Immune complex glomerulonephritis is induced in rats immunized with heterologous myeloperoxidase

What is the prognosis of ANCA-associated glomerulonephritis with immune deposition?

Objectives

This study aimed to analyze histological and clinical characteristics of patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) showing renal involvement to investigate the associations between immune complexes (IC) and clinicopathological indicators, and explore the renal outcomes of AAV.

Methods

We retrospectively evaluated the histopathological features and clinical characteristics of 80 renal biopsies of patients with AAV with renal involvement. Renal morphology was classified into two (with and without the presence of IC and complement deposition). Endpoints included end-stage kidney disease (ESKD) and death.

Results

Compared with patients without IC, patients with immune deposition had lower complement C3 (0.80 ± 0.27 vs. 0.93 ± 0.20, p = 0.024), more severe hematuria [133 (46–299) vs. 33 (15–115), p = 0.001] but had milder chronic pathology, including chronic tubular atrophy (p = 0.03), chronic interstitial fibrosis (p = 0.049). Patients in the immune deposition group showed a tendency to have more severe crescent formation and less glomerulosclerosis, but the difference was not statistically significant. Endpoints such as death and ESKD were not significantly different between the two groups.

Conclusions

Immune deposition may indicate lower complement C3, more severe hematuria and glomerular lesions, milder tubular atrophy, and interstitial fibrosis, but it cannot predict the renal outcome.

Therapeutic apheresis in kidney diseases: an updated review

Besides conventional medical therapies, therapeutic apheresis has become an important adjunctive or alternative therapeutic option to immunosuppressive agents for primary or secondary kidney diseases and kidney transplantation. The available therapeutic apheresis techniques used in kidney diseases, including plasma exchange, double-filtration plasmapheresis, immunoadsorption, and low-density lipoprotein apheresis. Plasma exchange is still the leading extracorporeal therapy. Recently, growing evidence supports the potential benefits of double-filtration plasmapheresis and immunoadsorption for more specific and effective clearance of pathogenic antibodies with fewer side effects. However, more randomized controlled trials are still needed. Low-density lipoprotein apheresis is also an important supplementary therapy used in patients with recurrent focal segmental glomerulosclerosis. This review collects the latest evidence from recent studies, focuses on the specific advantages and disadvantages of these techniques, and compares the discrepancy among them to determine the optimal therapeutic regimens for certain kidney diseases.

Mechanisms of vascular damage in ANCA vasculitis

The discovery of anti-neutrophil cytoplasmic antibodies (ANCA) and their antigenic targets, myeloperoxidase (MPO) and proteinase 3 (PR3), has led to further understanding as to the pathophysiologic processes that underlie vascular and tissue damage in ANCA vasculitis. ANCA trigger neutrophil activation leading to vascular damage in ANCA vasculitis. However, decades of study have determined that neutrophil activation alone is not sufficient to cause disease. Inflammatory stimuli are drivers of ANCA autoantigen expression and ANCA production. Certain infections or bacterial peptides may be crucial players in the initial steps of ANCA immunopathogenesis. Genetic and epigenetic alterations of gene encoding for MPO and PR3 provide additional disturbances to the immune homeostasis which provide a substrate for pathogenic ANCA formation from an adaptive immune system predisposed to autoreactivity. Promoted by inflammatory cytokines, ANCA binding leads to neutrophil activation, a process characterized by conformational changes, production and release of cytotoxic substances, and alternative complement pathway activation, thus creating an intense inflammatory milieu. This cascade of events perpetuates a vicious cycle of further inflammatory cell recruitment and activation, culminating in tissue necrosis. Our understanding of the pathogenic process in ANCA vasculitis paves the way for the development of therapies targeting crucial steps in this process. The greater appreciation of the role for complement, monocytes, and the adaptive immune system has already led to novel complement blockers and is poised to lead to further innovations which will allow for tailored antigen- or cell-specific immunotherapy targeting the autoimmune process without exposure to undue risks or toxicities.

Autoimmune-mediated renal disease and hypertension

Hypertension is a major risk factor for cardiovascular disease, chronic kidney disease (CKD), and mortality. Troublingly, hypertension is highly prevalent in patients with autoimmune renal disease and hastens renal functional decline. Although progress has been made over the past two decades in understanding the inflammatory contributions to essential hypertension more broadly, the mechanisms active in autoimmune-mediated renal diseases remain grossly understudied. This Review provides an overview of the pathogenesis of each of the major autoimmune diseases affecting the kidney that are associated with hypertension, and describes the current state of knowledge regarding hypertension in these diseases and their management. Specifically, discussion focuses on Systemic Lupus Erythematosus (SLE) and Lupus Nephritis (LN), Immunoglobulin A (IgA) Nephropathy, Idiopathic Membranous Nephropathy (IMN), Anti-Neutrophil Cytoplasmic Antibody (ANCA)-associated glomerulonephritis, and Thrombotic Thrombocytopenic Purpura (TTP). A summary of disease-specific animal models found to exhibit hypertension is also included to highlight opportunities for much needed further investigation of underlying mechanisms and novel therapeutic approaches.

Characterisation of an enhanced preclinical model of experimental MPO-ANCA autoimmune vasculitis

Experimental autoimmune vasculitis (EAV) is a model of antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) induced by immunisation of susceptible rat strains with myeloperoxidase (MPO). Animals develop circulating MPO-ANCA, pulmonary haemorrhage, and glomerulonephritis, although renal injury is mild and recovers spontaneously without treatment. In this study we aimed to augment the severity of glomerulonephritis. Following induction of EAV on day 0, a sub-nephritogenic dose of nephrotoxic serum (NTS) containing heterologous antibodies to glomerular basement membrane was administered on day 14. This resulted in a significant increase in disease severity at day 28 compared to MPO immunisation alone - with more urinary abnormalities, infiltrating glomerular leucocytes, and crescent formation that progressed to glomerular and tubulointerstitial scarring by day 56, recapitulating important features of human disease. Importantly, the glomerulonephritis remained pauci-immune, and was strictly dependent on the presence of autoimmunity to MPO, as there was no evidence of renal disease following administration of sub-nephritogenic NTS alone or after immunisation with a control protein in place of MPO. Detailed phenotyping of glomerular leucocytes identified an early infiltrate of non-classical monocytes following NTS administration that, in the presence of autoimmunity to MPO, may initiate the subsequent influx of classical monocytes which augment glomerular injury. We also showed that this model can be used to test novel therapeutics by using a small molecule kinase inhibitor (fostamatinib) that rapidly attenuated both glomerular and pulmonary injury over a 4-day treatment period. We believe that this enhanced model of MPO-AAV will prove useful for the study of glomerular leucocyte behaviour and novel therapeutics in AAV in the future. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

The role of plasma exchange in antineutrophil cytoplasmic antibody-associated vasculitis: a meta-analysis

BACKGROUND

Plasma exchange (PLEX) in addition to standard immunosuppressive treatment in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AVV) remains controversial. The aim of this study is to evaluate the effect of PLEX on AVV outcomes.

METHODS

Literature search was performed using Medline, Scopus, Cochrane Central Register of Controlled Trials, Clinicaltrials.gov databases, and Google Scholar. The statistical meta-analysis and leave-one-out analysis were conducted using the Review Manager 5.3 and Open Meta-Analyst software, respectively.

RESULTS

Ten studies were included in the meta-analysis comprising 1235 patients; 633 received conventional treatment and 602 were treated with PLEX in conjunction with induction therapy. PLEX was not associated with lower rates of either mortality at 3 (RR: 0.79, 95% CI: 0.19-3.25) and 12 months (RR: 0.73, 95% CI: 0.40-1.34) or ESRD at 3 (RR: 0.30, 95% CI: 0.30-2.42) and 12 months (RR: 1.32, 95% CI: 0.53-3.25). Similarly, no differences were captured concerning disease relapses (RR: 0.92, 95% CI: 0.62-1.36), the incidence of infections (RR: 1.05, 95% CI: 0.63-1.76), and severe adverse effects (RR: 1.04, 95% CI: 0.59-1.81). Time-to-event analysis revealed lower incidence of ESRD (HR: 0.71, 95% CI: 0.55-0.92) among patients who received PLEX, while the overall mortality was similar (HR: 0.96, 95% CI: 0.72-1.29) between the two groups.

CONCLUSION

The present meta-analysis does not support the wide use of PLEX for the management of AAV in routine clinical practice. Future well-designed randomized controlled trials focusing on specific disease-related manifestations are necessary to reach firm conclusions about the potential efficacy of PLEX. Key Points • PLEX is not widely recommended for the management of ANCA-associated vasculitis. • PLEX performance may reduce the overall incidence of ESRD in severe ANCA-associated vasculitis. • Well-designed randomized controlled trials focusing on specific disease-related manifestations are necessary to reach firm conclusions about the potential efficacy of PLEX on AAV-related outcome.

Vascular Hyperactivity in the Rat Renal Aorta Participates in the Association between Immune Complex-Mediated Glomerulonephritis and Systemic Hypertension

Introduction: systemic hypertension (SH) involving endothelial dysfunction contributes to immune complex-mediated glomerulonephritis (ICGN). Objective, we demonstrate a relationship between ICGN and SH by analyzing vascular reactivity in renal aortic rings. Methods: 48 male Wistar rats were divided into four groups: (a) control (C); (b) injected with bovine serum albumin (BSA); (c) receiving 200 mg/L NAME (an analog of arginine that inhibits NO production) in drinking water; and (d) receiving BSA and 200 mg/L NAME. Rats were pre-immunized subcutaneously with BSA and Freund's adjuvant. After 10 days, groups (b) and (c) received 1 mg/mL of BSA in saline intravenous (IV) daily for 35 days. The urine of 24 h was measured at days 0, 15, 30 and 45. Results: vascular reactivity to norepinephrine (NE), acetylcholine (Ach) and NAME were tested. Creatinine clearance, vasodilatation, eNOS and elastic fibers were diminished (p ≤ 0.001). Blood pressure, vasoconstriction, iNOS were increased, and glomerular alterations were observed in groups (b), (c) and (d) when compared to group (a) (p ≤ 0.001). Conclusions: SH contributes to the development of progressive renal disease in ICGN. Alterations of the vascular reactivity are mediated by the endothelium in the renal aorta. Thus, the endothelium plays a determinant role in the production of vasoactive substances such as NO during this process.

The Clinicopathologic Spectrum of Rapidly Progressive Glomerulonephritis Based on Glomerular Immune Deposition and Antineutrophil Cytoplasmic Antibody

Rapidly progressive glomerulonephritis presents crescentic glomerulonephritis (CrGN) pathologically. Immune complex (IC)-mediated CrGN is characterized by glomerular IC deposits, whereas pauci-immune CrGN is characterized by presence of antineutrophil cytoplasmic antibody (ANCA) and absence of glomerular IC deposits. CrGN cases presenting both IC deposits and ANCA were common. We retrospectively investigated 91patients with rapidly progressive glomerulonephritis, including 36 patients with idiopathic IC-mediated CrGN and 55 patients with pauci-immune CrGN. On the basis of ANCA and IC deposits, there were 42 patients with ANCA alone (ANCA+IC-), 6 patients with IC deposits alone (ANCA-IC+), 30 patients with both ANCA and IC deposits (ANCA+IC+), and 13 patients with neither ANCA nor IC deposits. The patients with IC-mediated CrGN had more proteinuria, lower estimated glomerular filtration rate (eGFR), higher percentage of cellular crescent formation, and a worse renal outcome compared with those with pauci-immune CrGN. The ANCA+IC+ CrGN patients had lower eGFR level, higher percentage of crescent formation and a tendency of more proteinuria, and worse renal outcome compared with ANCA+IC- CrGN patients, but had no significant differences on the above characteristics compared with ANCA-IC+ CrGN patients. Within a median 7.1 months, 22 patients developed end-stage renal disease. Cox regression revealed the factors including lower eGFR level, more proteinuria, lower platelet level, higher glomerular global sclerosis rate, and glomerular IgG deposits were the independent factors for worse renal outcome. In conclusion, the clinicopathologic spectrum of ANCA+IC+ CrGN was similar with IC-mediated CrGN and glomerular IgG deposition was one of the independent factors for worse renal outcome.

Pauci-Immune Crescentic Glomerulonephritis: An ANCA-Associated Vasculitis

Rapidly progressive glomerulonephritis (RPGN) is a syndrome signified by a precipitous loss of renal function, with features of glomerulonephritis including dysmorphic erythrocyturia and glomerular proteinuria. RPGN is associated with extensive crescent formation, and, thus, the clinical term RPGN is often used interchangeably with the pathologic term crescentic glomerulonephritis (CGN). From an immunopathologic standpoint, primary RPGN is divided into pauci-immune GN (PICG), anti-GBM GN, and immune complex GN. PICG, the most common etiology of primary RPGN, refers to a necrotizing glomerulonephritis with few or no immune deposits by immunofluorescence (IF) or electron microscopy (EM). In most patients, pauci-immune CGN is a component of a systemic small vessel vasculitis such as granulomatosis with polyangiitis (GPA). Approximately 90% of patients with PICG have circulating ANCA antibodies, leading to the nomenclature ANCA-associated vasculitis (AAV). Recent research has identified several other antibodies associated with PICG, which is now understood to be a complex spectrum of disease with considerable overlap in terms of clinical phenotype and outcomes. In addition, several genetic and environmental factors have recently been implicated in the pathogenesis of this disorder. With new prognostic classifications, enhanced understanding of immunopathologic mechanisms, and novel treatment paradigms, clinical and experimental interest in PICG remains high.

Plasma exchange in antineutrophil cytoplasm antibody-associated vasculitis

PURPOSE OF REVIEW

This article reviews the use of plasma exchange for the treatment of antineutrophil cytoplasm antibody-associated vasculitis (AAV) with a focus on current controversies and knowledge gaps.

RECENT FINDINGS

Experimental evidence suggesting that antineutrophil cytoplasm antibodies are pathogenic continues to evolve and support the theory that rapid removal of antineutrophil cytoplasm antibody with plasma exchange may be beneficial. Although early, small trials of plasma exchange in rapidly progressive glomerulonephritis and vasculitis suggested that plasma exchange may improve a patient's potential for renal recovery, more recent analyses have called the net benefit of plasma exchange into question. Furthermore, there is uncertainty as to whether plasma exchange is beneficial to patients with particular organ manifestations of their AAV (e.g., lung hemorrhage).

SUMMARY

Whether plasma exchange should be used routinely in antineutrophil cytoplasm antibody-associated vasculitis, in patients with certain manifestations or severity of disease only, or not at all, remains unclear. Given that plasma exchange is expensive and invasive, further research to resolve these uncertainties is required.

Fulminant primary manifestations of Wegener's granulomatosis might not be pauci-immune

Wegener’s granulomatosis is an ANCA-associated small vessel vasculitis. Because histologically immune complex deposits are frequently lacking, the term pauci-immune has been introduced for this subgroup. We report a patient with fulminant, severe PR3-ANCA-positive Wegener’s granulomatosis and multi-organ involvement (upper respiratory tract, lung, kidneys, skin and general symptoms), who showed pronounced immunoglobulin and complement deposits within the skin biopsy. Our observation supports the hypothesis that immune complex deposits may be under-recognized in early lesions of ANCA-associated Wegener’s granulomatosis.

Complement deposition in renal histopathology of patients with ANCA-associated pauci-immune glomerulonephritis

BACKGROUND

The pathogenesis of ANCA-associated pauci-immune glomerulonephritis has not been fully elucidated. Several studies had suggested that complement deposition could be detected in renal histopathology. The current study investigated the clinical and pathological significance of complement deposition in renal histopathology of patients with ANCA-associated pauci-immune glomerulonephritis.

METHODS

Renal biopsy specimens from 112 patients with ANCA-associated pauci-immune glomerulonephritis were investigated using direct immunofluorescence, light and electron microscopy. For direct immunofluorescence, IgG, IgA, IgM, C3c and C1q staining on fresh frozen renal tissue were routinely performed immediately after a renal biopsy. Complement deposition was defined as the presence of C3c or C1q for at least 1+ in a 0-4+ scale. Clinical and histopathological data between patients with and without complement deposition were compared.

RESULTS

In direct immunofluorescence microscopy, C3c and C1q could be detected in glomerular capillary wall and/or mesangium in the specimens of 37/112 (33.0%), 7/112 (6.3%) patients, respectively. Compared with patients without C3c deposition, patients with C3c deposition had a higher level of urinary protein (P < 0.01) and poorer initial renal function (P < 0.05).

CONCLUSION

Complement deposition was not rare in renal histopathology of human ANCA-associated pauci-immune glomerulonephritis, which was associated with more severe renal injury.

Natural and disease associated anti-myeloperoxidase (MPO) autoantibodies

Myeloperoxidase (MPO) is a cationic protein present in primary azurophilic granules of neutrophils and monocytes. MPO produces a highly deleterious reactive oxygen species, the hypochlorous acid (HOCl), using hydrogen peroxide (H(2)O(2)) and chloride ions as substrate. Anti-MPO antibodies (Abs) are present in 70% of the cases in patients with microscopic polyangiitis (MPA), a small-sized vessel vasculitis. Anti-MPO Abs from patients with MPA can trigger the release of MPO by neutrophils and monocytes. Anti-MPO Abs can activate MPO to generate an oxidative stress deleterious for the endothelium. Thus, we recently demonstrated that MPA sera with anti-MPO Abs activated MPO in vitro, and generated hypochlorous acid, whereas sera from MPA patients with no anti-MPO Abs or healthy individuals did not. Both hypochlorous acid production and endothelial lysis were abrogated by N-acetylcysteine (NAC), an antioxidant molecule. Thus, anti-MPO Abs could play a pathogenic role in vivo by triggering an oxidative burst leading to severe endothelial damages.

Clinical and pathological characteristics and outcomes of Chinese patients with primary anti-neutrophil cytoplasmic antibodies-associated systemic vasculitis with immune complex deposition in kidney

AIM

To analyse the clinical and pathological characteristics of Chinese patients with immune complex deposition in kidney in anti-neutrophil cytoplasmic antibodies (ANCA)-positive vasculitis.

METHODS

Enrolled in this study are patients with immune complex deposition in kidney in ANCA-positive vasculitis diagnosed in Peking University First Hospital. Their clinical and pathological data were collected and analysed.

RESULTS

Twenty-three patients were eligible. Fifteen patients were with microscopic polyangiitis and eight patients were with Wegener's granulomatosis. The mean age was 48.8 years and with a male/female ratio of 10/13. The interval, between onset of disease and the diagnosis of disease, was 429.6 +/- 693.3 days. All patients had clinical evidence of renal involvement. The major immunoglobulin deposited was IgM and the main locations were mesangial and sub-epithelial area. Four patients also presented features of membranous nephropathy and six patients presented features of IgA nephropathy. About 52.2% of patients had hypocomplementaemia. All patients received immunosuppressive therapy and all of them achieved clinical remission. Patients were followed for about 28.8 +/- 25.3 months. Nine patients kept clinical remission, nine patients progressed to end-stage renal disease and five patients died. When these patients are compared with patients who had classical pauci-immune vasculitis, they had greater proteinuria (P < 0.05), higher prevalence of hypocomplementaemia (P < 0.05) and greater glomerular cellularity (P < 0.05).

CONCLUSION

The present study showed that the features of patients with ANCA-associated vasculitis with immune complex deposition in kidney were similar with classical 'pauci-immune' vasculitis except for more proteinuria, more hypocomplementaemia and greater glomerular hypercellularity.

Mechanisms of vasculitis: how pauci-immune is ANCA-associated renal vasculitis?

Both the innate and the acquired immune system are involved in the pathophysiology of renal vasculitis. However, anti-neutrophil cytoplasmic antibody (ANCA)-associated renal vasculitis is characterized by a 'pauci-immune' pattern of immunofluorescence during kidney biopsy, indicating the relative lack of immunoglobulin and complement deposition within the kidney. On the other hand, evidence is accumulating that ANCA, autoantibodies against constituents of primary granules of neutrophils and the lysosomes of monocytes, play a pathogenic role in renal vasculitis. In this review we will discuss both in vitro and in vivo experimental data providing compelling evidence that ANCA are a primary pathogenic factor in renal vasculitis, mainly by augmenting leukocyte-endothelial interactions. We will also address novel data, pointing at the role of, in addition to ANCA, non-specific proinflammatory signals. Finally, we propose a working hypothesis of the pathogenesis of ANCA-associated renal vasculitis.

Antineutrophil cytoplasm antibodies directed against myeloperoxidase augment leukocyte-microvascular interactions in vivo

Systemic small vessel vasculitis is associated with antineutrophil cytoplasm antibodies (ANCAs). While there is mounting in vitro evidence to suggest that ANCAs are capable of enhancing leukocyte-endothelial interactions, no in vivo evidence for this has been provided. In this study a novel rat model of ANCA-associated experimental autoimmune vasculitis (EAV), induced by immunization with human myeloperoxidase (MPO), was used to analyze directly the potential effect of ANCAs on leukocyte-venular wall interactions in vivo as observed by intravital microscopy. These rats developed anti-MPO antibodies directed against rat leukocytes, showed pathologic evidence of small vessel vasculitis, and had enhanced leukocyte adhesion and transmigration in response to the chemokine Groα (CXCL1 [CXC ligand 1]). Passive transfer of immunoglobulin from rats with EAV to naive rats conferred enhanced adhesion and transmigration responses in the recipients. Furthermore, rats with EAV and recipients of ANCA-positive immunoglobulin developed extensive microvascular injury, as manifested by mesenteric hemorrhage, in response to CXCL1. This study provides the first direct in vivo evidence for the ability of ANCAs to enhance leukocyteendothelial interactions and cause microvascular hemorrhage, thereby providing a mechanism by which ANCAs could exert pathogenic effects in systemic vasculitis. (Blood. 2005;106:2050-2058)

Shunt nephritis with positive titers for ANCA specific for proteinase 3

The authors report a case of shunt nephritis with antineutrophil cytoplasmic autoantibody (ANCA) and review 2 similar cases. A 55-year-old man was admitted to our hospital for continuous fever and foot edema in 2002. A ventriculoperitoneal shunt was implanted because of a brain abscess and subsequent hydrocephalus in 1987; it was changed to a ventriculoatrial (VA) shunt in 1995. Urinary analysis showed proteinuria (5.4 g/d) and microscopic hematuria. Laboratory data showed renal dysfunction and hypocomplementemia. ANCA specific for proteinase 3 (PR3-ANCA) was positive in his serum, and blood culture grew Propionibacterium acnes. Renal biopsy results showed membranoproliferative glomerulonephritis type I. Therefore, the VA shunt was replaced, and antibiotics were administered. Oral prednisolone was initiated at a dose of 50 mg/d. Proteinuria and the serum levels of creatinine were improved concomitant with normalization of the serum complement levels and the decrease in serum PR3-ANCA titer. Similarly, another 2 cases reported in the literature of PR3-ANCA-positive shunt nephritis caused by P acnes and Gemella morbillorum showed good outcomes after removal of the shunt and administration of antibiotics with or without steroid therapy.

Antineutrophil cytoplasmic autoantibodies and pathophysiology: new insights from animal models

PURPOSE OF REVIEW

Since the discovery of antineutrophil cytoplasmic autoantibodies (ANCA) and their association with the occurrence of several types of small-vessel vasculitis, a causal relation between the two has been suggested. Various in vitro and in vivo experimental data provide indirect evidence in support of this view. This article comprises a review of the animal models that have been used to investigate the pathogenesis of ANCA-associated vasculitis, and focuses on recent developments in this field.

RECENT FINDINGS

Xiao et al. provide definite proof of the pathogenic potential of ANCA in a novel mouse model of myeloperoxidase (MPO)-ANCA-associated vasculitis, in which transfer of splenocytes or IgG from MPO-/- mice immunized with murine MPO, to naive wild-type or Rag2-/- (lacking mature B and T lymphocytes) mice causes a disease remarkably similar to its human counterpart. In addition, preliminary studies by Smyth et al. show that immunization of Wistar Kyoto rats with human MPO induces antihuman MPO antibodies that cross-react with rat MPO, as well as a disease closely resembling human small-vessel vasculitis. Another murine ANCA model is the SCG/Kj mouse. A recent publication by Neumann et al., however, puts an important limitation on the use of this mouse model for the study of ANCA-associated vasculitis, demonstrating multiple immune complex deposits in the spontaneously occurring vascular lesions. SUMMARY Recently developed animal models of MPO-ANCA-associated vasculitis convincingly demonstrate that MPO-ANCA are pathogenic. Whether similar strategies can be used to develop an appropriate model for proteinase 3-ANCA-associated vasculitis remains to be investigated.

SCG/Kinjoh mice: a model of ANCA-associated crescentic glomerulonephritis with immune deposits

BACKGROUND

Spontaneous crescentic glomerulonephritis-forming/Kinjoh (SCG/Kj) mice spontaneously develop crescentic glomerulonephritis (CGN), systemic vasculitis, and perinuclear ANCA (pANCA), and have been suggested as an animal model for human antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AASV). Since no systematic serologic, immunohistologic, or structural evaluation had been performed thus far, we reinvestigated the development of ANCA and CGN in these mice.

METHODS

SCG/Kj mice were subjected to serologic and urinary analysis, as well as histologic evaluation of the kidneys by standard light, immunofluorescence, and electron microscopy at regular intervals during the course of the disease.

RESULTS

Perinuclear ANCA developed as early as the 6th week of life, increasing both in frequency and titer in up to 100% of animals at week 20. Crescent formation began at week 10 and peaked at week 16, maximally affecting 57% of glomeruli. Crescent formation was initiated by "activated" podocytes that formed cell bridges between tuft and Bowman's capsule. The typical picture of a diffuse immune complex nephritis was found in all animals as early as 8 weeks. Fluorescence intensity increased with age and became strongly positive for immunoglobulin (Ig)A, IgM, IgG, and C3 in the mesangium and along the peripheral capillary loops.

CONCLUSION

Although ANCAs were found in the majority of animals, the massive presence of glomerular immune deposits differed from the pauci-immune pattern found in human AASV, making this model not completely representative for human ANCA-associated CGN. However, the spontaneous and concomitant development of pANCA, small vessel vasculitis, and CGN raises the opportunity to analyze pathogenetic links between these disease manifestations in vivo.

Difference in antigenic determinant profiles between human and rat myeloperoxidase

We tested whether rat and human MPO have similar antigenic determinants using 36 human MPO-ANCA positive sera, one mouse anti-rat MPO and four mouse anti-human MPO monoclonal reagents. Purified rat and human MPO were used in ELISA, with or without crossinhibition by preincubation with human MPO or irrelevant antigen in the liquid phase. Only one human MPO ANCA positive serum exhibited significant binding in rat MPO ELISA. This binding was poorly inhibited by preincubation with human MPO in the liquid phase, but was conserved after adsorption of non specific anti-rat activity in a chromatography column. Three mouse anti-human MPO IgG monoclonal antibodies did not recognize rat MPO. Only one mouse anti-human MPO IgA monoclonal antibody bound to rat MPO. This binding was poorly inhibited by preincubation with human MPO (35% at 2 micro g/ml). Conversely, the mouse anti-rat MPO monoclonal did not bind human MPO. We have concluded that: (1) Most human MPO-ANCA recognize antigenic determinants on human MPO which are absent on rat MPO. Therefore, human auto-antibodies bind to epitopes which recently appeared after species evolution; (2) Inversely, the mouse anti-rat MPO monoclonal do not bind human MPO. Therefore, rat MPO epitopes have been altered during species evolution; (3) Mice injected with human MPO preferentially develop antibodies against xeno-epitopes which are not present in rodents. Therefore, human MPO may not be the best antigen to raise ANCA in animal models and (4) A comparison of the amino acid sequences of rat and human MPO may help elucidate the major antigenic epitopes.

Antibodies to human myeloperoxidase in glomerular immune deposits of systemic lupus erythematosus

Antibodies to human myeloperoxidase and cathepsin G have been detected in the serum of some patients with systemic lupus erythematosus. Therefore, the presence of antibodies to human myeloperoxidase and cathepsin G was examined in glomerular immune deposits. Glomerular basement membrane fragments were prepared from renal tissues obtained at autopsy from 19 patients with systemic lupus erythematosus. IgG was extracted from the glomerular basement membrane fragments and tested with sensitive immunoassays for antibodies to myeloperoxidase and cathepsin G. Antibodies to cathepsin G were not detected in the extracts but antibodies to human myeloperoxidase were found in extracts of one specimen. In the extract with 6M guanidine hydrochloride these antibodies were enriched 103-fold, compared to the initial supernatant of glomeruli, which served as a serum surrogate. The recovered antibodies to myeloperoxidase accounted for 12% of the recovered IgG. These findings add autoantibodies to human myeloperoxidase to the list of antibodies that have been shown to be present in glomerular immune deposits of patients with lupus glomerulonephritis.

Internalization of proteinase 3 is concomitant with endothelial cell apoptosis and internalization of myeloperoxidase with generation of intracellular oxidants

The important issue addressed by the studies presented here is the mechanism of neutrophil-mediated damage to endothelial and epithelial cells during inflammation. Binding of neutrophil-released granule proteins to endothelial cells may be involved in vascular damage in patients with inflammatory vascular diseases. We have determined whether granule proteins proteinase 3(PR3) and/or myeloperoxidase (MPO) are internalized into endothelial cells, as examined by UV light, confocal, and electron microscopy. Coincident induction of apoptosis and/or the generation of intracellular oxidants were monitored. The results indicate that human endothelial cells (human umbilical vein endothelial cells, human umbilical arterial endothelial cells, human lung microvascular endothelial cells) internalize both PR3 and MPO, which are detected on the cell surface, in the cytoplasm, and possibly nuclear. Epithelial cells (small airway epithelial cells) internalized MPO but not PR3, implying that the mechanism of PR3 internalization may be cell-type specific and different from that of MPO. Internalization of PR3, but not MPO, correlated with activation of apoptosis. Internalization of MPO correlated with an increase in intracellular oxidant radicals. The requirement for the proteolytic activity of PR3 for the induction of apoptosis was examined by generating PR3-truncated fragments that did not contain the components of the catalytic triad. An apoptotic function was localized to the C-terminal portion of PR3. These studies reveal novel mechanisms by which the neutrophil granule proteins PR3 and MPO contribute to tissue injury at sites of inflammation.

Theodore E. Woodward Award. Do ANCA cause small vessel vasculitis?

ANCA may be a pathogenetic force, but to date, support for this contention remains indirect. Active immunization with antigen or passive transfer of ANCA has not reproduced small vessel vasculitis (SVV). It is more than likely that if ANCA are pathogenetic, they are involved as one of many simultaneously occurring mechanisms acting in concert with other synergistic inflammatory mediators of disease. These include not only environmental factors such as infection or environmental toxins such as silica, but also genetic factors that are only now being described. The paradigm for this autoimmune process must include several events that occur simultaneously or sequentially, including ANCA, leukocyte activation and injured endothelium.

Fate of immune complexes, glomerulonephritis, and cell-mediated vasculitis in lupus-prone MRL/Mp lpr/lpr mice

Immune complex formation was induced by the injection of (125)I-BSA into female MRL/Mp lpr/lpr mice, which develop spontaneous systemic lupus erythematosus (SLE)-like disease, and MRL/Mp +/+ mice, which do not. At designated intervals following the injection of 10 mg of (125)I-bovine serum albumin (BSA), the nonlupus mice developed sparse, small electron-dense deposits in mesangial areas and subepithelial immune deposits that underwent partial resolution. By contrast, glomeruli of the SLE-prone mouse kidneys revealed proliferation of mesangial cells and some increase in mesangial matrix material. Numerous subepithelial and mesangial electron-dense deposits were present. Some subendothelial and intramembranous deposits were also demonstrated. Capillary lumens contained massive electron-dense deposits. The resolving subepithelial deposits observed were fewer than half the number found in kidneys of the non-SLE mice. Whole body counts were also recorded daily following the injection of (125)I-BSA. Whereas, both lupus-prone and non-SLE control mice eliminated (125)I-BSA at equivalent rates through day 12 postinoculation, those with SLE-like disease showed a decreased (125)I-BSA elimination rate between days 6 and 12. Results suggest an impairment in the ability of SLE-prone mice to resolve immune complexes, whether they are nuclear-antinuclear or from an exogenous source, i.e., BSA-anti-BSA, compared to controls in this experimental model of the superimposition of exogenous immune complex formation on systemic lupus erythematosus-like disease.

Rapidly progressive glomerulonephritis with D-penicillamine

We present 3 cases of anti-myeloperoxidase, anti-neutrophil cytoplasmic antibody (MPO-ANCA)-positive rapidly progressive glomerulonephritis developed during the treatment with D-penicillamine (D-PC) for rheumatoid arthritis. Rheumatoid arthritis was diagnosed in these patients, and D-PC was administered to them at doses of 100, 200, and 300 mg per day for 32, 42, and 39 months, respectively. They developed proteinuria, hematuria, renal insufficiency, and anemia, and D-PC was stopped. On admission, MPO-ANCA was strongly positive in their sera. Renal biopsy showed glomerulonephritis with cellular crescents. Immunofluorescence examination revealed deposits of granular IgG, IgM, IgA, C1q, and C3 in the mesangium. The 3 patients were treated with steroid pulse therapy along with administration of anticoagulants, and cyclophosphamide was also used in 2 patients. Their renal function improved gradually and MPO-ANCA disappeared after immunosuppressive treatment.

Are animal models of vasculitis suitable tools?

Several rodent models have been proposed for various forms of systemic vasculitis. The MRL-lpr mouse has been studied extensively as a model for systemic lupus erythematosus. Backcross experiments in combination with genetic linkage studies have firmly established that the phenotype of autoimmune disease is dependent on the combination of various background genes. It has also become apparent that environmental factors, particularly infections, modulate the disease phenotype. Specific interventions, such as the treatment of Brown Norway rats with agents resulting in polyclonal B cell stimulation or immunization with human myeloperoxidase and subsequent localized perfusion with neutrophil lysosomal extract and H2O2, have provided substantial insights into the cellular and molecular mechanisms leading to the development of vasculitis and glomerulonephritis. Even though the existing models may not exactly mirror any specific human disease, they offer reproducible, highly controlled conditions to answer specific questions about pathogenesis and novel therapeutic approaches.

Pathogenesis of vasculitis

This review discusses current thoughts on the pathogenesis of vasculitis. Secondary vasculitides, frequently associated with infections or systemic autoimmune diseases, are, in most cases, characterized by immune deposits in the vessel wall, which probably underlies the development of lesions. In the primary vasculitides, immune deposits are generally absent. A group of primary vasculitides is, however, strongly associated with anti-neutrophil cytoplasmic autoantibodies (ANCA). Various in vitro and in vivo experimental data suggest that those ANCA are involved in the pathogenesis of lesions in the associated disorders.

Systemic necrotizing vasculitis

The revival of interest in systemic necrotizing vasculitis was initiated by the discovery of its association with anti-neutrophil cytoplasmic antibodies (ANCA). The close association of certain ANCA subspecificities, for example, proteinase 3 (Pr3) and myeloperxoidase ANCA, with Wegener's granulomatosis, microscopic polyangiitis and Churg-Strauss syndrome has led to their designation as 'ANCA-associated vasculitides'. This article describes the common and divergent clinical and immunological features of the members of this 'new' family of systemic necrotizing vasculitis, which continues to grow with the widespread use of ANCA testing. In addition, the 'standard' treatment for systemic necrotizing vasculitis (daily 'low dose' cyclophosphamide plus glucocorticosteroids or 'Fauci's scheme') is compared with new stage and activity adapted therapeutic regimens.

Apoptosis of endothelial cells induced by the neutrophil serine proteases proteinase 3 and elastase

The pathogenesis of vasculitis associated with anti-neutrophil cytoplasmic antibodies is not established. The anti-neutrophil cytoplasmic antibody autoanigens proteinase 3 (PR3) and elastase induce detachment and cytolysis of endothelial cells in vitro. We investigated whether PR3 and elastase trigger endothelial cell apoptosis. Primary bovine pulmonary artery endothelial cells were treated with either PR3, elastase, or myeloperoxidase (MPO) and apoptosis assessed by four different methods. By the cell death detection enzyme-linked immunosorbent assay, DNA fragmentation increased to 208 +/- 84% or 153 +/- 27% of control with 1 micrograms/ml PR3 or elastase at 24 hours. By ultraviolet light microscopy, the percentage of apoptotic cells significantly increased (P < 0.05) with 5 or 10 micrograms/ml PR3 and 25 or 50 micrograms/ml elastase at 6, 12, or 24 hours. Values at the 24-hour time point are 15.3 +/- 6.4% or 25.8 +/- 6.6% for 5 or 10 micrograms/ml PR3 and 13.9 +/- 3.6% or 20.7 +/- 1.8% for 25 or 50 micrograms/ml elastase compared with 2.2 +/- 1.2% for control. Similarly, with flow cytometry, 5 or 10 micrograms/ml PR3 and 25 or 50 micrograms/ml elastase for 6, 12, or 24 hours demonstrated increasing apoptosis in a dose- and time-dependent manner with the highest values achieved at 24 hours (23.4 +/- 4.0% and 35.6% for 5 and 10 micrograms/ml PR3 and 31.8 +/- 4.0% and 47.8% for 25 and 50 micrograms/ml elastase compared with 7.9 +/- 2.2% in control). Typical DNA laddering was apparent from 6 to 24 hours at 5 or 10 micrograms/ml PR3 and 25 or 50 micrograms/ml elastase. Myeloperoxidase did not induce cell apoptosis. Release of PR3 and elastase by activated neutrophils during acute inflammation, including anti-neutrophil cytoplasmic antibody-associated vasculitis, may result in vascular damage by endothelial cell apoptosis.

Autoantibodies to myeloperoxidase aggravate mild anti-glomerular-basement-membrane-mediated glomerular injury in the rat

Autoantibodies to myeloperoxidase (MPO) are present in sera from patients with various forms of vasculitis-associated glomerulonephritis. Evidence for a pathogenic role of anti-MPO antibodies has been provided mainly by in vitro studies. We studied the pathogenic role of autoantibodies to MPO in a rat model of mild immune-mediated glomerular injury. Brown Norway rats were immunized with human MPO in complete Freund's adjuvant or with complete Freund's adjuvant alone. At 2 weeks after immunization, rats had developed antibodies to human and rat MPO as detected by indirect immunofluorescence, enzyme-linked immunosorbent assay, and immunoprecipitation. At this time point, rats were intravenously injected with a subnephritogenic dose of 150 micrograms of rabbit anti-rat GBM. Rats were sacrificed at 4 hours, 24 hours, 4 days, and 10 days after antibody administration. Control immunized rats developed mild glomerulonephritis characterized by slight proteinuria at day 10 (14.8 +/- 8.1 mg/24 hours) and moderate intraglomerular accumulation of ED1+ macrophages. Crescent formation, tuft necrosis, and tubular atrophy were not observed in those rats. In contrast, rats immunized with MPO developed severe glomerulonephritis characterized by the early occurrence of severe hematuria, marked proteinuria at day 10 (76.2 +/- 18.2 mg/24 hours), and massive glomerular deposition of fibrin. Complement and rat IgG were present in insudative lesions, but no linear pattern along the glomerular capillary wall was observed. By light microscopy, severe glomerular lesions were found at day 10 consisting of crescent formation and fibrinoid necrosis of capillary loops. In the interstitium, tubular necrosis and atrophy and marked interstitial mononuclear infiltration were found in conclusion, autoantibodies to MPO severely aggravate subclinical anti-GBM disease demonstrating their in vivo pathogenic potential.

Animal models in ANCA-vasculitis

The animal models described to date suggest pathogenicity of ANCA. Unfortunately, none of the models unequivocally proves that ANCA are pathogenic. Further search for a suitable animal model to document or exclude causal significance of ANCA in vasculitis is needed.

Renal ischemia/reperfusion injury contributes to renal damage in experimental anti-myeloperoxidase-associated proliferative glomerulonephritis

The occurrence of focal fibrinoid necrosis of capillary loops in the very early stages of ANCA-associated necrotizing crescentic glomerulonephritis (NCGN) and the increased prevalence of this disease at older age suggest that renal ischemia may play an additional role in its pathophysiology. In the present study we investigated the contribution of renal ischemia to the induction of anti-myeloperoxidase (MPO) associated NCGN in a previously described rat model of this disease. The development of renal lesions is dependent on the presence of an anti-MPO immune response and the localization of a lysosomal extract containing lytic enzymes and MPO in combination with hydrogen peroxide (H2O2) along the glomerular basement membrane (GBM). The hypothesis tested whether perfusion of hydrogen peroxide (H2O2) could be replaced by ischemia/reperfusion (I/R) injury, as I/R injury activates endothelial cells to produce oxygen metabolites. I/R was induced by clamping the renal artery for 20 minutes in kidneys in which the circulation had been restored several minutes after perfusion with the lysosomal extract in MPO immunized rats. Rats developed lesions characterized by intra- and extracapillary cell proliferation, periglomerular infiltration, ruptures in Bowman's capsule, ischemic tubuli, and interstitial mononuclear infiltrate. Immune deposits, however, persisted for a longer time along the GBM after perfusion of lytic enzymes followed by I/R injury compared to previous studies in which H2O2 in conjunction with lytic enzymes were perfused in MPO-immunized rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Antineutrophil cytoplasmic autoantibodies, autoantigens, and systemic vasculitis

Antineutrophil cytoplasmic antibodies (ANCA) encompass a heterogeneous group of autoantibodies targeting antigens in neutrophils (PMN), monocytes, and endothelial cells. ANCA are routinely detected by the indirect immunofluorescence technique (IFT) and at least three different patterns of fluorescence can be distinguished which have been assigned the acronyms cANCA, pANCA and aANCA. cANCA is mostly induced by proteinase 3 (PR3) antibodies (PR3-ANCA), and pANCA by myeloperoxidase (MPO) antibodies (MPO-ANCA), while aANCA has unidentified subspecificity. Over the past decade, ANCA have been the subject of extensive investigation. They have proved to be of significant value both as diagnostic tools and for follow-up in several forms of systemic vasculitis (e.g. Wegener's granulomatosis, WG; microscopic polyarteritis, MPA; Churg-Strauss syndrome, CSS) which are now termed 'ANCA-associated vasculitides'. Furthermore, it is suspected that the presence of ANCA is an important factor in the pathogenesis of these disease groups. Data regarding the detection of ANCA and their diagnostic value and role in the pathogenesis of vasculitic disorders will be discussed in this review. Growing evidence points to a pathophysiological and diagnostic relevance of the distribution of the ANCA target antigens PR3 and MPO (presence in the circulation, on cell membranes, and in tissue extracellularly). An autoimmune process has been implicated in the pathogenesis of ANCA-associated vasculitis, but it is uncertain which mechanism underlies the induction of the ANCA-related immunoresponse. In this paper mechanisms such as antigenic cross-reactivity between human PMN proteins and extrinsic antigens by molecular mimicry, idiotypic immunoglobulin regulation, and T-cell reactivity to PR3 and MPO will be discussed.