PR3-ANCA Vasculitis Research Articles

A case of hypercalcemia from Pneumocystis jirovecii in an immunosuppressed non-HIV patient

BackgroundThe prevalence of non-HIV related Pneumocystis jirovecii pneumonia (PJP) is increasing with use of immunosuppressive therapies. There are case reports of solid organ transplant recipients on immunosuppressive therapy presenting with mild hypercalcemia, leading to a diagnosis of PJP. Recent studies have shown efficacy of PJP prophylaxis for patients treated with rituximab with a favourable adverse effect profile.Case PresentationA 78-year-old male with a history of PR3-ANCA vasculitis, chronic kidney disease and heart failure with reduced ejection fraction presented to our tertiary care hospital with a two-week history of confusion and non-productive cough. Background immunosuppression with rituximab was completed every six months. The patient was found to have hypercalcemia and new infiltrates and ground glass opacities on cross-sectional imaging. Bronchoscopy was performed that was positive for Pneumocystis jirovecii. He was treated with 21 days of trimethoprim-sulfamethoxazole and prednisone with resolution of symptoms and hypercalcemia.ConclusionsHerein, we present a novel case of PJP in a non-transplant recipient preceded by hypercalcemia. Our case demonstrates the importance for a high suspicion for PJP in chronically immunosuppressed patients on rituximab presenting with PTH-independent hypercalcemia.

Antineutrophil cytoplasmic antibody-associated vasculitis classification by cluster analysis based on clinical phenotypes: a single-center retrospective cohort study.

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) refers to a group of small vessel inflammatory disorders. Overlapping clinical phenotypes of AAV subgroups continually provoke controversies over their diagnostic and classification criteria. Using the agglomerative hierarchical clustering method, we classified 210 Korean patients diagnosed with AAV into mutually exclusive clusters according to Birmingham Vasculitis Activity Score items, ANCA specificity, sex, and age. We analyzed the resulting clusters' outcomes to investigate the clinical significance of the classification. We proposed a distance-based algorithm of patient assignment and explored its clinically relevant modification. In total, 116 patients (55%) had microscopic polyangiitis, 53 (25%) had granulomatosis with polyangiitis, and 42 (20%) had eosinophilic granulomatosis with polyangiitis. Our model grouped the patients into five clusters, namely, "limited proteinase 3 (PR3)-ANCA vasculitis," "generalized PR3-ANCA vasculitis," "ANCA-negative vasculitis," "renal-limited vasculitis," and "myeloperoxidase-ANCA vasculitis." Patients clustered under "generalized PR3-ANCA vasculitis" had a higher relapse rate (hazard ratio [HR] = 2.12, P = 0.067). The incidence of end-stage renal disease was higher in patients belonging to the "renal-limited vasculitis" cluster (HR=1.50, P=0.03), and those in the "ANCA-negative vasculitis" cluster experienced a relatively milder clinical course of AAV (mortality = 0). Because the clusters were naturally derived from their distinguished phenotypes and have different clinical courses, our clustering method may be a more clinically relevant classification system for AAV, revealing its phenotypic diversity. We also proposed a simple and intuitive distance-based assignment algorithm, which can be easily modified according to specific clinical needs. Key Points • In this study with a single-center AAV cohort, we showed that AAV can be divided into five distinct subclasses with different disease courses based on the clinical and laboratory features of the patients. • Our study revealed ethnic differences in AAV manifestation and suggests that physicians may need to analyze their own AAV patients to assess the disease status of AAV patients. • We proposed a distance-based cluster membership assignment method that can be clinically modified to fit the specific purpose of grouping patients.

Renal Limited PR3-ANCA Vasculitis due to Abiotrophia defectiva Infective Endocarditis

Renal Limited PR3-ANCA Vasculitis due to Abiotrophia defectiva Infective Endocarditis

Association of baseline soluble immune checkpoints with the risk of relapse in PR3-ANCA vasculitis following induction of remission

ObjectivesWe investigated whether soluble immune checkpoints (sICPs) predict treatment resistance, relapse and infections in patients with antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV).MethodsPlasma sICP concentrations from available samples obtained during conduct...

Immunological Interaction of HLA-DPB1 and Proteinase 3 in ANCA Vasculitis is Associated with Clinical Disease Activity.

PR3-ANCA vasculitis has a genetic association with HLA-DPB1. We explored immunologic and clinical features related to the interaction of HLA-DPB1*04:01 with a strongly binding PR3 peptide epitope (PR3225-239). Patients with ANCA vasculitis with active disease and disease in remission were followed longitudinally. Peripheral blood mononuclear cells from patients and healthy controls with HLA-DPB1*04:01 were tested for HLA-DPB1*04:01 expression and interaction with a PR3 peptide identified via in silico and in vitro assays. Tetramers (HLA/peptide multimers) identified autoreactive T cells in vitro. RESULTS: The HLA-DPB1*04:01 genotype was associated with risk of relapse in PR3-ANCA (HR for relapse 2.06; 95% CI, 1.01 to 4.20) but not in myeloperoxidase (MPO)-ANCA or the combined cohort. In silico predictions of HLA and PR3 peptide interactions demonstrated strong affinity between ATRLFPDFFTRVALY (PR3225-239) and HLA-DPB1*04:01 that was confirmed by in vitro competitive binding studies. The interaction was tested in ex vivo flow cytometry studies of labeled peptide and HLA-DPB1*04:01-expressing cells. We demonstrated PR3225-239 specific autoreactive T cells using synthetic HLA multimers (tetramers). Patients in long-term remission off therapy had autoantigenic peptide and HLA interaction comparable to that of healthy volunteers. The risk allele HLA-DPB1*04:01 has been associated with PR3-ANCA, but its immunopathologic role was unclear. These studies demonstrate that HLA-DPB1*04:01 and PR3225-239 initiate an immune response. Autoreactive T cells specifically recognized PR3225-239 presented by HLA-DPB1*04:01. Although larger studies should validate these findings, the pathobiology may explain the observed increased risk of relapse in our cohort. Moreover, lack of HLA and autoantigen interaction observed during long-term remission signals immunologic nonresponsiveness.

FC062: Baseline Soluble Immune Checkpoints Predict Relapse Risk in PR3-Anca Vasculitis Following Rituximab Induction Therapy

Abstract BACKGROUND AND AIMS We investigated whether soluble immune checkpoints (sICPs) predict treatment-resistance, relapse risk and risk of infections in patients with antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV). METHOD Plasma levels of sICPs were measured by enzyme-linked immunosorbent assay from samples obtained at baseline and during follow-up from patients with AAV in the RAVE trial and were correlated with selected clinical outcomes. Log-rank test was used to evaluate survival benefits, and optimal cut-off values of the marker molecules were calculated using Yeldons J. RESULTS Among 95 patients receiving rituximab as induction therapy, lower soluble (s)Lag-3 (<90 pg/mL) and higher sCD27 (>3000 pg/mL) were predictive of not achieving remission. Among patients with remission, 32.9% relapsed with a median relapse free survival of 5.64 months. Low baseline values of sTim-3 (<1200 pg/mL), sCD27 (<1250 pg/mL) and sBTLA (<1000 pg/mL) were associated with disease relapse. In addition, patients with high levels of at least one of these markers were prone to infectious complications. These findings were restricted to patients with proteinase 3 (PR3)-ANCA vasculitis and not observed in patients with myeloperoxidase (MPO)-ANCA vasculitis. Moreover, these relationships do not hold for the group of patients randomized to receive cyclophosphamide/azathioprine. CONCLUSION Rituximab-treated patients achieved remission less frequently when sLag-3 was low and sCD27 was high. Higher expression of sTim-3, sCD27 and sBTLA at baseline was associated with a lower risk of relapse in PR3-ANCA vasculitis following rituximab. These results will require confirmation in future studies, but may contribute to personalized medicine in AAV.

Targeting Cathepsin C in PR3-ANCA Vasculitis.

The ANCA autoantigens proteinase 3 (PR3) and myeloperoxidase (MPO) are exclusively expressed by neutrophils and monocytes. ANCA-mediated activation of these cells is the key driver of the vascular injury process in ANCA-associated vasculitis (AAV), and neutrophil serine proteases (NSPs) are disease mediators. Cathepsin C (CatC) from zymogens activates the proteolytic function of NSPs, including PR3. Lack of NSP zymogen activation results in neutrophils with strongly reduced NSP proteins. To explore AAV-relevant consequences of blocking NSP zymogen activation by CatC, we used myeloid cells from patients with Papillon-Lefèvre syndrome, a genetic deficiency of CatC, to assess NSPs and NSP-mediated endothelial cell injury. We also examined pharmacologic CatC inhibition in neutrophil-differentiated human hematopoietic stem cells, primary human umbilical vein cells, and primary glomerular microvascular endothelial cells. Patients with Papillon-Lefèvre syndrome showed strongly reduced NSPs in neutrophils and monocytes. Neutrophils from these patients produced a negative PR3-ANCA test, presented less PR3 on the surface of viable and apoptotic cells, and caused significantly less damage in human umbilical vein cells. These findings were recapitulated in human stem cells, in which a highly specific CatC inhibitor, but not prednisolone, reduced NSPs without affecting neutrophil differentiation, reduced membrane PR3, and diminished neutrophil activation upon PR3-ANCA but not MPO-ANCA stimulation. Compared with healthy controls, neutrophils from patients with Papillon-Lefèvre syndrome transferred less proteolytically active NSPs to glomerular microvascular endothelial cells, the cell type targeted in ANCA-induced necrotizing crescentic glomerulonephritis. Finally, both genetic CatC deficiency and pharmacologic inhibition, but not prednisolone, reduced neutrophil-induced glomerular microvascular endothelial cell damage. These findings may offer encouragement for clinical studies of adjunctive CatC inhibitor in patients with PR3-AAV.

82 Response to mRNA COVID Vaccine in a Patient With PR3 ANCA Vasculitis Treated With Rituximab and Prednisone

82 Response to mRNA COVID Vaccine in a Patient With PR3 ANCA Vasculitis Treated With Rituximab and Prednisone

Infection is associated with increased risk of MPO- but not PR3-ANCA-associated vasculitis.

To determine whether development of ANCA-associated vasculitis (AAV) shows a relationship with a prior infection and if prior infection affects disease characteristics and outcome. All incident cases of AAV diagnosed in a defined region of Sweden from 2000 through 2016 were identified. For each case, 10 individuals from the general population, matched for age, sex and area of residence, were selected. Infections occurring in AAV patients and controls prior to the date of AAV diagnosis (index date for respective controls) were identified using an administrative database. Conditional logistic regression models were used to calculate odds ratios (OR) of developing AAV. Occurrence, clinical characteristics and outcome of AAV were analysed with respect to prior infection. Two-hundred and seventy patients with AAV (48% female) and 2687 controls were included. Prior to diagnosis/index date, 146 (54%) AAV patients had been diagnosed with infection vs 1282 (48%) controls, with OR for AAV 1.57 (95% CI 1.18, 2.19) in those with infections of the upper respiratory tract and 1.68 (1.02, 2.77) in those with pneumonia. Difference from controls was significant in patients with MPO-ANCA 1.99 (95% CI 1.25, 3.1) but not in those with PR3-ANCA 1.0 (0.61, 1.52). Patients with prior infection showed higher disease activity at AAV diagnosis. No differences in disease characteristics, comorbidities or outcome in those with and without prior infections were observed. Respiratory tract infections are positively associated with development of MPO- but not PR3-ANCA vasculitis. Prior infection is associated with higher disease activity at AAV diagnosis.

MO293NEUTROPHIL-TO-LYMPHOCYTE RATIO AND OUTCOME IN CRESCENTIC GLOMERULONEPHRITIS

Abstract Background and Aims Crescent formation is a nonspecific response to severe injury to the glomerular capillary wall, which may be seen with any form of inflammatory glomerulopathy. Despite improved therapeutic interventions, patients with crescentic glomerulonephritis (CGN) still have a severe kidney prognosis and high mortality. Since neutrophil-to-lymphocyte ratio (NLR) is an inflammatory marker linked to worse outcomes in patients with malignancies, chronic kidney disease, myocardial infarction, and other clinical settings, we aimed to assess if NLR can predict kidney outcome and mortality in subjects with CGN. Method Eighty-four adults with biopsy-proven CGN between 1st Jan. 2008 and 31st Dec. 2017 [age 56 (95%CI 53 to 59) years, 50% males, eGFR 9.3 (95%CI 7.8-12.7) mL/min] were retrospectively enrolled in this single-centre study. Subjects were followed for a median of 31 (95%CI 6 to 56) months, until 31st May 2018. Seven subjects with inadequate biopsy sample and insufficient data were excluded. Demographic (age, gender), clinical and laboratory data at the time of biopsy were obtained from medical records. Kaplan-Meier method was used to evaluate kidney and patient survival. Variables related to kidney outcome were evaluated in a multivariate Cox proportional hazard (CPH) model. According to median NLR value (4.3, 95%CI 3.5 to 5.2) subjects were clustered in low NLR group (≤4.3; n=38 pts.) and high NLR group (>4.3; n=38 pts.). The primary endpoints were time to renal replacement therapy (RRT) initiation and all-cause mortality. Results The most common CGN subtype was pauci-immune GN (76.3%; i.e. myeloperoxidase-ANCA vasculitis - 48.7%, PR3-ANCA vasculitis - 15.8% and ANCA-negative vasculitis - 11.8%) followed by. anti-GBM antibody and immune complex related GN, with similar frequencies (11.8% each). According to kidney biopsy (KB) findings, half of the subjects had fibro-cellular crescents (55.3%), while cellular and fibrous crescents were found in 35.5% and 9.2%, respectively. Almost all subjects received corticosteroids (97.4%) and 82.9% received cyclophosphamide. Baseline eGFR was lower in the high-NLR group (8.5 vs. 11.6 mL/min, p=0.04), but no other differences in laboratory findings at baseline between the two groups were found. In bivariate analysis, NLR was negatively associated with serum albumin (rs=-0.26, p=0.02). NLR was not associated with other inflammation markers, Charlson comorbidity score, nor with the type of crescents at KB. During the follow-up period 53.9% started RRT and 19.7% died. There were no differences regarding mortality between the two groups. The mean kidney survival time was 47.6 (95%CI 33.5, 61.7) months. Kidney survival at 12, 24, 48 and 60 months were 44, 41, 38, and 33% respectively. In univariate time-dependent analysis (Figure) patients with low-NLR (68.95%CI 48 to 88 months) had better kidney survival than those with high-NLR (25, 95%CI 13 to 38 months; log rank p=0.004). Moreover, the kidney survival advantage remained (OR 1.06, 95%CI 1.002 to 1.16) after adjusting for eGFR, proteinuria, C reactive protein, immunosuppressive treatment and CGN etiology. Lower eGFR-ul was also associated with poor kidney survival (OR 0.96, 95%CI 0.88 to 0.97). Conclusion In adults with biopsy-proven crescentic glomerulonephritis and advanced kidney function decline, a higher neutrophil-to-lymphocyte ratio seems to predict worse kidney survival, but not the risk of mortality.

O02 Persistent non-fulminant COVID-19 infection in a GPA patient on rituximab

Case report - IntroductionBased on initial clinical data, it was suggested that patients with vasculitis who were immunosuppressed, would have a more severe COVID-19 infection. Here we present a case of a young 26-year old lady with granulomatosis with polyangiitis (GPA) on rituximab who developed COVID-19 infection while on active GPA treatment. Her COVID-19 infection confirmed on PCR serology, has been protracted but non-fulminant. She did not require mechanical respiratory support. At the same time her GPA remained active and worsened requiring further immunosuppression after she developed mild pulmonary haemorrhage. She is currently still receiving vasculitis treatment.Case report - Case descriptionA 26-year-old lady with a background history of obstructive sleep apnoea and fibromyalgia was diagnosed with ENT-limited GPA in 2017. She was initially treated with azathioprine then methotrexate, and later switched to Rituximab in 2018 after she developed organ-threatening manifestations with bilateral hearing loss. She was stable on periodic infusions of rituximab at 6 to 9-monthly intervals and did not develop other organ-threatening features.She had been given one dose of rituximab for a flare of her GPA. In between rituximab doses, she was admitted with acute COVID-19 infection with related pneumonia and treated with antibiotics, fluids, and oxygen. Shortly after discharge, she was readmitted with worsening symptoms of non-resolving COVID-19 pneumonia which was evident on chest x-ray and levofloxacin treatment was initiated. Her condition improved and she was discharged. No mechanical respiratory support was required. She had her 2nd dose of rituximab after it had been delayed by about 2 weeks. She had been afebrile after the acute COVID-19 infection and her persistent positive results were explained as related viral shedding over a period of 8 weeks.One week later, she represented to hospital with fever, cough and shortness of breath, and her blood results showed a remarkable rise in inflammatory markers, including a CRP of 242. She was treated for non-resolving COVID-19 pneumonitis with worsening chest x-ray features. After hospital discharge, her GPA continued to flare with persistent epistaxis with nasal crusting. She also had worsening inflammatory arthritis with purpuric rash on her legs. An ENT review confirmed nasal septum perforation, but no renal involvement was found. Additional cyclophosphamide was commenced via the day-case unit. Her SARS-CoV-2 serology was negative prior to commencing cyclophosphamide. She is now SARS-CoV-2 positive after two doses of cyclophosphamide, but she is afebrile and stable.Case report – DiscussionCOVID-19 infection carries a high mortality rate in patients with multiple co-morbidities, but recent literature suggests that patients on immunosuppressants may not actually have fulminant COVID-19 disease. This case illustrates the challenges of treating active vasculitis in the context of ongoing COVID-19 infection. Her vasculitis remained active requiring escalation of immunosuppression with caution, while she was concomitantly fighting SARS-CoV-2 and superadded bacterial infection. A similar case has been published by Guilpain et al of a 52-year-old woman with PR3-ANCA vasculitis on maintenance therapy with rituximab and low-dose prednisone who developed COVID-19 infection. They reported milder evolution of COVID-19 infection in comparison with previous reports.It is now well known that some disease-modifying anti-rheumatic drugs (DMARDs) such as tocilizumab, hydroxychloroquine and tofacitinib could suppress the cytokine profile seen in severe COVID-19 infection. In addition, several case reports have even reported possible protective effect of immunosuppressants against severe complications of COVID-19 in patients with rheumatological and non-rheumatological conditions. Another complexity in this case was monitoring the disease progression, since both COVID-19 and GPA can have similar findings on chest CT scan of ground glass opacity. In order to better understand the role of immunosuppressants in rheumatological patients with COVID-19 infection, more data is required, currently European League Against Rheumatism (EULAR) is collecting data to monitor and report outcomes of COVID-19 in adult and paediatric population, this will provide invaluable insight for Rheumatologists. Case report - Key learning points This case poses a challenge for Rheumatologists in managing a patient with active vasculitis and concomitant COVID-19 infection due to limited data available literature. It has also stressed the importance of working in a multidisciplinary team when managing such complex patients. Importance of continuous surveillance of patients receiving immunosuppressive therapy is advised due to possible increased risk to SARS-CoV-2.

A novel glucocorticoid-free maintenance regimen for anti-neutrophil cytoplasm antibody-associated vasculitis.

Glucocorticoids (GCs) are a mainstay of treatment for patients with ANCA-associated vasculitis (AAV) but are associated with significant adverse effects. Effective remission induction in severe AAV using extremely limited GC exposure has not been attempted. We tested an early rapid GC withdrawal induction regimen for patients with severe AAV. Patients with active MPO- or PR3-ANCA vasculitis or ANCA-negative pauci-immune glomerulonephritis were included. Induction treatment consisted of two doses of rituximab, 3 months of low-dose CYC and a short course of oral GC (for between 1 and 2 weeks). Clinical, biochemical and immunological outcomes as well as adverse events were recorded. A total of 49 patients were included, with at least 12 months of follow-up in 46. All patients achieved remission, with decreases observed in creatinine, proteinuria, CRP, ANCA level and BVAS. Three patients requiring dialysis at presentation became dialysis independent. Two patients required the introduction of maintenance GC for treatment of vasculitis. Overall outcomes were comparable to those of two matched cohorts (n = 172) from previous European Vasculitis Society (EUVAS) trials, but with lower total exposure to CYC and GCs (P < 0.001) and reduced rates of severe infections (P = 0.02) compared with the RITUXVAS (rituximab versus cyclophosphamide in AAV) trial. We found no new cases of diabetes in the first year compared with historic rates of 8.2% from the EUVAS trials (P = 0.04). Early GC withdrawal in severe AAV is as effective for remission induction as the standard of care and is associated with reduced GC-related adverse events.

Measuring Circulating Complement Activation Products in MPO and PR3 ANCA Vasculitis

Measuring Circulating Complement Activation Products in MPO and PR3 ANCA Vasculitis

Lessons from a double-transgenic neutrophil approach to induce antiproteinase 3 antibody-mediated vasculitis in mice.

ANCA to either PR3 or MPO are found in patients with necrotizing vasculitis and glomerulonephritis. ANCA binding to their target antigens on neutrophils and subsequent neutrophil activation are pivotal disease mechanisms that lead to vascular inflammation and necrosis. ANCA interaction with PR3 is more complex than with MPO as the neutrophil-specific CD177 receptor is involved in PR3 surface expression and PR3-ANCA-induced neutrophil activation. Modeling human disease is important to clinical research. Highly successful mouse models of MPO-ANCA vasculitis exist; however, recapitulating PR3-ANCA vasculitis has not been successful. We generated double-transgenic (DT) mice that expressed human PR3 and CD177 under a myeloid-specific huMRP8 promoter in an attempt to model PR3-ANCA vasculitis. DT mice strongly expressed the human transgenes in and on murine neutrophils and bound murine and human anti-PR3 antibodies. Nevertheless, passive transfer of these antibodies into LPS-primed DT mice or immunization of C57BL/6 mice with human PR3 followed by irradiation and transplantation of DT bone marrow failed to induce glomerulonephritis. Further analyses revealed that anti-PR3 antibodies did not activate DT neutrophils as shown by superoxide generation. Moreover, we found that mice did not properly process human pro-PR3 into mature PR3 and, consequently, the signaling complex between PR3, CD177, and CD11b, which promotes neutrophil activation by anti-PR3 antibodies, failed to form. We conclude that important species differences in PR3 and CD177 exist between men and mice that prevented successful generation of a murine anti-PR3 antibody model.

Difference in relapse-rate and clinical phenotype by autoantibody-subtype in Japanese patients with anti-neutrophil cytoplasmic antibody-associated vasculitis

Objective: To correlate the serotype specificity to myeloperoxidase (MPO) and proteinase-3 (PR3) with clinical characteristics in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV).Methods: Clinical characteristics and outcomes of patients with AAV in our division from 2005 to 2014 were retrospectively compared on the basis of ANCA subtype.Results: We collected the data from 88 patients with MPO–ANCA vasculitis, and 17 with PR3-ANCA vasculitis. Patients with PR3-ANCA vasculitis were younger, and had higher involvement-rates in the eye, nose, and ear. In both MPO- and PR3-ANCA vasculitis, the most frequently involved organ was the respiratory system. Interstitial pneumonia was more frequent in MPO-ANCA vasculitis (52.3% versus 5.9%, p < 0.01), whereas nodular shadow was more frequent in PR3-ANCA vasculitis (9.1% versus 58.8%, p < 0.01). Multivariable Cox proportional hazard regression analysis showed that the hazard ratio of PR3-ANCA for relapse was 2.48 (95% confidence interval 1.14–5.42, p = 0.02). There was no difference in the survival and the progression to end-stage kidney disease and respiratory failure between the two vasculitides.Conclusion: MPO-ANCA vasculitis was a predominant form of AAV in Japan. Classification based on ANCA subtype would be clinically relevant in the prediction of organ involvement and relapse.

Pathogenesis of ANCA-associated vasculitis

To provide an update on animal models of antineutrophil cytoplasmic autoantibody (ANCA)-mediated vasculitis and highlight recent insights gained from studies in these models pertaining to immunopathogenesis. Animal models support the pathogenic potential of myeloperoxidase (MPO)-ANCA. Alternative pathway complement activation has been identified as a novel inflammatory pathway in disease induction and a potential target for intervention. Interventions targeting B cells, antibodies, and signal transduction pathways may hold promise as well. The role of T cells is beginning to be explored, and studies indicate a prominent role for Th17 responses. The link between infection and ANCA vasculitis is well established. In animal models, Toll-like receptor (TLR)4 ligation is involved in disease induction. Ligation of TLRs contributes to the initiation of anti-MPO autoimmune responses in which TLR2 activation induces a Th17 response and TLR9 activation directs a Th1 response. An animal model for PR3-ANCA vasculitis is not available yet but models with a humanized immune system are being developed and show promising first results. Animal models of MPO-ANCA vasculitis have contributed substantially to our understanding of disease immunopathogenesis and have illuminated novel targets for intervention. The development of PR3-ANCA animal models remains a challenge but recent observations in humanized model systems offer hope.

Antibodies with Dual Reactivity to Plasminogen and Complementary PR3 in PR3-ANCA Vasculitis

Patients with inflammatory vascular disease caused by anti-neutrophil cytoplasmic autoantibodies (ANCA) can harbor antibodies not only to the autoantigen proteinase 3 (PR3) but also to complementary PR3 (cPR3(105-201)), a recombinant protein translated from the antisense strand of PR3 cDNA. The purpose of this study was to identify potential endogenous targets of anti-cPR3(105-201) antibodies. Patients' plasmapheresis material was tested for the presence of antigens reactive with affinity-purified rabbit and chicken anti-cPR3(105-201) polyclonal antibodies. Antigen-containing fractions were tested with patients' anti-cPR3(105-201) affinity-purified IgG, and putative protein targets were sequenced by mass spectrometry. Unexpectedly, plasminogen was identified as a target of anti-cPR3(105-201). Reactivity of affinity-purified antibodies from two patients was lost when plasminogen was converted to plasmin, indicating restricted specificity. Antiplasminogen antibodies from five patients bound plasminogen at a surface-exposed loop structure within the protease domain. This loop contains an amino acid motif that is also found in a portion of recombinant cPR3(105-201); site-directed mutagenesis of this sequence decreased antibody reactivity by 30%. Functionally, antiplasminogen antibodies delayed the conversion of plasminogen to plasmin and increased the dissolution time of fibrin clots. Serologically, antiplasminogen antibody levels were higher in PR3-ANCA patients (n = 72) than healthy control subjects (n = 63), myeloperoxidase-ANCA patients (n = 34), and patients with idiopathic thrombosis (n = 57; P = 0.001). Of the patients with PR3-ANCA, nine had documented deep venous thrombosis events, five of whom were positive for antiplasminogen antibodies. In summary, capitalizing on interactions with complementary proteins, specifically complementary PR3, this study identified plasminogen as a previously undescribed autoantigen in PR3-ANCA vasculitis.

Lack of Association of Alpha-1 Antichymotrypsin Gene Polymorphism with PR3-ANCA and MPO-ANCA Associated Vasculitis

In patients with PR3-ANCA associated vasculitides the carrier frequency of f 1-antitrypsin (AAT) deficiency allele PI*Z is increased and linkage disequilibrium between polymorphic markers within a cluster of serine protease inhibitor (serpin) genes, including AAT gene, at chromosome 14q32.1 has been described. A 1 -antichymotrypsin (AACT), part of an extended serpin gene cluster, was discussed to contribute to PR3-ANCA associated vasculitis formation. To analyse, if an AACT gene polymorphism within the signal peptide sequence is associated with antineutrophil cytoplasm autoantibodies (ANCA) vasculitis allelic frequencies of AACT polymorphism were analysed in 128 control persons, 79 PR3-ANCA, and 30 MPO-ANCA patients. In MPO-ANCA patients also phenotyping of AAT was performed as well as frequency and linkage analysis of simple tandem repeat polymorphisms in the genes of cortisol-binding globulin, AAT, protein C inhibitor, and three extragenic markers (S48, S55, S51) of the gene cluster. Allelic frequencies of the AACT polymorphism did not differ between controls and vasculitis patients. In the MPO-ANCA group no patient expressed the Pi*Z defective allele of AAT and the allelic frequencies of polymorphic markers within the serpin gene cluster did not differ from those of the controls. Strong linkage disequilibrium was detected in MPO-ANCA patients neither. Therefore, we can not support the hypothesis that AACT polymorphism contributes to the pathogenesis of PR3-ANCA vasculitis. Nor is it probable that any factor, coded by the serpin gene cluster, contributes to MPO-ANCA vasculitis.

Induction of neutrophil responsiveness to myeloperoxidase antibodies by their exposure to supernatant of degranulated autologous neutrophils

AbstractAntibodies against myeloperoxidase (MPO) and proteinase 3 (PR3) are the predominant autoantibodies present in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis. Their binding to the corresponding antigen on the surface of polymorphonuclear neutrophils (PMNs) is believed to trigger the disease process. Cytokines released during an inflammatory reaction are thought to prime resting PMNs, making them responsive to autoantibodies. In the present study we found that MPO but not PR3 could be detected on the cell surface of unstimulated PMNs after incubation with the supernatants of activated autologous PMNs. MPO was shown to be acquired from these supernatants, because PMNs did not express MPO when the supernatants were specifically MPO-depleted. In addition, purified soluble MPO bound to unstimulated PMNs. Unstimulated PMNs that had passively acquired MPO released oxygen radicals when incubated with monoclonal antibody anti-MPO or the immunoglobulin G fraction of a patient with MPO-ANCA. The data presented here suggest that, in ANCA-associated vasculitis, soluble MPO released by activated PMNs may bind to unstimulated PMNs, thereby making them reactive to anti-MPO antibodies. This mechanism of dispersing PMN activation would be specific for MPO-ANCA and may explain differences in the pathologic and clinical expression of MPO-ANCA versus PR3-ANCA vasculitis.

Induction of neutrophil responsiveness to myeloperoxidase antibodies by their exposure to supernatant of degranulated autologous neutrophils

Antibodies against myeloperoxidase (MPO) and proteinase 3 (PR3) are the predominant autoantibodies present in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis. Their binding to the corresponding antigen on the surface of polymorphonuclear neutrophils (PMNs) is believed to trigger the disease process. Cytokines released during an inflammatory reaction are thought to prime resting PMNs, making them responsive to autoantibodies. In the present study we found that MPO but not PR3 could be detected on the cell surface of unstimulated PMNs after incubation with the supernatants of activated autologous PMNs. MPO was shown to be acquired from these supernatants, because PMNs did not express MPO when the supernatants were specifically MPO-depleted. In addition, purified soluble MPO bound to unstimulated PMNs. Unstimulated PMNs that had passively acquired MPO released oxygen radicals when incubated with monoclonal antibody anti-MPO or the immunoglobulin G fraction of a patient with MPO-ANCA. The data presented here suggest that, in ANCA-associated vasculitis, soluble MPO released by activated PMNs may bind to unstimulated PMNs, thereby making them reactive to anti-MPO antibodies. This mechanism of dispersing PMN activation would be specific for MPO-ANCA and may explain differences in the pathologic and clinical expression of MPO-ANCA versus PR3-ANCA vasculitis.