Wegener autoantigen induces maturation of dendritic cells and licenses them for Th1 priming via the protease-activated receptor-2 pathway

Transcriptomic characterization of the human segmental endotoxin challenge model

Segmental instillation of lipopolysaccharide (LPS) by bronchoscopy safely induces transient airway inflammation in human lungs. This model enables investigation of pulmonary inflammatory mechanisms as well as pharmacodynamic analysis of investigational drugs. The aim of this work was to describe the transcriptomic profile of human segmental LPS challenge with contextualization to major respiratory diseases. Pre-challenge bronchoalveolar lavage (BAL) fluid and biopsies were sampled from 28 smoking, healthy participants, followed by segmental instillation of LPS and saline as control. Twenty-four hours post instillation, BAL and biopsies were collected from challenged lung segments. Total RNA of cells from BAL and biopsy samples were sequenced and analysed for differentially expressed genes (DEGs). After challenge with LPS compared with saline, 6316 DEGs were upregulated and 241 were downregulated in BAL, but only one DEG was downregulated in biopsy samples. Upregulated DEGs in BAL were related to molecular functions such as "Inflammatory response" or "chemokine receptor activity", and upregulated pro-inflammatory pathways such as "Wnt-"/"Ras-"/"JAK-STAT" "-signaling pathway". Furthermore, the segmental LPS challenge model resembled aspects of the five most prevalent respiratory diseases chronic obstructive pulmonary disease (COPD), asthma, pneumonia, tuberculosis and lung cancer and featured similarities with acute exacerbations in COPD (AECOPD) and community-acquired pneumonia. Overall, our study provides extensive information about the transcriptomic profile from BAL cells and mucosal biopsies following LPS challenge in healthy smokers. It expands the knowledge about the LPS challenge model providing potential overlap with respiratory diseases in general and infection-triggered respiratory insults such as AECOPD in particular.

The cathepsin-S/protease-activated receptor-(PAR)-2 axis drives chronic allograft vasculopathy and is a molecular target for therapeutic intervention

BACKGROUND

Cathepsin S (CatS) and proteinase-activated receptor (PAR)-2 are involved in the remodelling of vascular walls and neointima formation as well as in alloantigen presentation and T-cell priming. Therefore, we hypothesized that CatS/PAR-2 inhibition/deficiency would attenuate chronic allograft vasculopathy.

METHODS

Heterotopic aortic murine transplantation was performed from C57BL/6J donors to C57BL/6J recipients (syngeneic control group), Balb/c to C57BL/6J without treatment (allogenic control group), Balb/c to C57BL/6J with twice daily oral CatS inhibitor (allogenic treatment group) and Balb/c to Par2-/- C57BL/6J (allogenic knockout group). The recipients were sacrificed on day 28 and the grafts were harvested for histological analysis and RT-qPCR.

RESULTS

After 28 days, mice of the allogenic control group exhibited significant neointima formation and massive CD8 T-cell infiltration into the neointima while the syngeneic control group showed negligible allograft vasculopathy. The mRNA expression level of CatS in allografts was 5-fold of those in syngeneic grafts. Neointima formation and therefore intima/media-ratio were significantly decreased in the treatment and knockout group in comparison to the allogenic control group. Mice in treatment group also displayed significantly fewer CD8 T cells in the neointima compared with allogeneic controls. Additionally, treatment with the CatS inhibitor and PAR2-deficiency decreased mRNA-levels of interleukins and cytokines.

CONCLUSION

In conclusion, our data indicate that inhibiting CatS and PAR-2 deficiency led to a marked reduction of neointima formation and associated inflammation in a murine heterotopic model for allograft vasculopathy.

The genomic landscape of ANCA-associated vasculitis: Distinct transcriptional signatures, molecular endotypes and comparison with systemic lupus erythematosus

Introduction

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAVs) present with a complex phenotype and are associated with high mortality and multi-organ involvement. We sought to define the transcriptional landscape and molecular endotypes of AAVs and compare it to systemic lupus erythematosus (SLE).

Methods

We performed whole blood mRNA sequencing from 30 patients with AAV (granulomatosis with polyangiitis/GPA and microscopic polyangiitis/MPA) combined with functional enrichment and network analysis for aberrant pathways. Key genes and pathways were validated in an independent cohort of 18 AAV patients. Co-expression network and hierarchical clustering analysis, identified molecular endotypes. Multi-level transcriptional overlap analysis to SLE was based on our published data from 142 patients.

Results

We report here that “Pan-vasculitis” signature contained 1,982 differentially expressed genes, enriched in leukocyte differentiation, cytokine signaling, type I and type II IFN signaling and aberrant B-T cell immunity. Active disease was characterized by signatures linked to cell cycle checkpoints and metabolism pathways, whereas ANCA-positive patients exhibited a humoral immunity transcriptional fingerprint. Differential expression analysis of GPA and MPA yielded an IFN-g pathway (in addition to a type I IFN) in the former and aberrant expression of genes related to autophagy and mRNA splicing in the latter. Unsupervised molecular taxonomy analysis revealed four endotypes with neutrophil degranulation, aberrant metabolism and B-cell responses as potential mechanistic drivers. Transcriptional perturbations and molecular heterogeneity were more pronounced in SLE. Molecular analysis and data-driven clustering of AAV uncovered distinct transcriptional pathways that could be exploited for targeted therapy.

Discussion

We conclude that transcriptomic analysis of AAV reveals distinct endotypes and molecular pathways that could be targeted for therapy. The AAV transcriptome is more homogenous and less fragmented compared to the SLE which may account for its superior rates of response to therapy.

Longitudinal monitoring of circulating immune cell phenotypes in anti-neutrophil cytoplasmic antibody-associated vasculitis

Anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) is a necrotizing multiorgan autoimmune disease that affects small- to medium-sized blood vessels. Despite the improvements in treatments, half of the patients with AAV still experience disease relapses. In this review, we focus on peripheral leukocyte properties and phenotypes in patients with AAV. In particular, we explore longitudinal changes in circulating immune cell phenotypes during the active phase of the disease and treatment. The numbers and phenotypes of leukocytes in peripheral blood were differs between AAV and healthy controls, AAV in active versus inactive phase, AAV in treatment responders versus non-responders, and AAV with and without severe infection. Therefore, biomarkers detected in peripheral blood immune cells may be useful for longitudinal monitoring of disease activity in AAV.

Targeting immune checkpoints in anti-neutrophil cytoplasmic antibodies associated vasculitis: the potential therapeutic targets in the future

Anti-neutrophil cytoplasmic autoantibodies (ANCA) associated vasculitis (AAV) is a necrotizing vasculitis mainly involving small blood vessels. It is demonstrated that T cells are important in the pathogenesis of AAV, including regulatory T cells (Treg) and helper T cells (Th), especially Th2, Th17, and follicular Th cells (Tfh). In addition, the exhaustion of T cells predicted the favorable prognosis of AAV. The immune checkpoints (ICs) consist of a group of co-stimulatory and co-inhibitory molecules expressed on the surface of T cells, which maintains a balance between the activation and exhaustion of T cells. CD28, inducible T-cell co-stimulator (ICOS), OX40, CD40L, glucocorticoid induced tumor necrosis factor receptor (GITR), and CD137 are the common co-stimulatory molecules, while the programmed cell death 1 (PD-1), cytotoxic T lymphocyte-associated molecule 4 (CTLA-4), T cell immunoglobulin (Ig) and mucin domain-containing protein 3 (TIM-3), B and T lymphocyte attenuator (BTLA), V-domain Ig suppressor of T cell activation (VISTA), T-cell Ig and ITIM domain (TIGIT), CD200, and lymphocyte activation gene 3 (LAG-3) belong to co-inhibitory molecules. If this balance was disrupted and the activation of T cells was increased, autoimmune diseases (AIDs) might be induced. Even in the treatment of malignant tumors, activation of T cells by immune checkpoint inhibitors (ICIs) may result in AIDs known as rheumatic immune-related adverse events (Rh-irAEs), suggesting the importance of ICs in AIDs. In this review, we summarized the features of AAV induced by immunotherapy using ICIs in patients with malignant tumors, and then reviewed the biological characteristics of different ICs. Our aim was to explore potential targets in ICs for future treatment of AAV.

GPR97 triggers inflammatory processes in human neutrophils via a macromolecular complex upstream of PAR2 activation

Neutrophils play essential anti-microbial and inflammatory roles in host defense, however, their activities require tight regulation as dysfunction often leads to detrimental inflammatory and autoimmune diseases. Here we show that the adhesion molecule GPR97 allosterically activates CD177-associated membrane proteinase 3 (mPR3), and in conjugation with several protein interaction partners leads to neutrophil activation in humans. Crystallographic and deletion analysis of the GPR97 extracellular region identified two independent mPR3-binding domains. Mechanistically, the efficient binding and activation of mPR3 by GPR97 requires the macromolecular CD177/GPR97/PAR2/CD16b complex and induces the activation of PAR2, a G protein-coupled receptor known for its function in inflammation. Triggering PAR2 by the upstream complex leads to strong inflammatory activation, prompting anti-microbial activities and endothelial dysfunction. The role of the complex in pathologic inflammation is underscored by the finding that both GPR97 and mPR3 are upregulated on the surface of disease-associated neutrophils. In summary, we identify a PAR2 activation mechanism that directs neutrophil activation, and thus inflammation. The PR3/CD177/GPR97/PAR2/CD16b protein complex, therefore, represents a potential therapeutic target for neutrophil-mediated inflammatory diseases.

Kinetics of human leukocyte antigen receptor HLA-DR+ monocytes and T lymphocytes during remission induction therapy in ANCA-associated vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis is characterized by small vessel inflammation and the presence of autoantibodies against cytoplasmic proteases, most often proteinase-3 and myeloperoxidase. Peripheral blood monocytes are an important source of local macrophage accumulation within parenchymal organs, as evidenced by their presence in early lesions in ANCA-associated glomerulonephritis. Major histocompatibility complex (MHC) II cell surface receptor human leukocyte antigen receptor (HLA-DR) allows antigen presentation to T cells and is crucial for the initiation of an immune response. We herein report HLA-DR abundance in AAV and the kinetics of HLA-DR⁺ monocytes and T lymphocytes during remission induction therapy in AAV. Life-threatening AAV with pulmonary hemorrhage and renal involvement was associated with the presence of HLA-DR in a considerable population of peripheral blood monocytes and T lymphocytes, and relapsing disease manifested despite persistent B cell depletion after remission induction with rituximab. Moreover, remission induction in AAV with steroids, plasma exchange and intravenous cyclophosphamide, and improvement of clinical symptoms were associated with a decrease in HLA-DR⁺ differing between monocytes and T lymphocytes. Particularly, persistent suppression of HLA-DR⁺ monocytes was observed during remission induction, while an initial decrease in HLA-DR⁺ T lymphocytes was followed by recovery of this population during the further course. Detailed insights into HLA-DR kinetics could pave the way towards an increased understanding of immunopathology and identify patients that could mostly benefit from distinct remission induction regimens.

Epidemiology and genetics of granulomatosis with polyangiitis

Granulomatosis with polyangiitis (GPA) previously known as Wegener's granulomatosis (WG) is a rare rheumatic disease affecting subjects of all ages. Prevalence and incidence of this systemic disease greatly varies across different ethnic groups. GPA is the commonest form of ANCA-associated vasculitis (AAV) with PR3 positivity among 85-95% of the cases. Scientific investigations of GPA is warranted because its severity, clinical heterogeneity, fast disease manifestation and end-organ damage. The etiology of GPA is still unknown. Major role of HLA and non-HLA genes with immune functions were identified, however, very limited replication was observed in different ethnic populations. In the present review, we have discussed the updates on the global epidemiology and contribution of HLA and major non-HLA genes/loci in GPA. We have also highlighted the cross disease association of GPA associated genes that may help in better disease management and predictive medicine. We proposed that high-resolution HLA typing and development of genetic risk model would help in early disease diagnosis and understanding the prognosis.

PAR2 deficiency enhances myeloid cell-mediated immunosuppression and promotes colitis-associated tumorigenesis

Protease-activated receptor 2 (PAR2) is a member of G-protein coupled receptors, which is widely expressed in intestinal epithelium and immune cells and plays critical roles in intestinal homeostasis. Activation of PAR2 has been implicated in inflammatory process and carcinogenesis. However, it remains unclear whether and how endogenous PAR2 affects colorectal tumorigenesis. Here, we found that PAR2 expression was enhanced in patients with inflammatory bowel disease and colorectal cancer. Intriguingly, PAR2 deficiency significantly aggravated colitis and promoted tumor development in AOM/DSS model. This finding was accompanied with upregulated pro-inflammatory factors IL-6, TNFα, COX2 and NOS2 in tumors of Par2^-/- mice. Moreover, PAR2 deficiency reshaped the tumor microenvironment through accumulation of tumor-promoting myeloid cells including tumor-associated macrophages and myeloid-derived suppressor cells (MDSCs) and reduction of anti-tumor T cells, which established an immunosuppressive microenvironment and facilitated tumor progression. Mechanistically, absence of PAR2 in MDSCs directly enhanced their immunosuppressive activity by promoting STAT3-mediated reactive oxygen species production. Our study reveals an unrecognized role of PAR2 in limiting colorectal carcinogenesis by regulating the tumor microenvironment. Specifically targeting PAR2 may be a potential alternative for colorectal cancer immunotherapy.

A secreted schistosome cathepsin B1 cysteine protease and acute schistosome infection induce a transient T helper 17 response

The natural history of schistosome infection in the mammalian host is determined by CD4⁺ T helper responses mounted against different parasite life cycle stages. A T helper 2 (T_H2) response to schistosome eggs is required for host survival and establishment of chronic infection. However, a T_H2 cell-derived cytokine also contributes to an immune milieu that is conducive to schistosome growth and development. Thus, the same responses that allow for host survival have been co-opted by schistosomes to facilitate parasite development and transmission, underscoring the significance of CD4⁺ T cell responses to both worms and eggs in the natural history of schistosome infection. Here we show that a cathepsin B1 cysteine protease secreted by schistosome worms not only induces T_H2 responses, but also T_H1 and T_H17 responses, by a mechanism that is dependent on the proteolytic activity of the enzyme. Further investigation revealed that, in addition to the expected T_H1 and T_H2 responses, acute schistosome infection also induces a transient T_H17 response that is rapidly down-regulated at the onset of oviposition. T_H17 responses are implicated in the development of severe egg-induced pathology. The regulation of worm-induced T_H17 responses during acute infection could therefore influence the expression of high and low pathology states as infection progresses.

Schistosomiasis, a neglected tropical disease caused by parasites of the genus Schistosoma, is prevalent throughout the developing world, with more than 230 million people infected. Left untreated, schistosome infection may cause relatively mild disease with some morbidity, or, in a minority of cases, result in severe pathology and death. These variable outcomes are recapitulated in animal models, where the natural history of schistosome infection is profoundly influenced by the responses of host CD4⁺ T helper cells. Type 2 CD4⁺ T cell (T_H2) responses, which allow for host survival by limiting pathology, have ironically also been co-opted by schistosomes to promote parasite development. On the other hand, T_H17 responses have been implicated in the development of severe pathology, in both experimentally infected animals and naturally infected humans. Here we show that a schistosome proteolytic enzyme (SmCB1), produced in the parasite gut and released into the bloodstream, induces both T_H2 and T_H17 responses by a mechanism that requires the enzyme’s inherent proteolytic activity. Further investigation revealed that acute schistosome infection also induces a transient T_H17 response that is rapidly down-regulated once parasite egg-laying commences. Regulation of T_H17 responses during early infection may help determine whether mild or severe pathology develops as the infection progresses.

Towards precision medicine in ANCA-associated vasculitis

ANCA-associated vasculitis (AAV) is characterized by inflammation and destruction of small and medium-sized vessels. Current management strategies for AAV have been validated in large groups of patients. However, recent insights indicate that distinct patient subsets may actually exist within AAV, thereby justifying the development of more personalized treatment strategies. In this review, we discuss current evidence for a better classification of AAV based on ANCA type. We describe how thus defined categories of AAV patients may differ in genetic background, clinical presentation, immune pathology, response to treatment and disease outcome. We also explore how these insights may provide a rationale for targeted treatments in different categories of AAV patients. Finally, we provide recommendations on how to further establish precision medicine in AAV.

Membrane-Associated Proteinase 3 on Granulocytes and Acute Myeloid Leukemia Inhibits T Cell Proliferation

Proteinase 3 (P3), a serine protease expressed by myeloid cells, localized within azurophil granules, and also expressed on the cellular membrane of polymorphonuclear neutrophils (PMN), is the target of autoimmunity in granulomatosis with polyangiitis. PR1, an HLA-A2 restricted nonameric peptide derived from P3, has been targeted effectively in myeloid leukemia. We previously showed (Molldrem et al. 2003. JClinInvest 111: 639-647) that overexpression of P3 in chronic myeloid leukemia induces apoptosis of high-affinity PR1-specific T cells, leading to deletional tolerance and leukemia outgrowth. In this study, we investigated the effect of membrane P3 (mP3)-expressing PMN and acute myeloid leukemia (AML) blasts on the proliferation of CD4 and CD8 T cells in vitro. We demonstrate that mP3-expressing PMN significantly inhibits autologous healthy donor T cell proliferation but does not affect cytokine production in activated T cells and that this effect requires cell proximity and was abrogated by P3 blockade. This inhibition required P3 enzyme activity. However, suppression was not reversed by either the addition of catalase or the inhibition of arginase I. In addition to P3 blockade, anti-low density lipoprotein receptor-related protein 1 (LRP1) Ab also restored T cells' capacity to proliferate. Last, we show dose-dependent inhibition of T cell proliferation by mP3-expressing AML blasts. Together, our findings demonstrate a novel mechanism whereby PMN- and AML-associated mP3 inhibits T cell proliferation via direct LRP1 and mP3 interaction, and we identify P3 as a novel target to modulate immunity in myeloid leukemia and autoimmune disease.

Development of an interleukin (IL)-33 sandwich ELISA kit specific for mature IL-33

Interleukin (IL)-33 is an inflammatory cytokine and belongs to the IL-1 family of cytokines. There are eleven members of the IL-1 family of cytokines and all have important roles in host defense against infections. Their levels are increased during infection and in various auto-inflammatory diseases. IL-33 is also associated with autoimmune diseases such as asthma, atopic dermatitis, rheumatoid arthritis, and atherosclerosis. IL-33 receptors consist of IL-1R4 and IL-1R3 to induce both Th1 and Th2 type immune response. Here we present the development of monoclonal antibodies (mAbs) against human mature IL-33. Recombinant human mature IL-33 protein was expressed in E. coli and purified by multi-step affinity chromatography. The human IL-33 activity was examined in HMC-1 and Raw 264.7 cells. Mice were immunized with the biologically active mature IL-33 to generate mAb against IL-33. The anti-IL-33 mAb (clone/4) was used as a capture antibody for a sandwich enzyme-linked immunosorbent assay (ELISA). This assay detects mature IL-33 with a high sensitivity (80 pg/mL) but does not recognize the biologically inactive precursor IL-33. This article describes the methods for a newly developed IL-33 ELISA kit that is specific for mature IL-33 and may be used to analyze bioactive mature IL-33 in various immunological diseases.

Identification of Functional and Expression Polymorphisms Associated With Risk for Antineutrophil Cytoplasmic Autoantibody-Associated Vasculitis

Objective

To identify risk alleles relevant to the causal and biologic mechanisms of antineutrophil cytoplasmic antibody (ANCA)–associated vasculitis (AAV).

Methods

A genome‐wide association study and subsequent replication study were conducted in a total cohort of 1,986 cases of AAV (patients with granulomatosis with polyangiitis [Wegener's] [GPA] or microscopic polyangiitis [MPA]) and 4,723 healthy controls. Meta‐analysis of these data sets and functional annotation of identified risk loci were performed, and candidate disease variants with unknown functional effects were investigated for their impact on gene expression and/or protein function.

Results

Among the genome‐wide significant associations identified, the largest effect on risk of AAV came from the single‐nucleotide polymorphism variants rs141530233 and rs1042169 at the HLA–DPB1 locus (odds ratio [OR] 2.99 and OR 2.82, respectively) which, together with a third variant, rs386699872, constitute a triallelic risk haplotype associated with reduced expression of the HLA–DPB1 gene and HLA–DP protein in B cells and monocytes and with increased frequency of complementary proteinase 3 (PR3)–reactive T cells relative to that in carriers of the protective haplotype. Significant associations were also observed at the SERPINA1 and PTPN22 loci, the peak signals arising from functionally relevant missense variants, and at PRTN3, in which the top‐scoring variant correlated with increased PRTN3 expression in neutrophils. Effects of individual loci on AAV risk differed between patients with GPA and those with MPA or between patients with PR3‐ANCAs and those with myeloperoxidase‐ANCAs, but the collective population attributable fraction for these variants was substantive, at 77%.

Conclusion

This study reveals the association of susceptibility to GPA and MPA with functional gene variants that explain much of the genetic etiology of AAV, could influence and possibly be predictors of the clinical presentation, and appear to alter immune cell proteins and responses likely to be key factors in the pathogenesis of AAV.

Characterization of the CD177 interaction with the ANCA antigen proteinase 3

Proteinase 3 is a serine protease found in neutrophil granules and on the extracellular neutrophil membrane (mPR3). mPR3 is a major antigen for anti-neutrophil cytoplasmic antibodies (PR3-ANCAs), autoantibodies causing fatal autoimmune diseases. In most individuals, a subpopulation of neutrophils also produce CD177, proposed to present additional PR3 on the surface, resulting in CD177^neg/mPR3^low and CD177^pos/mPR3^high neutrophil subsets. A positive correlation has been shown between mPR3 abundance, disease incidence, and clinical outcome. We present here a detailed investigation of the PR3:CD177 complex, verifying the interaction, demonstrating the effect of binding on PR3 proteolytic activity and explaining the accessibility of major PR3-ANCA epitopes. We observed high affinity PR3:CD177 complex formation by surface plasmon resonance. Using flow cytometry and a PR3-specific FRET assay, we found that CD177 binding reduced the proteolytic activity of PR3 in vitro using purified proteins, in neutrophil degranulation supernatants containing wtPR3 and directly on mPR3^high neutrophils and PR3-loaded HEK cells. Finally, CD177^pos/mPR3^high neutrophils showed no migration advantage in vitro or in vivo when migrating from the blood into the oral cavity. We illuminate details of the PR3:CD177 interaction explaining mPR3 membrane orientation and proteolytic activity with relevance to ANCA activation of the distinct mPR3 neutrophil populations.

Proteinase 3 on apoptotic cells disrupts immune silencing in autoimmune vasculitis

Granulomatosis with polyangiitis (GPA) is a systemic necrotizing vasculitis that is associated with granulomatous inflammation and the presence of anti-neutrophil cytoplasmic antibodies (ANCAs) directed against proteinase 3 (PR3). We previously determined that PR3 on the surface of apoptotic neutrophils interferes with induction of antiinflammatory mechanisms following phagocytosis of these cells by macrophages. Here, we demonstrate that enzymatically active membrane-associated PR3 on apoptotic cells triggered secretion of inflammatory cytokines, including granulocyte CSF (G-CSF) and chemokines. This response required the IL-1R1/MyD88 signaling pathway and was dependent on the synthesis of NO, as macrophages from animals lacking these pathways did not exhibit a PR3-associated proinflammatory response. The PR3-induced microenvironment facilitated recruitment of inflammatory cells, such as macrophages, plasmacytoid DCs (pDCs), and neutrophils, which were observed in close proximity within granulomatous lesions in the lungs of GPA patients. In different murine models of apoptotic cell injection, the PR3-induced microenvironment instructed pDC-driven Th9/Th2 cell generation. Concomitant injection of anti-PR3 ANCAs with PR3-expressing apoptotic cells induced a Th17 response, revealing a GPA-specific mechanism of immune polarization. Accordingly, circulating CD4+ T cells from GPA patients had a skewed distribution of Th9/Th2/Th17. These results reveal that PR3 disrupts immune silencing associated with clearance of apoptotic neutrophils and provide insight into how PR3 and PR3-targeting ANCAs promote GPA pathophysiology.

Innate immune cells in the pathogenesis of primary systemic vasculitis

Innate immune system forms the first line of defense against foreign substances. Neutrophils, eosinophils, erythrocytes, platelets, monocytes, macrophages, dendritic cells, γδ T cells, natural killer and natural killer T cells comprise the innate immune system. Genetic polymorphisms influencing the activation of innate immune cells predispose to development of vasculitis and influence its severity. Abnormally activated innate immune cells cross-talk with other cells of the innate immune system, present antigens more efficiently and activate T and B lymphocytes and cause tissue destruction via cell-mediated cytotoxicity and release of pro-inflammatory cytokines. These secreted cytokines further recruit other cells to the sites of vascular injury. They are involved in both the initiation as well as the perpetuation of vasculitis. Evidences suggest reversal of aberrant activation of immune cells in response to therapy. Understanding the role of innate immune cells in vasculitis helps understand the potential of therapeutic modulation of their activation to treat vasculitis.

Inhibition of human γδ T cell proliferation and effector functions by neutrophil serine proteases

Human peripheral blood γδ T cells expressing the Vγ9Vδ2 T cell receptor are activated by microbial or endogenous pyrophosphate antigens and indirectly by nitrogen-containing bisphosphonates. Apart from proliferation, such phosphoantigens induce proinflammatory cytokine production including TNF-α and IFN-γ and trigger cytotoxic effector function. Neutrophil granulocytes are known to modulate T cell activation. The neutrophil serine proteases proteinase 3, elastase and cathepsin G have multiple potential targets and promote microbial killing. In this study, we investigated the effect of the three serine proteases on the in vitro proliferation and effector functions of γδ T cells cultured in serum-free medium. All three proteases inhibited the proliferative activity, suppressed the cytokine production and decreased the cytotoxicity of γδ T cells. Further studies indicated that proteolytic cleavage of IL-2 and modulation of butyrophilin 3A1 (CD277) expression might contribute to the overall inhibition.

Prolonged B cell depletion with rituximab is effective in treating refractory pulmonary granulomatous inflammation in granulomatosis with polyangiitis (GPA)

Pulmonary nodule formation is a frequent feature of granulomatosis with polyangiitis (GPA). Traditional induction therapy includes methotrexate or cyclophosphamide, however, pulmonary nodules generally respond slower than vasculitic components of disease. Efficacy of rituximab (RTX) solely for the treatment of pulmonary nodules has not been assessed. In this observational cohort study, we report patient outcomes with RTX in GPA patients with pulmonary nodules who failed to achieve remission following conventional immunosuppression. Patients (n = 5) with persistent pulmonary nodules were identified from our clinic database and retrospectively evaluated. Systemic manifestations, inflammatory markers, disease activity, concurrent immunosuppression, and absolute B cell numbers were recorded pre-RTX and at 6 monthly intervals following treatment. Chest radiographs at each time point were scored by an experienced radiologist, blinded to clinical details. Five patients with GPA and PR3-ANCA were evaluated (2 male, 3 female), mean age 34 (22-52) years. Pulmonary nodules (median 4, range 2-6), with or without cavitation were present in all patients. RTX induced initial B cell depletion (<5 cells/μL) in all patients but re-population was observed in 3 patients. Repeated RTX treatment in these 3 and persistent B cell depletion in the whole cohort was associated with further significant radiological improvement. Radiographic scoring at each time interval showed reduction in both number of nodules (P =  <0.0001) and largest nodule diameter (P =  <0.0001) in all patients for at least 18 months following B cell depletion. In summary, RTX therapy induces resolution of pulmonary granulomatous inflammation in GPA following prolonged B cell depletion.

Neutrophil extracellular traps downregulate lipopolysaccharide-induced activation of monocyte-derived dendritic cells

Polymorphonuclear neutrophils (PMN) play a central role in inflammation and participate in its control, notably by modulating dendritic cell (DC) functions via soluble mediators or cell-cell contacts. Neutrophil extracellular traps (NETs) released by PMN could play a role in this context. To evaluate NET effects on DC maturation, we developed a model based on monocyte-derived DC (moDC) and calibrated NETs isolated from fresh human PMN. We found that isolated NETs alone had no discernable effect on moDC. In contrast, they downregulated LPS-induced moDC maturation, as shown by decreased surface expression of HLA-DR, CD80, CD83, and CD86, and by downregulated cytokine production (TNF-α, IL-6, IL-12, IL-23), with no increase in the expression of tolerogenic DC genes. Moreover, the presence of NETs during moDC maturation diminished the capacity of these moDC to induce T lymphocyte proliferation in both autologous and allogeneic conditions, and modulated CD4(+) T lymphocyte polarization by promoting the production of Th2 cytokines (IL-5 and IL-13) and reducing that of Th1 and Th17 cytokines (IFN-γ and IL-17). Interestingly, the expression and activities of the lymphoid chemokine receptors CCR7 and CXCR4 on moDC were not altered when moDC matured in the presence of NETs. Together, these findings reveal a new role for NETs in adaptive immune responses, modulating some moDC functions and thereby participating in the control of inflammation.

An increase of CD83+ dendritic cells ex vivo correlates with increased regulatory T cells in patients with active eosinophilic granulomatosis and polyangiitis

BACKGROUND

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare disease characterized by the presence of allergic granulomatosis and necrotizing vasculitis with eosinophilic infiltration. The etiology of EGPA is unknown. Dendritic cells (DCs) are not only critical for the induction of primary immune responses; they may also be important for the induction of immunological tolerance and the regulation of the type of T-cell-mediated immune response. To investigate whether DC maturation is associated with EGPA disease status, we examined the relationship between the maturation of DCs and the differentiation of regulatory T (Treg) cells in EGPA patients. We exposed the CD14+ blood monocytes of 19 patients with EGPA in remission or relapse to stimulation with GM-CSF and IL-4 for 6 d and lipopolysaccharide for 24 h to obtain mature CD83+ DCs and immature CD206+ DCs. Using immunohistochemistry, we examined four patients for the presence of CD83+ and CD206+ DCs in the lung at the onset of EGPA.

RESULTS

The percentage of CD83+ cells among DCs differentiated from CD14+ monocytes was lower for EGPA patients in relapse than in remission. The percentage of CD83+ DCs was inversely correlated with the percentage of CD206+ DCs and was significantly correlated with the numbers of naturally occurring CD4+ regulatory Treg (nTreg; FOXP3+CD4+) cells and inducible Treg (iTreg; CD4+CD25+ T cells producing IL-10 or TGF-β) cells but not the number of eosinophils. The percentage of CD206+ DCs was significantly inversely correlated with the percentages of nTreg and iTreg cells but not the number of eosinophils. Immunohistochemistry revealed both CD206+ DCs and CD83+ DCs in alveoli and interstitial spaces at the onset of EGPA.

CONCLUSION

The maturation of DCs from monocytes was related to disease activity in patients with EGPA. Increased CD83+ DCs in EGPA patients may induce the differentiation of iTreg and nTreg cells, thereby suppressing inflammation and disease activity.

The immunopathology of ANCA-associated vasculitis

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

Tissue-specific microvascular endothelial cells show distinct capacity to activate NK cells: implications for the pathophysiology of granulomatosis with polyangiitis

The relevance of tissue specificity of microvascular endothelial cells (MECs) in the response to inflammatory stimuli and sensitivity to immune cell-mediated injury is not well defined. We hypothesized that such MEC characteristics might shape their interaction with NK cells through the use of different adhesion molecules and NK cell receptor ligands or the release of different soluble factors and render them more or less vulnerable to NK cell injury during autoimmune vasculitis, such as granulomatosis with polyangiitis (GPA). To generate a comprehensive expression profile of human MECs of renal, lung, and dermal tissue origin, we characterized, in detail, their response to inflammatory cytokines and to proteinase 3, a major autoantigen in GPA, and analyzed the effects on NK cell activation. In this study, we show that renal MECs were more susceptible than lung and dermal MECs to the effect of inflammatory signals, showing upregulation of ICAM-1 and VCAM-1 on their surface, as well as release of CCL2, soluble fractalkine, and soluble VCAM-1. Proteinase 3-stimulated renal and lung MECs triggered CD107a degranulation in control NK cell. Notably, NK cells from GPA patients expressed markers of recent in vivo activation (CD69, CD107a), degranulated more efficiently than did control NK cells in the presence of renal MECs, and induced direct killing of renal MECs in vitro. These results suggest that, upon inflammatory conditions in GPA, renal MECs may contribute to the recruitment and activation of NK cells in the target vessel wall, which may participate in the necrotizing vasculitis of the kidney during this disease.

Protease-activated receptor-2 signalling by tissue factor on dendritic cells suppresses antigen-specific CD4+ T-cell priming

The precise function of tissue factor (TF) expressed by dendritic cells (DC) is uncertain. As well as initiating thrombin generation it can signal through protease-activated receptor 2 (PAR-2) when complexed with factor VIIa. We investigated the expression and function of TF on mouse bone marrow (BM) -derived DC; 20% of BM-derived DC expressed TF, which did not vary after incubation with lipopolysaccharide (LPS) or dexamethasone (DEX). However, the pro-coagulant activity of DEX-treated DC in recalcified plasma was 30-fold less than LPS-treated DC. In antigen-specific and allogeneic T-cell culture experiments, the TF on DEX-treated DC provided a signal through PAR-2, which contributed to the reduced ability of these cells to stimulate CD4(+) T-cell proliferation and cytokine production. In vivo, an inhibitory anti-TF antibody and a PAR-2 antagonist enhanced antigen-specific priming in two models where antigen was given without adjuvant, with an effect approximately 50% that seen with LPS, suggesting that a similar mechanism was operational physiologically. These data suggest a novel TF and PAR-2-dependent mechanism on DEX-DC in vitro and unprimed DC in vivo that contributes to the low immunogenicity of these cells. Targeting this pathway has the potential to influence antigen-specific CD4(+) T-cell activation.

B cell homeostasis is disturbed by immunosuppressive therapies in patients with ANCA-associated vasculitides

B-lymphocytes play a pivotal role in ANCA-associated vasculitides (AAV). The homeostasis of peripheral human B-lymphocyte subpopulations is tightly regulated, but may be disturbed in autoimmune disease or following immunosuppressive therapies. To elucidate the effect of immunosuppression and the relevance of B-lymphocyte disturbances, the B-lymphocyte compartment was analysed in 61 AAV patients. After immunosuppressive treatment a general B-lymphocytopenia developed in AAV patients. Within the B-lymphocyte subpopulations transitional B cells are the first maturation stage found in the peripheral blood. Transitional B-lymphocytes were significantly lower in AAV patients after immunosuppressive therapy compared to healthy controls. Furthermore, marginal zone B cells--a B-lymphocyte population protecting against encapsulated bacteria--were markedly lowered after immunosuppressive therapy in AAV patients. AAV patients treated with immunosuppressants had lower numbers of naïve and memory B-lymphocytes. Numbers of marginal zone B cells, memory B cells and plasmablasts correlated with concentrations of immunoglobulins. We evaluated plasmablasts for a potential correlation with disease activity. Different from what has been reported for e.g. large vessel vasculitis, absolute numbers of plasmablasts were not increased in patients with AAV and showed no correlation to disease activity. As low transitional B cells after treatment with immunosuppressants indicated an impaired early B-lymphocyte development, seven patients treated with the B cell depleting agent rituximab (RTX) because of relapsing disease activity were analysed for their B cell repopulation kinetics. In the majority of these patients repopulation of the peripheral B cell compartment by newly formed transitional B cells after RTX treatment was constricted and delayed.

The role of antigen cross-presentation from leukemia blasts on immunity to the leukemia-associated antigen PR1

Cross-presentation is an important mechanism by which exogenous tumor antigens are presented to elicit immunity. Because neutrophil elastase (NE) and proteinase-3 (P3) expression is increased in myeloid leukemia, we investigated whether NE and P3 are cross-presented by dendritic cells (DC) and B cells, and whether the NE and P3 source determines immune outcomes. We show that NE and P3 are elevated in leukemia patient serum and that levels correlate with remission status. We demonstrate cellular uptake of NE and P3 into lysosomes, ubiquitination, and proteasome processing for cross-presentation. Using anti-PR1/human leukocyte antigen-A2 monoclonal antibody, we provide direct evidence that B-cells cross-present soluble and leukemia-associated NE and P3, whereas DCs cross-present only leukemia-associated NE and P3. Cross-presentation occurred at early time points but was not associated with DC or B-cell activation, suggesting that NE and P3 cross-presentation may favor tolerance. Furthermore, we show aberrant subcellular localization of NE and P3 in leukemia blasts to compartments that share common elements of the classic major histocompatibility class I antigen-presenting pathway, which may facilitate cross-presentation. Our data demonstrate distinct mechanisms for cross-presentation of soluble and cell-associated NE and P3, which may be valuable in understanding immunity to PR1 in leukemia.

Evaluation of antibodies directed against human protease-activated receptor-2

Protease-activated receptor 2 (PAR2) is a G protein-coupled receptor activated by intramolecular docking of a tethered ligand that is released by the actions of proteases, mainly of the serine protease family. Here, we evaluate four commercially available anti-PAR2 antibodies, SAM11, C17, N19 and H99, demonstrating marked differences in the ability of these reagents to detect the target receptor in Western blot, immunocytochemical and flow cytometry applications. In Western blot analysis, we evaluated antibody reactivity against both ectopic and endogenous receptors. Against material from transfected cells, we show that SAM11 and N19, and to a lesser extent C17, but not H99, are able to detect ectopic PAR2. Interestingly, these Western blot analyses indicate that N19 and C17 detect conformations of ectopic PAR2 distinct to those recognised by SAM11. Significantly, our data also indicate that Western blot signal detected by SAM11 and C17, and much of the signal detected by N19, against cells endogenously expressing PAR2 is non-specific. Despite confounding non-specific signals, we were able to discern N19 reactivity against endogenous PAR2 as a broad smear that we also observed in ectopically expressing human and mouse cells and that is sensitive to loss of N-glycosylation. In immunocytochemistry analysis, each antibody is able to detect ectopic PAR2 although it appears that H99 detects only a subset of the ectopically expressed receptor. In addition, SAM11 and N19 are able to detect both ectopic and endogenous cell surface PAR2 by flow cytometry. In summary: (1) each antibody can detect ectopic PAR2 by immunocytochemical analysis with SAM11 and N19 suitable for cell surface detection of both ectopic and endogenous receptor by flow cytometry; (2) in Western blot analysis, N19, SAM11 and C17 can detect ectopically expressed PAR2, with only N19 able to detect the endogenous receptor by this technique and (3) in each of these approaches, appropriate controls are essential to ensure that non-specific reactivity is identified.

Overexpression of cathepsin S induces chronic atopic dermatitis in mice

Atopic dermatitis (AD) is a chronically relapsing, non contagious pruritic skin disease with two phases: acute and chronic. Cysteine protease cathepsin S (CTSS) is involved in inflammatory processes, possibly leading to atherosclerosis and asthma. Recently, it has been reported that CTSS can arouse a predominant sensation of itch accompanied by classical ligand–receptor signaling [corrected]. Recently, CTSS was shown to be a ligand for proteinase-activated receptor-2 (PAR-2), which is associated with itching. In this study, we show that CTSS-overexpressing transgenic (TG) mice spontaneously develop a skin disorder similar to chronic AD. The results of this study suggest that CTSS overexpression triggers PAR-2 expression in dendritic cells (DCs), resulting in the promotion of CD4(+) differentiation, which is involved in major histocompatibility complex (MHC) class II expression. In addition, we investigated mast cells and macrophages and found significantly higher mean levels of T helper type 1 (Th1) cell-associated cytokines than T helper type 2 (Th2) cell-associated cytokines in CTSS-overexpressing TG mice. These results suggest that increased PAR-2 expression in DCs as a result of CTSS overexpression induces scratching behavior and Th1 cell-associated cytokine expression, and can trigger chronic AD symptoms.

Protease-activated receptor 2 signaling in inflammation

Protease-activated receptors (PARs) are G protein-coupled receptors that are activated by proteolytical cleavage of the amino-terminus and thereby act as sensors for extracellular proteases. While coagulation proteases activate PARs to regulate hemostasis, thrombosis, and cardiovascular function, PAR2 is also activated in extravascular locations by a broad array of serine proteases, including trypsin, tissue kallikreins, coagulation factors VIIa and Xa, mast cell tryptase, and transmembrane serine proteases. Administration of PAR2-specific agonistic and antagonistic peptides, as well as studies in PAR2 knockout mice, identified critical functions of PAR2 in development, inflammation, immunity, and angiogenesis. Here, we review these roles of PAR2 with an emphasis on the role of coagulation and other extracellular protease pathways that cleave PAR2 in epithelial, immune, and neuronal cells to regulate physiological and pathophysiological processes.

Membrane-bound proteinase 3 and PAR2 mediate phagocytosis of non-opsonized bacteria in human neutrophils

The molecular mechanisms underlying the non-opsonic phagocytosis of bacteria by neutrophils are poorly understood. We previously reported the efficient uptake of Streptococcus sanguinis by human neutrophils in the absence of opsonins. To characterize the phagocytosis receptor, protein lysates from neutrophils and HL-60 cells were subjected to affinity chromatography using epoxy beads coated with S. sanguinis. Denaturing electrophoresis of the eluted proteins and subsequent mass spectrometry revealed that one of the proteins eluted from neutrophils was proteinase 3 (PR3). Enzymatic cleavage of the glycosylphosphatidylinositol linker of NB1, a co-receptor for membrane-bound PR3 (mPR3), significantly reduced the phagocytosis of S. sanguinis. In addition, the neutralization of mPR3 with antibody reduced both binding and phagocytosis of S. sanguinis. Treatment of neutrophils with a serine proteinase inhibitor indicated that protease activity is required for phagocytosis. Thus, we studied whether protease-activated receptor 2 (PAR2) is involved in signal transmission from mPR3 during this process. Indeed, neutralizing antibodies against PAR2 inhibited phagocytosis and S. sanguinis-induced calcium mobilization desensitized PAR2. Furthermore, the phagocytosis of S. sanguinis and the concomitant activation of Rho family GTPases were inhibited by the intracellular calcium chelator, BAPTA-AM. Collectively, mPR3 acts as a non-opsonic phagocytosis receptor for bacteria probably by activating PAR2 in neutrophils.

Decreased numbers of blood dendritic cells and defective function of regulatory T cells in antineutrophil cytoplasmic antibody-associated vasculitis

Background

Dendritic cells (DC) and regulatory cells (Treg) play pivotal roles in controlling both normal and autoimmune adaptive immune responses. DC are the main antigen-presenting cells to T cells, and they also control Treg functions. In this study, we examined the frequency and phenotype of DC subsets, and the frequency and function of Treg from patients with ANCA-associated vasculitis (AAV).

Methodology/Principal Findings

Blood samples from 19 untreated patients with AAV during flares and before any immunosuppressive treatment were analyzed, along with 15 AAV patients in remission and 18 age-matched healthy controls. DC and Treg numbers, and phenotypes were assessed by flow cytometry, and in vitro suppressive function of Treg was determined by co-culture assay. When compared to healthy volunteers, absolute numbers of conventional and plasmacytoid DC were decreased in AAV patients. During the acute phase this decrease was significantly more pronounced and was associated with an increased DC expression of CD62L. Absolute numbers of Treg (CD4⁺CD25^highCD127^low/− Tcells) were moderately decreased in patients. FOXP3 and CD39 were expressed at similar levels on Treg from patients as compared to controls. The suppressive function of Treg from AAV patients was dramatically decreased as compared to controls, and this defect was more pronounced during flares than remission. This Treg functional deficiency occurred in the absence of obvious Th17 deviation.

Conclusion

In conclusion, these data show that AAV flares are associated with both a decrease number and altered phenotype of circulating DC and point to a role for Treg functional deficiency in the pathogenesis of AAV.

Transcription of proteinase 3 and related myelopoiesis genes in peripheral blood mononuclear cells of patients with active Wegener's granulomatosis

OBJECTIVE

Wegener's granulomatosis (WG) is a systemic inflammatory disease that is associated with substantial morbidity. The aim of this study was to understand the biology underlying WG and to discover markers of disease activity that would be useful for prognosis and treatment guidance.

METHODS

Gene expression profiling was performed using total RNA from peripheral blood mononuclear cells (PBMCs) and granulocyte fractions from 41 patients with WG and 23 healthy control subjects. Gene set enrichment analysis (GSEA) was performed to search for candidate WG-associated molecular pathways and disease activity biomarkers. Principal components analysis was used to visualize relationships between subgroups of WG patients and controls. Longitudinal changes in proteinase 3 (PR3) gene expression were evaluated using reverse transcription-polymerase chain reaction, and clinical outcomes, including remission status and disease activity, were determined using the Birmingham Vasculitis Activity Score for WG (BVAS-WG).

RESULTS

Eighty-six genes in WG PBMCs and 40 in WG polymorphonuclear neutrophils (PMNs) were significantly up-regulated relative to controls. Genes up-regulated in WG PBMCs were involved in myeloid differentiation, and these included the WG autoantigen PR3. The coordinated regulation of myeloid differentiation genes was confirmed by GSEA. The median expression values of the 86 up-regulated genes in WG PBMCs were associated with disease activity (P = 1.3 x 10(-4)), and WG patients with low-level expression of the WG signature genes showed expression profiles that were only modestly different from that in healthy controls (P = 0.07). PR3 transcription was significantly up-regulated in WG PBMCs (P = 1.3 x 10(-5), false discovery rate [FDR] 0.002), but not in WG PMNs (P = 0.03, FDR 0.28), and a preliminary longitudinal analysis showed that the fold change in PR3 RNA levels in WG PBMCs corresponded to changes in the BVAS-WG score over time.

CONCLUSION

Transcription of PR3 and related myeloid differentiation genes in PBMCs may represent novel markers of disease activity in WG.

T cells in ANCA-associated vasculitis: what can we learn from lesional versus circulating T cells?

Anti-neutrophil cytoplasmic antibody (ANCA) - associated vasculitis (AAV) is a life-threatening autoimmune disease characterized by an antibody-mediated glomerulonephritis and necrotizing vasculitis. Apart from antibodies, T cells are also involved in disease pathogenesis. This review stresses the hallmarks of T cell-mediated pathology in AAV and highlights the characteristics of lesional and circulating T cells in the immune response in AAV. Circulating effector T-cell populations are expanded and are in a persistent state of activation. Circulating regulatory T-cell subsets are less well characterized but seem to be impaired in function. Lesional effector T cells are present in granulomas, vasculitic lesions, and nephritis. Lesional T cells usually show pro-inflammatory properties and promote granuloma formation. Apart from T cells, dendritic cells are abundantly present at the sites of inflammation and locally orchestrate the immune response. Targeting the above-mentioned T cell-mediated disease mechanisms will potentially provide powerful therapeutic tools for AAV.

Clinical and immunological features of drug-induced and infection-induced proteinase 3-antineutrophil cytoplasmic antibodies and myeloperoxidase-antineutrophil cytoplasmic antibodies and vasculitis

PURPOSE OF REVIEW

Drugs and infections may induce antineutrophil cytoplasmic antibodies (ANCA) and vasculitic manifestations mimicking ANCA-associated vasculitides (AAV) and mechanisms relevant in their pathogenesis. This review summarizes the most recent findings in this field.

RECENT FINDINGS

Drug-induced and infection-induced proteinase 3 (PR3)-ANCA and myeloperoxidase (MPO)-ANCA may be associated with a vasculitis clinically resembling AAV. Mechanisms relevant for the break of tolerance and induction of ANCA (e.g. danger signals, superantigens, neutrophil extracellular traps, protease-activated receptor-2, IL-17 cells) may be shared to some extent between drug-induced and infection-induced ANCA-positive vasculitis and AAV, especially with regard to the potential role of infection in Wegener's granulomatosis. Differences in immunopathology, clinical presentation, and functional aspects of ANCA help to distinguish drug-induced and infection-induced ANCA-positive vasculitis from AAV, and present new avenues for future research in this field.

SUMMARY

Medications and infections, which induce PR3-ANCA and MPO-ANCA, have to be considered in the differential diagnosis of primary AAV. Moreover, there is clinical and experimental evidence for an association between certain drugs and infections with ANCA-production. Analysis of ANCA-induction in such conditions also sheds new light on our understanding of immune mechanisms relevant in the break of tolerance and ANCA-production in AAV.

A functionally relevant IRF5 haplotype is associated with reduced risk to Wegener's granulomatosis

Wegener's granulomatosis (WG), characterized by systemic vasculitis and granulomatous inflammation, is a rare chronic rheumatic condition potentially sharing some etiopathological principles with other autoimmune disorders, e.g., rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Several large association studies have identified genetic risk factors for RA and SLE. Thereof, we have evaluated the relevance of the most promising ones in WG. 22 single nucleotide polymorphisms (SNPs) within or in the vicinity of CCL21, CD40, CDK6, IL21, IL2RB, IRF5, KIF5A, KLF12, MMEL1, PRKCQ, STAT4, TNFAIP3, and TRAF1/C5 have been genotyped in >600 German WG cases and >800 matched controls. While most polymorphisms did not show suspicious effects on WG susceptibility, SNPs representing TNFAIP3 (rs6922466, p = 0.032, odds ratio (OR) 0.83, 95% confidence interval (CI) 0.7--0.98) and CDK6 (rs42041, p = 0.0201, OR 1.21, 95% CI 1.03-1.43) revealed nominally significant differences in allele distribution. The strongest association was detected for a functionally relevant four SNP haplotype of IRF5, which comprised a protective effect (p = 0.0000897, p (corrected) = 0.0012, OR 0.73, 95% CI 0.62-0.85) similar to those previously seen in RA and SLE. Thus, we suggest that WG, SLE, and RA share some, but not many, genetic risk factors, which supports models of partly overlapping etiopathological mechanisms in these disorders.

Antineutrophil cytoplasmic antibody-associated vasculitides: could geographic patterns be explained by ambient ultraviolet radiation?

OBJECTIVE

This ecological study describes and quantifies the association between ambient ultraviolet (UV) radiation levels, including daily winter vitamin D effective UV radiation levels and the incidence of the 3 antineutrophil cytoplasmic antibody-associated vasculitides (AAVs): Wegener's granulomatosis (WG), microscopic polyangiitis (MPA), and Churg-Strauss syndrome (CSS). Latitudinal variation in occurrence of the AAVs, especially WG, has been previously reported. For other autoimmune diseases such as multiple sclerosis and type 1 diabetes mellitus, inverse associations with latitude are hypothesized to indicate a causative role for low UV radiation exposure, possibly acting via vitamin D status.

METHODS

Published epidemiologic studies provided data on incident cases, total population of study regions, age-specific incidence rates, and study location. From these data and online age-specific population data, we calculated crude incidence rates, the expected number of cases (to control for possible age confounding), and measures of ambient UV radiation. Negative binomial regression models were used to calculate the incidence rate ratio (IRR) for a 1,000 joules/m(2) increase in ambient UV radiation.

RESULTS

The incidence of WG and CSS increased with increasing latitude and decreasing ambient UV radiation, with a stronger and more consistent effect across different UV radiation measures for WG, e.g., for average daily ambient clear sky erythemal UV radiation (WG: IRR 0.64 [95% confidence interval (95% CI) 0.44-0.94], P = 0.02; CSS: IRR 0.67 [95% CI 0.43-1.05], P = 0.08; MPA: IRR 1.16 [95% CI 0.92-1.47], P = 0.22). There was no apparent latitudinal variation in MPA incidence.

CONCLUSION

Our findings are consistent with a protective immunomodulatory effect of ambient UV radiation on the onset of WG and CSS. We discuss possible mechanisms, including the effect of vitamin D on the immune system.

Anti-neutrophil cytoplasmic antibody pathogenesis in small-vessel vasculitis: an update

Vasculitides associated with serum positivity for anti-neutrophil cytoplasmic antibodies (ANCAs) that affect small- to medium-sized vessels are commonly known as ANCA-associated vasculitis (AAV) and include Wegener's granulomatosis, microscopic polyangiitis, and Churg-Strauss syndrome. Evidence derived from both in vitro studies and recent animal models points to a pathogenic role of ANCAs in AAV. In 2002, the first in vivo breakthrough in the pathogenesis of ANCAs showed that mouse ANCAs against myeloperoxidase (MPO) led to intrinsic pauci-immune renal vasculitis in mice. In 2004, a report using both in vitro and in vivo studies proposed that proteinase 3 (PR3)-directed autoimmunity involved the complementary peptide of PR3 (cPR3), which is encoded by the antisense strand of the PR3 gene. The last breakthrough came in October 2008 with a previously undescribed molecular explanation for the origin and development of injury in pauci-immune renal vasculitis, with potential clinical implications. This report showed that infection by fimbriated bacteria may trigger cross-reactive autoimmunity to a previously characterized ANCA antigen, lysosomal membrane protein-2, which is contained in the same vesicles that harbor MPO and PR3. Infection by fimbriated bacteria resulted in the production of autoantibodies, which activated neutrophils and killed human microvascular endothelium in vitro and caused renal vasculitis in rats. Although the evidence for a pathogenic role of ANCAs, mainly MPO-ANCAs, is striking, various questions remain unanswered. Understanding the key pathogenic mechanisms of AAV may provide a safer, more rational therapeutic approach than the traditional (ie, corticosteroids and immunosuppressants) treatment strategy.

Granuloma formation in ANCA-associated vasculitides

Granuloma formation is a key pathologic finding in two of the anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitides: Wegener's granulomatosis (WG) and Churg-Strauss syndrome (CSS). So far, no animal models have been established convincingly reproducing both vasculitic and granulomatous features typical of WG and CSS. In biopsies, granulomatous lesions are found both at distant extravascular sites and in the vicinity of inflamed vessels, e.g. in the lung. Intriguingly, WG-granulomata appear to display features of tertiary lymphoid tissue. Cartilaginous and osseous destruction is caused by granulomatous inflammation invading adjacent tissues. Rhinosinusitis is regularly encountered in WG and CSS. Septal perforation, saddle nose deformity, middle and inner ear symptoms, and granulomatous invasion of the palate, orbita, meninges, or the pituitary gland may complicate WG. Both common (e.g. FCGR3B copy number) and distinct (e.g. HLA-DP, IL-10.2) genetic factors have been identified in AAV potentially favouring inflammation and autoimmunity. The HLA-DPB1/RING1/RXRB region constitutes a quantitative trait locus for ANCA-positive WG with the strongest association to be reported up to now. A profound alteration of the T-cell response including Th1 and Th17 responses, anomalously NK-receptor-expressing 'NK-like' T cells, and dysfunctional regulatory T cells could facilitate and sustain granuloma formation and autoimmunity.

Protease-activated receptor 2 signalling promotes dendritic cell antigen transport and T-cell activation in vivo

Deficiency of protease-activated receptor-2 (PAR2) modulates inflammation in several models of inflammatory and autoimmune disease, although the underlying mechanism(s) are not understood. PAR2 is expressed on endothelial and immune cells, and is implicated in dendritic cell (DC) differentiation. We investigated in vivo the impact of PAR2 activation on DCs and T cells in PAR2 wild-type (WT) and knockout (KO) mice using a specific PAR2 agonist peptide (AP2). PAR2 activation significantly increased the frequency of mature CD11c(high) DCs in draining lymph nodes 24 hr after AP2 administration. Furthermore, these DCs exhibited increased expression of major histocompatibility complex (MHC) class II and CD86. A significant increase in activated (CD44(+) CD62(-)) CD4(+) and CD8(+) T-cell frequencies was also observed in draining lymph nodes 48 hr after AP2 injection. No detectable change in DC or T-cell activation profiles was observed in the spleen. The influence of PAR2 signalling on antigen transport to draining lymph nodes was assessed in the context of delayed-type hypersensitivity. PAR2 WT mice that were sensitized by skin-painting with fluorescein isothiocyanate (FITC) to induce delayed-type hypersensitivity possessed elevated proportion of FITC(+) DCs in draining lymph nodes 24 hr after FITC painting when compared with PAR2 KO mice (0.95% versus 0.47% of total lymph node cells). Collectively, these results demonstrate that PAR2 signalling promotes DC trafficking to the lymph nodes and subsequent T-cell activation, and thus provides an explanation for the pro-inflammatory effect of PAR2 in animal models of inflammation.