ANCA induces β2integrin and CXC chemokine-dependent neutrophil-endothelial cell interactions that mimic those of highly cytokine-activated endothelium

Semaglutide modulates prothrombotic and atherosclerotic mechanisms, associated with epicardial fat, neutrophils and endothelial cells network

BACKGROUND

Obesity has increased in recent years with consequences on diabetes and other comorbidities. Thus, 1 out of 3 diabetic patients suffers cardiovascular disease (CVD). The network among glucose, immune system, endothelium and epicardial fat has an important role on pro-inflammatory and thrombotic mechanisms of atherogenesis. Since semaglutide, long-acting glucagon like peptide 1- receptor agonist (GLP-1-RA), a glucose-lowering drug, reduces body weight, we aimed to study its effects on human epicardial fat (EAT), aortic endothelial cells and neutrophils as atherogenesis involved-cardiovascular cells.

METHODS

EAT and subcutaneous fat (SAT) were collected from patients undergoing cardiac surgery. Differential glucose consumption and protein cargo of fat-released exosomes, after semaglutide or/and insulin treatment were analyzed by enzymatic and TripleTOF, respectively. Human neutrophils phenotype and their adhesion to aortic endothelial cells (HAEC) or angiogenesis were analyzed by flow cytometry and functional fluorescence analysis. Immune cells and plasma protein markers were determined by flow cytometry and Luminex-multiplex on patients before and after 6 months treatment with semaglutide.

RESULTS

GLP-1 receptor was expressed on fat and neutrophils. Differential exosomes-protein cargo was identified on EAT explants after semaglutide treatment. This drug increased secretion of gelsolin, antithrombotic protein, by EAT, modulated CD11b on neutrophils, its migration and endothelial adhesion, induced by adiposity protein, FABP4, or a chemoattractant. Monocytes and neutrophils phenotype and plasma adiposity, stretch, mesothelial, fibrotic, and inflammatory markers on patients underwent semaglutide treatment for 6 months showed a 20% reduction with statistical significance on FABP4 levels and an 80% increase of neutrophils-CD88.

CONCLUSION

Semaglutide increases endocrine activity of epicardial fat with antithrombotic properties. Moreover, this drug modulates the pro-inflammatory and atherogenic profile induced by the adiposity marker, FABP4, which is also reduced in patients after semaglutide treatment.

The potential pathogenic roles of S100A8/A9 and S100A12 in patients with MPO-ANCA-positive vasculitis

Background

The significance of S100A8/A9 and S100A12 in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) has not been clarified. This study was dedicated to exploring the potential pathogenic roles of S100A8/A9 and S100A12 in patients with myeloperoxidase (MPO)-ANCA-positive vasculitis.

Methods

Serum and urine concentrations of S100A8/A9 and S100A12 of forty-two AAV patients were evaluated. The influence of S100A8/A9 and S100A12 on the chemotaxis, the apoptosis, the release of IL-1β, the complement activation, the respiratory burst, as well as the neutrophil extracellular traps (NETs) formation of MPO-ANCA-activated neutrophils was investigated.

Results

The serum and urine S100A8/A9 and S100A12 of active MPO-AAV significantly increased (compared with inactive AAV and healthy controls, p < 0.001) and were correlated with the severity of the disease. In vitro study showed that S100A8/A9 and S100A12 activated the p38 MAPK/NF-κB p65 pathway, increased the chemotaxis index (CI) and the release of IL-1β, extended the life span, and enhanced the complement activation ability of MPO-ANCA-activated neutrophils. The Blockade of TLR4 and RAGE inhibited the effects of S100A8/A9 and S100A12. All above-mentioned effects of S100A8/A9 and S100A12 were ROS-independent because neither S100A8/A9 nor S100A12 enhanced the ROS formation and NETs formation of MPO-ANCA-activated neutrophils.

Conclusion

S100A8/A9 and S100A12 serve as markers for assessing the disease severity, and they may also play a role in MPO-AAV pathogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12865-022-00513-4.

Pathogenicity of Proteinase 3-Anti-Neutrophil Cytoplasmic Antibody in Granulomatosis With Polyangiitis: Implications as Biomarker and Future Therapies

Granulomatosis with polyangiitis (GPA) is a rare but serious necrotizing auto-immune vasculitis. GPA is mostly associated with the presence of Anti-Neutrophil Cytoplasmic Antibody (ANCA) targeting proteinase 3 (PR3-ANCA), a serine protease contained in neutrophil granules but also exposed at the membrane. PR3-ANCAs have a proven fundamental role in GPA: they bind neutrophils allowing their auto-immune activation responsible for vasculitis lesions. PR3-ANCAs bind neutrophil surface on the one hand by their Fab binding PR3 and on the other by their Fc binding Fc gamma receptors. Despite current therapies, GPA is still a serious disease with an important mortality and a high risk of relapse. Furthermore, although PR3-ANCAs are a consistent biomarker for GPA diagnosis, relapse management currently based on their level is inconsistent. Indeed, PR3-ANCA level is not correlated with disease activity in 25% of patients suggesting that not all PR3-ANCAs are pathogenic. Therefore, the development of new biomarkers to evaluate disease activity and predict relapse and new therapies is necessary. Understanding factors influencing PR3-ANCA pathogenicity, i.e. their potential to induce auto-immune activation of neutrophils, offers interesting perspectives in order to improve GPA management. Most relevant factors influencing PR3-ANCA pathogenicity are involved in their interaction with neutrophils: level of PR3 autoantigen at neutrophil surface, epitope of PR3 recognized by PR3-ANCA, isotype and glycosylation of PR3-ANCA. We detailed in this review the advances in understanding these factors influencing PR3-ANCA pathogenicity in order to use them as biomarkers and develop new therapies in GPA as part of a personalized approach.

Response of chemokine receptors CXCR2 and integrin β2 after Streptococcus agalactiae and Aeromonas hydrophila challenge in GIFT strain of Nile tilapia Oreochromis niloticus

CXCR2 is a G-protein-coupled cell surface chemokine receptor, and integrins are heterodimeric transmembrane (TM) glycoproteins. These proteins work together to activate neutrophils in the immune defense, but knowledge of their function in tilapia is limited. RACE technology was used to clone the full length of the Nile tilapia Oreochromis niloticus Cxcr2 gene, which included a 954 bp open reading frame encoding 318 amino acids, and the integrin β2 gene, with a 2373 bp open reading frame and 791 amino acids. Sequence analyses showed that Cxcr2 and integrin β2 are conserved among species. Expression profile was performed using qRT-PCR and indicated that Cxcr2 and integrin β2 were distributed throughout the examined organ tissues, with highest expression observed in the immune tissues. Expression of Cxcr2 and integrin β2 were increased after challenged with Streptococcus agalactiae or Aeromonas hydrophila. Results suggest that Cxcr2 and integrin β2 genes play a role in immune response in Nile tilapia and provide basic data for molecular-assistant selection of disease-resistant bloodstock to improve the production.

Efficacy of plasma exchange for antineutrophil cytoplasmic antibody-associated systemic vasculitis: a systematic review and meta-analysis

Objective

To assess through systematic review and meta-analysis whether plasma exchange (PE) is associated with prognosis in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) patients.

Methods

A systematic search of PubMed, MEDLINE, Embase, and CENTRAL databases from inception to 17 June 2020 was conducted. Ongoing or unpublished trials were also searched in ClinicalTrials.gov and the World Health Organization trials portal. Randomised controlled trials (RCTs) comparing PE vs. non-PE in AAV patients (microscopic polyangiitis [MPA], granulomatosis with polyangiitis [GPA], or eosinophilic granulomatosis with polyangiitis [EGPA]) were included. The combined risk ratio (RR) was calculated by the random-effects model using the Mantel-Haenszel method. Heterogeneity was measured using the I² statistic. Primary outcomes were mortality, clinical remission (CR), and adverse events (AEs).

Results

Four RCTs comparing PE vs. no PE (N = 827) and 1 RCT comparing PE vs. pulse steroid treatment (N = 137) were included. All participants were MPA or GPA patients (no EGPA patients). PE was not associated with main primary outcomes compared with no PE (mortality RR 0.93 [95% confidence interval {CI} 0.70–1.24], I² = 0%; CR RR 1.02 [95% CI 0.91–1.15], I² = 0%; and AE RR 1.10 [95% CI 0.73–1.68], I² = 37%) or pulse steroid (mortality RR 0.99 [95% CI 0.71–1.37]; CR [the Birmingham Vasculitis Activity score] mean difference − 0.53 [95% CI − 1.40–0.34]; and AE RR 1.05 [95% CI 0.74–1.48]). Focusing on the early treatment phases, PE was associated with a reduction in end-stage renal disease incidence compared with both no PE (PE 1/43 vs. no PE 10/41; RR 0.14 [0.03–0.77] at 3 months) and pulse steroid (PE 11/70 vs. pulse steroid 23/67; RR 0.46 [0.24–0.86] at 3 months).

Conclusion

We carried out a systematic review and meta-analysis targeting all AAV patients, including MPA, GPA, and EGPA. In AAV patients, performing PE was not associated with the risk of mortality, CR, and AE. No RCT exists evaluating the efficacy of PE for EGPA; hence, this is required in the future. The results may affect the development of guidelines for AAV and may indicate the direction of future clinical research on AAV.

Trial registration

UMIN R000045239, PROSPERO CRD42020182566.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02415-z.

4C3 Human Monoclonal Antibody: A Proof of Concept for Non-pathogenic Proteinase 3 Anti-neutrophil Cytoplasmic Antibodies in Granulomatosis With Polyangiitis

Granulomatosis with polyangiitis (GPA) is a severe autoimmune vasculitis associated with the presence of anti-neutrophil cytoplasmic antibodies (ANCA) mainly targeting proteinase 3 (PR3), a neutrophilic serine proteinase. PR3-ANCA binding to membrane-bound PR3 on neutrophils induce their auto-immune activation responsible for vascular lesions. However, the correlation between PR3-ANCA level and disease activity remains inconsistent, suggesting the existence of non-pathogenic PR3-ANCA. In order to prove their existence, we immortalized B lymphocytes from blood samples of GPA patients in remission having persistent PR3-ANCA to isolate non-activating PR3-ANCA. We obtained for the first time a non-activating human IgG1κ anti-PR3 monoclonal antibody (mAb) named 4C3. This new mAb binds soluble PR3 with a high affinity and membrane-bound PR3 on an epitope close to the PR3 hydrophobic patch and in the vicinity of the active site. 4C3 is able to bind FcγRIIA and FcγRIIIB and has a G2F glycosylation profile on asparagine 297. 4C3 did not induce activation of neutrophils and could inhibit human polyclonal PR3-ANCA-induced activation suggesting that 4C3 is non-pathogenic. This characteristic relies on the recognized epitope on PR3 rather than to the Fc portion properties. The existence of non-pathogenic PR3-ANCA, which do not activate neutrophils, could explain the persistence of high PR3-ANCA levels in some GPA patients in remission and why PR3-ANCA would not predict relapse. Finally, these results offer promising perspectives particularly regarding the understanding of PR3-ANCA pathogenicity and the development of new diagnostic and therapeutic strategies in GPA.

ANCA-associated vasculitis

The anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAVs) are a group of disorders involving severe, systemic, small-vessel vasculitis and are characterized by the development of autoantibodies to the neutrophil proteins leukocyte proteinase 3 (PR3-ANCA) or myeloperoxidase (MPO-ANCA). The three AAV subgroups, namely granulomatosis with polyangiitis (GPA), microscopic polyangiitis and eosinophilic GPA (EGPA), are defined according to clinical features. However, genetic and other clinical findings suggest that these clinical syndromes may be better classified as PR3-positive AAV (PR3-AAV), MPO-positive AAV (MPO-AAV) and, for EGPA, by the presence or absence of ANCA (ANCA⁺ or ANCA^-, respectively). Although any tissue can be involved in AAV, the upper and lower respiratory tract and kidneys are most commonly and severely affected. AAVs have a complex and unique pathogenesis, with evidence for a loss of tolerance to neutrophil proteins, which leads to ANCA-mediated neutrophil activation, recruitment and injury, with effector T cells also involved. Without therapy, prognosis is poor but treatments, typically immunosuppressants, have improved survival, albeit with considerable morbidity from glucocorticoids and other immunosuppressive medications. Current challenges include improving the measures of disease activity and risk of relapse, uncertainty about optimal therapy duration and a need for targeted therapies with fewer adverse effects. Meeting these challenges requires a more detailed knowledge of the fundamental biology of AAV as well as cooperative international research and clinical trials with meaningful input from patients.

ANCA-Associated Vasculitis: Pathogenesis, Models, and Preclinical Testing

Our understanding of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis has developed greatly since the discovery of ANCA, directed against neutrophil components, in 1982. Observations in human disease, and increasingly sophisticated studies in vitro and in rodent models in vivo, have allowed a nuanced understanding of many aspects of the immunopathogenesis of disease, including the significance of ANCA as a diagnostic and monitoring tool as well as a mediator of microvascular injury. The mechanisms of leukocyte recruitment and tissue injury, and the role of T cells increasingly are understood. Unexpected findings, such as the role of complement, also have been uncovered through experimental studies and human observations. This review focusses on the pathogenesis of ANCA-associated vasculitis, highlighting the challenges in finding new, less-toxic treatments and potential therapeutic targets in this disease. The current suite of rodent models is reviewed, and future directions in the study of this complex and fascinating disease are suggested.

Granulomatosis with polyangiitis: a 17 year experience from a tertiary care hospital in Pakistan

Objective

Granulomatosis with Polyangiitis (GPA) is an autoimmune, multi-system, small and medium vessel vasculitis with granulomatous inflammation. Aim of this study was to assess the clinical and radiological presentations of patients with GPA amongst the Pakistani population. It is a single centre retrospective single observation study.

Results

Study was conducted at the Aga Khan University Hospital, Karachi with records were reviewed from January 2000 to December 2017. Definitive diagnosis was made using a combination of serological anti-neutrophil cytoplasmic antibody (ANCA) testing along with the clinical and radiological presentation. A total of 51 patients met the diagnostic criteria in the time frame of the study. There were 23 males and 28 females with mean age of 44.0 ± 17.8 years on presentation. Arthritis was the most common symptom present in 41.2% of the cases followed by cough in 32.0%. Sixteen patients showed pulmonary infiltrates on chest X-ray. C-ANCA was positive in all of the patients compared with 21.6% p-ANCA positivity. A total of 13 biopsies were done. The median Birmingham Vasculitis Activity Score was 12. We report a 17.6% mortality rate with 5 deaths occurring due to respiratory failure. GPA is a diagnostic challenge leading to late diagnosis which can contribute to significant morbidity and mortality specially in the Third World.

Antimyeloperoxidase antibody is a biomarker for progression of diabetic retinopathy

AIM

To study the correlation between serum antimyeloperoxidase (MPO) antibody levels with severity of diabetic retinopathy (DR).

METHODS

Study subjects included 60 consecutive cases of type 2 diabetes mellitus (DM): no diabetic retinopathy (NODR, n=20); nonproliferative DR (NPDR, n=20); proliferative DR (PDR, n=20) and 20 healthy controls. Best corrected visual acuity (BCVA) was measured on logMAR scale. Serum anti-MPO antibody levels were evaluated using ELISA IgG kit. Serum urea and creatinine was measured using standard protocol. Data were analysed statistically.

RESULTS

Mean serum anti-MPO antibody (RU/ml) was 16.94 ± 4.85 in controls, 17.66 ± 4.78 in NODR, 21.51 ± 5.27 in NPDR and 37.27 ± 11.92 in PDR groups. On ANOVA, significant difference in visual acuity was found among the study groups (F=73.46, p<0.001). Serum anti-MPO antibody was correlated significantly with decrease in visual acuity (F=48.40, p<0.001), increase in serum urea (F=128.13, p<0.001) and creatinine (F=77.10, p<0.001).

CONCLUSION

Increase in serum anti-MPO antibody levels correlate with increased severity of DR. Serum anti-MPO antibody may be a noteworthy biochemical marker for progression of retinopathy from nonproliferative to proliferative stage.

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.

Podocytes regulate neutrophil recruitment by glomerular endothelial cells via IL-6-mediated crosstalk

Stromal cells actively modulate the inflammatory process, in part by influencing the ability of neighboring endothelial cells to support the recruitment of circulating leukocytes. We hypothesized that podocytes influence the ability of glomerular endothelial cells (GEnCs) to recruit neutrophils during inflammation. To address this, human podocytes and human GEnCs were cultured on opposite sides of porous inserts and then treated with or without increasing concentrations of TNF-α prior to addition of neutrophils. The presence of podocytes significantly reduced neutrophil recruitment to GEnCs by up to 50% when cultures were treated with high-dose TNF-α (100 U/ml), when compared with GEnC monocultures. Importantly, this phenomenon was dependent on paracrine actions of soluble IL-6, predominantly released by podocytes. A similar response was absent when HUVECs were cocultured with podocytes, indicating a tissue-specific phenomenon. Suppressor of cytokine signaling 3 elicited the immunosuppressive actions of IL-6 in a process that disrupted the presentation of chemokines on GEnCs by altering the expression of the duffy Ag receptor for chemokines. Interestingly, suppressor of cytokine signaling 3 knockdown in GEnCs upregulated duffy Ag receptor for chemokines and CXCL5 expression, thereby restoring the neutrophil recruitment. In summary, these studies reveal that podocytes can negatively regulate neutrophil recruitment to inflamed GEnCs by modulating IL-6 signaling, identifying a potential novel anti-inflammatory role of IL-6 in renal glomeruli.

Neutrophil migration: moving from zebrafish models to human autoimmunity

There has been a resurgence of interest in the neutrophil's role in autoimmune disease. Classically considered an early responder that dies at the site of inflammation, new findings using live imaging of embryonic zebrafish and other modalities suggest that neutrophils can reverse migrate away from sites of inflammation. These 'inflammation-sensitized' neutrophils, as well as the neutrophil extracellular traps and other products made by neutrophils in general, may have many implications for autoimmunity. Here, we review what is known about the role of neutrophils in three different autoimmune diseases: rheumatoid arthritis, systemic lupus erythematosus, and small vessel vasculitis. We then highlight recent findings related to several cytoskeletal regulators that guide neutrophil recruitment including Lyn, Rac2, and SHIP. Finally, we discuss how our improved understanding of the molecules that control neutrophil chemotaxis may impact our knowledge of autoimmunity.

Pathogenesis of antineutrophil cytoplasmic autoantibody-associated small-vessel vasculitis

Clinical, in vitro, and experimental animal observations indicate that antineutrophil cytoplasmic autoantibodies (ANCA) are pathogenic. The genesis of the ANCA autoimmune response is a multifactorial process that includes genetic predisposition, environmental adjuvant factors, an initiating antigen, and failure of T cell regulation. ANCA activate primed neutrophils (and monocytes) by binding to certain antigens expressed on the surface of neutrophils in specific inflammatory microenvironments. ANCA-activated neutrophils activate the alternative complement pathway, establishing an inflammatory amplification loop. The acute injury elicits an innate inflammatory response that recruits monocytes and T lymphocytes, which replace the neutrophils that have undergone karyorrhexis during acute inflammation. Extravascular granulomatous inflammation may be initiated by ANCA-induced activation of extravascular neutrophils, causing tissue necrosis and fibrin formation, which would elicit an influx of monocytes that transform into macrophages and multinucleated giant cells. Over time, the neutrophil-rich acute necrotizing lesions cause the accumulation of more lymphocytes, monocytes, and macrophages and produce typical granulomatous inflammation.

Toll-like receptor TLR2 and TLR9 ligation triggers neutrophil activation in granulomatosis with polyangiitis

OBJECTIVE

The aim of the study was to characterize the expression of TLR2, TLR4 and TLR9 in PMNs of patients with granulomatosis with polyangiitis (GPA) and to elucidate the role of these receptors in GPA with respect to neutrophil activation.

METHODS

The expression of TLR2, TLR4 and TLR9 was determined on ex vivo PMNs in whole blood samples of GPA patients (n = 35) and healthy controls (HCs) (n = 24). Isolated PMNs were stimulated in vitro with TLR agonists and assessed for degranulation, membrane proteinase 3 (mPR3) expression, soluble l-selectin shedding and cytokine production (IL-8) in five GPA patients and five HCs. The priming effects of TLR2 and TLR9 ligation were assessed by measurement of serine protease activity after stimulation with PR3-ANCA.

RESULTS

There were no significant differences in the ex vivo expression of TLRs on PMNs in HCs and GPA patients. Stimulation of TLR4 and TLR9 induced MPO release, stimulation with TLR2, TLR4 and TLR9 ligands elicited IL-8 production and stimulation of TLR2 and TLR9 led to an upregulation in mPR3 expression on PMNs with no significant differences between GPA and HC after 1 or 24 h stimulation. Priming of PMNs with TLR2 and TLR9 ligands induced degranulation after subsequent stimulation with PR3-ANCA, which was comparable to priming with TNF-α.

CONCLUSION

Expression of TLR2, TLR4 and TLR9 in PMNs and the TLR-induced activation of PMNs was comparable in GPA and HC. mPR3 upregulation by TLR2 and TLR9 stimulation and the priming effect of TLR ligands on PMNs may have a potential implication for triggering disease activity during infection in GPA.

Endothelium-neutrophil interactions in ANCA-associated diseases

The two salient features of ANCA-associated vasculitis (AAV) are the restricted microvessel localization and the mechanism of inflammatory damage, independent of vascular immune deposits. The microvessel localization of the disease is due to the ANCA antigen accessibility, which is restricted to the membrane of neutrophils engaged in β2-integrin-mediated adhesion, while these antigens are cytoplasmic and inaccessible in resting neutrophils. The inflammatory vascular damage is the consequence of maximal proinflammatory responses of neutrophils, which face cumulative stimulations by TNF-α, β2-integrin engagement, C5a, and ANCA by the FcγRII receptor. This results in the premature intravascular explosive release by adherent neutrophils of all of their available weapons, normally designed to kill IgG-opsonized bacteria after migration in infected tissues.

PR3 and elastase alter PAR1 signaling and trigger vWF release via a calcium-independent mechanism from glomerular endothelial cells

Neutrophil proteases, proteinase-3 (PR3) and elastase play key roles in glomerular endothelial cell (GEC) injury during glomerulonephritis. Endothelial protease-activated receptors (PARs) are potential serine protease targets in glomerulonephritis. We investigated whether PAR1/2 are required for alterations in GEC phenotype that are mediated by PR3 or elastase during active glomerulonephritis. Endothelial PARs were assessed by flow cytometry. Thrombin, trypsin and agonist peptides for PAR1 and PAR2, TFLLR-NH(2) and SLIGKV-NH(2,) respectively, were used to assess alterations in PAR activation induced by PR3 or elastase. Endothelial von Willebrand Factor (vWF)release and calcium signaling were used as PAR activation markers. Both PR3 and elastase induced endothelial vWF release, with elastase inducing the highest response. PAR1 peptide induced GEC vWF release to the same extent as PR3. However, knockdown of PARs by small interfering RNA showed that neither PAR1 nor PAR2 activation caused PR3 or elastase-mediated vWF release. Both proteases interacted with and disarmed surface GEC PAR1, but there was no detectable interaction with cellular PAR2. Neither protease induced a calcium response in GEC. Therefore, PAR signaling and serine protease-induced alterations in endothelial function modulate glomerular inflammation via parallel but independent pathways.

High basal activity of the PTPN22 gain-of-function variant blunts leukocyte responsiveness negatively affecting IL-10 production in ANCA vasculitis

Consequences of expression of the protein tyrosine phosphatase nonreceptor 22 (PTPN22) gain-of-function variant were evaluated in leukocytes from patients with anti-neutrophil cytoplasmic autoantibody (ANCA) disease. The frequency of the gain-of-function allele within the Caucasian patient cohort was 22% (OR 1.45), compared to general American Caucasian population (16.5%, p = 0.03). Examination of the basal phosphatase activity of PTPN22 gain-of-function protein indicated persistently elevated activity in un-stimulated peripheral leukocytes, while basal activity was undetectable in leukocytes from patients without the gain-of-function variant. To examine consequences of persistently high PTPN22 activity, the activation status of ERK and p38 MAPK were analyzed. While moderate levels of activated ERK were observed in controls, it was undetectable in leukocytes expressing PTPN22 gain-of-function protein and instead p38MAPK was up-regulated. IL-10 transcription, reliant on the ERK pathway, was negatively affected. Over the course of disease, patients expressing variant PTPN22 did not show a spike in IL-10 transcription as they entered remission in contrast to controls, implying that environmentally triggered signals were blunted. Sustained activity of PTPN22, due to the gain-of-function mutation, acts as a dominant negative regulator of ERK activity leading to blunted cellular responsiveness to environmental stimuli and expression of protective cytokines.

α-1-Antitrypsin and IFN-γ reduce the severity of IC-mediated vasculitis by regulation of leukocyte recruitment in vivo

IC-mediated vasculitis (ICV) can be life threatening. The cellular and immune mechanisms controlling ICV are poorly understood. Therefore, we investigated the role of α-1-antitrypsin (α1AT) and IFN-γ in reducing the severity of ICV in a mouse model in vivo. To induce ICV, mice were challenged with the reverse passive Arthus reaction (RPA), the prototypic in vivo model for leukocytoclastic vasculitis (LcV), and the modulation of vascular permeability, edema formation, and leukocyte recruitment was studied. To further analyze the dynamics of RPA, we applied intravital microscopy in the dorsal skinfold chamber. α1AT continuously led to reduced leukocyte recruitment. α1AT interfered with neutrophil recruitment through a KC-dependent mechanism and reduced KC-elicited neutrophil activation. In contrast to α1AT, IFN-γ-reduced leukocyte recruitment during RPA was clearly independent of KC. We also revealed that the recruitment of neutrophils during RPA was a prerequisite for full KC expression. Thus, therapeutic administration of α1AT and IFN-γ might be beneficial for limiting the duration and severity of ICV.

The Molecular Biology and Treatment of Systemic Vasculitis in Children

Primary systemic vasculitides are rare in childhood but are associated with significant morbidity and mortality. The cause of the majority of vasculitides is unknown, although it is likely that a complex interaction between environmental factors, such as infections and inherited host responses, triggers the disease and determines the vasculitis phenotype. Several genetic polymorphisms in vasculitides have now been described, which may be relevant in terms of disease predisposition or development of disease complications. Treatment regimens continue to improve with the use of different immunosuppressive medications and newer therapeutic approaches such as biologic agents. This chapter reviews recent studies shedding light on the pathogenesis of vasculitis with emphasis on molecular biology where known, and summarizes current treatment strategies. We discuss new emerging challenges particularly with respect to the long-term cardiovascular morbidity for children with systemic vasculitis and emphasize the importance of future international multicenter collaborative studies to further increase and standardize the scientific base investigating and treating childhood vasculitis.

Conditions in subjects with rheumatic diseases: pulmonary manifestations of vasculitides

Pulmonary involvement is a common complication of vasculitides, especially small vessel vasculitides. This review provides an overview of vasculitic manifestations of the lung as well as of other organs involved in vasculitides. Furthermore, it provides the diagnostic procedures required to asses a patient with vasculitic lung involvement and gives an overview of current treatment strategies.

Pathophysiological importance of antineutrophil antibodies in vasculitis

PURPOSE OF REVIEW

We endeavour to provide a brief overview of the recent advances in understanding of how antineutrophil cytoplasmic antibodies (ANCAs) contribute to the pathophysiology of vasculitis.

RECENT FINDINGS

Substantial progress has been made in our understanding of the immunopathogenesis of ANCA-associated vasculitides. Compelling evidence from in-vitro studies and experimental models in conjunction with clinical trials has confirmed that ANCAs directly contribute to the evolution and progression of the disease process. A new ANCA, directed against human lysosome membrane protein-2 (LAMP-2), has recently been described as a sensitive and specific marker for renal vasculitis and we discuss its potential impact for diagnosis and therapy. Furthermore, high-throughput approaches are starting to identify genetic patterns that may identify patients likely to respond to specific therapy or having a high probability of relapse.

SUMMARY

It has become increasingly clear over the last two decades that ANCA IgG is pathogenic in vasculitis. Novel therapies aimed at selected cell populations or blocking specific pathogenic pathways offer hope for more selectively treating this heterogeneous group of patients, while avoiding nonspecific immunosuppression and its adverse effects.

The paradox of the neutrophil's role in tissue injury

The neutrophil is an essential component of the innate immune system, and its function is vital to human life. Its production increases in response to virtually all forms of inflammation, and subsequently, it can accumulate in blood and tissue to varying degrees. Although its participation in the inflammatory response is often salutary by nature of its normal interaction with vascular endothelium and its capability to enter tissues and respond to chemotactic gradients and to phagocytize and kill microrganisms, it can contribute to processes that impair vascular integrity and blood flow. The mechanisms that the neutrophil uses to kill microorganisms also have the potential to injure normal tissue under special circumstances. Its paradoxical role in the pathophysiology of disease is particularly, but not exclusively, notable in seven circumstances: 1) diabetic retinopathy, 2) sickle cell disease, 3) TRALI, 4) ARDS, 5) renal microvasculopathy, 6) stroke, and 7) acute coronary artery syndrome. The activated neutrophil's capability to become adhesive to endothelium, to generate highly ROS, and to secrete proteases gives it the potential to induce local vascular and tissue injury. In this review, we summarize the evidence for its role as a mediator of tissue injury in these seven conditions, making it or its products potential therapeutic targets.

Pathogenesis of ANCA-associated vasculitis

Antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) comprises a group of systemic inflammatory vasculitides associated with circulating autoantibodies directed against the neutrophil granule components proteinase 3 and myeloperoxidase. ANCA interact with their target antigens on cytokine primed neutrophils, causing neutrophil activation via several signaling pathways that culminates in endothelial interaction, degranulation, cytokine production, and endothelial and tissue damage. The presence of autoantibodies implies the assistance of autoreactive T-helper cells and B cells, and a failure of regulatory mechanisms. This article reviews the current evidence for the pathogenic mechanisms culminating in autoantibody production, the effects of ANCA-neutrophil and neutrophil-endothelial interactions, and the mechanisms of tissue damage.

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.

Chimeric IgG4 PR3-ANCA induces selective inflammatory responses from neutrophils through engagement of Fcgamma receptors

Anti-proteinase 3 antibodies are implicated in the pathogenesis of small vessel vasculitis. These are primarily immunoglobulin G (IgG), with different subclasses predominating at different stages of disease. However, little is known of their respective roles in pathogenesis. We have previously shown that patient IgG4 was able to induce superoxide release from human neutrophils. To circumvent difficulties in separating the subclasses and additional differences in polyclonal patient antibodies we have generated monoclonal mouse/human IgG1 and IgG4 anti-proteinase 3 antibodies. Using these antibodies we have compared effects of IgG1 and IgG4 on human neutrophils in terms of superoxide release, cytokine production, degranulation and adhesion. Additionally we have investigated the interaction of the subclasses with Fc receptors expressed by the neutrophil. Chimeric antibodies were generated using human constant regions of each subclass and a variable region taken from a monoclonal antibody directed against proteinase 3. Superoxide release from neutrophils was measured by the reduction of ferricytochrome C, degranulation by the conversion of a synthetic colour substrate, cytokine release by interleukin-8 enzyme-linked immunosorbent assay, and adhesion by a flow-based adhesion assay. Fc receptor binding was assessed using blocking antibodies. The IgG4 anti-proteinase 3 was able to induce a dose-dependent release of superoxide, degranulation and adhesion. The antibody was not able to stimulate the secretion of interleukin-8. Fc receptors were essential for neutrophil stimulation and the constitutive Fc receptors were necessary for different stimulatory pathways. The IgG4 anti-proteinase 3 antibodies are able to stimulate neutrophils to undergo a pro-inflammatory response and may play a role in the pathogenesis of small vessel vasculitis.

Phosphoinositol 3-kinase-gamma mediates antineutrophil cytoplasmic autoantibody-induced glomerulonephritis

Antineutrophil cytoplasmic autoantibodies (ANCA) are associated with necrotizing crescentic glomerulonephritis (NCGN) and systemic vasculitis. We examined the role of phosphoinositol 3 kinase-gamma isoform (PI3Kgamma) in ANCA-activated neutrophil functions. Further, we tested whether its inhibition protects a mouse model of ANCA NCGN from developing NCGN. We transplanted bone marrow from wild-type mice or PI3Kgamma-deficient mice into myeloperoxidase-deficient mice immunized with myeloperoxidase. Bone marrow from PI3Kgamma(-/-) mice protected against development of the disease. Similarly, bone marrow transplanted from wild-type mice followed by treatment with the specific PI3Kgamma inhibitor AS605240 also protected these mice against NCGN in this model. AS605240 significantly abrogated myeloperoxidase- or proteinase 3-ANCA-stimulated superoxide production in vitro. Furthermore, ANCA-induced degranulation and GM-CSF-stimulated migration in a transwell assay of isolated human neutrophils were also abrogated by the drug. We found that PI3Kgamma plays a pivotal role in ANCA-induced NCGN and suggest that its specific inhibition may provide a novel treatment target.

Myeloperoxidase: molecular mechanisms of action and their relevance to human health and disease

Myeloperoxidase (MPO) is a heme-containing peroxidase abundantly expressed in neutrophils and to a lesser extent in monocytes. Enzymatically active MPO, together with hydrogen peroxide and chloride, produces the powerful oxidant hypochlorous acid and is a key contributor to the oxygen-dependent microbicidal activity of phagocytes. In addition, excessive generation of MPO-derived oxidants has been linked to tissue damage in many diseases, especially those characterized by acute or chronic inflammation. It has become increasingly clear that MPO exerts effects that are beyond its oxidative properties. These properties of MPO are, in many cases, independent of its catalytic activity and affect various processes involved in cell signaling and cell-cell interactions and are, as such, capable of modulating inflammatory responses. Given these diverse effects, an increased interest has emerged in the role of MPO and its downstream products in a wide range of inflammatory diseases. In this article, our knowledge pertaining to the biologic role of MPO and its downstream effects and mechanisms of action in health and disease is reviewed and discussed.

Spatiotemporal expression of chemokines and chemokine receptors in experimental anti-myeloperoxidase antibody-mediated glomerulonephritis

Myeloperoxidase (MPO)-anti-neutrophil cytoplasmic autoantibody (ANCA)-associated necrotizing crescentic glomerulonephritis (NCGN) is characterized by abundant leucocyte infiltration. Chemokines are chemotactic cytokines involved in receptor-mediated recruitment of leucocytes. Our objective was to analyse spatiotemporal gene expression of chemokines and chemokine receptors in anti-MPO-mediated NCGN, to find potential targets for intervening with leucocyte influx. NCGN was induced in mice by co-administration of anti-MPO immunoglobulin (Ig)G and lipopolysaccharide. mRNA expression levels of chemokines and chemokine receptors were analysed in whole kidney lysates as well as in laser microdissected glomeruli and tubulo-interstitial tissue 1 and 7 day(s) after NCGN induction. Several chemokines and chemokine receptors were induced or up-regulated in anti-MPO-mediated NCGN, both on day 1 (chemokines CCL3, 5; CXCL2, 5, 13; receptor CXCR2) and on day 7 (chemokines CCL2, 5, 7, 8, 17, 20; CXCL1, 2, 5, 10; CX(3)CL1; receptors CCR2, 8; CX(3)CR1). The expression levels of most chemokines and receptors were higher in glomeruli than in the tubulo-interstitium. Because of the temporal induction of CXCR2 on day 1, we hypothesized CXCR2 as a potential target for treatment in anti-MPO-induced NCGN. Inhibition of CXCR2 using a goat-anti-CXCR2 serum prior to NCGN induction increased glomerular neutrophil influx but did not affect crescent formation and albuminuria. In conclusion, expression levels of various chemokines and chemokine receptors were increased in anti-MPO NCGN, and expressed particularly in glomeruli. These chemokines and receptors may serve as potential targets for treatment. Inhibition of a single target, CXCR2, did not attenuate anti-MPO NCGN. Combinatorial interventions may be necessary to avoid redundancy.

ANCA-small vessel vasculitides: what have we (not yet) learned from animal models?

Anti-neutrophil cytoplasmic autoantibodies (ANCA) with a specificity for myeloperoxidase or proteinase 3 are closely associated with small vessel vasculitides (SVV). In vitro, ANCA activate primed neutrophils to release toxic substances that destroy endothelial cells, suggesting a pathogenic role for these autoantibodies in disease development. However, to study the complex interplay between ANCA, neutrophils, and the local environment in vivo, animal models are required. Here, we will review the animal models developed for ANCA-SVV and discuss how these models have been applied to study ANCA-SVV pathogenesis. In addition, some directions for future research pertaining to unresolved issues relevant for the pathogenesis and immunogenesis of ANCA-SVV are proposed.

Antimyeloperoxidase antibodies rapidly induce alpha-4-integrin-dependent glomerular neutrophil adhesion

Patients with antineutrophil cytoplasmic antibodies (ANCAs) frequently develop severe vasculitis and glomerulonephritis. Although ANCAs, particularly antimyeloperoxidase (anti-MPO), have been shown to promote leukocyte adhesion in postcapillary venules, their ability to promote adhesion in the glomerular vasculature is less clear. We used intravital microscopy to examine glomerular leukocyte adhesion induced by anti-MPO. In mice pretreated with LPS, 50 microg anti-MPO induced LFA-1-dependent adhesion in glomeruli. In concert with this finding, in mice pretreated with LPS, more than 80% of circulating neutrophils bound anti-MPO within 5 minutes of intravenous administration. However, even in the absence of LPS, more than 40% of circulating neutrophils bound anti-MPO in vivo, a response not seen in MPO(-/-) mice. In addition, a higher dose of anti-MPO (200 microg) induced robust glomerular leukocyte adhesion in the absence of LPS. The latter response was beta2-integrin independent, instead requiring the alpha4-integrin, which was up-regulated on neutrophils in response to anti-MPO. These data indicate that anti-MPO antibodies bind to circulating neutrophils, and can induce glomerular leukocyte adhesion via multiple pathways. Lower doses induce adhesion only after an infection-related stimulus, whereas higher doses are capable of inducing responses in the absence of an additional inflammatory stimulus, via alternative adhesion mechanisms.

Review article: Leukocyte-endothelial dysregulation in systemic small vessel vasculitis

Aberrant interaction between the leukocyte and the endothelial cell (EC) results in the uncontrolled inflammation seen in systemic small vessel vasculitis. This review discusses our current understanding of this process and includes consideration of the role of adhesion molecules, proteases and the neutrophil respiratory burst. The effects of anti-neutrophil cytoplasm antibodies and anti-endothelial cell antibodies and their pathogenic roles are examined, and we look at experimental disease models. Specificity of disease-targetted endothelial beds and the role of circulating EC are discussed.

Mechanisms of ANCA-mediated leukocyte-endothelial cell interactions in vivo

Anti-myeloperoxidase (anti-MPO) antibodies have been implicated in the pathogenesis of small-vessel vasculitis, but the molecular mechanisms by which these antibodies contribute to disease are unknown. For determination of how anti-MPO antibodies affect inflammatory cell recruitment in small-vessel vasculitis, intravital microscopy was used to monitor leukocyte behavior in the accessible cremasteric microvessels under various experimental conditions. After local pretreatment of the cremaster muscle with cytokines (TNF-alpha, IL-1beta, or keratinocyte-derived chemokine), administration of anti-MPO IgG to wild-type mice reduced leukocyte rolling in favor of augmented adhesion to and transmigration across the endothelium. This led to a decrease in the number of systemic circulating leukocytes and, similar to the early events in the development of vasculitic lesions, an increase in leukocyte recruitment to renal and pulmonary tissue. TNF-alpha led to the greatest recruitment of inflammatory cells, and IL-1beta led to the least. When anti-CD18 was co-administered, anti-MPO IgG did not affect leukocyte rolling, adhesion, or transmigration; similarly, anti-MPO IgG did not produce these effects in Fc receptor gamma chain-/- mice. This study provides direct in vivo evidence of enhanced leukocyte-endothelial cell interactions in the presence of anti-MPO IgG and highlights the critical roles of Fcgamma receptors and beta2 integrins in mediating these interactions. In addition, it suggests that neutrophils primed by cytokines in the presence of anti-MPO IgG can have systemic effects and target specific vascular beds.