Animal models of anti-neutrophil cytoplasmic antibody-associated vasculitis

Antimyeloperoxidase antibodies modulate inflammatory responses and activate profibrotic pathways in human monocytes

Antimyeloperoxidase (anti-MPO) and antiproteinase 3 (anti-PR3) antibodies are found in anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV). We investigated the effect of both anti-MPO and anti-PR3 IgG on human monocytes. Peripheral blood monocytes were cultured under a range of conditions that included TLR agonists, anti-MPO IgG and anti-PR3 IgG with appropriate controls. Experiments included whole transcriptome profiling and an assessment of the role of Fc receptors. When monocytes were stimulated with LPS or R848, anti-MPO but not anti-PR3 IgG, caused a reduction in IL-10 secretion and had a profound effect on cell-surface marker expression. Anti-MPO but not anti-PR3 IgG enhanced monocyte survival in the absence of TLR stimulation. These effects depended on the Fc receptor CD32a. With TLR stimulation, the effect of anti-MPO but not anti-PR3 IgG on the transcriptional response at 6 h was variable, but we identified a core set of transcripts likely to be important. Without TLR stimulation, there was a robust effect of anti-MPO but not anti-PR3 IgG on the transcriptional response at 24 h, and there was a highly significant enrichment of genes encoding extracellular matrix and extracellular matrix-associated proteins. Analysis with nCounter confirmed many of the differentially expressed transcripts and supported a role for CD32a. These data show that anti-MPO, but not anti-PR3 IgG, from patients with AAV has wide-ranging effects on monocytes which depend on CD32a. The activation of a profibrotic transcriptional response by anti-MPO but not anti-PR3 IgG may give insights into the differences in disease phenotype.

Impacts of Porphyromonas gingivalis periodontitis on rheumatoid arthritis autoimmunity

In RA patients' synovial sites, citrullinated RA-related antigens such as type II collagens, fibrin (ogen), vimentin, and α-enolase could be targeted by ACCPAs. Since ACCPA production can be initiated a long time before RA sign appearance, primary auto-immunization against these citrullinated proteins can be originated from extra-articular sites. It has been shown that there is a significant association between P. gingivalis periodontitis, anti- P. gingivalis antibodies, and RA. P. gingivalis gingipains (Rgp, Kgp) can degrade proteins such as fibrin and α-enolase into some peptides in the form of Arg in the C-terminal which is converted to citrulline by PPAD. Also, PPAD can citrullinate type II collagen and vimentins (SA antigen). P. gingivalis induces inflammation and chemoattraction of immune cells such as neutrophils and macrophages through the increase of C5a (gingipain C5 convertase-like activity) and SCFA secretion. Besides, this microorganism stimulates anoikis, a special type of apoptosis, and NETosis, an antimicrobial form of neutrophil death, leading to the release of PAD1-4, α-enolase, and vimentin from apoptotic cells into the periodontal site. In addition, gingipains can degrade macrophages CD14 and decrease their ability in apoptotic cell removal. Gingipains also can cleave IgGs in the Fc region and transform them into rheumatoid factor (RF) antigens. In the present study, the effects of P. gingivalis on rheumatoid arthritis autoimmune response have been reviewed, which could attract practical insight both in bench and clinic.

The lectin pathway does not contribute to glomerular injury in the nephrotoxic nephritis model

AIMS

Rapidly progressive crescentic glomerulonephritis occurs in number systemic and primary glomerular diseases, including anti-glomerular basement membrane disease, anti-neutrophil cytoplasmic antibody vasculitis and lupus nephritis. Our understanding of pathogenic mechanisms comes from animal models of disease such as the nephrotoxic nephritis model. The lectin pathway of complement activation has been shown to play a key role in several models of inflammation including renal ischaemia reperfusion. However, the lectin pathway is not required for crescentic glomerulonephritis in the anti-myeloperoxidase model of anti-neutrophil cytoplasmic antibody vasculitis. The aim of the current study was to explore the role of the lectin pathway in the nephrotoxic nephritis model, which is another model of crescentic glomerulonephritis.

METHODS

Nephrotoxic nephritis was induced in wild type and mannan-binding lectin-associated serine protease-2 deficient mice. Diseases were assessed by quantifying glomerular crescents and macrophages, in addition to albuminuria and serum creatinine.

RESULTS

There was no difference between wild type and MASP-2 deficient mice in any of the histological or biochemical parameters of disease assessed. In addition, there was no difference in the humoral immune response to sheep IgG.

CONCLUSION

These data show that the lectin pathway of complement activation is not required for the development of crescentic glomerulonephritis in the nephrotoxic nephritis model, reinforcing previous findings in the anti-myeloperoxidase model.

Emerging Cellular Therapies for Anti-myeloperoxidase Vasculitis and Other Autoimmune Diseases

Anti-myeloperoxidase vasculitis (MPO-AAV) is a life-threatening autoimmune disease which causes severe inflammation of small blood vessels, mainly in the kidney. As for many other autoimmune diseases, current treatments, which consist of general immunosuppressants, are partially effective, toxic and broadly immunosuppressive, causing significant and serious adverse effects in many patients. Therefore, there is an urgent need for more targeted and less harmful therapies. Tolerogenic dendritic cells, regulatory T cells and stem cells have emerged as attractive, new and safer options for the treatment for various autoimmune diseases due to their unique and selective immunosuppressive capacity. In this review, we will discuss how these cellular therapies offer potential to become novel and safer treatments for MPO-AAV.

Tocilizumab monotherapy uncovered the role of the CCL22/17-CCR4+ Treg axis during remission of crescentic glomerulonephritis

Objectives

Tocilizumab (TCZ) is a humanised anti‐interleukin (IL)‐6 receptor (IL‐6R) monoclonal antibody that is a promising agent to treat various autoimmune diseases. However, the mechanism of TCZ efficacy is unclear. This study aims to elucidate the relationship between Tregs and IL‐6R blockade in autoimmunity‐mediated renal disease based on a TCZ‐treated cohort of patients with anti‐neutrophil cytoplasmic antibody (ANCA)‐associated vasculitis (AAV) and in an experimental model of crescentic glomerulonephritis (cGN).

Methods

We examined multiple serum levels of cytokines and chemokines and peripheral blood mononuclear cells in patients with AAV who received TCZ monotherapy and achieved drug‐free remission. Moreover, we investigated the mechanistic role of IL‐6R blockade in accelerated cGN model to analyse the local sites of inflammation.

Results

Serum chemokines CCL22 and CCL17, in addition to the CCR4⁺Foxp3⁺ Treg population, increased in patients who demonstrated drug‐free remission after the cessation of TCZ. In the cGN model, IL‐6R blockade ameliorated the disease, elevated CCL22/17 in CD206⁺CD11b⁺CD11c⁺ kidney M2‐like type macrophages, and increased the migration of Tregs into the kidney and regional lymph nodes. The local administration of CCL22 in the kidney facilitated Treg accumulation and reduced glomerular crescent formation.

Conclusions

This study revealed a new mechanism whereby effector Tregs migrate into the inflammatory kidney via the CCL22/17–CCR4 axis that is facilitated by M2‐like type macrophages that are induced by IL‐6R blockade.

Anti-neutrophil cytoplasmic antibodies (ANCA): Antigen interactions and downstream effects

Neutrophils are the most abundant leukocytes in circulation and are key "first responders" in the immune response to infectious and non-infectious stimuli. Unlike other immune cells, neutrophils can mount a robust response (including a change in surface markers and the production of extracellular traps and reactive oxygen species) just minutes after sensing a disturbance. It has been speculated that, in some individuals, the activation of neutrophils inadvertently leads to the generation of anti-neutrophil cytoplasmic autoantibodies (ANCA) against particular neutrophil proteins (antigens) such as myeloperoxidase (MPO) and proteinase 3 (PR3). In these individuals, continuous ANCA-antigen interactions are thought to drive persistent activation of neutrophils, chronic immune activation, and disease, most notably, small vessel vasculitis. There are significant gaps however in our understanding of the underlying mechanisms and even the pathogenicity of ANCA given that vasculitis can develop in the absence of ANCA, and that ANCA have been found in circulation in other conditions with no apparent contribution to disease. These gaps are particularly evident in the context of human studies. Herein, we review knowledge on neutrophil-derived ANCA antigens PR3 and MPO, ANCA generation, and ANCA-antigen interaction(s) that may promote immune activation and disease.

Role of CD8+ T cells in crescentic glomerulonephritis

Crescentic glomerulonephritis (cGN) comprises three main types according to the pathogenesis and immunofluorescence patterns: anti-glomerular basement membrane antibody cGN, vasculitis-associated cGN and post-infectious immune complex cGN. In this brief review of the immune-pathogenesis of cGN, the focus is mainly on the role of CD8+ T cells in the progression of cGN. Under control conditions, Bowman's capsule (BC) provides a protected immunological niche by preventing access of cytotoxic CD8+ T cells to Bowman's space and thereby podocytes. Even in experimental nephrotoxic nephritis, leukocytes accumulate around the glomeruli, but remain outside of BC, as long as the latter remains intact. However, when and where breaches in BC occur, the inflammatory cells can gain access to and destroy podocytes, thus converting cGN into rapidly progressive glomerulonephritis (RPGN). These conclusions also apply to human cGN, where biopsies show that loss of BC integrity is associated with RPGN and progression to end-stage kidney disease. We propose a two-hit hypothesis for the role of cytotoxic CD8+ T cells in the progression of cGN. The initial insult occurs in response to the immune complex formation or deposition, resulting in local capillary and podocyte injury (first hit). The injured podocytes release neo-epitopes, eventually causing T-cell activation and migration to the glomerulus. Upon generation of breaches in BC, macrophages and CD8+ T cells can now gain access to the glomerular space and destroy neo-epitope expressing podocytes (second hit), resulting in RPGN. While further investigation will be required to test this hypothesis, future therapeutic trials should consider targeting of CD8+ T cells in the therapy of progressive cGN.

Reduced activated regulatory T cells and imbalance of Th17/activated Treg cells marks renal involvement in ANCA-associated vasculitis

The role of naturally occurring regulatory T cells (Treg) in the control of the immune tolerance of ANCA-associated vasculitis (AAV) has not been well defined. Therefore, we separate the phenotypically heterogeneous Treg cells into different subsets based on the expression of FOXP3 and CD45RA during AAV pathogenesis. Fifty-four AAV patients (38 patients with renal involvement) and 19 healthy controls (HCs) were enrolled in this study. Levels of CD4⁺T cell subsets and cytokines were detected by flow cytometry. Treg immunesuppression capacity was measured in co-culture experiments. The diagnostic value for Treg subsets was evaluated by the areas under the receiver operating characteristic curves (AUC). Patients with AAV had lower percentages and numbers of activated Treg cells (aTreg, P = 0.044, P = 0.002), while higher levels of total Treg cells (P = 0.001, P = 0.026) with diminished immunosuppression capacity. The proportions of effector memory T-cell subpopulation (P < 0.001) were increased in AAV patients. Interestingly, the AUC of the aTreg improved significantly the diagnostic potential of AAV. Furthermore, the ratio of Th17/aTreg was significantly increased in active and renal vasculitis patient and positive correlation between Th17/Treg subset ratio and creatinine or BUN. In addition, we found that cytokine IL-2 and IL-4 exhibited a downward while IL-6, IL-10, TNF-α, IFN-γ and IL-17A trend upward in AAV patients. Increase in total Treg levels, along with functional deficiency, and decrease in aTreg cells constitute potential novel biomarkers for AAV. And the ratio of Th17/aTreg might serve as an important tool to recognize and monitor AAV patients with renal involvement and disease remission.

Pathophysiology of ANCA-associated Vasculitis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis is characterized as inflammation of small-sized to medium-sized blood vessels and encompasses several clinicopathologic entities including granulomatosis with polyangiitis, microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis, and renal-limited ANCA-associated vasculitis. Over the past several decades, significant progress has been made in understanding the pathophysiology of ANCA-associated vasculitis. Although neutrophils contain a multitude of granular proteins, clinically significant autoantibodies are only recognized against myeloperoxidase and proteinase 3, both of which are present in the azurophilic granules. The propensity to develop these antibodies depends on a variety of predisposing factors such as microbial infection, genetic factors, environmental agents, and therapeutic drugs among others. These factors are usually associated with production of proinflammatory cytokines with capacity to prime the neutrophils. As a result a high proportion of neutrophils in circulation may be primed resulting in exposure of cytoplasmic proteins including myeloperoxidase and proteinase 3 on the surface of the neutrophils. Primed neutrophils are activated by interaction with ANCA in circulation. Activated neutrophils attach to and transmigrate through endothelium and accumulate within the vessel wall. These neutrophils degranulate and produce reactive oxygen radicals and ultimately die, causing tissue injury. Endothelial injury results in leakage of serum proteins and coagulation factors causing fibrinoid necrosis. B cells produce ANCAs, as well as neutrophil abnormalities and imbalances in different T-cell subtypes with excess of Th17, which perpetuate the inflammatory process.

Anti-myeloperoxidase antibodies attenuate the monocyte response to LPS and shape macrophage development

Anti-neutrophil cytoplasmic antibody (ANCA) vasculitis is characterized by the presence of autoantibodies to myeloperoxidase and proteinase-3, which bind monocytes in addition to neutrophils. While a pathological effect on neutrophils is acknowledged, the impact of ANCA on monocyte function is less well understood. Using IgG from patients we investigated the effect of these autoantibodies on monocytes and found that anti-myeloperoxidase antibodies (MPO-ANCA) reduced both IL-10 and IL-6 secretion in response to LPS. This reduction in IL-10 and IL-6 depended on Fc receptors and enzymatic myeloperoxidase and was accompanied by a significant reduction in TLR-driven signaling pathways. Aligning with changes in TLR signals, oxidized phospholipids, which function as TLR4 antagonists, were increased in monocytes in the presence of MPO-ANCA. We further observed that MPO-ANCA increased monocyte survival and differentiation to macrophages by stimulating CSF-1 production. However, this was independent of myeloperoxidase enzymatic activity and TLR signaling. Macrophages differentiated in the presence of MPO-ANCA secreted more TGF-β and further promoted the development of IL-10– and TGF-β–secreting CD4⁺ T cells. Thus, MPO-ANCA may promote inflammation by reducing the secretion of antiinflammatory IL-10 from monocytes, and MPO-ANCA can alter the development of macrophages and T cells to potentially promote fibrosis.

Anti-myeloperoxidase antibodies from patients with anti-neutrophil cytoplasmic antibody (ANCA) vasculitis alter monocyte function in addition to previously described effects on neutrophils.

Induction of proteinase 3-anti-neutrophil cytoplasmic autoantibodies by proteinase 3-homologous bacterial protease in mice

Proteinase 3 (PR3) is the principal target of antineutrophil cytoplasmic autoantibodies (ANCA) associated with granulomatosis with polyangiitis. The aim of this study was to investigate whether bacterial PR3-homologous protease can induce autoantibodies to PR3 and ANCA-associated pathology in mice. Among the bacterial proteases that have greater than 30 % identity with PR3, a trypsin-like serine protease of Saccharomonospora viridis, a bacterium that causes hypersensitivity pneumonitis, was chosen. When the mice were immunized with the recombinant protease of S. viridis (SvPR), 75 % of NZBWF1 and 100 % of C57BL/6 mice developed high levels of autoantibodies to mouse PR3 (mPR3). The levels of antibodies to mPR3 had a strong positive correlation with those to SvPR. In addition, more than half of the mPR3-reactive sera (63 %) reacted to purified human PR3 (hPR3), and the levels of antibodies to hPR3 had a positive correlation with those to mPR3. The sera from the immunized mice strongly stained murine neutrophils in a C-ANCA pattern. Although granulomatous inflammation and signs of vasculitis were observed in several mice, they were attributable to the use of complete Freund's adjuvant in the immunization. Collectively, exposure to PR3-homologous bacterial protease could induce ANCA in mice, and this finding may provide a new insight into the triggering mechanisms for the production of PR3-ANCA.

Spleen Tyrosine Kinase: A Crucial Player and Potential Therapeutic Target in Renal Disease

Spleen tyrosine kinase (Syk), a 72 kDa cytoplasmic non-receptor protein-tyrosine kinase, plays an important role in signal transduction in a variety of cell types. Ever since its discovery in the early 1990s, there has been accumulating evidence to suggest a pathogenic role of Syk in various allergic disorders, autoimmune diseases and malignancies. Additionally, there is emerging data from both pre-clinical and clinical studies that Syk is implicated in the pathogenesis of proliferative glomerulonephritis (GN), including anti-glomerular basement membrane disease, anti-neutrophil cytoplasmic antibody-associated GN, lupus nephritis and immunoglobulin A nephropathy (IgAN). Moreover, recent animal studies have shed light on the importance of Syk in mediating acute renal allograft rejection, Epstein Barr virus-associated post-transplant lymphoproliferative disease and kidney fibrosis. Fostamatinib, an oral Syk inhibitor, has undergone clinical testing in rheumatoid arthritis, refractory immune thrombocytopenic purpura, leukemia and lymphoma. The recent STOP-IgAN trial showed that the addition of non-selective immunosuppressive therapy to intensive supportive care did not improve clinical outcomes in high-risk IgAN patients. A Syk-targeted approach may be beneficial and is currently being evaluated in a phase II randomized controlled trial. In this review, we will discuss the pathogenic role of Syk and potential use of Syk inhibitor in a variety of renal diseases.

Optimizing the translational value of animal models of glomerulonephritis: insights from recent murine prototypes

Animal models are indispensable for the study of glomerulonephritis, a group of diseases that destroy kidneys but for which specific therapies do not yet exist. Novel interventions are urgently needed, but their rational design requires suitable in vivo platforms to identify and test new candidates. Animal models can recreate the complex immunologic microenvironments that foster human autoimmunity and nephritis and provide access to tissue compartments not readily examined in patients. Study of rat Heymann nephritis identified fundamental disease mechanisms that ultimately revolutionized our understanding of human membranous nephropathy. Significant species differences in expression of a major target antigen, however, and lack of spontaneous autoimmunity in animals remain roadblocks to full exploitation of preclinical models in this disease. For several glomerulonephritides, humanized models have been developed to circumvent cross-species barriers and to study the effects of human genetic risk variants. Herein we review humanized mouse prototypes that provide fresh insight into mediators of IgA nephropathy and origins of antiglomerular basement membrane nephritis and Goodpasture's disease, as well as a means to test novel therapies for ANCA vasculitis. Additional and refined model systems are needed to mirror the full spectrum of human disease in a genetically diverse population, to facilitate development of patient-specific interventions, to determine the origin of nephritogenic autoimmunity, and to define the role of environmental exposures in disease initiation and relapse.

Neutrophil-Mediated Regulation of Innate and Adaptive Immunity: The Role of Myeloperoxidase

Neutrophils are no longer seen as leukocytes with a sole function of being the essential first responders in the removal of pathogens at sites of infection. Being armed with numerous pro- and anti-inflammatory mediators, these phagocytes can also contribute to the development of various autoimmune diseases and can positively or negatively regulate the generation of adaptive immune responses. In this review, we will discuss how myeloperoxidase, the most abundant neutrophil granule protein, plays a key role in the various functions of neutrophils in innate and adaptive immunity.

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.

Impact of anti-glomerular basement membrane antibodies and glomerular neutrophil activation on glomerulonephritis in experimental myeloperoxidase-antineutrophil cytoplasmic antibody vasculitis

BACKGROUND

Antineutrophil cytoplasmic antibody (ANCA) and neutrophil interactions play important roles in ANCA-associated vasculitis (AAV) pathogenesis. However, mechanisms underlying the pathogenesis of crescent formation in ANCA-associated vasculitis have not been completely elucidated. To ascertain the involvement of these interactions in necrotizing crescentic glomerulonephritis (NCGN), we used an AAV rat model and investigated the effects of the anti-myeloperoxidase (MPO) antibody (Ab) titer, tumor necrosis factor α (TNF-α), granulocyte colony-stimulating factor (G-CSF) and subnephritogenic anti-glomerular basement membrane (GBM) Abs, as proinflammatory stimuli.

METHODS

NCGN was induced in Wistar Kyoto rats by human MPO (hMPO) immunization. Renal function, pathology, and glomerular cytokine and chemokine expression were evaluated in hMPO-immunized rats with/without several co-treatments (TNF-α, G-CSF or subnephritogenic anti-GBM Abs). Rat neutrophils activation by IgG purified from rat serum in each group was examined in vitro.

RESULTS

The hMPO-immunized rats had significantly higher level of anti-hMPO Ab production. The induced anti-hMPO Abs cross-reacted with TNF-α- or G-CSF-primed rat neutrophils secreting TNF-α and interleukin-1β in vitro. The reactivity of anti-MPO Abs against rat MPO, crescent formation with neutrophil extracellular traps and glomerular-activated neutrophil infiltration in the rat model were significantly enhanced by subnephritogenic anti-GBM Ab but not by TNF-α or G-CSF administration. The model rats injected with the subnephritogenic anti-GBM Abs showed increased urinary albumin excretion and serum TNF-α, chemokine (C-X-C) ligand 1 (CXCL1) and CXCL2 levels. TNF-α, CXCL1, CXCL2 and CXCL8 increased in the glomeruli with significant amounts of crescent formation. In addition, in vitro activated neutrophils decreased CXC chemokine receptor 1 (CXCR1) and CXCR2 expressions.

CONCLUSIONS

The coexistence of subnephritogenic anti-GBM Abs leads to the inflammatory environment in glomeruli that is amplified by the interaction of ANCA and neutrophils. Development of NCGN in MPO-AAV may be necessary for not only the accumulation of neutrophils in glomeruli, but also the aberrant neutrophil activation on glomerulonephritis.

Renal participation of myeloperoxidase in antineutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis

Myeloperoxidase (MPO) is an important neutrophil lysosomal enzyme, a major autoantigen, and a potential mediator of tissue injury in MPO-ANCA-associated vasculitis (MPO-AAV) and glomerulonephritis. Here we examined MPO deposition in kidney biopsies from 47 patients with MPO-AAV. Leukocyte accumulation and fibrin deposition consistent with cell-mediated immunity was a major feature. Tubulointerstitial macrophage, CD4+ and CD8+ T-cell, and neutrophil numbers correlated with low presenting eGFR. MPO was not detected in kidneys from patients with minimal change or thin basement membrane disease, but was prominent in glomerular, periglomerular, and tubulointerstitial regions in MPO-AAV. Extracellular MPO released from leukocytes was pronounced in all MPO-AAV patients. Similar numbers of neutrophils and macrophages expressed MPO in the kidneys, but colocalization studies identified neutrophils as the major source of extracellular MPO. Extraleukocyte MPO was prominent in neutrophil extracellular traps in the majority of patients; most of which had traps in half or more glomeruli. These traps were associated with more neutrophils and more MPO within glomeruli. Glomerular MPO-containing macrophages generated extracellular trap-like structures. MPO also localized to endothelial cells and podocytes. The presence of the most active glomerular lesions (both segmental necrosis and cellular crescents) correlated with intraglomerular CD4+ cells and MPO+ macrophages. Thus, cellular and extracellular MPO may cause glomerular and interstitial injury.

Proteinase 3-ANCA Vasculitis versus Myeloperoxidase-ANCA Vasculitis

In patients with GN or vasculitis, ANCAs are directed against proteinase 3 (PR3) or myeloperoxidase (MPO). The differences between PR3-ANCA-associated vasculitis (AAV) and MPO-AAV described in the past have been supplemented during the last decade. In this review, we discuss the differences between these two small-vessel vasculitides, focusing especially on possible etiologic and pathophysiologic differences. PR3-AAV is more common in northern parts of the world, whereas MPO-AAV is more common in southern regions of Europe, Asia, and the Pacific, with the exception of New Zealand and Australia. A genetic contribution has been extensively studied, and there is a high prevalence of the HLA-DPB1*04:01 allele in patients with PR3-AAV as opposed to patients with MPO-AAV and/or healthy controls. Histologically, MPO-AAV and PR3-AAV are similar but show qualitative differences when analyzed carefully. Clinically, both serotypes are difficult to distinguish, but quantitative differences are present. More organs are affected in PR3-AAV, whereas renal limited vasculitis occurs more often in patients with MPO-AAV. For future clinical trials, we advocate classifying patients by ANCA serotype as opposed to the traditional disease type classification.

The kidneys and ANCA-associated vasculitis: from pathogenesis to diagnosis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV) are a group of pauci-immune small vessel vasculitides that often affect the kidneys manifesting as rapidly progressive glomerulonephritis. Although the exact pathogenesis of AAV is not fully known, evidence from in vitro, in vivo and clinical studies all point to the involvement of ANCA in the pathogenesis of AAV. In this review, we highlight the contributory roles played by various factors (e.g. genetics, environment, B and T-regulatory cells, toll-like receptors, etc.) in the pathogenesis of AAV. Furthermore, we discuss renal involvement in AAV in terms of clinical features and the various histopathological classification patterns, which are also known to be of prognostic importance. We also present information on useful imaging techniques for localizing kidney and other organ system involvement in AAV, and also on novel laboratory methods and assays useful for rapid and more specific determination of patients' ANCA status. Finally, we demonstrate evidence on novel serum biomarkers that have been shown to correlate with disease activity in AAV.

Scientific and Regulatory Policy Committee Points-to-consider Paper*

Drug-induced vascular injury (DIVI) is a recurrent challenge in the development of novel pharmaceutical agents. Although DIVI in laboratory animal species has been well characterized for vasoactive small molecules, there is little available information regarding DIVI associated with biotherapeutics such as peptides/proteins or antibodies. Because of the uncertainty about whether DIVI in preclinical studies is predictive of effects in humans and the lack of robust biomarkers of DIVI, preclinical DIVI findings can cause considerable delays in or even halt development of promising new drugs. This review discusses standard terminology, characteristics, and mechanisms of DIVI associated with biotherapeutics. Guidance and points to consider for the toxicologist and pathologist facing preclinical cases of biotherapeutic-related DIVI are outlined, and examples of regulatory feedback for each of the mechanistic types of DIVI are included to provide insight into risk assessment.

Innovative human-specific investigational approaches to autoimmune disease

An organ-on-chip disease model approach, including “pre-clinical trial-on-chip” is introduced for understanding of human autoimmune disease pathophysiology and drug development.

Intravascular immunity as a key to systemic vasculitis: a work in progress, gaining momentum

Vascular inflammation contributes to the defence against invading microbes and to the repair of injured tissues. In most cases it resolves before becoming apparent. Vasculitis comprises heterogeneous clinical entities that are characterized by the persistence of vascular inflammation after it has served its homeostatic function. Most underlying mechanisms have so far remained elusive. Intravascular immunity refers to the surveillance of the vasculature by leucocytes that sense microbial or sterile threats to vessel integrity and initiate protective responses that entail most events that determine the clinical manifestations of vasculitis, such as end-organ ischaemia, neutrophil extracellular traps generation and thrombosis, leucocyte extravasation and degranulation. Understanding how the resolution of vascular inflammation goes awry in patients with systemic vasculitis will facilitate the identification of novel pharmacological targets and bring us a step closer in each patient to the selection of more effective and less toxic treatments.

What is the evidence for antibodies to LAMP-2 in the pathogenesis of ANCA associated small vessel vasculitis?

PURPOSE OF REVIEW

This review critically analyses the data implicating antibodies to lysosome associated membrane protein-2 (hLAMP-2) in ANCA-associated vasculitis (AAV). It addresses recent controversies over prevalence of anti-hLAMP-2 antibodies as well as their potential for diagnosis and monitoring disease activity.

RECENT FINDINGS

Anti-hLAMP-2 antibodies were first described in the 1990s and have become the focus of intense clinical interest in the past 4 years. This followed the demonstration of their very high prevalence in untreated patients presenting with AAV but absence when patients were in remission. The data also demonstrated molecular mimicry between hLAMP-2 and the bacterial protein FimH. The same group later confirmed the original findings and showed the anti-hLAMP-2 autoantibodies have different kinetics to those recognising myeloperoxidase and proteinase-3 and are less likely to be detectable when the disease is in remission. By contrast, a different group reported a lower prevalence of anti-hLAMP-2 antibodies in AAV and questioned their relevance to pathogenesis. Critical analysis of these studies suggests that the differences are largely attributable to selection criteria of the AAV patients studied and the assays used.

SUMMARY

Anti-hLAMP-2 antibodies are frequently found in AAV but attempts to define their consequences have been frustrated by lack of generally available assays for them.

p38 mitogen-activated protein kinase (p38 MAPK)-mediated autoimmunity: lessons to learn from ANCA vasculitis and pemphigus vulgaris

Evidence is beginning to accumulate that p38 mitogen activated protein kinase (p38 MAPK) signaling pathway plays an important role in the regulation of cellular and humoral autoimmune responses. The exact mechanisms and the degree by which the p38 MAPK pathway participates in the immune-mediated induction of diseases have started to emerge. This review discusses the recent advances in the molecular dissection of the p38 MAPK pathway and the findings generated by reports investigating its role in the pathogenesis of autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and autoimmune hepatitis. Application of newly-developed protocols based on sensitive flow cytometric detection has proven to be a useful tool in the investigation of the phosphorylation of p38 MAPK within different peripheral blood mononuclear cell populations and may help us to better understand the enigmatic role of this signaling cascade in the induction of autoimmunity as well as its role in immunosuppressive-induced remission. Special attention is paid to reported data proposing a specific role for autoantibody-induced activation of p38 MAPK-mediated immunopathology in the pathogenesis of autoimmune blistering diseases and anti-neutrophilic antibody-mediated vasculitides.

Role of serine proteases in inflammation: Bowman-Birk protease inhibitor (BBI) as a potential therapy for autoimmune diseases

Serine proteases, a sub-category of the protease family, participate in various physiologic and pathologic conditions. Serine proteases are involved in different arms of the immune system and play an important role in inflammation. They have been evaluated as therapeutic targets in several inflammatory diseases. The Bowman-Birk protease inhibitor (BBI), a soybean-derived serine protease inhibitor, is resistant to temperature and acidic conditions. These characteristics make it a good candidate for oral administration, with no major side effects. In addition, the therapeutic effect of BBI has been shown in inflammatory diseases and cancer. We have demonstrated the immunoregulatory and anti-inflammatory effects of BBI in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis. Here we review the role of serine proteases in inflammatory diseases, with emphasis on the potential of BBI as a novel oral therapy for multiple sclerosis.