In Goodpasture's disease, CD4(+) T cells escape thymic deletion and are reactive with the autoantigen alpha3(IV)NC1

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.

Neutralization of IL-6 inhibits formation of autoreactive TH17 cells but does not prevent loss of renal function in experimental autoimmune glomerulonephritis

In anti-glomerular basement membrane glomerulonephritis (anti-GBM GN), antibodies and T cells directed against the Goodpasture antigen, the non-collagenous domain of the α3-chain of type IV collagen (α3(IV)NC1), provoke renal inflammation resulting in rapidly progressing crescentic GN. Interleukin 6 (IL-6) is a pleiotropic cytokine with both pro- and anti-inflammatory activities, and IL-6 blockade is successfully used for treatment of diseases associated with acute and chronic inflammation. However, the role of IL-6 in anti-GBM GN is unclear. Here, we use the mouse model of experimental autoimmune glomerulonephritis (EAG) to study the role of IL-6 in anti-GBM GN. DBA/1J mice were immunized with α3(IV)NC1 and developed fatal crescentic GN. Treatment of mice with neutralizing anti-IL-6 antibodies impaired the generation of α3(VI)NC1-specific TH1 and TH17 cells. However, despite lasting reduction of the TH17 cell response, antibody treatment did not prevent crescentic GN. Antibody treatment was also ineffective in a therapeutic setting with pre-existing autoantibodies and T cells. In conclusion, our results indicate that although the blockade of IL-6 impairs the development of autoimmunity against α3(VI)NC1, this treatment does not ameliorate crescentic GN both in a preemptive and a therapeutic approach.

HLA-DR15-specific inhibition attenuates autoreactivity to the Goodpasture antigen

Goodpasture's disease manifests as rapidly progressive glomerulonephritis. Current immunosuppressive treatments do not specifically target the pathological immune response and have significant side effects. Like most autoimmune diseases, the strongest genetic association is with the HLA alleles. Inheritance of HLA-DR15 confers susceptibility, and structure-function studies have shown that HLA-DR15 plays a causative role in activating autoreactive pro-inflammatory T cells. Thus, specific inhibition of HLA-DR15 would provide a targeted therapeutic approach. We hypothesised that PV-267, an HLA-DR15-specific inhibitor, would effectively block HLA-DR15 presentation of the dominant epitope, attenuate the activation of autoreactive T cells, and limit disease. Using humanised HLA-DR15 transgenic mice, α3_135-145-specific, pro-inflammatory T cell recall responses were measured using IFN-γ and IL-17A ELISPOTs and by proliferation assay. To determine if PV-267 could limit disease, experimental autoimmune anti-GBM glomerulonephritis was induced in HLA-DR15 transgenic mice (on an Fcgr2b^-/- background), and functional and histological disease endpoints were measured. PV-267 effectively inhibited α3_135-145-specific immune responses and disease development. Mice treated prior to immunization with α3_135-145 had reduced α3_135-145-specific recall responses, and limited disease by albuminuria, histological glomerular injury, IgG deposition, and inflammatory cell infiltrates. PV-267 treatment commencing after the onset of active anti-α3(IV)NC1 autoimmunity attenuated functional and histological renal injury. When treatment was administered after disease was established, PV-267 limited the severity of histological injury. In conclusion, HLA-DR15 inhibition attenuates α3(IV)NC1-specific pro-inflammatory responses and could be used as an adjunct therapy for anti-GBM disease.

Role of regulatory T cells in experimental autoimmune glomerulonephritis

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

Anti-Glomerular Basement Membrane Disease

Anti-glomerular basement membrane (anti-GBM) disease is a rare autoimmune small vessel vasculitis characterized by autoreactivity to antigens in type IV collagen chains expressed in glomerular and alveolar basement membrane. The detection of circulating anti-GBM antibodies, which are shown to be directly pathogenic, is central to disease diagnosis. Clinically, anti-GBM disease usually presents with rapidly progressive glomerulonephritis with or without alveolar hemorrhage. Rapid diagnosis and early treatment are required to prevent mortality and to preserve renal function. Relapse in anti-GBM disease is uncommon. Variant and atypical forms of anti-GBM disease are increasingly recognised.

T cell responses to peptides of Goodpasture autoantigen in patients with anti-glomerular basement membrane disease

AIM

Cell-mediated autoimmunity, especially autoreactive T cells, is crucial in the initiation of anti-glomerular membrane (GBM) disease. Epitopes for T cells on Goodpasture autoantigen are not fully defined. This study investigated T cell epitopes in anti-GBM patients, aiming to identify the epitopes and their clinical significance.

METHODS

Peripheral blood mononuclear cells (PBMC) were collected from 13 patients with anti-GBM disease. Twenty-four overlapping linear peptides were synthesized covering the whole sequence of human α3(IV)NC1. PBMC response to each peptide was detected by proliferation assay. Their associations with clinical features were further analyzed.

RESULTS

Peripheral blood mononuclear cells proliferative responses to linear peptides on α3(IV)NC1 could be detected in all patients. Five major epitopes were identified as stimulatory in over half of the patients: α3(IV)NC1_127-148 (P14) (69.2%), α3(IV)NC1_159-178 (77.8%), α3(IV)NC1_179-198 (55.6%), α3(IV)NC1_189-208 (P19) (75.0%) and α3(IV)NC1_141-154 (57.1%). P14 and P19 were highly recognized in patients comparing with healthy controls (69.2% vs. 0.0%, P = 0.011; 75.0% vs. 0.0%, P = 0.021, respectively).

CONCLUSION

T cell proliferation to linear epitopes was detected in human anti-GBM disease. α3_127-148 was a mutual T and B cell epitope, implying its initial role in epitope spreading process.

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.

Goodpasture's autoimmune disease - A collagen IV disorder

Goodpasture's (GP) disease is an autoimmune disorder characterized by the deposition of pathogenic autoantibodies in basement membranes of kidney and lung eliciting rapidly progressive glomerulonephritis and pulmonary hemorrhage. The principal autoantigen is the α345 network of collagen IV, which expression is restricted to target tissues. Recent discoveries include a key role of chloride and bromide for network assembly, a novel posttranslational modification of the antigen, a sulfilimine bond that crosslinks the antigen, and the mechanistic role of HLA in genetic susceptibility and resistance to GP disease. These advances provide further insights into molecular mechanisms of initiation and progression of GP disease and serve as a basis for developing of novel diagnostic tools and therapies for treatment of Goodpasture's disease.

Inflammasomes in the Kidney

Inflammasomes influence a diverse range of kidney disease, including acute and chronic kidney diseases, and those mediated by innate and adaptive immunity. Both IL-18 and in particular IL-1β are validated therapeutic targets in several kidney diseases. In addition to leukocyte-derived inflammasomes, renal tissue cells express functional inflammasome components. Furthermore, a range of endogenous substances that directly activate inflammasomes also mediate kidney injury. Many of the functional studies have focussed on the NLRP3 inflammasome, and there is also evidence for the involvement of other inflammasomes in some conditions. While, at least in some disease, the mechanistic details of the involvement of the inflammasome remain to be elucidated, therapies focussed on inflammasomes and their products have potential in treating kidney disease in the future.

Anti-Glomerular Basement Membrane Disease

Anti-glomerular basement membrane (anti-GBM) disease is a rare small vessel vasculitis that affects the capillary beds of the kidneys and lungs. It is an archetypic autoimmune disease, caused by the development of directly pathogenic autoantibodies targeting a well characterized autoantigen expressed in the basement membranes of these organs, although the inciting events that induce the autoimmune response are not fully understood. The recent confirmation of spatial and temporal clustering of cases suggests that environmental factors, including infection, may trigger disease in genetically susceptible individuals. The majority of patients develop widespread glomerular crescent formation, presenting with features of rapidly progressive GN, and 40%-60% will have concurrent alveolar hemorrhage. Treatment aims to rapidly remove pathogenic autoantibody, typically with the use of plasma exchange, along with steroids and cytotoxic therapy to prevent ongoing autoantibody production and tissue inflammation. Retrospective cohort studies suggest that when this combination of treatment is started early, the majority of patients will have good renal outcome, although presentation with oligoanuria, a high proportion of glomerular crescents, or kidney failure requiring dialysis augur badly for renal prognosis. Relapse and recurrent disease after kidney transplantation are both uncommon, although de novo anti-GBM disease after transplantation for Alport syndrome is a recognized phenomenon. Copresentation with other kidney diseases such as ANCA-associated vasculitis and membranous nephropathy seems to occur at a higher frequency than would be expected by chance alone, and in addition atypical presentations of anti-GBM disease are increasingly reported. These observations highlight the need for future work to further delineate the immunopathogenic mechanisms of anti-GBM disease, and how to better refine and improve treatments, particularly for patients presenting with adverse prognostic factors.

Plasma from patients with anti-glomerular basement membrane disease could recognize microbial peptides

Infection has long been suspected as a trigger of autoimmune diseases, and molecular mimicry mechanism was hypothesized in this study. Microbe originated peptides were searched from the Uniprot database based on a previous defined critical amino acid motif within α3_129−150, isoleucine137, tryptophan140, glycine142, phenylalanine 143 and phenylalanine 145. 23826 microbial peptides were identified using our searching strategy, among which seven were related with human infections. Circulating IgG and IgM antibodies against the seven microbial peptides were detected using ELISA in 76 patients with anti-GBM disease. Four peptides were recognized by both IgG and IgM antibodies, and one peptide was recognized by IgG antibodies only. Peptides from Bacteroides, Saccharomyces cerevisiae, and Bifidobacterium thermophilum possessed the highest recognition frequency with the prevalence of 73.7%, 61.8% and 67.1% for IgG, 56.6%, 44.7% and 67.1% for IgM in anti-GBM patients. Patients with antibodies against these microbial peptides showed more severe kidney injury, including higher serum creatinine and higher percentage of crescent formation. In conclusion, antibodies against microbial peptides were identified in the circulation of anti-GBM patients, implying its etiological role in eliciting autoimmune response against α3(IV)NC1 through molecular mimicry.

The NLRP3 inflammasome in kidney disease and autoimmunity

The NLRP3 inflammasome is an intracellular platform that converts the pro-inflammatory cytokines interleukin (IL)-1β and IL-18 to their active forms in response to 'danger' signals, which can be either host or pathogen derived, and mediates a form of inflammatory cell death called pyroptosis. This component of the innate immune system was initially discovered because of its role in rare autoinflammatory syndromes called cryopyrinopathies, but it has since been shown to mediate injurious inflammation in a broad range of diseases. Inflammasome activation occurs in both immune cells, primarily macrophages and dendritic cells, and in some intrinsic kidney cells such as the renal tubular epithelium. The NLRP3 inflammasome has been implicated in the pathogenesis of a number of renal conditions, including acute kidney injury, chronic kidney disease, diabetic nephropathy and crystal-related nephropathy. The inflammasome also plays a role in autoimmune kidney disease, as IL-1β and IL-18 influence adaptive immunity through modulation of T helper cell subsets, skewing development in favour of Th17 and Th1 cells that are important in the development of autoimmunity. Both IL-1 blockade and two recently identified specific NLRP3 inflammasome blockers, MCC950 and β-hydroxybutyrate, have shown promise in the treatment of inflammasome-mediated conditions. These targeted therapies have the potential to be of benefit in the growing number of kidney diseases in which the NLRP3 inflammasome has been implicated.

Regulatory T cells in immune-mediated renal disease

Regulatory T cells (Tregs) are CD4+ T cells that can suppress immune responses by effector T cells, B cells and innate immune cells. This review discusses the role that Tregs play in murine models of immune-mediated renal diseases and acute kidney injury and in human autoimmune kidney disease (such as systemic lupus erythematosus, anti-glomerular basement membrane disease, anti-neutrophil cytoplasmic antibody-associated vasculitis). Current research suggests that Tregs may be reduced in number and/or have impaired regulatory function in these diseases. Tregs possess several mechanisms by which they can limit renal and systemic inflammatory immune responses. Potential therapeutic applications involving Tregs include in vivo induction of Tregs or inducing Tregs from naïve CD4+ T cells or expanding natural Tregs ex vivo, to use as a cellular therapy. At present, the optimal method of generating a phenotypically stable pool of Tregs with long-lasting suppressive effects is not established, but human studies in renal transplantation are underway exploring the therapeutic potential of Tregs as a cellular therapy, and if successful may have a role as a novel therapy in immune-mediated renal diseases.

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.

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.

AKI in an HIV patient

The renal manifestations of patients infected with HIV are diverse. Patients may have podocytopathies ranging from a minimal-change-type lesions to FSGS or collapsing glomerulopathy. Furthermore, such patients produce a variety of autoantibodies without clinical signs of the disease. Antiretroviral drugs also cause renal injury, including crystals and tubular injury, acute interstitial nephritis, or mitochondrial toxicity. In these circumstances, it is essential to perform a renal biopsy for diagnosis and to guide treatment. Here we describe a patient with HIV who presented with AKI and hematuria without concomitant systemic manifestations. Renal biopsy elucidated the cause of acute deterioration of kidney function.

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.

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.

Genetic susceptibility to experimental autoimmune glomerulonephritis in the Wistar Kyoto rat

In experimental autoimmune glomerulonephritis (EAG), a model of Goodpasture's disease, Wistar Kyoto (WKY) rats immunized with collagenase-solubilized glomerular basement membrane (GBM) or the recombinant NC1 domain of the α3 chain of type IV collagen [α3(IV)NC1] develop anti-GBM antibodies and focal necrotizing glomerulonephritis with crescent formation. However, Lewis (LEW) rats, which share the same major histocompatibility complex (MHC) haplotype, are resistant to EAG development. A genome-wide linkage analysis of backcrossed animals with EAG revealed a major quantitative trait locus (QTL) on rat chromosome 13 (LOD = 3.9) linked to the percentage of glomerular crescents. To investigate the role of this QTL in EAG induction, reciprocal congenic rats were generated (LEW.WCrgn1 congenic and WKY.LCrgn1 congenic), immunized with recombinant rat α3(IV)NC1, and assessed for EAG development. WKY.LCrgn1 rats showed a marked reduction in albuminuria, severity of crescentic nephritis, and number of glomerular macrophages compared with WKY controls. No reduction in antibody levels was observed. However, LEW.WCrgn1 rats were resistant to EAG development, as were LEW controls. Macrophage activation in vitro was assessed in parental and congenic rat bone marrow-derived macrophages (BMDMs). WKY.LCrgn1 BMDMs showed a significant reduction in Fc receptor-mediated oxidative burst, phagocytosis of opsonised polystyrene beads, and LPS-induced levels of MCP-1 secretion and iNOS mRNA expression compared with WKY rats. These results confirm the importance of Crgn1 on chromosome 13 in EAG susceptibility, mediated partly through differences in Fc receptor-mediated macrophage activation.

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.

Membranous nephropathy with crescents

Membranous nephropathy is a common cause of nephrotic syndrome in adults and can be primary or secondary to systemic lupus erythematosus, chronic infection, or drugs. Rapid decline in renal function in patients with membranous nephropathy may be due to renal vein thrombosis, malignant hypertension, or an additional superimposed destructive process involving the renal parenchyma. Crescents are rare in primary membranous nephropathy and thus suggest another underlying disease process, such as combined membranous and focal or diffuse lupus nephritis. However, in some patients with membranous nephropathy and crescents, the crescentic lesion may be due to a distinct, separate disease process, such as anti-glomerular basement membrane antibodies or anti-neutrophil cytoplasmic antibodies-related pauci-immune glomerulonephritis. Here we describe a case with such renal biopsy findings, review previous reported cases, and discuss possible implications for pathogenesis of the coexistence of these lesions.

Asymptomatic autoantibodies associate with future anti-glomerular basement membrane disease

The pathophysiology of anti-glomerular basement membrane (anti-GBM) disease before clinical presentation is unknown. The presence of anti-GBM, anti-proteinase 3 (PR3), and anti-myeloperoxidase (MPO) antibodies associate with the disease at the time of diagnosis, but little is known about the presence of these autoantibodies before diagnosis. We used serum samples from the Department of Defense Serum Repository to conduct a case-control study involving 30 patients diagnosed with anti-GBM disease and 30 healthy controls matched for the age, gender, race, and age of the serum samples. We analyzed a maximum of three samples from each subject: the most recent sample before diagnosis, the penultimate sample before diagnosis, and the oldest sample available; the average time between the most recent sample and diagnosis was 195 days (range, 4 to 1346 days). Elevated anti-GBM levels (≥3 U/ml) were present in four patients, all less than 1 year before diagnosis but in no controls. Detectable anti-GBM antibody levels (≥1 U/ml but <3 U/ml) in a single serum sample before diagnosis were more frequent in cases than controls (70% versus 17%, P < 0.001). Only study patients had detectable anti-GBM levels in multiple samples before diagnosis (50% versus 0%, P < 0.001). Almost all patients had detectable anti-PR3 and/or anti-MPO that preceded the onset of disease. Among patients with a clear antecedent antibody, anti-PR3 or anti-MPO always became detectable before the anti-GBM antibody. In summary, our data describe the subclinical formation of autoantibodies, which improves our understanding of the pathophysiology of anti-GBM disease.

Crescentic glomerulonephritis: new aspects of pathogenesis

This review provides a summary of recent advances in the understanding of crescentic glomerulonephritis, focusing on antineutrophil cytoplasm antibody (ANCA)-associated vasculitis and anti-glomerular basement membrane (anti-GBM) antibody disease. In ANCA-associated vasculitis (AAV), four main conceptual advances are discussed as follows: (1) evidence for the pathogenicity of ANCA, (2) molecular mimicry and the role of infection in AAV, (3) evidence for aberrant T-cell responses and T-cell regulation in AAV, and (4) advances in understanding of genetic predisposition to AAV. In relation to anti-GBM disease we discuss the following: (1) the nature of the Goodpasture autoantigens, (2) T-cell responses and regulation in anti-GBM disease, and (3) human leukocyte antigen and non-human leukocyte antigen genetic associations.

Natural autoantibodies to myeloperoxidase, proteinase 3, and the glomerular basement membrane are present in normal individuals

Anti-neutrophil cytoplasmic antibodies (ANCAs) have a pathogenic role in ANCA-associated vasculitis. The origin of ANCAs and anti-glomerular basement membrane (GBM) antibodies, however, is unknown. In this study, we determined whether natural autoantibodies against myeloperoxidase (MPO), proteinase 3 (PR3), and GBM were present in each of 10 healthy Chinese and Swedish individuals, negative for all three antigens by routine ELISA. Antibodies were purified from isolated IgG by antigen-specific affinity columns. Natural anti-GBM autoantibodies gave a linear staining pattern along the GBM of human renal sections. On ethanol-fixed granulocytes, both natural anti-MPO and anti-PR3 autoantibodies gave cytoplasmic staining. The titers of natural anti-MPO/PR3 autoantibodies were significantly lower than those from patients with vasculitis. In competition ELISA, the binding of natural anti-MPO autoantibodies could be inhibited by MPO, but not by PR3 or noncollagenous domains from type IV collagen. The same specificity results were found for natural anti-PR3 and anti-GBM autoantibodies. Overall, individuals of the Chinese origin had more natural autoantibodies than did those of the Swedish origin, but no other differences were found. Hence, our study shows that healthy individuals have masked circulating, noncross-reactive, antigen-specific natural autoantibodies against MPO, PR3, and GBM in their serum and IgG fractions. Further studies are needed to determine their role if any in the etiology of ANCA-associated vasculitis and anti-GBM disease.

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.

Advances in the pathogenesis of Goodpasture's disease: from epitopes to autoantibodies to effector T cells

Goodpasture's disease, an "organ-specific" autoimmune disease is manifest by rapidly progressive glomerulonephritis and pulmonary hemorrhage. Studies into the pathogenesis of this disease have shed light on the autoantigen (the non-collagenous domain of the alpha3 chain of type IV collagen, alpha3(IV)NC1) and its epitopes, as well as the involvement of autoantibodies and cellular effectors in disease. The discovery of alpha3(IV)NC1 lead to studies that defined the structure and biology of type IV collagen and are defining B and T cell epitopes. Goodpasture autoantibody epitopes are "cryptic" in that they are structurally sequestered by adjacent non-collagenous domains of alpha4 and alpha5 type IV collagen. T cell epitope studies in rats demonstrated that a 13-mer could induce experimental autoimmune glomerulonephritis. T cells from patients with Goodpasture's recognize two epitopes, in regions which are highly susceptible in antigen processing by endosomal proteases. Goodpasture's disease is strongly associated with HLA DRB1 genes, whereby DRB1*1501 confers susceptibility and the DRB1*0701 and DRB1*0101 are dominantly protective. Experimental data implicate both autoantibodies and cell mediated immunity as disease effectors. Observations in humans suggest that regulatory T cells are associated with the development of self-immunoregulation in the convalescent phase of disease.

Mammalian collagen IV

Four decades have passed since the first discovery of collagen IV by Kefalides in 1966. Since then collagen IV has been investigated extensively by a large number of research laboratories around the world. Advances in molecular genetics have resulted in identification of six evolutionary related mammalian genes encoding six different polypeptide chains of collagen IV. The genes are differentially expressed during the embryonic development, providing different tissues with specific collagen IV networks each having unique biochemical properties. Newly translated alpha-chains interact and assemble in the endoplasmic reticulum in a chain-specific fashion and form unique heterotrimers. Unlike most collagens, type IV collagen is an exclusive member of the basement membranes and through a complex inter- and intramolecular interactions form supramolecular networks that influence cell adhesion, migration, and differentiation. Collagen IV is directly involved in a number of genetic and acquired disease such as Alport's and Goodpasture's syndromes. Recent discoveries have also highlighted a new and direct role for collagen IV in the development of rare genetic diseases such as cerebral hemorrhage and porencephaly in infants and hemorrhagic stroke in adults. Years of intensive investigations have resulted in a vast body of information about the structure, function, and biology of collagen IV. In this review article, we will summarize essential findings on the structural and functional relationships of different collagen IV chains and their roles in health and disease.

Autoepitopes and alloepitopes of type IV collagen: role in the molecular pathogenesis of anti-GBM antibody glomerulonephritis

Anti-glomerular basement membrane (anti-GBM) antibodies elicited by autoimmune or alloimmune mechanisms are associated with aggressive forms of rapid progressive glomerulonephritis. Pathogenic anti-GBM autoantibodies and alloantibodies target the noncollagenous (NC1) domains of the alpha3alpha4alpha5(IV) collagen, a major GBM component. In autoimmune anti-GBM glomerulonephritis, a breakdown of immune self-tolerance leads to the activation of autoreactive B and T cells recognizing epitopes within the alpha3NC1 subunit. In the GBM, the conformational epitopes targeted by anti-GBM autoantibodies are structurally sequestered within the alpha3alpha4alpha5NC1 hexamer complex formed upon assembly of collagen IV chains into trimeric molecules and networks. Autoantibodies selectively bind to and dissociate a subset of alpha3alpha4alpha5NC1 hexamers composed of monomer subunits, whereas hexamers containing NC1 dimer subunits are resistant to dissociation by autoantibodies. The crypticity of alpha3NC1 autoepitopes suggests that self-tolerance to alpha3(IV) collagen is broken by structural alterations of the native alpha3alpha4alpha5NC1 hexamer that unmask normally sequestered epitopes, triggering an autoimmune reaction. Post-transplant anti-GBM nephritis in the renal allograft of transplanted Alport patients is mediated by an alloimmune reaction to the NC1 domains of alpha3alpha4alpha5(IV) collagen, present in the allograft GBM but absent from Alport basement membranes. Alloantibodies from patients with autosomal-recessive Alport syndrome predominantly bind to the alpha3NC1 domain, whereas alloantibodies from X-linked Alport patients target preferentially, though not exclusively, epitopes within the alpha5NC1 subunit. The accessibility of the alloantigenic sites within the alpha3alpha4alpha5NC1 hexamers, contrasting with the crypticity of autoantigenic sites, suggest that different molecular forms of alpha3alpha4alpha5(IV) collagen initiate the immunopathogenic responses in the two forms of anti-GBM disease. Advances in elucidating the structure of the GBM antigen and the identification of the pathogenic B and T cell epitopes, along with new insights into the pathogenic mechanisms at cellular and molecular level will facilitate the development of targeted strategies for prevention, detection, and treatment of human anti-GBM antibody glomerulonephritis.

Presentation of the Goodpasture Autoantigen Requires Proteolytic Unlocking Steps That Destroy Prominent T Cell Epitopes

The most abundant autoreactive T cells in patients with Goodpasture's disease are specific for peptides in the autoantigen that have high affinity for the disease-associated HLA class II molecule, DR15. How can such T cells escape self-tolerance mechanisms? This study showed that these peptides are highly susceptible to destruction in the earliest stages of antigen processing, and some must be cleaved for antigen digestion to be possible ("unlocking"). Goodpasture autoantigen [collagen alpha3(IV)NC1; approximately 31 kD] that was incubated with B cell lysosomes was cleaved within a few minutes to form approximately 9- and approximately 22-kD fragments, then increasing quantities of smaller peptides. The processing was completely abrogated by pepstatin A, a specific inhibitor of cathepsin D/E, even though lysosomal extracts contain a rich array of proteases. Purified cathepsin D generated the same major alpha3(IV)NC1 fragments as entire lysosomes, suggesting that cathepsin D cleavages are required to initiate alpha3(IV)NC1 processing. The initial unlocking cleavages destroyed two major self-epitopes, and subsequent preferred cleavages destroyed all of the other T cell epitopes that are recognized by most patients' autoreactive T cells. The responses of T cell clones that are specific for a major disease-associated peptide to antigen-pulsed intact antigen-presenting cells were substantially enhanced by pepstatin A treatment. Therefore, cathepsin D activity significantly diminishes presentation of alpha3(IV)NC1 peptides that are recognized by patients' T cells by destroying the peptides in early processing. These observations can explain why the mature T cell repertoire includes reactivity toward these self-peptides and suggests that a key factor in disease initiation is likely to be a shift in antigen processing.

T cells in crescentic glomerulonephritis

Crescent formation in glomerulonephritis (GN) is a manifestation of severe glomerular injury that usually results in a poor clinical outcome. In humans, crescentic GN is frequently associated with evidence of either systemic or organ-specific autoimmunity. T cells play a major role in initiation of adaptive immune responses that lead to crescentic injury. In experimental models of crescentic GN, Th1 predominant immune responses have been shown to promote crescent formation. Perturbation of regulatory T cell function may contribute to development of autoimmune crescentic GN. The presence of T cells and macrophages in crescentic glomeruli, frequently in the absence of humoral mediators of immunity, suggest a dominant effector role for T cells in crescentic GN. The association of cellular immune mediators with local fibrin deposition implicates cell-mediated "delayed-type hypersensitivity-like" mechanisms in crescent formation. Intrinsic renal cells also contribute to T cell-driven effector mechanisms in crescentic GN, via expression of MHC II and co-stimulatory molecules and by production of chemokines and cytokines that amplify leukocyte recruitment and injury.

Natural autoantibodies against glomerular basement membrane exist in normal human sera

Autoimmunity to glomerular basement membrane (GBM) could induce Goodpasture disease, and natural autoantibodies against GBM in the sera of normal individuals were not reported. The aim of the study was to identify and characterize natural autoantibodies against GBM in normal human sera. Natural anti-GBM autoantibodies were purified from the sera of five healthy persons by affinity chromatography, using purified bovine alpha(IV)non-collagenous (NC1) as solid-phase ligands. Antigen specificity, immunoglobulin G (IgG) subclasses, and antibody avidity of the natural autoantibodies were investigated by enzyme-linked immunosorbant assay (ELISA), Western-blot analysis, indirect immunofluorescence, and antigen-inhibition ELISA, and compared with those of 32 patients with anti-GBM disease. Natural anti-GBM autoantibodies could be purified from IgG fractions of all the five persons, with an average amount of 0.5% of total IgG fractions. Antigen specificity of the natural autoantibodies was identified by blotting to human alpha(IV)NC1, reactivity to recombinant alpha3(IV)NC1, and linear staining along the GBM of normal kidney sections. Titers of the natural autoantibodies were much lower than those of patients (1:60.6 vs 1:993.6, P<0.001). IgG subclasses distribution of the natural autoantibodies was restricted to IgG2 (100%) and IgG4 (100%), while for patients it was mainly IgG1 (93.8%) and IgG4 (90.6%). Avidity of the natural autoantibodies was lower than that of patients, the amount of alpha(IV)NC1 used for 50% inhibition was 1.65 and 0.46 microg, respectively (P<0.05). In conclusion, natural anti-GBM autoantibodies exist in normal human sera. Antibody levels, IgG subclasses, and avidity of the natural autoantibodies were different from those of patients. Fine specificity of the natural autoantibodies needed to be elucidated.

Experimental autoimmune Goodpasture's disease: a pathogenetic role for both effector cells and antibody in injury

BACKGROUND

Goodpasture's disease [antiglomerular basement membrane (GBM) glomerulonephritis] is a classic autoimmune disease and the only organ-specific autoimmune renal disease in which the antigen is well described. The importance of antibodies against the non-collagenous domain of the alpha3 chain of type IV collagen [alpha3(IV)NC1] is well established. However, observational human studies and studies in experimental systems also imply a role for cell-mediated effector injury.

METHODS

Active experimental autoimmune glomerulonephritis (EAG) was induced by immunization with alpha3-alpha5(IV)NC1 heterodimers in B cell intact C57BL/6 mice and B cell (mu chain-deficient) mice. Passive disease was induced by transferring sera from B cell intact and B cell deficient mice with EAG to RAG-1-/- mice (that lack adaptive immunity). Histologic and functional injury was studied.

RESULTS

Despite the absence of B cells and immunoglobulin in B-cell-deficient mice, histologic and functional injury developed in mice immunized with alpha3-alpha5(IV)NC1, with T cells and macrophages in glomeruli. Injury occurred to a similar degree to that found in B-cell-intact mice. Transfer of sera from B-cell-intact mice with EAG containing antibodies (but not from B-cell-deficient mice with EAG) to RAG-1-/- mice induced linear immunoglobulin deposits on the glomerular basement membrane (GBM) and pathologic proteinuria.

CONCLUSION

Both cell-mediated and humoral effectors are capable of inducing renal injury in EAG. Given the similarity of the disease-initiating antigen in this model to the antigen in human anti-GBM glomerulonephritis, similar overlapping mechanisms are likely to operate in human disease.

Goodpasture autoantibodies unmask cryptic epitopes by selectively dissociating autoantigen complexes lacking structural reinforcement: novel mechanisms for immune privilege and autoimmune pathogenesis

Rapidly progressive glomerulonephritis in Goodpasture disease is mediated by autoantibodies binding to the non-collagenous NC1 domain of alpha3(IV) collagen in the glomerular basement membrane. Goodpasture epitopes in the native autoantigen are cryptic (sequestered) within the NC1 hexamers of the alpha3alpha4alpha5(IV) collagen network. The biochemical mechanism for crypticity and exposure for autoantibody binding is not known. We now report that crypticity is a feature of the quaternary structure of two distinct subsets of alpha3alpha4alpha5(IV) NC1 hexamers: autoantibody-reactive M-hexamers containing only monomer subunits and autoantibody-impenetrable D-hexamers composed of both dimer and monomer subunits. Goodpasture antibodies only breach the quaternary structure of M-hexamers, unmasking the cryptic epitopes, whereas D-hexamers are resistant to autoantibodies under native conditions. The epitopes of D-hexamers are structurally sequestered by dimer reinforcement of the quaternary complex, which represents a new molecular solution for conferring immunologic privilege to a potential autoantigen. Dissociation of non-reinforced M-alpha3alpha4alpha5(IV) hexamers by Goodpasture antibodies is a novel mechanism whereby pathogenic autoantibodies gain access to cryptic B cell epitopes. These findings provide fundamental new insights into immune privilege and the molecular mechanisms underlying the pathogenesis of human autoimmune Goodpasture disease.

Glomerular T Cells Are of Restricted Clonality and Express Multiple CDR3 Motifs across Different Vβ T-Cell Receptor Families in Experimental Autoimmune Glomerulonephritis

Experimental autoimmune glomerulonephritis (EAG) is an animal model of Goodpasture's disease which can be induced in Wistar-Kyoto (WKY) rats by a single intramuscular injection of collagenase-digested rat glomerular basement membrane (GBM) in adjuvant. This model is characterised by anti-GBM antibody production, accompanied by focal necrotising glomerulonephritis with crescent formation and glomerular infiltration by T cells and macrophages. Previous work has shown that EAG is a T-cell-dependent disease. We proposed that intraglomerular T cells might be directly involved in pathogenesis and would be oligoclonal. In this study, EAG was induced by standard methods, the kidneys perfused with saline at week 2 and week 4, and the glomeruli separated by a sieving method. Glomerular RNA was extracted and reverse transcribed. RT-PCR showed overexpression of an average of two Vbeta families in each kidney analysed. However, no predominant single Vbeta family was overexpressed in any of the experimental animals. CDR3 spectratyping of Fam-labelled PCR products showed a marked restriction involving different Vbeta families. Sequencing demonstrated multiple CDR3 motifs, each expressed in association with different Vbeta gene segments. Our results show that glomerular T cells are of restricted clonality and suggest a role for antigen-specific effector T cells in the pathogenesis of EAG.

The fine specificity and cytokine profile of T-helper cells responsive to the alpha3 chain of type IV collagen in Goodpasture's disease

Goodpasture's disease is a severe nephritis characterized by autoantibodies to the alpha3 chain of type IV collagen, alpha3(IV)NC1, in the glomerular basement membrane. The disease is very strongly associated with HLA-DR15, the affinities of alpha3(IV)NC1 peptides for DR15 are known, and elution experiments have identified major naturally processed sequences. Here, the fine specificity and cytokine profile of alpha3(IV)NC1-reactive T cells from patients with Goodpasture's disease is defined. Peripheral blood mononuclear cells from patients at diagnosis proliferated in response to significantly more peptides (chi(2) = 8.6, P = 0.004) from a panel spanning the sequence of alpha3(IV)NC1 than did those from control DR15-positive donors and were highly focused (P = 0.0002, binomial distribution) on two peptides, alpha3(71-90) and alpha3(131-150). Some peptides induced interferon-gamma, but none induced IL-4. Resolution of disease was accompanied by a striking deviation of the responses from proliferation to secretion of the T-regulatory cytokine IL-10, and addition of neutralizing antibody confirmed that such IL-10 production was suppressive. The affinity of the peptides for DR15 molecules was positively correlated (chi(2) = 14.6, P = 0.00067) with the ability to elicit proliferation. However, unlike foreign antigens, this hierarchy is not due to responses against the major naturally processed peptides, which rarely stimulated proliferation and which have only intermediate affinity for DR15 molecules. It is inferred that the helper response to alpha3(IV)NC1 in Goodpasture's disease is dominated by epitopes that are normally inefficiently presented because of processing constraints.

Pathogenesis of Goodpasture syndrome: a molecular perspective

Goodpasture (GP) syndrome is a form of anti-glomerular basement membrane (GBM) disease, in which autoantibodies bind to alpha3(IV) collagen in GBM causing rapidly progressive glomerulonephritis and pulmonary hemorrhage. The conformational GP epitopes have been mapped to 2 regions within the noncollagenous (NC1) domain of the alpha3(IV) chain. Recently, we described the molecular organization of the autoantigen in the native alpha3alpha4alpha5(IV) collagen network of the GBM. The crystal structure of the NC1 domain has revealed how the GP epitopes are sequestered in the native GBM. Further insight into the pathogenesis of disease has been obtained from better animal models. These advances provide a foundation for the development of new specific therapies.

Regulation by CD25+ lymphocytes of autoantigen-specific T-cell responses in Goodpasture's (anti-GBM) disease

BACKGROUND

Goodpasture's, or anti-glomerular basement membrane (GBM), disease is unusual among autoimmune diseases in that it rarely follows a relapsing-remitting course. Moreover, untreated, autoantibodies disappear spontaneously after 1 to 3 years and, following treatment, autoreactive T cells diminish in frequency. This suggests that operational tolerance toward the autoantigen is reestablished. However, the mechanisms underlying this have remained unclear. Recent data have suggested that a population of regulatory T lymphocytes can suppress both autoimmune and alloimmune responses in animal models and are present in normal individuals. However, to date, they have not been demonstrated to play a role in human renal autoimmune disease.

METHODS

We studied the role of regulatory CD25+ cells in suppressing T-cell responses to the Goodpasture autoantigen in nine patients with Goodpasture's disease.

RESULTS

At the time of acute presentation, there was no evidence of a regulatory cell population. However, from 3 months onward a population emerged, capable of suppressing the response to the Goodpasture autoantigen. Following depletion of CD25+ cells, the frequencies of autoreactive-, GBM-, or collagen alpha 3(IV)NC1-specific T cells were significantly increased (P = 0.031 by paired t test), with five of seven (71%) convalescent patients and no acute patients demonstrating regulation.

CONCLUSION

These data demonstrate that, in Goodpasture's disease, regulatory CD25+ T cells play a role in inhibiting the autoimmune response. Their emergence and persistence may underlie the "single hit" nature of this condition. Understanding the conditions required for the development and propagation of these cells would allow development of novel therapeutic strategies for inducing hyporesponsiveness in autoimmune disease.

The evolution of crescentic nephritis and alveolar haemorrhage following induction of autoimmunity to glomerular basement membrane in an experimental model of Goodpasture's disease

Goodpasture's, or anti-glomerular basement membrane (GBM), disease presents with rapidly progressive glomerulonephritis and lung haemorrhage, and is caused by autoimmunity to the NC1 domain of the alpha3 chain of type IV collagen (alpha3(IV)NC1). This study examines the development of crescentic nephritis and alveolar haemorrhage in a model of Goodpasture's disease, experimental autoimmune glomerulonephritis (EAG), induced in WKY rats by immunization with rat GBM in adjuvant. An increase in circulating anti-GBM antibodies and albuminuria was observed by week 2, which increased further by weeks 3 and 4, while a decrease in creatinine clearance was observed by week 2, which decreased further by weeks 3 and 4. The kidneys of animals with EAG showed linear deposits of IgG on the GBM and a transient glomerular infiltration by CD4+ T cells at week 2. By week 3 there were large deposits of fibrin in Bowman's space, and glomerular infiltration by CD8+ T cells and macrophages, accompanied by focal necrotizing glomerulonephritis with crescent formation. Ultrastructural studies showed glomerular endothelial cell swelling and epithelial cell foot process effacement at week 2. As the lesion progressed, capillary loops became occluded and the mesangium became expanded by mononuclear cells. By week 3 there was detachment of the endothelium from the GBM, and accumulation of fibrin beneath the disrupted endothelial cells and in Bowman's space. Occasional breaks were observed in the continuity of the basement membrane, and cytoplasmic projections from infiltrating mononuclear cells could be seen crossing the capillary wall between the lumen and the crescent. The lungs of animals with EAG showed patchy binding of IgG to the alveolar basement membrane (ABM) at week 2, and infiltration of the interstitium by CD8+ T cells and macrophages by weeks 3 and 4, accompanied by both interstitial and alveolar haemorrhage. Ultrastructural studies showed focal mononuclear cell infiltrates in alveolar walls at week 2. Occasional breaks were observed in the basement membrane and adjacent endothelium by weeks 3 and 4, together with accumulation of surfactant and erythrocytes within the alveolar spaces. This study defines for the first time the relationship between the immunological and pathological events during the evolution of EAG, and provides the basis for further work on the pathogenesis of Goodpasture's disease.

Pulmonary-renal vasculitic disorders: differential diagnosis and management

Pulmonary-renal syndrome (PRS) is a combination of diffuse pulmonary hemorrhage and glomerulonephritis. Pulmonary-renal syndrome is not a single entity and is caused by a variety of conditions, including Goodpasturés syndrome associated with autoantibodies to the glomerular and alveolar basement membranes, various forms of primary systemic vasculitis associated with serum positivity for antineutrophil cytoplasmic antibodies (ANCA), cryoglobulinemia, systemic lupus erythematosus, systemic sclerosis, antiphospholipid syndrome, environmental factors, and drugs. The majority of cases of PRS are associated with ANCAs. The antigen target in Goodpasturés syndrome is the alpha-3 chain of type IV collagen. The antigen target in PRS associated with systemic vasculitis is proteinase-3 and myeloperoxidase. Pulmonary-renal syndrome has been observed from the first to the ninth decade of life. The widespread adoption of serologic testing performed in an appropriate clinical context hopefully will limit diagnostic delay. The goals of treatment in PRS are to remove the circulating antibodies, to stop further production of autoantibodies, and to remove any antigen that stimulates antibody production. Treatment is based on plasmapheresis, steroids, and cyclophosphamide; however, infections are frequent contributors to death, and less toxic alternatives may improve outcome and prognosis resulting in a long-term survival. The degree of renal function and the percent of crescents on renal biopsy are better predictors of outcome. Renal transplantation can be safely carried out in PRS.

Immunology of anti-glomerular basement membrane disease

Anti-glomerular basement membrane disease is a form of autoimmune glomerulonephritis often accompanied by lung haemorrhage. It is characterized by circulating and deposited antibodies that bind basement membrane components in the glomerulus and lung alveolus. Since early descriptions of the deposition of immunoglobulin on the glomerular basement membrane, work has focused on the binding properties of the autoantibodies, and this has led to the identification of the autoantigen as the non-collagenous region of the alpha 3 chain of type IV collagen. Despite being thought of as a prototypic antibody mediated autoimmune disease, it is becoming apparent that both humoral and cellular immune mechanisms act in concert to initiate and perpetuate disease. Recent data have shed light on the molecular pathogenesis of anti-glomerular basement membrane disease and provided a more complete framework on which to build our understanding of autoimmune renal disease. This should lead to novel approaches to immunotherapy for patients with glomerulonephritis.