Susceptibility to anti-glomerular basement membrane disease and Goodpasture syndrome is linked to MHC class II genes and the emergence of T cell-mediated immunity in mice

An Updated Review of Membranous Nephropathy

Membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome in adults. The discovery of phospholipase A2 receptor (PLA2R) as a target antigen has led to a paradigm shift in the understanding and management of MN. At present, serum PLA2R antibodies are used for diagnosis, prognostication, and guiding treatment. Now, with the discovery of more than 20 novel target antigens, antigen mapping is almost complete. The clinical association of certain antigens provides clues for clinicians, such as the association of nerve epidermal growth factor-like 1 with malignancies and indigenous medicines. Serum antibodies are detected for most target antigens, except exostosin 1 and 2 and transforming growth factor-beta receptor 3, but their clinical utility is yet to be defined. Genome-wide association studies and studies investigating environmental factors, such as air pollution, shed more light on the underpinnings of MN. The standard therapy of MN diversified from cyclical cyclophosphamide and steroids to include rituximab and calcineurin inhibitors over the past decades. Here, we provide a cutting-edge review of MN, focusing on genetics, immune system and environmental factors, novel target antigens and their clinical characteristics, and currently available and emerging novel therapies in MN.

Anti-glomerular basement membrane vasculitis

Antiglomerular basement membrane disease (anti-GBM) is a rare life-threatening autoimmune vasculitis that involves small vessels and it is characterized by circulating autoantibodies directed against type IV collagen antigens expressed in glomerular and alveolar basement membrane. The typical clinical manifestations are the rapidly progressive glomerulonephritis and the alveolar hemorrhage. The diagnosis is usually confirmed by the detection of anti-GBM circulating antibodies. If not rapidly recognized, anti-GBM disease can lead to end stage kidney disease (ESKD). An early diagnosis and prompt treatment with immunosuppressive therapies and plasmapheresis are crucial to prevent a poor outcome. In this review, we discuss the primary form of anti-GBM (the so called Goodpasture syndrome) but also cases associated with other autoimmune diseases such as antineutrophil-cytoplasmic-antibody (ANCA) vasculitis, membranous nephropathy, IgA nephritis and systemic lupus erythematosus (SLE), as well as the few cases of anti-GBM vasculitis complicating kidney transplantation in the Alport syndrome.

Mechanical activation of TRPV4 channels controls albumin reabsorption by proximal tubule cells

Defects in protein reabsorption by the proximal tubule are toxic for epithelial cells in the nephron and may result in nephropathy. In this study, we showed that the ion channel TRPV4 modulated the endocytosis of albumin and low–molecular weight proteins in the proximal tubule. TRPV4 was found at the basolateral side of proximal tubule cells, and its mechanical activation by cell stretching induced Ca2+ entry into the cytosol, which promoted endocytosis. Trpv4−/− mice presented with mild proximal tubule dysfunction under basal conditions. To challenge endocytic function, the permeability of the glomerular filter was altered by systemic delivery of angiotensin II. The proteinuria induced by this treatment was more severe in Trpv4−/− than in Trpv4+/+ mice. Injecting antibodies against the glomerular basement membrane to induce glomerulonephritis is a more pathophysiologically relevant method of impairing glomerular filter permeability. Albuminuria was more severe in mice that lacked TRPV4 specifically in the proximal tubule than in control mice. These results emphasize the importance of TRPV4 in sensing pressure in the proximal tubule in response to variations in the amount of ultrafiltrate and unveil a mechanism that controls protein reabsorption.

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.

The Diagnostic and Clinical Utility of Autoantibodies in Systemic Vasculitis

Considerable progress has been made in understanding the role of autoantibodies in systemic vasculitides (SV), and consequently testing for anti-neutrophil cytoplasmic antibodies (ANCA), anti-glomerular basement membrane antibodies (anti-GBM), and anti-C1q antibodies is helpful and necessary in the diagnosis, prognosis, and monitoring of small-vessel vasculitis. ANCA-directed proteinase 3 (PR3-) or myeloperoxidase (MPO-) are sensitive and specific serologic markers for ANCA-associated vasculitides (AAV), anti-GBM antibodies are highly specific for the patients with anti-GBM antibody disease (formerly Goodpasture’s syndrome), and autoantibodies to C1q are characteristic of hypocomlementemic urticarial vasculitis syndrome (HUVS; anti-C1q vasculitis). The results of a current EUVAS study have led to changes in the established strategy for the ANCA testing in small-vessel vasculitis. The revised 2017 international consensus recommendations for ANCA detection support the primary use PR3- and MPO-ANCA immunoassays without the categorical need for additional indirect immunofluorescence (IIF). Interestingly, the presence of PR3- and MPO-ANCA have led to the differentiation of distinct disease phenotype of AAV: PR3-ANCA-associated vasculitis (PR3-AAV), MPO-ANCA-associated vasculitis (MPO-AAV), and ANCA-negative vasculitis. Further studies on the role of these autoantibodies are required to better categorize and manage appropriately the patients with small-vessel vasculitis and to develop more targeted therapy.

Antigen-Specificity in the Thymic Development and Peripheral Activity of CD4+FOXP3+ T Regulatory Cells

CD4⁺Foxp3⁺ T regulatory cells (Treg) are essential for the life of the organism, in particular because they protect the host against its own autoaggressive CD4⁺Foxp3^- T lymphocytes (Tconv). Treg distinctively suppress autoaggressive immunity while permitting efficient defense against infectious diseases. This split effect indicates that Treg activity is controlled in an antigen-specific manner. This specificity is achieved first by the formation of the Treg repertoire during their development, and second by their activation in the periphery. This review presents novel information on the antigen-specificity of Treg development in the thymus, and Treg function in the periphery. These aspects have so far remained imprecisely understood due to the lack of knowledge of the actual antigens recognized by Treg during the different steps of their life, so that most previous studies have been performed using artificial antigens. However, recent studies identified some antigens mediating the positive selection of autoreactive Treg in the thymus, and the function of Treg in the periphery in autoimmune and allergic disorders. These investigations emphasized the remarkable specificity of Treg development and function. Indeed, the development of autoreactive Treg in the thymus was found to be mediated by single autoantigens, so that the absence of one antigen led to a dramatic loss of Treg reacting toward that antigen. The specificity of Treg development is important because the constitution of the Treg repertoire, and especially the presence of holes in this repertoire, was found to crucially influence human immunopathology. Indeed, it was found that the development of human immunopathology was permitted by the lack of Treg against the antigens driving the autoimmune or allergic T cell responses rather than by the impairment of Treg activation or function. The specificity of Treg suppression in the periphery is therefore intimately associated with the mechanisms shaping the formation of the Treg repertoire during their development. This novel information refines significantly our understanding of the antigen-specificity of Treg protective function, which is required to envision how these cells distinctively regulate unwanted immune responses as well as for the development of appropriate approaches to optimally harness them therapeutically in autoimmune, malignant, and infectious diseases.

Identification of HLA-DQA1 as a Susceptibility Gene for Spinal Tuberculosis by Exome Sequencing

Background

Spinal tuberculosis (STB) is the main cause of bone and joint tuberculosis. This study aimed to screen and analyze the susceptibility genes for STB using whole-exome sequencing (WES).

Material/Methods

All exon regions of peripheral blood DNA from 6 STB patients were captured and sequenced using WES and the sequencing data were analyzed by modern bioinformatics methods to identify disease-causing mutations. Sanger sequencing was then used to validate the mutation sites in normal controls (207) and STB patients (193). The mRNA expression of the mutant gene and the serum levels of IL-6 and TNF-α were detected using qPCR or ELISA assay, respectively.

Results

A nonsynonymous single-nucleotide polymorphism (SNP) in the gene HLA-DQA1 (rs796778515, c.592delCinsG, CAG to GAG, p.Q198E) was identified and further validated by Sanger sequencing. The percentage of the 3 genotypes C/C, C/G and G/G in STB patients and normal controls were 37.3%, 32.1%, and 30.6% and 47.8%, 33.8%, and 18.4%, respectively. Furthermore, the C>G mutation was significantly associated with the occurrence of STB. In addition, the levels of HLA-DQA1 mRNA were significantly lower in blood cells from STB patients compared with normal controls, while the serum levels of IL-6 and TNF-α were significantly higher.

Conclusions

The C>G mutation in the HLA-DQA1 gene was associated with the occurrence of STB. This variation may result in the decreased level of HLA-DQA1 mRNA and increased serum levels of IL-6 and TNF-α, which finally led the STB susceptibility.

A methodological review of induced animal models of autoimmune diseases

Autoimmune disorders are characterized by a loss of immune tolerance and consequent autoimmunity-mediated disease manifestation. Experimental models are invaluable research tools helping us to understand disease pathogenesis and to search for novel therapeutics. Animal models of autoimmune diseases consist of two groups, spontaneous and induced models. In this review article, we focus on the induced models of autoimmune diseases. Due to the complex nature of autoimmune disorders, many strategies have been applied for the induction of corresponding experimental models in animals like monkeys, rabbits, rats, and mice. Methodologically, these strategies can be categorized into three categories, namely immunization with autoantigen, transfer of autoimmunity, and induction by environmental factors. In this review article, we aim to provide a comprehensive overview of the field of induced experimental autoimmune diseases. On the one hand, we describe and summarize the different strategies used for induction of experimental autoimmune disease. On the other hand, we discuss how to select a strategy for modeling human disease, including the choice of an appropriate species and method for such an approach.

Antibodies against linear epitopes on Goodpasture autoantigen in patients with anti-neutrophil cytoplasmic antibody-associated vasculitis

In a substantial number of patients with crescentic glomerulonephritis, both anti-glomerular basement membrane (GBM) antibodies and anti-neutrophil cytoplasmic antibodies (ANCA) are detected simultaneously. ANCA is presumed to be the initial event but the mechanism is unknown. In the present study, we investigated the antibodies against linear epitopes on Goodpasture autoantigen in sera from patients with ANCA-associated vasculitis, aiming to reveal the mechanisms of the coexistence of the two kinds of autoantibodies. Thirty-one patients with ANCA-associated vasculitis were enrolled in this study. Twenty-four overlapping linear peptides were synthesized across the whole sequence of Goodpasture autoantigen. Serum antibodies against linear peptides were detected by ELISA and their associations with clinical features were further analyzed. Twenty-five out of the thirty-one (80.6%) sera from patients with ANCA-associated vasculitis possessed antibodies against linear peptides on Goodpasture autoantigen. These antibodies could be detected in 50% of patients with normal renal function (Scr ≤ 133 μmol/L), 70% of patients with moderate renal dysfunction (133 μmol/L < Scr ≤ 600 μmol/L), and 94% of patients with renal failure (Scr > 600 μmol/L) (P = 0.032). The highest recognition frequencies were found for peptides P4 (51.6%), P14 (54.8%), and P24 (54.8%), which contained the sequences that constitute the conformational epitopes of E_A (P4) and E_B (P14) recognized by anti-GBM antibodies. The level of anti-P4 antibodies was positively correlated with the percentage of crescents in glomeruli (r = 0.764, P = 0.027). Patients with anti-P24 antibodies had a significantly higher prevalence of renal dysfunction on diagnosis (88.2 vs. 42.9%, P = 0.018). Antibodies against linear epitopes on Goodpasture autoantigen could be detected in sera of patients with ANCA-associated vasculitis, which might mediate the production of antibodies towards the conformational epitopes on Goodpasture autoantigen, namely, the anti-GBM antibodies.

The pathogenicity of T cell epitopes on human Goodpasture antigen and its critical amino acid motif

Goodpasture antigen, the non‐collagenous domain of α3 chain of type IV collagen [α3(IV)NC1], is the target antigen of anti‐glomerular basement membrane (GBM) antibodies. The pathogenicity of T cell epitopes is not elucidated clearly. In this study, we aim to define the nephritogenic T cell epitopes and its critical amino acid residues. Twenty‐four overlapping linear peptides were synthesized covering the whole sequence of human α3(IV)NC1. Wistar–Kyoto rats were immunized with linear peptides, and experimental autoimmune glomerulonephritis was evaluated. Critical amino acid was identified by the loss of nephritogenic function after each amino acid substitution by alanine. Of the 24 peptides, P14 (α3_127‐148) could induce 90.5% (19/21) of WKY rats developing anti‐GBM glomerulonephritis with proteinuria, elevated serum urea and creatinine, IgG linear deposit on GBM and substantial (in average 82.4 ± 5.6%) crescent formation in glomeruli. Lymphocytes of immunized rats proliferated in response to α3_127‐148 and α3(IV)NC1 in vitro. Sera of these rats recognized α3_127‐148 and later on together with intact human α3(IV)NC1. Antibodies towards α3_127‐148 and intact α3(IV)NC1 could also be detected from the kidney elutes. These antibodies showed no cross‐reaction with each other, which implies intramolecular epitope spreading during disease progress. After sequential amino acid substitution, the α3_127‐148 with substitution of tryptophan₁₃₆, isoleucine₁₃₇, leucine₁₃₉ or tryptophan₁₄₀ lost its nephritogenicity. Human α3_127‐148 is a nephritogenic T cell epitope in WKY rats, with the critical amino acids as W₁₃₆I₁₃₇xL₁₃₉W₁₄₀. These findings might facilitate future investigation on microbial aetiology and potential specific immunotherapy of anti‐GBM disease.

Basement membranes and autoimmune diseases

Basement membrane components are targets of autoimmune attack in diverse diseases that destroy kidneys, lungs, skin, mucous membranes, joints, and other organs in man. Epitopes on collagen and laminin, in particular, are targeted by autoantibodies and T cells in anti-glomerular basement membrane glomerulonephritis, Goodpasture's disease, rheumatoid arthritis, post-lung transplant bronchiolitis obliterans syndrome, and multiple autoimmune dermatoses. This review examines major diseases linked to basement membrane autoreactivity, with a focus on investigations in patients and animal models that advance our understanding of disease pathogenesis. Autoimmunity to glomerular basement membrane type IV is discussed in depth as a prototypic organ-specific autoimmune disease yielding novel insights into the complexity of anti-basement membrane immunity and the roles of genetic and environmental susceptibility.

Optimizing the translational value of animal models of glomerulonephritis: insights from recent murine prototypes

Animal models are indispensable for the study of glomerulonephritis, a group of diseases that destroy kidneys but for which specific therapies do not yet exist. Novel interventions are urgently needed, but their rational design requires suitable in vivo platforms to identify and test new candidates. Animal models can recreate the complex immunologic microenvironments that foster human autoimmunity and nephritis and provide access to tissue compartments not readily examined in patients. Study of rat Heymann nephritis identified fundamental disease mechanisms that ultimately revolutionized our understanding of human membranous nephropathy. Significant species differences in expression of a major target antigen, however, and lack of spontaneous autoimmunity in animals remain roadblocks to full exploitation of preclinical models in this disease. For several glomerulonephritides, humanized models have been developed to circumvent cross-species barriers and to study the effects of human genetic risk variants. Herein we review humanized mouse prototypes that provide fresh insight into mediators of IgA nephropathy and origins of antiglomerular basement membrane nephritis and Goodpasture's disease, as well as a means to test novel therapies for ANCA vasculitis. Additional and refined model systems are needed to mirror the full spectrum of human disease in a genetically diverse population, to facilitate development of patient-specific interventions, to determine the origin of nephritogenic autoimmunity, and to define the role of environmental exposures in disease initiation and relapse.

TH1 and TH17 cells promote crescent formation in experimental autoimmune glomerulonephritis

Autoimmunity against the Goodpasture antigen α3IV-NC1 results in crescentic glomerulonephritis (GN). Both antibodies and T cells directed against α3IV-NC1 have been implicated in disease development and progression. Using the model of experimental autoimmune glomerulonephritis (EAG) in DBA/1 mice, we aimed to characterize the frequency and function of α3IV-NC1-specific CD4(+) T cells in the kidneys. DBA/1 mice repeatedly immunized with human α3IV-NC1 developed necrotizing/crescentic GN. Kidneys with crescentic GN contained CD4(+) cells responding to α3IV-NC1 with the production of IFN-γ or IL-17A, demonstrating the accumulation of both α3IV-NC1-specific TH1 and TH17 cells. To test the functional relevance of TH1 and TH17 cells, EAG was induced in DBA/1 mice deficient in IFN-γR, IL-17A or IL-23p19. Mice of all knockout groups mounted α3IV-NC1 IgG, developed nephrotic range proteinuria, and IgG deposition to the glomerular basement membranes at levels similar to immunized wild-type mice. However, all knockout groups showed significantly fewer glomerular crescents and attenuated tubulointerstitial damage. Our results suggest that both α3IV-NC1-specific TH1 and TH17 cells accumulate in the kidneys and are crucial for the development of necrotizing/crescentic GN.

Identification of critical residues of linear B cell epitope on Goodpasture autoantigen

Background

The autoantigen of anti-glomerular basement membrane (GBM) disease has been identified as the non-collagenous domain 1 of α3 chain of type IV collagen, α3(IV)NC1. Our previous study revealed a peptide on α3(IV)NC1 as a major linear epitope for B cells and potentially nephrogenic, designated as P14 (α3129-150). This peptide has also been proven to be the epitope of auto-reactive T cells in anti-GBM patients. This study was aimed to further characterize the critical motif of P14.

Methods

16 patients with anti-GBM disease and positive anti-P14 antibodies were enrolled. A set of truncated and alanine substituted peptides derived from P14 were synthesized. Circulating antibodies against the peptides were detected by enzyme linked immunosorbent assay (ELISA).

Results

We found that all sera with anti-P14 antibodies reacted with the 13-mer sequence in the C-terminus of P14 (P14c) exclusively. The level of antibodies against P14 was highly correlated with the level of antibodies against P14c (r=0.970, P<0.001). P14c was the core immunogenic region and the amino acid sequence (ISLWKGFSFIMFT) was highly hydrophobic. Each amino acid residue in P14c was sequentially replaced by alanine. Three residues of glycine142, phenylalanine143, and phenylalanine145 were identified crucial for antibody binding based on the remarkable decline (P<0.001) of antibody reaction after each residue replacement.

Conclusions

We defined GFxF (α3142, 143,145) as the critical motif of P14. It may provide some clues for understanding the etiology of anti-GBM disease.

Autoimmunity to the alpha 3 chain of type IV collagen in glomerulonephritis is triggered by 'autoantigen complementarity'

'Autoantigen complementarity' is a theory proposing that the initiator of an autoimmune response is not necessarily the autoantigen or its molecular mimic, but may instead be a peptide that is 'antisense/complementary' to the autoantigen. We investigated whether such complementary proteins play a role in the immunopathogenesis of autoimmune glomerulonephritis. Experimental autoimmune glomerulonephritis, a model of anti-glomerular basement membrane (GBM) disease, can be induced in Wistar Kyoto (WKY) rats by immunization with the α3 chain of type IV collagen. In this study, WKY rats were immunized with a complementary α3 peptide (c-α3-Gly) comprised of amino acids that 'complement' the well characterized epitope on α3(IV)NC1, pCol(24-38). Within 8 weeks post-immunization, these animals developed cresentic glomerulonephritis, similar to pCol(24-38)-immunized rats, while animals immunized with scrambled peptide were normal. Anti-idiotypic antibodies to epitopes from c-α3-Gly-immunized animals were shown to be specific for α3 protein, binding in a region containing sense pCol(24-38) sequence. Interestingly, anti-complementary α3 antibodies were identified in sera from patients with anti-GBM disease, suggesting a role for 'autoantigen complementarity' in immunopathogenesis of the human disease. This work supports the idea that autoimmune glomerulonephritis can be initiated through an immune response against a peptide that is anti-sense or complementary to the autoantigen. The implications of this discovery may be far reaching, and other autoimmune diseases could be due to responses to these once unsuspected 'complementary' antigens.

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

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

T cell mediated autoimmune glomerular disease in mice

Many forms of glomerulonephritis are mediated by autoimmunity. While autoantibodies are often pathogenic, cell-mediated immunity plays an important role in a number of forms of rapidly progressive glomerulonephritis. This unit describes the induction of cell-mediated autoimmune glomerular disease in mice. One disease model, experimental anti-glomerular basement membrane (GBM) disease, features autoreactivity to a well-defined component of type IV collagen found in the GBM, α3(IV)NC1. The other models the cell-mediated effector response in forms of renal vasculitis, where autoantibodies to myeloperoxidase result in systemic neutrophil activation, resulting in their localization to the glomerulus and the subsequent deposition of myeloperoxidase within glomerular capillaries. There, myeloperoxidase acts as a "planted" autoantigen and is recognized by effector autoreactive myeloperoxidase-specific T cells. These models are useful both in defining mechanisms germane to the development of autoimmunity to α3(IV)NC1 and myeloperoxidase, and in dissecting the role of cell-mediated responses in effecting glomerular injury.

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.

The role of necrotic cell death in the pathogenesis of immune mediated nephropathies

Necrosis, an inflammatory form of cell death, has been considered to be an accidental death and/or cell death due to injury. However, the literature in the last decade has established that necrosis is a regulated form of cell death, and that inhibition of specific molecular pathways leading to necrosis can block it and reduce inflammation. Since necrotic lesions are observed in several immune mediated human pathologies, in this review we will discuss the impact that this form of programmed cellular demise has in the pathology of immune mediated nephropathies.

The HLA-DRB1*15:01-restricted Goodpasture's T cell epitope induces GN

Human anti-glomerular basement membrane (GBM) disease strongly associates with HLA-DRB1*15:01. The target autoantigen in this disease is the noncollagenous domain of the α3 chain of type IV collagen, α3(IV)NC1, but critical early T cell epitopes presented by this human MHC class II molecule are unknown. Here, by immunizing HLA-DRB1*15:01 transgenic mice with whole recombinant α3(IV)NC1 and with overlapping α3(IV)NC1 peptides, we defined a HLA-DRB1*15:01-restricted α3(IV)NC1 T cell epitope (α3136-146) with four critical residues. This peptide was not immunogenic in HLA-DRB1*01:01 transgenic or C57BL/6 mice. The T cell epitope is naturally processed from α3(IV)NC1. CD4(+) T cell clones, generated from HLA-DRB1*15:01 transgenic mice and specific for α3136-146, transferred disease into naive HLA-DRB1*15:01 transgenic mice, evidenced by the development of necrotizing crescentic GN, albuminuria, renal impairment, and accumulation of CD4(+) T cells and macrophages in glomeruli. Because Fcγ receptors are implicated in disease susceptibility, we crossed HLA transgenic mice onto an FcγRIIb-deficient background. Immunization with either α3136-146 or α3(IV)NC1 induced GN in HLA-DRB1*15:01 transgenic FcγRIIb-deficient mice, but HLA-DRB1*01:01 transgenic FcγRIIb-deficient mice were unaffected. Taken together, these results demonstrate that the HLA-DRB1*15:01-restricted T cell epitope α3136-146 can induce T cell responses and injury in anti-GBM GN.

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.

Antibodies against linear epitopes on the Goodpasture autoantigen and kidney injury

BACKGROUND AND OBJECTIVES

Linear epitopes on the Goodpasture autoantigen involved in human anti-glomerular basement membrane (GBM) disease are not fully defined. This study investigated the linear epitopes recognized by circulating antibodies in anti-GBM patients, aiming to identify the potential nephrogenic linear epitopes and their clinical significance.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Sixty-eight patients with anti-GBM disease were enrolled. Twenty-four overlapping linear peptides were synthesized across the whole sequence of the human Goodpasture autoantigen. ELISA detected circulating antibodies against linear epitopes. Their associations with clinical features were further analyzed.

RESULTS

Antibodies against linear peptides were detected in sera from 55 patients (80.9%). Three major epitopes with high frequencies were identified: P14 (41%), P16 (36.8%), and P18 (57%). P14, a formerly defined T cell epitope, was a mutual B cell epitope. Antibodies against P14 were frequently detected in patients with positive antineutrophil cytoplasmic antibodies (39.3% versus 12.5%; P=0.01). Patients with anti-P16 antibodies presented with higher serum creatinine on diagnosis (665.5±227.2 versus 443.7±296.8 μmol/L; P=0.001) and worse renal outcome during follow-up (hazard ratio, 2.10; 95% confidence interval, 1.10-3.90; P=0.02). The level of anti-P18 antibodies positively correlated with the percentage of crescents in glomeruli (r=0.54; P=0.008). Recognition of P22 was an independent predictor for patient death (hazard ratio, 3.02; 95% confidence interval, 1.20-7.57; P=0.02).

CONCLUSIONS

Antibodies against linear epitopes on the Goodpasture autoantigen could be detected in human anti-GBM disease and were associated with kidney injury. P14 was a mutual T and B cell epitope, implying its nephrogenic role in disease initiation.

Characterization of the renal CD4+ T-cell response in experimental autoimmune glomerulonephritis

Autoimmunity against the Goodpasture antigen α3IV-NC1 results in antiglomerular basement membrane glomerulonephritis. Although antibodies are central to the pathogenesis, there is good evidence for the participation of T cells in this disease. To define the contribution of T cells, we used the model of experimental autoimmune glomerulonephritis. Immunization of DBA/1 mice with α3IV-NC1 resulted in proteinuria, a biphasic course of the disease, and an eventual loss of kidney function. In the initial phase, the mice developed an α3IV-NC1-specific IgG response, had IgG deposition along the glomerular basement membrane, and steadily increased proteinuria, but only marginal signs of inflammation with limited leukocyte infiltration. After 9-13 weeks, mice proceeded to develop crescentic glomerulonephritis, extensive tubulointerstitial damage, and massive macrophage infiltration. T-cell infiltration was less pronounced, mostly confined to the interstitium, and T cells displayed an activated phenotype with a significant fraction of Th1 or Th17 CD4(+) T cells. Close examination revealed the presence of autoreactive T cells producing IFNγ upon restimulation with α3IV-NC1. Thus, our results suggest that accumulation of effector T cells, including autoreactive T cells, represents a critical step in the progression from mild glomerulonephritis, with limited glomerular damage, to severe crescentic glomerulonephritis accompanied by tubulointerstitial inflammation and loss of kidney function.

Cutting edge issues in Goodpasture's disease

Goodpasture's disease, or anti-glomerular basement membrane (anti-GBM) disease, is a systemic autoimmune disorder defined by anti-GBM antibody-mediated damage (mainly immunoglobulin G-1) resulting in progressive crescentic glomerulonephritis and, frequently, diffuse pulmonary alveolar hemorrhage. It may be regarded as a "conformeropathy" where the quaternary structure of the α345NC1 hexamer that constitutes GBM undergoes a conformational change, exposing pathogenic epitopes on the α3 and α5 chains, eliciting a pathogenic autoantibody anti-GBM response. Goodpasture's disease accounts for 20% of all patients presenting with a pulmonary-renal syndrome and may be associated with detectable perinuclear antineutrophil cytoplasmic autoantibody positivity in up to a third of patients. Associated triggers may include tobacco smoking, hydrocarbon solvent exposure, and cocaine abuse. Cough, hemoptysis, and dyspnea with fatigue are the commonest presenting features. It is critical to rapidly distinguish Goodpasture's disease from other causes of pulmonary-renal syndromes such as Wegener's granulomatosis. Early and intensive treatment with plasmapheresis and immunosuppression with systemic corticosteroids pending results of diagnostic testing, and later cyclophosphamide, is often beneficial, with 90% of patients surviving the acute presentation of Goodpasture's disease. The need for hemodialysis on initial presentation, a serum creatinine >5 mg/dL, and 50% to 100% crescents on renal biopsy, portend the necessity of long-term hemodialysis. Further elucidation of the molecular pathobiology of Goodpasture's disease, particularly the regulation of involved antigen-specific T cells, may improve early diagnosis, treatment, and outcomes in this rare but potentially lethal autoimmune disorder.

Epidermal growth factor receptor promotes glomerular injury and renal failure in rapidly progressive crescentic glomerulonephritis

Rapidly progressive glomerulonephritis (RPGN) is a clinical a morphological expression of severe glomerular injury. Glomerular injury manifests as a proliferative histological pattern (“crescents”) with accumulation of T cells and macrophages, and proliferation of intrinsic glomerular cells. We show de novo induction of heparin-binding epidermal growth factor-like growth factor (HB-EGF) in intrinsic glomerular epithelial cells (podocytes) from both mice and humans with RPGN. HB-EGF induction increases phosphorylation of the EGFR/ErbB1 receptor in mice with RPGN. In HB-EGF-deficient mice, EGFR activation in glomeruli is absent and the course of RPGN is improved. Autocrine HB-EGF induces a phenotypic switch in podocytes in vitro. Conditional deletion of the Egfr gene from podocytes of mice alleviates the severity of RPGN. Pharmacological blockade of EGFR also improves the course of RPGN, even when started 4 days after the induction of experimental RPGN. This suggests that targeting the HB-EGF/EGFR pathway could also be beneficial for treatment of human RPGN.

Novel targets for immunotherapy in glomerulonephritis

Glomerulonephritis is a common cause of chronic kidney disease and end stage renal failure. Current therapy relies on variably effective, nonspecific and toxic immunosuppression. Recent insights into underlying biology and disease pathogenesis in human glomerulonephritis combined with advances in the fields of inflammation and autoimmunity promise a cadre of novel targeted interventions. This review highlights the therapeutic potential of two antigens, alpha3 (IV)NC1 collagen and podocyte neutral endopeptidase, and two cell signaling and effector molecules, IgG Fc receptors and complement, judged to be particularly amenable to therapeutic manipulation in man. It is anticipated that continued dissection of pathogenesis in the diverse disorders that comprise the glomerulonephritides will provide the basis for individualized disease-specific therapy.

Strain differences and the genetic basis of experimental autoimmune anti-glomerular basement membrane glomerulonephritis

Goodpasture's, or anti-glomerular basement membrane (GBM), disease presents with rapidly progressive glomerulonephritis, caused by autoimmunity to a component of the GBM, the non-collagenous domain of the α3 chain of type IV collagen [α3(IV)NC1]. To investigate the mechanisms of inflammation in glomerulonephritis and to test new approaches to treatment, animal models of glomerulonephritis, termed experimental autoimmune glomerulonephritis (EAG), have been developed in susceptible strains of rats and mice. This review article describes how these models of EAG have been developed over the past three decades, discusses the evidence for the involvement of both humoral and cell-mediated immunity in the induction and pathogenesis of glomerulonephritis in these models and highlights recent, emerging data that have identified potential candidate genes that may control the genetic susceptibility in these different strains of rats and mice. The identification of these susceptibility genes has lead to a better understanding of the genetic basis of this model of anti-GBM disease, which may be relevant to the immunopathogenesis of Goodpasture's disease, and more generally to the progression from autoimmunity to target-organ damage.

Risk HLA-DQA1 and PLA(2)R1 alleles in idiopathic membranous nephropathy

BACKGROUND

Idiopathic membranous nephropathy is a major cause of the nephrotic syndrome in adults, but its etiologic basis is not fully understood. We investigated the genetic basis of biopsy-proven cases of idiopathic membranous nephropathy in a white population.

METHODS

We performed independent genomewide association studies of single-nucleotide polymorphisms (SNPs) in patients with idiopathic membranous nephropathy from three populations of white ancestry (75 French, 146 Dutch, and 335 British patients). The patients were compared with racially matched control subjects; population stratification and quality controls were carried out according to standard criteria. Associations were calculated by means of a chi-square basic allele test; the threshold for significance was adjusted for multiple comparisons (with the Bonferroni method).

RESULTS

In a joint analysis of data from the 556 patients studied (398 men), we identified significant alleles at two genomic loci associated with idiopathic membranous nephropathy. Chromosome 2q24 contains the gene encoding M-type phospholipase A(2) receptor (PLA(2)R1) (SNP rs4664308, P=8.6×10(-29)), previously shown to be the target of an autoimmune response. Chromosome 6p21 contains the gene encoding HLA complex class II HLA-DQ alpha chain 1 (HLA-DQA1) (SNP rs2187668, P=8.0×10(-93)). The association with HLA-DQA1 was significant in all three populations (P=1.8×10(-9), P=5.6×10(-27), and P=5.2×10(-36) in the French, Dutch, and British groups, respectively). The odds ratio for idiopathic membranous nephropathy with homozygosity for both risk alleles was 78.5 (95% confidence interval, 34.6 to 178.2).

CONCLUSIONS

An HLA-DQA1 allele on chromosome 6p21 is most closely associated with idiopathic membranous nephropathy in persons of white ancestry. This allele may facilitate an autoimmune response against targets such as variants of PLA2R1. Our findings suggest a basis for understanding this disease and illuminate how adaptive immunity is regulated by HLA.

Immunological Aspects of Systemic Vasculitis

Primary vasculitis are commonly multifactorial disorders involving environmental, genetic and immunological factors. Several immune-based effector mechanisms are implicated in the vascular wall damage. These effector mechanisms commonly imply auto-antibodies or immune complexes - mediated cytotoxicity but the contribution of a T-cell mediated immune response has also been described, particularly in large vascular vasculitis. Despite advances in understanding the pathophysiological mechanisms of vasculitis, the triggering events initiating the disease remain largely undefined in most cases. This review highlights the recent advances in the etiopathogenesis of primary vasculitis. A better understanding of the immunological aspects of these disorders may provide insight into the development of novel therapeutical strategies.

Alport alloantibodies but not Goodpasture autoantibodies induce murine glomerulonephritis: protection by quinary crosslinks locking cryptic α3(IV) collagen autoepitopes in vivo

The noncollagenous (NC1) domains of alpha3alpha4alpha5(IV) collagen in the glomerular basement membrane (GBM) are targets of Goodpasture autoantibodies or Alport posttransplant nephritis alloantibodies mediating rapidly progressive glomerulonephritis. Because the autoepitopes but not the alloepitopes become cryptic upon assembly of alpha3alpha4alpha5NC1 hexamers, we investigated how the accessibility of B cell epitopes in vivo influences the development of glomerulonephritis in mice passively immunized with human anti-GBM Abs. Alport alloantibodies, which bound to native murine alpha3alpha4alpha5NC1 hexamers in vitro, deposited linearly along the mouse GBM in vivo, eliciting crescentic glomerulonephritis in Fcgr2b(-/-) mice susceptible to Ab-mediated inflammation. Goodpasture autoantibodies, which bound to murine alpha3NC1 monomer and dimer subunits but not to native alpha3alpha4alpha5NC1 hexamers in vitro, neither bound to the mouse GBM in vivo nor induced experimental glomerulonephritis. This was due to quinary NC1 crosslinks, recently identified as sulfilimine bonds, which comprehensively locked the cryptic Goodpasture autoepitopes in the mouse GBM. In contrast, non-crosslinked alpha3NC1 subunits were identified as a native target of Goodpasture autoantibodies in the GBM of squirrel monkeys, a species susceptible to Goodpasture autoantibody-mediated nephritis. Thus, crypticity of B cell autoepitopes in tissues uncouples potentially pathogenic autoantibodies from autoimmune disease. Crosslinking of alpha3alpha4alpha5NC1 hexamers represents a novel mechanism averting autoantibody binding and subsequent tissue injury by posttranslational modifications of an autoantigen.

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.

Mannose receptor interacts with Fc receptors and is critical for the development of crescentic glomerulonephritis in mice

Crescentic glomerulonephritis (CGN), which frequently results in acute and chronic kidney disease, is characterized by and dependent on glomerular infiltration by macrophages. The mannose receptor (MR) is a pattern recognition receptor implicated in the uptake of endogenous and microbial ligands by macrophages, mesangial cells (MCs), and selected endothelial cells. It is upregulated on alternatively activated macrophages (i.e., macrophages associated with tissue repair and humoral immunity) and involved in antigen presentation to T cells. We used the mouse model of nephrotoxic nephritis to investigate the role of MR in CGN. Our results demonstrate what we believe to be a novel role for MR in the promotion of CGN that is independent of adaptive immune responses. MR-deficient (Mr-/-) mice were protected from CGN despite generating humoral and T cell responses similar to those of WT mice, but they demonstrated diminished macrophage and MC Fc receptor-mediated (FcR-mediated) functions, including phagocytosis and Fc-mediated oxygen burst activity. Mr-/- MCs demonstrated augmented apoptosis compared with WT cells, and this was associated with diminished Akt phosphorylation. Macrophage interaction with apoptotic MCs induced a noninflammatory phenotype that was more marked in Mr-/- macrophages than in WT macrophages. Our results demonstrate that MR augments Fc-mediated function and promotes MC survival. We suggest that targeting MR may provide an alternative therapeutic approach in CGN while minimizing the impact on adaptive immune responses, which are affected by conventional immunosuppressive approaches.

FCGR2B gene polymorphism rather than FCGR2A, FCGR3A and FCGR3B is associated with anti-GBM disease in Chinese

BACKGROUND

The Fcgamma receptors play important roles in anti-glomerular basement membrane antibody disease (anti-GBM disease) in animal models, and FCGR gene polymorphisms have been reported to be associated with numerous human autoimmune diseases. We aimed to clarify the genetic association of FCGR gene polymorphisms with anti-GBM disease in Chinese patients.

METHODS

A total of 48 patients with anti-GBM disease and 225 geographically and ethnically matched healthy controls were involved. Genotyping of the previously identified polymorphisms FCGR2A131H/R (rs1801274), FCGR2B 232I/T (rs1050501) and FCGR3A176F/V (rs396991) were detected by the TaqMan genotyping assay and FCGR3B NA1/2 by the PCR-sequence specific primer (SSP). Allele type, genotype and haplotype of identified polymorphisms were analysed between patients and controls.

RESULTS

Our results revealed that FCGR2A131H/R, FCGR3A176F/V and FCGR3B NA1/2 were not associated with anti-GBM disease. The frequency of the FCGR2B 232T allele (30.2% versus 15.6%, corrected P = 0.00028, 95% CI: 1.42-3.89) and genotypes of I232T (60.4% versus 31.1%, corrected P = 0.0004, 95% CI: 1.78-6.43) was significantly increased in patients compared with controls.

CONCLUSION

The present study demonstrates the genetic association of polymorphism of FCGR2B (I232T) with susceptibility to anti-GBM disease in Chinese.

New roles revealed for T cells and DCs in glomerulonephritis

Little is known about the potential role of T cells in the inflammatory renal disease glomerulonephritis (GN). GN has been historically viewed as a product of immune complex-mediated complement activation, and the presence of autoantibodies made identifying T cell-specific effector contributions difficult to elucidate. In this issue of the JCI, Heymann et al. generate what they believe to be a novel, transgenic murine model of GN, demonstrating a direct role for CD8+ T cells, activated CD4+ T cells, and DCs in the pathogenesis of GN (see the related article beginning on page 1286).

Mucosal tolerance induced by an immunodominant peptide from rat alpha3(IV)NC1 in established experimental autoimmune glomerulonephritis

Experimental autoimmune glomerulonephritis (EAG), an animal model of Goodpasture's disease, can be induced in Wistar Kyoto (WKY) rats by immunization with the noncollagenous domain of the alpha 3 chain of type IV collagen, alpha3(IV)NC1. Recent studies have identified an immunodominant peptide, pCol (24-38), from the N-terminus of rat alpha3(IV)NC1; this peptide contains the major B- and T-cell epitopes in EAG and can induce crescentic nephritis. In this study, we investigated the mechanisms of mucosal tolerance in EAG by examining the effects of the nasal administration of this peptide after the onset of disease. A dose-dependent effect was observed: a dose of 300 microg had no effect, a dose of 1000 microg resulted in a moderate reduction in EAG severity, and a dose of 3000 microg produced a marked reduction in EAG severity accompanied by diminished antigen-specific, T-cell proliferative responses. These results demonstrate that mucosal tolerance in EAG can be induced by nasal administration of an immunodominant peptide from the N-terminus of alpha3(IV)NC1 and should be of value in designing new therapeutic strategies for patients with Goodpasture's disease and other autoimmune disorders.

Kidney dendritic cell activation is required for progression of renal disease in a mouse model of glomerular injury

The progression of kidney disease to renal failure correlates with infiltration of mononuclear immune cells into the tubulointerstitium. These infiltrates contain macrophages, DCs, and T cells, but the role of each cell type in disease progression is unclear. To investigate the underlying immune mechanisms, we generated transgenic mice that selectively expressed the model antigens ovalbumin and hen egg lysozyme in glomerular podocytes (NOH mice). Coinjection of ovalbumin-specific transgenic CD8+ CTLs and CD4+ Th cells into NOH mice resulted in periglomerular mononuclear infiltrates and inflammation of parietal epithelial cells, similar to lesions frequently observed in human chronic glomerulonephritis. Repetitive T cell injections aggravated infiltration and caused progression to structural and functional kidney damage after 4 weeks. Mechanistic analysis revealed that DCs in renal lymph nodes constitutively cross-presented ovalbumin and activated CTLs. These CTLs released further ovalbumin for CTL activation in the lymph nodes and for simultaneous presentation to Th cells by distinct DC subsets residing in the kidney tubulointerstitium. Crosstalk between tubulointerstitial DCs and Th cells resulted in intrarenal cytokine and chemokine production and in recruitment of more CTLs, monocyte-derived DCs, and macrophages. The importance of DCs was established by the fact that DC depletion rapidly resolved established kidney immunopathology. These findings demonstrate that glomerular antigen-specific CTLs and Th cells can jointly induce renal immunopathology and identify kidney DCs as a mechanistic link between glomerular injury and the progression of kidney disease.

IL-23, not IL-12, directs autoimmunity to the Goodpasture antigen

The autoantigen in Goodpasture disease is the noncollagenous domain of alpha3 type IV collagen [alpha3(IV)NC1]. We previously demonstrated that IL-12p40(-/-) mice are protected from experimental autoimmune anti-glomerular basement membrane (anti-GBM) glomerulonephritis, seemingly defining a role for IL-12 in this disease; however, the recent identification of IL-23, a heterodimer composed of IL-12p40 and IL-23p19 subunits, raises the possibility that IL-23, rather than IL-12, may modulate this disease instead. We immunized wild-type, IL-12p35(-/-) (IL-12 deficient, IL-23 intact), IL-12p40(-/-) (deficient in both IL-12 and IL-23), and IL-23p19(-/-) (IL-12 intact, IL-23 deficient) mice with recombinant mouse alpha3(IV)NC1. Wild-type mice developed autoreactivity to alpha3(IV)NC1: Humoral responses, cellular responses, renal histologic abnormalities, leukocyte accumulation, autoantibody deposition, and IL-17A mRNA expression (a cytokine produced by the IL-23-maintained Th17 subset). IL-23 but not IL-12 was detected in the immune system. Regardless of the presence of IL-12, mice deficient in IL-23 were protected, but mice with IL-23 were not. Both IL-23-deficient strains exhibited lower autoantibody titers, reduced cellular reactivity, diminished cytokine production (IFN-gamma [Th1], IL-17A [Th17], TNF, and monocyte chemoattractant protein 1), and less renal disease and glomerular IgG deposition. The deficient responses in the absence of IL-23 were not due to increased regulatory T cells; IL-12p40(-/-) and IL-23p19(-/-) mice did not show increased proportions of CD4(+)CD25(+)FoxP3(+) cells or IL-10 levels early in the immune response. In conclusion, autoreactivity to the Goodpasture antigen is directed primarily by IL-23, absence of which results in hyporeactivity including but extending beyond a deficient Th17 response.

Identification of a nephritogenic immunodominant B and T cell epitope in experimental autoimmune glomerulonephritis

Experimental autoimmune glomerulonephritis (EAG) can be induced in Wistar Kyoto (WKY) rats by immunization with the non-collagenous domain (NC1) of the alpha 3 chain of type IV collagen, alpha3(IV)NC1. In patients with Goodpasture's disease, the major B cell epitope is located at the N-terminus of alpha3(IV)NC1. In order to investigate whether B and T cell responses in EAG are directed towards immunodominant peptides within the same region of rat alpha3(IV)NC1, we immunized WKY rats with recombinant rat alpha3(IV)NC1 (positive control) and five 15-mer overlapping synthetic peptides from the N-terminus of rat alpha3(IV)NC1: pCol(17-31), pCol(24-38), pCol(31-45), pCol(38-52) and pCol(45-59). Positive control animals immunized with alpha3(IV)NC1 produced an antibody response directed towards alpha3(IV)NC1 and pCol(24-38). Splenic T cells from these animals proliferated in response to alpha3(IV)NC1 and pCol(24-38). No significant antibody or T cell responses were observed to the other peptides examined. Animals immunized with pCol(24-38) developed linear deposits of immunoglobulin G on the glomerular basement membrane, albuminuria and focal necrotizing glomerulonephritis with crescent formation by week 6 after immunization. Circulating antibodies from these animals recognized pCol(24-38) and alpha3(IV)NC1, and their T cells proliferated in response to pCol(24-38) and alpha3(IV)NC1. Animals immunized with the other peptides developed no significant immune response to alpha3(IV)NC1 and no disease. In conclusion, these results demonstrate that a 15-mer peptide from the N-terminus of alpha3(IV)NC1 [pCol(24-38)] is recognized by B and T cells from rats immunized with recombinant alpha3(IV)NC1, and that the same peptide is capable of inducing crescentic glomerulonephritis. Identification of this immunodominant peptide will be of value in designing new therapeutic strategies for inducing mucosal tolerance in EAG, which may be applicable to patients with glomerulonephritis.

Central tolerance regulates B cells reactive with Goodpasture antigen alpha3(IV)NC1 collagen

Patients and rodents with Goodpasture's syndrome (GPS) develop severe autoimmune crescentic glomerulonephritis, kidney failure, and lung hemorrhage due to binding of pathogenic autoantibodies to the NC1 domain of the alpha3 chain of type IV collagen. Target epitopes are cryptic, normally hidden from circulating Abs by protein-protein interactions and the highly tissue-restricted expression of the alpha3(IV) collagen chain. Based on this limited Ag exposure, it has been suggested that target epitopes are not available as B cell tolerogens. To determine how pathogenic anti-GPS autoantibody responses are regulated, we generated an Ig transgenic (Tg) mouse model that expresses an Ig that binds alpha3(IV)NC1 collagen epitopes recognized by serum IgG of patients with GPS. Phenotypic analysis reveals B cell depletion and L chain editing in Tg mice. To determine the default tolerance phenotype in the absence of receptor editing and endogenous lymphocyte populations, we crossed Tg mice two generations with mice deficient in Rag. Resulting Tg Rag-deficient mice have central B cell deletion. Thus, development of Tg anti-alpha3(IV)NC1 collagen B cells is halted in the bone marrow, at which point the cells are deleted unless rescued by a Rag enzyme-dependent process, such as editing. The central tolerance phenotype implies that tolerizing self-Ag is expressed in bone marrow.

Macrophage diversity in renal injury and repair

Monocyte-derived macrophages can determine the outcome of the immune response and whether this response contributes to tissue repair or mediates tissue destruction. In addition to their important role in immune-mediated renal disease and host defense, macrophages play a fundamental role in tissue remodeling during embryonic development, acquired kidney disease, and renal allograft responses. This review summarizes macrophage phenotype and function in the orchestration of kidney repair and replacement of specialized renal cells following injury. Recent advances in our understanding of macrophage heterogeneity in response to their microenvironment raise new and exciting therapeutic possibilities to attenuate or conceivably reverse progressive renal disease in the context of fibrosis. Furthermore, parallels with pathological processes in many other organs also exist.