Human antiglomerular basement membrane autoantibody disease in XenoMouse II

Kidney-targeted inhibition of protein kinase C-α ameliorates nephrotoxic nephritis with restoration of mitochondrial dysfunction

To investigate the role of protein kinase C-α (PKC-α) in glomerulonephritis, the capacity of PKC-α inhibition to reverse the course of established nephrotoxic nephritis (NTN) was evaluated. Nephritis was induced by a single injection of nephrotoxic serum and after its onset, a PKC-α inhibitor was administered either systemically or by targeted glomerular delivery. By day seven, all mice with NTN had severe nephritis, whereas mice that received PKC-α inhibitors in either form had minimal evidence of disease. To further understand the underlying mechanism, label-free shotgun proteomic analysis of the kidney cortexes were performed, using quantitative mass spectrometry. Ingenuity pathway analysis revealed 157 differentially expressed proteins and mitochondrial dysfunction as the most modulated pathway. Functional protein groups most affected by NTN were mitochondrial proteins associated with respiratory processes. These proteins were down-regulated in the mice with NTN, while their expression was restored with PKC-α inhibition. This suggests a role for proteins that regulate oxidative phosphorylation in recovery. In cultured glomerular endothelial cells, nephrotoxic serum caused a decrease in mitochondrial respiration and membrane potential, mitochondrial morphologic changes and an increase in glycolytic lactic acid production; all normalized by PKC-α inhibition. Thus, PKC-α has a critical role in NTN progression, and the results implicate mitochondrial processes through restoring oxidative phosphorylation, as an essential mechanism underlying recovery. Importantly, our study provides additional support for targeted therapy to glomeruli to reverse the course of progressive disease.

Immune complexes and complexity: investigating mechanisms of renal disease

The deposition of immune complexes is the causal factor in distinct renal pathologies, e.g., lupus nephritis and membranous nephritis. The location of these deposits within a tissue biopsy is often the key to establishing a diagnosis. However, how immune complexes come to be deposited below the vascular endothelium was, until now, a mystery, as was their contribution to inducing inflammation. A recent paper in Cell by Stamatiades et al. (Cell 164(4):991-1003, 2016) demonstrates the active transport of immune complexes by the vascular endothelial cells and an Fc receptor-dependent uptake by tissue-resident macrophages. This leads to the activation of these macrophages and the release of pro-inflammatory cytokines, which in turn recruits immune cells from the blood into the kidney. The identification of these mechanisms should lead to a better stratification of kidney diseases and hopefully to the development of specific therapies.

A human monoclonal antibody against the collagen type IV α3NC1 domain is a non-invasive optical biomarker for glomerular diseases

Progressive kidney disease is a significant clinical problem. However, despite research aimed toward developing improved predictors of disease, the major tool to assess kidney ultrastructure damage is the kidney biopsy. Here we tested the capability of a labeled human monoclonal antibody (F1.1), directed against the NC1 domain of α3(IV) collagen, to detect pathologic kidney alterations in vivo using mouse models of nephrotoxic serum-induced nephritis and puromycin aminoglycoside nephrosis. The F1.1 antibody-fluorophore conjugate signal rapidly localized specifically to injured glomeruli in both the severe and mild kidney disease models while minimally labeling healthy kidney. This differential labeling is likely due to cryptic NC1-domain exposure as enzymatic or chemical treatment of healthy human or mouse kidney sections significantly increased F1.1 binding to the glomeruli. Finally, kidney tissue from patients with renal disease show significant glomerular staining by F1.1 indicating that exposure of the NC1 domain occurs in clinically relevant circumstances. Thus, NC1 domain exposure may represent an in situ biomarker for assessment of kidney injury. Our study suggests that F1.1 and similar antibodies may represent a new class of non-invasive renal imaging reagents.

Heterologous protein incites abnormal plasma cell accumulation and autoimmunity in MRL-MpJ mice

Although it is evident that there is complex interplay among genetic and environmental factors contributing to systemic autoimmunity, the events inciting autoreactivity are incompletely understood. Previously we demonstrated that MRL-MpJ mice posses a genetic background susceptible to autoimmunity development under conditions of altered inhibitory signaling. To gain better understanding of the influence of exogenous factors on autoreactivity in susceptible individuals, young MRL-MpJ mice were challenged with a single injection of heterologous protein and evaluated for evidence of autoimmunity. We found that MRL-MpJ mice developed high titer serum reactivity to DNA within 1 week of protein administration reaching maximal levels within 1 month. Importantly, the level of autoimmunity was sustained for an extended period of time (6 months). This was accompanied by a substantial increase in germinal center B cell and plasma cell numbers. In contrast, control mice showed no change in autoreactivity or lymphocyte homeostasis. Autoimmunity was dependent on marginal zone B cells as their depletion reduced serum auto-reactivity after challenge, thus suggesting immune stimulation with heterologous proteins can precipitate loss of B cell tolerance and autoimmunity in genetically prone individuals. This model may provide an important tool to further investigate the mechanisms whereby environmental stimuli trigger autoimmune reactivity in susceptible hosts.

Goodpasture's disease: molecular architecture of the autoantigen provides clues to etiology and pathogenesis

PURPOSE OF REVIEW

Goodpasture's disease is an autoimmune disorder characterized by the deposition of pathogenic autoantibodies in basement membranes of kidney and lung, which induces rapidly progressive glomerulonephritis and pulmonary hemorrhage. The target antigen is the α3NC1 domain of collagen IV, which is expressed in target organs as an α345 network. Recent studies of specificity and epitopes of Goodpasture's autoantibodies and discovery of novel posttranslational modification of the antigen, a sulfilimine bond, provide further insight into mechanisms of initiation and progression of Goodpasture's disease.

RECENT FINDINGS

Analysis of the specificity of Goodpasture's autoantibodies revealed a distinct subset of circulating and kidney-bound antiα5NC1 antibody, which is associated with loss of kidney function. Structural integrity of the α345NC1 hexamer is stabilized by the novel sulfilimine crosslinks conferring immune privilege to the Goodpasture's autoantigen. Native antibodies may contribute to establishment of immune tolerance to autoantigen. Structural analysis of epitopes for autoantibodies and alloantibodies indicates a critical role of conformational change in the α345NC1 hexamer in eliciting an autoimmune response in Goodpasture's disease.

SUMMARY

Understanding of the quaternary structure of the Goodpasture's autoantigen continues to provide insights into autoimmune mechanisms that serve as a basis for development of novel diagnostic tools and therapies for Goodpasture's disease.

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.

Modeling of human anti-GBM antibody-alpha3(IV)NC1 interactions predicts antigenic cross-linking through contact of both heavy chains with repeating epitopes on alpha3(IV)NC1

BACKGROUND/AIMS

Patients with anti-glomerular basement membrane diseases produce pathogenic autoantibodies (autoAb) that deposit in the kidney and initiate severe inflammation. Restricted antigenic specificity of the autoAb against 2 regions (with related sequences) within alpha3(IV)NC1, along with shared idiotypes (i.e. structural determinants), among pathogenic human autoAb suggested that common genetic elements encode the autoAb. The aim of this study was to determine whether the idiotypic relatedness of the autoAb was due to the fact that unique and similar genes were used to encode them, divergent genes were used to produce Ab with similar Ag-binding properties and conformation, or if other mechanisms were operative.

METHODS

The encoding V gene sequences of pathogenic human anti-alpha3(IV)NC1 Ab, derived following immunization of XenoMice which produce human but not murine IgG, with alpha3(IV)NC1 were determined. Predicted conformations of autoAb-alpha3(IV)NC1 interactions were derived using the Ab sequences and molecularmodels of the alpha3(IV)NC1 structure.

RESULTS

The pathogenic Ab were encoded by multiple, common V(H) and V(L) gene families indicating that they were not encoded by a unique subset of genes and that normal individuals have the capacity to produce them. However, modeling of the Ag-Ab interactions suggested that although the contact regions varied for individual Ab, the optimized energy constraints facilitate interaction of both Ab-binding regions with pathogenically relevant epitopes on alpha3(IV)NC1.

CONCLUSIONS

The results suggest that the repetitive nature and relatedness of the alpha3(IV)NC1 antigenic epitopes facilitate cross-linking of pathogenic Ab, in vivo, by allowing both IgG Fab to bind to the basement membrane. This most likely accounts for the high-affinity Ab binding we and others observed among human anti-alpha3(IV)NC1 Ab. Based on these observations, we postulate that this interaction provides for the stability of the Ab interaction, resulting in a high-affinity interaction that serves as an ideal scaffold for optimal FcR engagement and complement activation, thereby accelerating inflammation and contributing to the rapidly progressive nature of this disease.

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.

Bench-to-bedside review: pulmonary-renal syndromes--an update for the intensivist

The term Pulmonary-renal syndrome refers to the combination of diffuse alveolar haemorrhage and rapidly progressive glomerulonephritis. A variety of mechanisms such as those involving antiglomerular basement membrane antibodies, antineutrophil cytoplasm antibodies or immunocomplexes and thrombotic microangiopathy are implicated in the pathogenesis of this syndrome. The underlying pulmonary pathology is small-vessel vasculitis involving arterioles, venules and, frequently, alveolar capillaries. The underlying renal pathology is a form of focal proliferative glomerulonephritis. Immunofluorescence helps to distinguish between antiglomerular basement membrane disease (linear deposition of IgG), lupus and postinfectious glomerulonephritis (granular deposition of immunoglobulin and complement) and necrotizing vasculitis (pauci-immune glomerulonephritis). Patients may present with severe respiratory and/or renal failure and require admission to the intensive care unit. Since the syndrome is characterized by a fulminant course if left untreated, early diagnosis, exclusion of infection, close monitoring of the patient and timely initiation of treatment are crucial for the patient's outcome. Treatment consists of corticosteroids in high doses, and cytotoxic agents coupled with plasma exchange in certain cases. Renal transplantation is the only alternative in end-stage renal disease. Newer immunomodulatory agents such as those causing TNF blockade, B-cell depletion and mycophenolate mofetil could be used in patients with refractory disease.

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.

Isolation and characterization of human anti-acetylcholine receptor monoclonal antibodies from transgenic mice expressing human immunoglobulin loci

The isolation of human antibodies against muscle acetylcholine receptor (AChR), the autoantigen involved in myasthenia gravis (MG), is important for the development of therapeutically useful reagents. Monovalent antibody fragments from monoclonal antibodies against the main immunogenic region (MIR) of AChR protect the receptor from the destructive activity of MG autoantibodies. Human anti-AChR alpha-subunit antibody fragments with therapeutic potential have been isolated using phage display antibody libraries. An alternative approach for obtaining human mAb has been provided by the development of humanized mice. In this report, we show that immunization of transgenic mouse strains with the extracellular domain of the human AChR alpha-subunit results in antibody responses and isolation of hybridomas producing human mAb. Four specific IgM mAb were isolated and analyzed. mAb170 recognized the native receptor the best and was capable of inducing AChR antigenic modulation, suggesting its specificity for a pathogenic epitope. Moreover, the recombinant antigen-binding (Fab) fragment of this mAb competed with an anti-MIR mAb, revealing that its antigenic determinant lies in or near the MIR. Finally, Fab170 was able to compete with MG autoantibodies and protect the AChR against antigenic modulation induced by MG sera. This approach will be useful for isolating additional mAb with therapeutic potential against the other AChR subunits.

Histopathology of humorally mediated anti-glomerular basement membrane (GBM) glomerulonephritis in mice

BACKGROUND

From a diagnostic point of view it would be important to learn more about the relationship between the immune responses underlying glomerulonephritis and the patterns of glomerular lesions. A murine model of anti-GBM glomerulonephritis in which inflammation is driven by delayed-type hypersensitivity (DTH) has been studied extensively. The aim of this study was to uncover histological features that might be specific for anti-GBM glomerulonephritis driven by a humoral immune response.

METHODS

BALB/c mice were immunized with rabbit IgG in incomplete Freund's adjuvant. Six days later, on day 0, they received rabbit anti-GBM serum intravenously. Proteinuria was assessed with dipsticks. Mice were killed on days 4, 8 or 14. Kidneys from days 4 and 8 were processed for immunofluorescence and histology. On day 14 mice were perfusion-fixed for electron microscopy.

RESULTS

Proteinuria started on day 3. Autologous IgG and of C3 were found along the GBM. There was only slight infiltration with macrophages and no measurable infiltration by CD4 T cells, indicating the virtual absence of DTH. Besides infiltration with neutrophils there were little histological alterations on day 4. On day 8 many loops were hyalinized. On day 14, cellular crescents were found in 23% of glomeruli. Subendothelial spaces contained hyaline material, cells and fibrin. Podocytes displayed effacement of foot processes and apical microprotrusions. Podocyte bridges were common. These alterations were identical to those reported in the standard model that produces a DTH-like inflammation.

CONCLUSION

The qualitative pattern of histological damage in a murine model of anti-GBM glomerulonephritis does not depend on the underlying immunological process.

Immunodominant epitopes of α3(IV)NC1 induce autoimmune glomerulonephritis in rats

BACKGROUND

The major Goodpasture antibody binding epitopes have been localized to the amino-terminal third of the noncollagenous domain (NC1) of the alpha3 chain of type IV collagen [alpha3(IV)NC1]. The present study determined whether the same epitopes induce glomerulonephritis in rats.

METHODS

We immunized Wistar Kyoto (WKY) rats with human alpha3(IV)/alpha1(IV)NC1 chimeric proteins or full-length recombinant alpha3(IV)NC1 (alpha3732). Chimeric protein constructs were thirds of alpha3(IV)NC1 (CP333) replaced by corresponding sequences of homologous nonreactive alpha1(IV)NC1 (CP111). All chimeric proteins contained 30 amino acids of type X collagen at the amino terminus except alpha3732. Two other constructs, T195 EA (EA) and T194 EB (EB), were entirely alpha1(IV)NC1, except for antibody-immunodominant amino acids from the first and second thirds of alpha3(IV)NC1.

RESULTS

Construct immunized animals developed specific antibody responses to recombinant proteins and native human, bovine and rat NC1. CP311 immunized rats, as well as alpha3732 rats, had glomerular IgG, fibrin, and glomerulonephritis with proteinuria by 3 weeks. CP331 produced more severe disease, comparable to positive controls. CP111 produced no disease. EA, but not EB, induced severe glomerulonephritis. Half-dose each of EA plus EB induced disease identical to full-dose EA alone.

CONCLUSION

The amino third of alpha3(IV)NC1 which contains the major epitope for Goodpasture antibody binding, also induces glomerulonephritis in rats. The middle third of alpha3(IV)NC1 does not induce glomerulonephritis but appears to enhance disease with the amino terminal third. Finally, the presence of the collagen X leader sequence appears to convey greater nephritogenicity. These studies suggest that not only the nephritogenic epitope itself, but flanking sequences and the conformational context of the nephritogenic epitope may influence its ability to cause glomerulonephritis.

A human-mouse chimera of the alpha3alpha4alpha5(IV) collagen protomer rescues the renal phenotype in Col4a3-/- Alport mice

Collagen IV is a major structural component of basement membranes. In the glomerular basement membrane (GBM) of the kidney, the alpha3, alpha4, and alpha5(IV) collagen chains form a distinct network that is essential for the long-term stability of the glomerular filtration barrier, and is absent in most patients affected with Alport syndrome, a progressive inherited nephropathy associated with mutation in COL4A3, COL4A4, or COL4A5 genes. To investigate, in vivo, the regulation of the expression, assembly, and function of the alpha3alpha4alpha5(IV) protomer, we have generated a yeast artificial chromosome transgenic line of mice carrying the human COL4A3-COL4A4 locus. Transgenic mice expressed the human alpha3 and alpha4(IV) chains in a tissue-specific manner. In the kidney, when expressed onto a Col4a3(-/-) background, the human alpha3(IV) chain restored the expression of and co-assembled with the mouse alpha4 and alpha5(IV) chains specifically at sites where the human alpha3(IV) was expressed, demonstrating that the expression of all three chains is required for network assembly. The co-assembly of the human and mouse chains into a hybrid network in the GBM restores a functional GBM and rescues the Alport phenotype, providing further evidence that defective assembly of the alpha3-alpha4-alpha5(IV) protomer, caused by mutations in any of the three chains, is the pathogenic mechanism responsible for the disease. This line of mice, humanized for the alpha3(IV) collagen chain, will also provide a valuable model for studying the pathogenesis of Goodpasture syndrome, an autoimmune disease caused by antibodies against this chain.

Antibody discovery: the use of transgenic mice to generate human monoclonal antibodies for therapeutics

Technical advances made in the 1980s and early 1990s resulted in monoclonal antibodies that are now approved for human therapy. Novel transgenic mouse strains provide a powerful technology platform for creating fully human monoclonal antibodies as therapeutics; ten such antibodies have entered clinical trials since 1998 and more are in preclinical testing. Improved transgenic mouse strains provide a powerful technology platform for creating human therapeutics in the future.