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P2RX7, an ionotropic receptor for extracellular ATP, is expressed on immune cells, including macrophages, monocytes and dendritic cells and is up-regulated on non-immune cells following injury. P2RX7 plays a role in many biological processes, including production of pro-inflammatory cytokines such as IL-1β via the canonical inflammasome pathway. P2RX7 has been shown to be important in inflammation and fibrosis and may also play a role in autoimmunity. We have developed and phenotyped a novel P2RX7 knock-out (KO) inbred rat strain and taking advantage of the human-resembling unique histopathological features of rat models of glomerulonephritis, we induced three models of disease: nephrotoxic nephritis, experimental autoimmune glomerulonephritis, and experimental autoimmune vasculitis. We found that deletion of P2RX7 does not protect rats from models of experimental glomerulonephritis or the development of autoimmunity. Notably, treatment with A-438079, a P2RX7 antagonist, was equally protective in WKY WT and P2RX7 KO rats, revealing its 'off-target' properties. We identify a novel ATP/P2RX7/K+ efflux-independent and caspase-1/8-dependent pathway for production of IL-1β in rat dendritic cells, which was absent in macrophages. Taken together, these results comprehensively establish that inflammation and autoimmunity in glomerulonephritis is independent of P2RX7 and reveals the off-target properties of drugs previously known as selective P2RX7 antagonists. Rat mononuclear phagocytes may be able to utilise an 'alternative inflammasome' pathway to produce IL-1β independently of P2RX7, which may account for the susceptibility of P2RX7 KO rats to inflammation and autoimmunity in glomerulonephritis. This article is protected by copyright. All rights reserved.

Objective The objective of our study is to investigate the Fc glycosylation profiles of both antigen-specific IgG targeted against proteinase 3 (PR3-ANCA) and total IgG as prognostic markers of relapse in patients with Granulomatosis with Polyangiitis (GPA). Methods Seventy-five patients with GPA and a PR3-ANCA rise during follow-up were included, of whom 43 patients relapsed within a median period of 8 (2–16) months. The N-glycan at Asn297 of affinity-purified and denatured total IgG and PR3-ANCA was determined by mass spectrometry of glycopeptides in samples obtained at the time of the PR3-ANCA rise and at the time of the relapse or time-matched during remission. Results Patients with total IgG1 exhibiting low galactosylation or low sialylation were highly prone to relapse after an ANCA rise (HR 3.46 [95%-CI 1.73–6.96], p, Highlights • Low galactosylation and sialyation in total IgG predicts disease reactivation in GPA patients who experience an ANCA rise • Total IgG changes towards a more inflammation-associated phenotype in relapsing patients but not in non-relapsing patients • Glycosylation profiles may be useful in pre-emptive therapy studies using ANCA rises as guideline Patients with Granulomatosis with Polyangiitis suffer from (life-threatening) symptoms which can be kept under control using immunosuppressive therapy. However, these symptoms return in some patients, for reasons we do not yet fully understand. The disease is most likely caused by an antibody, a protein that is normally made in response to a foreign substance but can also be targeted against parts of our own body. We questioned whether there are differences in the antibodies that cause symptoms to return in some patients but not in all patients. To do this, within a group of patients in which the disease was inactive we investigated a glycan, a type of sugar group, that is attached to immunoglobulin G, the most common class of antibody. We found that the composition of this glycan showed variation in the number of certain monosaccharides, such as galactose and sialic acids. Patients in which the antibodies carried less galactose or sialic acid were more likely to suffer from symptoms of disease reactivation in the future. Moreover, the amount of sialic acid and galactose decreased over time in patients that developed symptoms, but not in patients for which the disease remained dormant. These findings may in the future be used to monitor people with inactive disease, so that timely treatment can be started if the disease becomes active.

Purpose of reviewTo 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.Recent findingsAnimal 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.SummaryAnimal 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.

Clinical observations, including a report of neonatal vasculitis occurring in a child born from a mother with anti-neutrophil cytoplasmic antibody directed to myeloperoxidase (MPO-ANCA)-associated vasculitis, suggest a pathogenic role for ANCA. Such a role is supported by in vitro experimental data showing that ANCA can activate primed neutrophils to the production of reactive oxygen species and lytic enzymes resulting in lysis of endothelial cells. An interplay between neutrophils, the alternative pathway of complement, and MPO-ANCA resulting in systemic vasculitis including necrotizing glomerulonephritis has clearly been demonstrated in animal models. An in vivo pathogenic role of ANCA directed to proteinase 3 (PR3-ANCA) has, however, not been substantiated. In PR3-ANCA-associated vasculitis, granulomatous inflammation points to involvement of cell-mediated immunity. In vitro studies, indeed, suggest that PR3-specific Th17 CD4-positive lymphocytes are operative in lesion development. The triggering role of microbial factors is becoming more clear. In particular Staphylococcus aureus carriage and infection with Gram-negative bacteria could contribute to induction and persistence of ANCA-associated vasculitis (AAV). Insight into the pathogenic pathways involved in AAV have opened and will further open new ways to targeted treatment.

Antimyeloperoxidase antibodies can cause crescentic glomerulonephritis and pulmonary hemorrhage. Toll-like receptors (TLRs) respond to infectious agents activating host defenses, whereas infections potentially initiate disease and provoke relapses. Neutrophils were found to be key effector cells of injury in experimental models, as disease does not occur in their absence and injury is enhanced by lipopolysaccharide (LPS). In this study, highly purified LPS (a pure TLR4 ligand) acted with antimyeloperoxidase antibodies to synergistically increase kidney and lung neutrophil recruitment and functional injury; effects abrogated in TLR4-deficient mice. Increased kidney TLR4 expression after stimulation predominantly occurred in glomerular endothelial cells. Enhanced glomerular neutrophil recruitment correlated with increased kidney mRNA expression of CXCL1 and CXCL2 (homologs of human CXCL8), whereas their preemptive neutralization decreased neutrophil recruitment. Disease induction in bone marrow chimeric mice showed that TLR4 in both bone marrow and renal parenchymal cells is required for maximal neutrophil recruitment and glomerular injury. Further studies in human glomerular cell lines stimulated with LPS found that glomerular endothelial cells were the prominent sources of CXCL8. Thus, our results define a role for TLR4 expression in bone marrow-derived and glomerular endothelial cells in neutrophil recruitment and subsequent functional and histological renal injury in experimental antimyeloperoxidase glomerulonephritis. Kidney International (2010) 78, 1263-1274; doi:10.1038/ki.2010.327; published online 15 September 2010