonephritis (GN) is still unclear. Therefore, we investigated the activity and role of IDO in crescentic GN using a model of nephrotoxic serum nephritis (NTN), and IDO activity was inhibited by 1-methyl-tryptophan (1-MT) in vivo. Our results showed that activity of IDO, as determined by high performance liquid chromatography analysis of the kynurenine/tryptophan ratio, was increased markedly in the serum and renal tissue of NTN mice, and immunohistochemistry revealed that expression of IDO was up-regulated significantly in glomeruli and renal tubular epithelial cells during NTN. Treatment with 1-MT resulted in significantly exacerbated kidney disease with increased glomerular crescent formation, accumulation of CD4(+)T cells and macrophages in renal tissue, and augmented renal injury compared with phosphate-buffered saline-treated NTN mice, which was associated with enhanced Th1 responses and intrarenal cellular proliferation. These findings suggest that the development of NTN was regulated negatively by increased IDO activity, and IDO might play an important role in the pathogenesis of crescentic GN.

Anti-inflammatory and renal protective actions of stanniocalcin-1 in a model of anti-glomerular basement membrane glomerulonephritis

We have previously shown that stanniocalcin-1 (STC1) inhibits the transendothelial migration of macrophages and T cells, suppresses superoxide generation in macrophages, and attenuates macrophage responses to chemoattractants. To study the effects of STC1 on inflammation, in this study we induced a macrophage- and T-cell-mediated model of anti-glomerular basement membrane disease in STC1 transgenic mice, which display elevated serum STC1 levels and preferentially express STC1 in both endothelial cells and macrophages. We examined the following parameters both at baseline and after anti-glomerular basement membrane antibody treatment: blood pressure; C(3a) levels; urine output; proteinuria; blood urea nitrogen; and kidney C(3) deposition, fibrosis, histological changes, cytokine expression, and number of T cells and macrophages. Compared with wild-type mice, after anti-glomerular basement membrane treatment STC1 transgenic mice exhibited: i) diminished infiltration of inflammatory macrophages in the glomeruli; ii) marked reduction in crescent formation and sclerotic glomeruli; iii) decreased interstitial fibrosis; iv) preservation of kidney function and lower blood pressure; v) diminished C(3) deposition in the glomeruli; and vi) reduced expression of macrophage inhibitory protein-2 and transforming growth factor-beta2 in the kidney. Compared with baseline, wild-type mice, but not STC1 transgenic mice, had higher proteinuria and a marked reduction in urine output. STC1 had minimal effects, however, on both T-cell number in the glomeruli and interstitium and on cytokine expression characteristic of either TH1 or TH2 activation. These data suggest that STC1 is a potent anti-inflammatory and renal protective protein.

Preventive and therapeutic effects of imatinib in Wistar-Kyoto rats with anti-glomerular basement membrane glomerulonephritis

Imatinib is a selective tyrosine kinase inhibitor that can block activity of the platelet-derived growth factor receptor (PDGFR) and that has immunomodulatory effects on various cell types. Here we measured the protective effects of imatinib in Wistar-Kyoto rats with nephrotoxic serum nephritis, a kidney disease model where CD8+ T cells and macrophages play pathogenetic roles. Groups of animals were given imatinib from one day before up to 13 days following induction of nephritis and from day 7 to 20 following disease induction. Compared to control rats, at each time point imatinib treatment caused significantly less proteinuria, lowered serum blood urea nitrogen and creatinine, and decreased the number of glomeruli with necrosis, crescents, and fibrin deposits. Imatinib-treated rats had a significant reduction in glomerular macrophage accumulation and reduced renal cortical PDGFR-beta and M-CSF receptor mRNA expression. Using colocalization we found that glomerular macrophages had reduced IL-1beta and MCP-1 protein expression. Late imatinib treatment significantly reduced proteinuria, serum blood urea nitrogen, and creatinine, and reversed renal histopathological changes. We show that imatinib has renoprotective and therapeutic properties and provide pre-clinical work that will need to be confirmed in patients with crescentic glomerulonephritis.

Cryptococcosis associated with crescentic glomerulonephritis

Crescentic glomerulonephritis (CGN) is an uncommon form of renal injury in childhood. Whereas many infectious processes are known to be linked to CGN, fungal infections typically are not. This report describes an 11-year-old girl who presented with CGN, cutaneous anergy, and cryptococcal mediastinitis. Whereas cryptococcal disease in children is usually associated with immunodeficiency (inherited or acquired), extensive immunologic evaluation of the patient was notable only for relative CD4 lymphopenia with normal CD4/CD8 ratios. Testing for human immunodeficiency virus was negative. Clinical and diagnostic studies are presented, along with a review of the literature regarding glomerular disease and cryptococcal infections.

Lymphocytes are dispensable for glomerulonephritis but required for renal interstitial fibrosis in matrix defect-induced Alport renal disease

One current theory for the emergence of glomerular nephritis implicates Th1-type cellular responses associated with delayed-type hypersensitivity, involving T cells and macrophages. Using a mouse model for progressive glomerulonephritis, we investigate the role of B and T cells in the pathogenesis of glomerular inflammation. Deletion of alpha3 chain of type IV collagen in mice (alpha3(IV) collagen null mice) results in GBM defects, glomerulonephritis and tubulointerstitial inflammation, fibrosis and significant immune infiltration including activated B- and T-lymphocytes. To evaluate the contribution of lymphocytes to the pathogenesis of glomerulonephritis and renal fibrosis, we generated mice that are deficient in both the alpha3(IV) collagen and Rag-1 (alpha3/Rag-1 DKO). Lymphocyte deficiency significantly reduces fibrosis in the renal interstitium, but ultrastructural GBM defects persist. Interestingly, glomerulonephritis in the double null mice persists at a similar level with comparable proteinuria. Here we demonstrate that despite the presence of B-cell and T-cells in the inflamed glomeruli, their deletion does not impede the emergence of glomerulonephritis but has a negative impact on the progression of renal interstitial fibrosis.

T-bet deficiency attenuates renal injury in experimental crescentic glomerulonephritis

T-bet is a transcription factor that is essential for T helper (Th)1 lineage commitment and optimal IFN-gamma production by CD4(+) T cells. We examined the role of T-bet in the development of experimental crescentic glomerulonephritis, which is induced by Th1-predominant, delayed-type hypersensitivity-like responses directed against a nephritogenic antigen. Anti-glomerular basement membrane (GBM) glomerulonephritis was induced in T-bet(-/-) and wild-type C57BL/6 mice. Compared with wild-type controls, renal injury was attenuated in T-bet(-/-) mice with glomerulonephritis, evidenced by less proteinuria, glomerular crescents, and tubulointerstitial inflammation. Accumulation of glomerular CD4(+) T cells and macrophages was decreased, and was associated with reduced intrarenal expression of the potent Th1 chemoattractants CCL5/RANTES and CXCL9/Mig. Supporting the pro-inflammatory nature of T-bet signaling, assessment of systemic immunity confirmed that T-bet(-/-) mice had a reduction in Th1 immunity. The kinetic profile of T-bet mRNA in wild-type mice supported the hypothesis that T-bet deficiency attenuates renal injury in part by shifting the Th1/Th2 balance away from a Th1 phenotype. Expression of renal and splenic IL-17A, characteristically expressed by the Th17 subset of effector T cells, which have been implicated in the pathogenesis of autoimmune disease, was increased in T-bet(-/-) mice. We conclude that T-bet directs Th1 responses that induce renal injury in experimental crescentic glomerulonephritis.

Decoy receptor 3 ameliorates an autoimmune crescentic glomerulonephritis model in mice

Autoimmune crescentic glomerulonephritis (ACGN) is a variant of crescentic glomerulonephritis. The outcome of treatment of crescentic glomerulonephritis is poor. Binding of decoy receptor 3 (DCR3) to its ligand is capable of downregulating the alloresponsiveness of T cells. DCR3 has also been shown to benefit an experimental autoimmune model of diabetes. This study tested the hypothesis that a potential immune regulator, DCR3, could prevent the evolution of ACGN. With the use of an established ACGN model in mice, mice were treated with 100 microg/10 g body wt human DCR3 by hydrodynamics-based gene delivery at 14-d intervals. The results showed that the gene therapy resulted in (1) suppression of T and B cell activation and T cell proliferation; (2) a reduction in serum levels of proinflammatory cytokines; (3) improvement of proteinuria and renal dysfunction; (4) prevention of glomerular crescent formation, renal interstitial inflammation, and glomerulosclerosis; (5) a reduction in serum levels of autoantibodies and glomerular immune deposits; (6) inhibition of apoptosis in the spleen and kidney; (7) prevention of T cell and macrophage infiltration of the kidney; and (8) suppression of fibrosis-related gene expression in the kidney compared with empty vector-treated (disease control) ACGN mice. On the basis of these findings, it is proposed that human DCR3 exerts its preventive and protective effects on ACGN through modulation of T cell activation/proliferation, B cell activation, protection against apoptosis, and suppression of mononuclear leukocyte infiltration in the kidney.

Smad7 gene therapy ameliorates an autoimmune crescentic glomerulonephritis in mice

Autoimmune crescentic glomerulonephritis is characterized by severe immune response with glomerular crescentic formation and fibrosis in the kidney. Recent studies indicate that overexpression of renal Smad7 attenuates both renal fibrosis and inflammation in rat remnant kidney. However, little attention has been paid to the potential role of TGF-beta/Smad signaling in autoimmune kidney disease. This study tested the hypothesis that blocking TGF-beta signaling by overexpression of Smad7 may have a therapeutic effect in a mouse model of autoimmune crescentic glomerulonephritis that was induced in C57BL/6 x DBA/2J F1 hybrid mice by giving DBA/2J donor lymphocytes. Smad7 gene was transfected into the kidney using the ultrasound-microbubble-mediated system. Results showed that overexpression of Smad7 blocked both renal fibrosis and inflammatory pathways in terms of Smad2/3 and NF-kappaB activation (P < 0.01), thereby inhibiting alpha-smooth muscle actin; collagen I, III, and IV accumulation; and expression of inflammatory cytokines (IL-1beta and IL-6), adhesion molecule/chemokine (intercellular adhesion molecule-1, monocyte chemoattractant protein-1), and inducible nitric oxide synthase (all P < 0.01). Leukocyte infiltration (CD4(+) cells and macrophages) was also suppressed (P < 0.005). Severe histologic damage (glomerular crescent formation and tubulointerstitial injury) and functional injury including proteinuria were significantly improved (all P < 0.05). This study provides important evidence that overexpression of Smad7 may have therapeutic potential for autoimmune kidney disease.

Macrophage migration inhibitory factor deficiency attenuates macrophage recruitment, glomerulonephritis, and lethality in MRL/lpr mice

Systemic lupus erythematosus (SLE) is a serious systemic autoimmune disease of unknown etiology. Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that is operative in innate and adaptive immunity and important in immune-mediated diseases such as rheumatoid arthritis and atherosclerosis. The functional relevance of MIF in systemic autoimmune diseases such as SLE is unknown. Using the lupus-prone MRL/lpr mice, we aim to examine the expression and function of MIF in this murine model of systemic autoimmune disease. These experiments revealed that renal MIF expression was significantly higher in MRL/lpr mice compared with nondiseased control mice (MRL/MpJ), and MIF was also markedly up-regulated in skin lesions of MRL/lpr mice. To examine the effect of MIF on development of systemic autoimmune disease, we generated MRL/lpr mice with a targeted disruption of the MIF gene (MIF(-/-)MRL/lpr), and compared their disease manifestations to MIF(+/+)MRL/lpr littermates. MIF(-/-)MRL/lpr mice exhibited significantly prolonged survival, and reduced renal and skin manifestations of SLE. These effects occurred in the absence of major changes in T and B cell markers or alterations in autoantibody production. In contrast, renal macrophage recruitment and glomerular injury were significantly reduced in MIF(-/-)MRL/lpr mice, and this was associated with reduction in the monocyte chemokine MCP-1. Taken together, these data suggest MIF as a critical effector of organ injury in SLE.

Endogenous myeloperoxidase promotes neutrophil-mediated renal injury, but attenuates T cell immunity inducing crescentic glomerulonephritis

Myeloperoxidase (MPO) is an enzyme that is found in neutrophils and monocytes/macrophages. Intracellularly, it plays a major role in microbial killing, but extracellularly, it may cause host tissue damage. The role of endogenous MPO was studied during neutrophil-mediated (heterologous) and T helper 1 (Th1)/macrophage-mediated (autologous) phases of crescentic glomerulonephritis. Glomerulonephritis was induced in C57BL/6 wild-type (WT) and MPO-deficient (MPO(-/-)) mice by intravenous injection of sheep anti-mouse glomerular basement membrane globulin. MPO activity was increased in kidneys of WT mice during both the heterologous and autologous phases of glomerulonephritis. During the heterologous phase of glomerulonephritis, proteinuria was decreased, whereas glomerular neutrophil accumulation and P-selectin expression were enhanced in MPO(-/-) mice. In the autologous, crescentic phase of glomerulonephritis, MPO(-/-) mice had increased accumulation of CD4(+) cells and macrophages in glomeruli compared with WT mice. However, no difference in renal injury (crescent formation, proteinuria, and serum creatinine levels) was observed. Neutrophils and macrophages from MPO(-/-) mice exhibited reduced production of reactive oxygen species. Assessment of systemic immunity to sheep globulin showed that MPO(-/-) mice had increased splenic CD4(+) cell proliferation, cytokine production, and dermal delayed-type hypersensitivity, as well as enhanced levels of circulating IgG, IgG1, and IgG3. MPO(-/-) mice also had an augmented Th1:Th2 ratio compared with WT mice (IFN-gamma:IL-4 and IgG3:IgG1 ratios). These results suggest that endogenous MPO locally contributes to glomerular damage during neutrophil-mediated glomerulonephritis, whereas it attenuates initiation of the adaptive immune response inducing crescentic, autologous-phase glomerulonephritis by suppressing T cell proliferation, cytokine production, and Th1:Th2 ratio.

FcR-bearing myeloid cells are responsible for triggering murine lupus nephritis

Lupus glomerulonephritis is initiated by deposition of IgG-containing immune complexes in renal glomeruli. FcR engagement by immune complexes (IC) is crucial to disease development as uncoupling this pathway in FcRgamma(-/-) abrogates inflammatory responses in (NZB x NZW)F1 mice. To define the roles of FcR-bearing hemopoietic cells and of kidney resident mesangial cells in pathogenesis, (NZB x NZW)F1 bone marrow chimeras were generated. Nephritis developed in (NZB x NZW)F1 mice expressing activating FcRs in hemopoietic cells. Conversely, recipients of FcRgamma(-/-) bone marrow were protected from disease development despite persistent expression of FcRgamma in mesangial cell populations. Thus, activating FcRs on circulating hemopoietic cells, rather than on mesangial cells, are required for IC-mediated pathogenesis in (NZB x NZW)F1. Transgenic FcRgamma(-/-) mice expressing FcRgamma limited to the CD11b+ monocyte/macrophage compartment developed glomerulonephritis in the anti-glomerular basement disease model, whereas nontransgenic FcRgamma(-/-) mice were completely protected. Thus, direct activation of circulating FcR-bearing myeloid cells, including monocytes/macrophages, by glomerular IC deposits is sufficient to initiate inflammatory responses.