Reactivity against complementary proteinase-3 is not increased in patients with PR3-ANCA-associated vasculitis

[Pathogenesis of ANCA-associated vasculitides in 2021: An update]

Anticytoplasmic neutrophil antibodies (ANCA)-associated vasculitis (AAV) are rare systemic immune-mediated diseases characterized by small vessel necrotizing vasculitis and/or respiratory tract inflammation. Over the last 2 decades, anti-MPO vasculitis mouse model has enlightened the role of ANCA, neutrophils, complement activation, T helper cells (Th1, Th17) and microbial agents. In humans, CD4T cells have been extensively studied, while the dramatic efficacy of rituximab demonstrated the key role of B cells. Many areas of uncertainty remain, such as the driving force of GPA extra-vascular granulomatous inflammation and the relapse risk of anti-PR3 AAV pathogenesis. Animal models eventually led to identify complement activation as a promising therapeutic target. New investigation tools, which permit in depth immune profiling of human blood and tissues, may open a new era for the studying of AAV pathogenesis.

The Nasal Microbiome in ANCA-Associated Vasculitis: Picking the Nose for Clues on Disease Pathogenesis

PURPOSE OF REVIEW

The onset and progression of small vessel vasculitis associated with anti-neutrophil cytoplasmic antibodies has been linked to microbial infections. Here, we provide a brief overview of the association of nasal colonization of Staphylococcus aureus with ANCA-associated vasculitis (AAV) and discuss several recent studies mapping the nasal microbiome in AAV patients in particular.

RECENT FINDINGS

Nasal microbiome studies revealed dysbiosis as a common trait in active AAV which tends to normalize upon immunosuppressive treatment and quiescent disease. However, due to differences in study design, patient selection, and methodology, the reported microbiome profiles differ considerably precluding conclusions on causal relationships. The microbiome is an emerging area of research in AAV warranting further investigation. Ideally, such studies should be combined with mechanistic studies to unravel key elements related to host-microbe interactions and their relevance for AAV pathogenesis.

Human Proteinase 3, an important autoantigen of c-ANCA associated vasculitis, shares cross-reactive epitopes with serine protease allergens from mites: an in silico analysis

Background: In autoimmune vasculitis, autoantibodies to Human Proteinase 3 (PR3), a human serine protease, seems to have a role on the inception of c-ANCA associated vasculitis. The origin of this autoreactive response remains unclear. However, for several autoreactive responses, molecular mimicry between environmental antigens and human proteins is key to trigger autoantibodies and finally autoimmunity manifestations. Considering that PR3 is a serine protease and house dust mite (HDM) group 3 allergens share this biochemical activity, the aim of this study was to identify cross-reactive epitopes between serine proteases from human and mites using an in silico approach. Methods: Multi alignment among amino acid sequences of PR3 and HDM group 3 allergens was performed to explore identity and structural homology. ElliPro and BepiPred  in silico tools were used to predict B and T cell epitopes. Consurf tool was used to conduct identification of conserved regions in serine proteases family. Results: PR3 and HDM group 3 allergens shared moderate identity and structural homology (root mean square deviation < 1). One B cell cross reactive epitope among serine proteases was identified (29I, 30V, 31G, 32G, 34E, 36K, 37A, 38L, 39A and 54C) and two T cell epitopes. Conclusions: PR3 have structural homology and share cross reactive epitopes with HDM group 3 allergens.

Human Proteinase 3, an important autoantigen of c-ANCA associated vasculitis, shares cross-reactive epitopes with serine protease allergens from mites: an in silico analysis

Background: In autoimmune vasculitis, autoantibodies to Human Proteinase 3 (PR3), a human serine protease, seems to have a role on the inception of c-ANCA associated vasculitis. The origin of this autoreactive response remains unclear. However, for several autoreactive responses, molecular mimicry between environmental antigens and human proteins is key to trigger autoantibodies and finally autoimmunity manifestations. Considering that PR3 is a serine protease and house dust mite (HDM) group 3 allergens share this biochemical activity, the aim of this study was to identify cross-reactive epitopes between serine proteases from human and mites using an in silico approach. Methods: Multi alignment among amino acid sequences of PR3 and HDM group 3 allergens was performed to explore identity and structural homology. ElliPro and BepiPred  in silico tools were used to predict B and T cell epitopes. Consurf tool was used to conduct identification of conserved regions in serine proteases family. Results: PR3 and HDM group 3 allergens shared moderate identity and structural homology (root mean square deviation < 1). One B cell cross reactive epitope among serine proteases was identified (29I, 30V, 31G, 32G, 34E, 36K, 37A, 38L, 39A and 54C) and two T cell epitopes. Conclusions: PR3 have structural homology and share cross reactive epitopes with HDM group 3 allergens.

ANCA-associated vasculitis

The anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAVs) are a group of disorders involving severe, systemic, small-vessel vasculitis and are characterized by the development of autoantibodies to the neutrophil proteins leukocyte proteinase 3 (PR3-ANCA) or myeloperoxidase (MPO-ANCA). The three AAV subgroups, namely granulomatosis with polyangiitis (GPA), microscopic polyangiitis and eosinophilic GPA (EGPA), are defined according to clinical features. However, genetic and other clinical findings suggest that these clinical syndromes may be better classified as PR3-positive AAV (PR3-AAV), MPO-positive AAV (MPO-AAV) and, for EGPA, by the presence or absence of ANCA (ANCA⁺ or ANCA^-, respectively). Although any tissue can be involved in AAV, the upper and lower respiratory tract and kidneys are most commonly and severely affected. AAVs have a complex and unique pathogenesis, with evidence for a loss of tolerance to neutrophil proteins, which leads to ANCA-mediated neutrophil activation, recruitment and injury, with effector T cells also involved. Without therapy, prognosis is poor but treatments, typically immunosuppressants, have improved survival, albeit with considerable morbidity from glucocorticoids and other immunosuppressive medications. Current challenges include improving the measures of disease activity and risk of relapse, uncertainty about optimal therapy duration and a need for targeted therapies with fewer adverse effects. Meeting these challenges requires a more detailed knowledge of the fundamental biology of AAV as well as cooperative international research and clinical trials with meaningful input from patients.

ANCA-associated vasculitis - clinical utility of using ANCA specificity to classify patients

The anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV) are a heterogeneous group of rare syndromes characterized by necrotizing inflammation of small and medium-sized blood vessels and the presence of ANCAs. Several clinicopathological classification systems exist that aim to define homogeneous groups among patients with AAV, the main syndromes being microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA) and eosinophilic GPA (EGPA). Two main types of ANCA can be detected in patients with AAV. These ANCAs are defined according to their autoantigen target, namely leukocyte proteinase 3 (PR3) and myeloperoxidase (MPO). Patients with GPA are predominantly PR3-ANCA-positive, whereas those with MPA are predominantly MPO-ANCA-positive, although ANCA specificity overlaps only partially with these clinical syndromes. Accumulating evidence suggests that ANCA specificity could be better than clinical diagnosis for defining homogeneous groups of patients, as PR3-ANCA and MPO-ANCA are associated with different genetic backgrounds and epidemiology. ANCA specificity affects the phenotype of clinical disease, as well as the patient's initial response to remission-inducing therapy, relapse risk and long-term prognosis. Thus, the classification of AAV by ANCA specificity rather than by clinical diagnosis could convey clinically useful information at the time of diagnosis.

Emerging concepts in the pathogenesis of antineutrophil cytoplasmic antibody-associated vasculitis

PURPOSE OF REVIEW

Antineutrophil cytoplasmic antibodies (ANCAs) remain central to our current understanding of the pathogenesis of ANCA-associated vasculitis (AAV), and this review considers recent developments in the context of four key questions: are there targets for ANCA beyond myeloperoxidase (MPO) and proteinase 3 (PR3); are all ANCA pathogenic; how are ANCAs generated; and how do ANCA cause disease?

RECENT FINDINGS

B-cell epitope mapping raises the possibility that only a subset of ANCA may be pathogenic. Anti-lysosomal-associated membrane protein 2 autoantibodies have recently emerged as a novel form of ANCA and can be found in anti-MPO and anti-PR3 negative disease. These also provide recent evidence for molecular mimicry in the pathogenesis of AAV, but a definitive proof in human AAV remains elusive. Neutrophil extracellular traps may represent an important mechanism by which MPO and PR3 are taken up by dendritic cells for presentation to the adaptive immune system, and the role of the alternative pathway of complement in AAV has recently been emphasized, with therapeutic implications.

SUMMARY

Our current understanding of the pathogenesis of AAV not only reinforces the central role of neutrophils but also provides a sound rationale for B-cell and complement-directed therapies.

Pathophysiological Relationship between Infections and Systemic Vasculitis

The development of autoimmune disorders requires a combination of genetic, immunological, and environmental factors. Infectious agents, such as viruses and bacteria, can trigger autoimmunity through different mechanisms, and for systemic vasculitis in particular, microbial agents have been suggested to be involved in its pathogenesis. Although the exact mechanisms have not been fully elucidated, different theories have been postulated. This review considers the role of infections in the etiology of primary vasculitis, emphasizing their related immunological events.

The immunopathology of ANCA-associated vasculitis

The small-vessel vasculitides are a group of disorders characterised by variable patterns of small blood vessel inflammation producing a markedly heterogeneous clinical phenotype. While any vessel in any organ may be involved, distinct but often overlapping sets of clinical features have allowed the description of three subtypes associated with the presence of circulating anti-neutrophil cytoplasmic antibodies (ANCA), namely granulomatosis with polyangiitis (GPA, formerly known as Wegener’s Granulomatosis), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (eGPA, formerly known as Churg-Strauss syndrome). Together, these conditions are called the ANCA-associated vasculitidies (AAV). Both formal nomenclature and classification criteria for the syndromes have changed repeatedly since their description over 100 years ago and may conceivably do so again following recent reports showing distinct genetic associations of patients with detectable ANCA of distinct specificities. ANCA are not only useful in classifying the syndromes but substantial evidence implicates them in driving disease pathogenesis although the mechanism by which they develop and tolerance is broken remains controversial. Advances in our understanding of the pathogenesis of the syndromes have been accompanied by some progress in treatment, although much remains to be done to improve the chronic morbidity associated with the immunosuppression required for disease control.

The association between anti-plasminogen antibodies and disease activity in ANCA-associated vasculitis

OBJECTIVE

Previous studies have shown that in patients with ANCA-associated vasculitis (AAV), anti-plasminogen antibodies were associated with reduced renal function and the presence of fibrinoid necrosis and cellular crescents in renal histology. The purpose of the current study was to investigate whether anti-plasminogen antibodies are associated with the systemic disease activity of AAV.

METHODS

One hundred and four Chinese patients with AAV were recruited. Anti-plasminogen antibodies were detected in sequential serum samples at initial onset and remission of the disease. Associations of anti-plasminogen antibodies with clinicopathological parameters were analysed.

RESULTS

The prevalence of anti-plasminogen antibodies was significantly higher in AAV patients than in healthy controls (19/104 vs 0/50, χ(2) = 8.8, P = 0.003). The prevalence of anti-plasminogen antibodies was significantly higher in the active stage of AAV than in remission (19/104 vs 1/48, χ(2) = 7.5, P = 0.013). The level of anti-plasminogen antibodies (expressed as a percentage of the positive controls) correlated with the ESR (r = 0.207, P = 0.042), serum creatinine (r = 0.302, P = 0.002), d-dimer (r = 0.273, P = 0.009) and the percentage of glomeruli with crescents in renal specimens (r = 0.393, P = 0.004). The level of Birmingham vasculitis activity scores and the prevalence of arthralgia and gastrointestinal involvement in patients with anti-plasminogen antibodies were significantly higher than in patients without anti-plasminogen antibodies [22.5 (s.d. 5.63) vs. 19.4 (s.d. 4.66), P = 0.015; 63.2% vs. 25.8%, P = 0.002; 57.9% vs. 21.1%, P = 0.001, respectively].

CONCLUSION

Circulating anti-plasminogen antibodies were associated with systemic disease activity and renal disease activity of AAV.

The immune system and kidney disease: basic concepts and clinical implications

The kidneys are frequently targeted by pathogenic immune responses against renal autoantigens or by local manifestations of systemic autoimmunity. Recent studies in rodent models and humans have uncovered several underlying mechanisms that can be used to explain the previously enigmatic immunopathology of many kidney diseases. These mechanisms include kidney-specific damage-associated molecular patterns that cause sterile inflammation, the crosstalk between renal dendritic cells and T cells, the development of kidney-targeting autoantibodies and molecular mimicry with microbial pathogens. Conversely, kidney failure affects general immunity, causing intestinal barrier dysfunction, systemic inflammation and immunodeficiency that contribute to the morbidity and mortality of patients with kidney disease. In this Review, we summarize the recent findings regarding the interactions between the kidneys and the immune system.

Crescentic Glomerulonephritis: an update on Pauci-immune and Anti-GBM diseases

Crescentic glomerulonephritis (GN) in a renal biopsy is a widely accepted "critical diagnosis" in Anatomic Pathology practice. Prompt biopsy evaluation and notification of the referring physician is essential to facilitate rapid therapeutic intervention. The differential diagnostic categories of crescentic GN include pauci-immune GN, anti-glomerular basement membrane (GBM) nephritis and immune complex-mediated GN, distinguished from one another by immunofluorescence and electron microscopic study of the renal biopsy. Immune complex-mediated GN is characterized by abundant glomerular deposits and encompasses several diseases including but not limited to lupus nephritis, cryoglobulinemic GN and immunoglobulin A nephropathy. Pauci-immune GN, with paucity of deposits, correlates closely with antineutrophil cytoplasmic antibody disease due to the identifiable circulating pathogenic antineutrophil cytoplasmic antibody in most patients. Recent studies have identified other antibodies in pauci-immune GN and implicated infectious organisms in triggering autoimmunity in a susceptible host by molecular mimicry of host antigens. Anti-GBM nephritis is a rare but potentially life-threatening autoimmune disease with circulating antibodies against GBM epitopes in α3 chain of type IV collagen. It is characterized by a linear immunoglobulin G deposition along GBM on immunofluorescence microscopy. Environmental triggers including infections and solvent exposure seem to change the tertiary structure of the type IV collagen α345 hexamer in GBM, expose neoepitopes, and initiate autoimmunity. Even in light of advances in understanding of pathophysiology and serologic testing, renal biopsy remains the mainstay of diagnosis of crescentic GN.

Molecular recognition theory and sense-antisense interaction: therapeutic applications in autoimmunity

Perhaps behind only the understanding of the genetic code in importance is the comprehension of protein sequence and structure in its effect on modern scientific investigation. How proteins are structured and interact dictates a considerable amount of the body's processes in maintaining homeostasis. Unfortunately, in diseases of autoimmunity, these processes are directed against the body itself and most of the current clinical responses are severely lacking. This review addresses current therapeutics involved in the treatment of various autoimmune diseases and details potential future therapeutics designed with a more targeted approach. Detailed in this manuscript is the concept of utilizing peptides possessing an inverse hydropathy to the immunogenic region of proteins to generate anti-idiotypic (anti-Id) and anti-clonotypic T cell receptor (TCR) antibodies (Abs). Theoretically, the anti-Id Abs cross react with Id Abs and negate the powerful machinery of the adaptive immune response with little to no side effects. A series of studies by a number of groups have shown this to be an exciting and intriguing concept that will likely play a role in the future treatment of autoimmune diseases.

Molecular recognition theory and sense-antisense interaction: therapeutic applications in autoimmunity

Perhaps behind only the understanding of the genetic code in importance is the comprehension of protein sequence and structure in its effect on modern scientific investigation. How proteins are structured and interact dictates a considerable amount of the body's processes in maintaining homeostasis. Unfortunately, in diseases of autoimmunity, these processes are directed against the body itself and most of the current clinical responses are severely lacking. This review addresses current therapeutics involved in the treatment of various autoimmune diseases and details potential future therapeutics designed with a more targeted approach. Detailed in this manuscript is the concept of utilizing peptides possessing an inverse hydropathy to the immunogenic region of proteins to generate anti-idiotypic (anti-Id) and anti-clonotypic T cell receptor (TCR) antibodies (Abs). Theoretically, the anti-Id Abs cross react with Id Abs and negate the powerful machinery of the adaptive immune response with little to no side effects. A series of studies by a number of groups have shown this to be an exciting and intriguing concept that will likely play a role in the future treatment of autoimmune diseases.

Pathogenesis of ANCA-associated vasculitis

Antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) comprises a group of systemic inflammatory vasculitides associated with circulating autoantibodies directed against the neutrophil granule components proteinase 3 and myeloperoxidase. ANCA interact with their target antigens on cytokine primed neutrophils, causing neutrophil activation via several signaling pathways that culminates in endothelial interaction, degranulation, cytokine production, and endothelial and tissue damage. The presence of autoantibodies implies the assistance of autoreactive T-helper cells and B cells, and a failure of regulatory mechanisms. This article reviews the current evidence for the pathogenic mechanisms culminating in autoantibody production, the effects of ANCA-neutrophil and neutrophil-endothelial interactions, and the mechanisms of tissue damage.