Pulmonary pathology in vasculitis.

Pulmonary involvement is frequent in vasculitis, particularly in ANCA-associated small vessel vasculitis. Laboratory and radiological data alone are often sufficient to confirm the clinical hypothesis, but sometimes the pathologist plays a crucial role in the differential diagnosis and the patient's management. In this review, the pathologic features of pulmonary vasculitis and the pathologist's role in this field are illustrated.

Pathogenesis of Pulmonary Manifestations in ANCA-Associated Vasculitis and Goodpasture Syndrome.

Pulmonary manifestations of vasculitis are associated with significant morbidity and mortality in affected individuals. They result from a complex interplay between immune dysregulation, which leads to vascular inflammation and tissue damage. This review explored the underlying pathogenesis of pulmonary involvement in vasculitis, encompassing various forms such as granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), eosinophilic granulomatosis with polyangiitis (EGPA), and anti-GBM disease. Mechanisms involving ANCA and anti-GBM autoantibodies, neutrophil activation, and neutrophil extracellular trap (NETs) formation are discussed, along with the role of the complement system in inducing pulmonary injury. Furthermore, the impact of genetic predisposition and environmental factors on disease susceptibility and severity was considered, and the current treatment options were presented. Understanding the mechanisms involved in the pathogenesis of pulmonary vasculitis is crucial for developing targeted therapies and improving clinical outcomes in affected individuals.

Proteinase 3-specific antineutrophil cytoplasmic antibody-associated vasculitis.

Proteinase 3 (PR3)-specific antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis is one of two major ANCA-associated vasculitis variants and is pathogenically linked to granulomatosis with polyangiitis (GPA). GPA is characterised by necrotising granulomatous inflammation that preferentially affects the respiratory tract. The small vessel vasculitis features of GPA are shared with microscopic polyangiitis. Necrotising granulomatous inflammation of GPA can lead to PR3-ANCA and small vessel vasculitis via activation of neutrophils and monocytes. B cells are central to the pathogenesis of PR3-ANCA-associated vasculitis. They are targeted successfully by remission induction and maintenance therapy with rituximab. Relapses of PR3-ANCA-associated vasculitis and toxicities associated with current standard therapy contribute substantially to remaining mortality and damage-associated morbidity. More effective and less toxic treatments are sought to address this unmet need. Advances with cellular and novel antigen-specific immunotherapies hold promise for application in autoimmune disease, including PR3-ANCA-associated vasculitis. This Series paper describes the inter-related histopathological and clinical features, pathophysiology, as well as current and future targeted treatments for PR3-ANCA-associated vasculitis.

Transcription factor Nrf2 activation regulates NETosis, endothelial injury, and kidney disease in myeloperoxidase-positive antineutrophil cytoplasmic antibody-associated vasculitis.

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease pathologically characterized by vascular necrosis with inflammation. During AAV development, activated neutrophils produce reactive oxygen species (ROS), leading to the aberrant formation of neutrophil extracellular traps (NETs) via NETosis and subsequent fibrinoid vascular necrosis. Nuclear factor-erythroid 2-related factor 2 (Nrf2) functions as an intracellular defense system to counteract oxidative stress by providing antioxidant properties. Herein, we explored the role of Nrf2 in the pathogenesis of AAV. The role and mechanism of Nrf2 in ANCA-stimulated neutrophils and subsequent endothelial injury were evaluated in vitro using Nrf2 genetic deletion and Nrf2 activator treatment. In corresponding in vivo studies, the role of Nrf2 in ANCA-transfer AAV and spontaneous AAV murine models was examined. Pharmacological activation of Nrf2 in vitro suppressed ANCA-induced NET formation via the inhibition of ROS. In contrast, NET formation was enhanced in Nrf2-deficient neutrophils. Furthermore, Nrf2 activation protected endothelial cells from ANC-induced NETs-mediated injury. In vivo, Nrf2 activation ameliorated glomerulonephritis in two AAV models by upregulating antioxidants and inhibiting ROS-mediated NETs. Furthermore, Nrf2 activation restrained the expansion of splenic immune cells, including T lymphocytes and limited the infiltration of Th17 cells into the kidney. In contrast, Nrf2 genetic deficiency exacerbated vasculitis in a spontaneous AAV model. Thus, the pathophysiological process in AAV may be downregulated by Nrf2 activation, potentially leading to a new therapeutic strategy by regulating NETosis.

Protective effect of astaxanthin on ANCA-associated vasculitis.

OBJECTIVE: Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease characterized by inflammation and fibrinoid necrosis of medium and small vessels, and its pathogenesis is closely related to inflammation and oxidative stress. Astaxanthin (ATX) is a carotenoid with anti-inflammatory, antioxidant, and immunomodulatory effects. We hypothesized that ATX could play a role in AAV treatment. This study aimed to investigate whether ATX has a protective effect against AAV and to elucidate its regulatory mechanism. METHODS: In vitro experiments, neutrophils isolated from healthy people were treated with ATX or not and cultured with serum from myeloperoxidase (MPO) -ANCA-positive patients and healthy persons. The levels of IL-6 and TNF-α in neutrophil culture supernatant before and after stimulation were measured. Neutrophil extracellular traps (NETs) and intracellular reactive oxygen species (ROS) in neutrophils were detected after stimulation. In vivo study, experimental autoimmune vasculitis (EAV) rat models were established and then treated with ATX via intragastric administration for 6 consecutive weeks. Urinary erythrocytes, urinary proteins, and serum creatinine were detected and HE staining was performed to assess renal injury in rats. Lung hemorrhage was observed by gross dissection and microscopic Prussian blue staining. The level of serum MPO-ANCA was detected. Serum IL-6, TNF-α, superoxide dismutase (SOD), and glutathione peroxidase (GSH-px) in rats were measured to explore the effects of ATX on oxidative stress and inflammation in EAV rats. The deposition of MPO in kidney and lung of rats was detected by immunohistochemistry. RESULTS: ATX significantly inhibited neutrophil secretion of inflammatory factors IL-6 and TNF-α. ATX reduced the elevated levels of ROS in neutrophils stimulated by serum from AAV patients and alleviated the release of NETs. ATX administration was observed to reduce the degree of hematuria, proteinuria, and glomerular crescent formation in EAV rats. The degree of pulmonary hemorrhage was significantly reduced. Besides, the serum levels of IL-6 and TNF-α were attenuated, and antioxidant SOD and GSH-px increased in serum. Pathological results showed that MPO deposition was decreased in lung and kidney tissues after ATX treatment. CONCLUSION: ATX could ameliorate the organ damages in EAV rats. It could serve as a hopeful therapy for AAV by its anti-inflammatory and anti-oxidative feature as a unique nature carotenoid.

Keratin Expression in Podocytopathies, ANCA-Associated Vasculitis and IgA Nephropathy.

Keratins are the main components of the cell cytoskeleton of epithelial cells. Epithelial cells under stressful stimuli react by modifying their keratin expression pattern. Glomerular diseases are pathological conditions that may lead to loss of kidney function if not timely diagnosed and treated properly. This study aims to examine glomerular and tubular keratin expression in podocytopathies, ANCA-associated vasculitis, and IgA nephropathy and how this expression correlates to clinical outcomes. We included 45 patients with podocytopathies (minimal change disease and focal segmental glomerulosclerosis), ANCA-associated vasculitis, and IgA nephropathy, with or without crescentic lesions, and healthy controls. All tissues were assessed by photon microscopy and immunohistochemistry. Biopsy sections were examined for keratins 7, 8, 18, and 19 expression in the glomerular and tubulointerstitial areas separately. Moreover, we examined how keratin expression was correlated with long-term kidney function outcomes. All four studied keratins had significantly increased glomerular expression in patients with ANCA vasculitis compared to controls and MCD patients. Tubular expression of keratins 7, 8, and 19 was related to kidney outcome in all groups. Patients with crescents had higher expression of all keratins in both glomeruli and tubulointerstitium. The presence of tubular atrophy, interstitial fibrosis, mesangial hyperplasia, and interstitial inflammation did not affect keratin expression. Keratins, an abundant component of renal epithelial cells, have the potential to be featured as a biomarker for kidney function prognosis in patients with glomerular diseases.

Renal pathology in adult and paediatric population of Japan: review of the Japan renal biopsy registry database from 2007 to 2017.

BACKGROUND: The Japan Renal Biopsy Registry (J-RBR), a nationwide, web-based, registry system, started in 2007. This study aimed to summarise the epidemiology of biopsy-diagnosed kidney disease in Japan over 10 years. METHODS: We analysed the J-RBR database, from 2007 to 2017. Patients' clinical data collected at the time of biopsy and histopathological diagnoses were used for epidemiological and clinicopathologic analyses. RESULTS: The predominant renal biopsy diagnoses were immunoglobulin A nephropathy (39.2%), lupus nephritis (6.5%) and minimal change disease (6.0%) in younger adults (19-64 years), and membranous nephropathy (17.4%), antineutrophil cytoplasmic antibody-associated vasculitis or anti-glomerular basement membrane glomerulonephritis (13.0%), and immunoglobulin A nephropathy (12.5%) in older adults (≥ 65 years). The percentages of patients diagnosed with membranoproliferative glomerulonephritis and immunoglobulin A nephropathy decreased, whereas those with immunoglobulin A vasculitis and diabetic nephropathy increased over the decade. In paediatric patients (< 19 years), immunoglobulin A nephropathy (36.1%), minimal change disease (17.6%), and immunoglobulin A vasculitis (8.6%) were the predominant diagnoses. The percentage of patients diagnosed with immunoglobulin A vasculitis increased over the decade. Based on the sex distribution, minimal change disease and membranous nephropathy were predominant in men aged < 20 and > 40 years, respectively, whereas immunoglobulin A vasculitis and antineutrophil cytoplasmic antibody-associated vasculitis or anti-glomerular basement membrane glomerulonephritis were predominant in women in their 20s and 30s and aged < 50 years, respectively. Immunoglobulin A nephropathy was predominant in men at most ages and in women in their 20s to 40s. CONCLUSIONS: This study describes the distribution and changes in kidney biopsy diagnoses over 10 years in Japan and paves the way for future research on kidney diseases in adults and children.

The intricate relationship between autoimmunity disease and neutrophils death patterns: a love-hate story.

Autoimmune diseases are pathological conditions that result from the misidentification of self-antigens in immune system, leading to host tissue damage and destruction. These diseases can affect different organs and systems, including the blood, joints, skin, and muscles. Despite the significant progress made in comprehending the underlying pathogenesis, the complete mechanism of autoimmune disease is still not entirely understood. In autoimmune diseases, the innate immunocytes are not functioning properly: they are either abnormally activated or physically disabled. As a vital member of innate immunocyte, neutrophils and their modes of death are influenced by the microenvironment of different autoimmune diseases due to their short lifespan and diverse death modes. Related to neutrophil death pathways, apoptosis is the most frequent cell death form of neutrophil non-lytic morphology, delayed or aberrant apoptosis may contribute to the development anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV). In addition, NETosis, necroptosis and pyroptosis which are parts of lytic morphology exacerbate disease progression through various mechanisms in autoimmune diseases. This review aims to summarize recent advancements in understanding neutrophil death modes in various autoimmune diseases and provide insights into the development of novel therapeutic approaches for autoimmune diseases.

[Pharmacological and clinical profiles of avacopan (TAVNEOS® capsule), a selective C5a receptor antagonist].

Avacopan (TAVNEOS® capsules) is an orally available selective C5a receptor (C5aR) antagonist. It has been approved in Japan since 2021 for the treatment of microscopic polyangiitis (MPA) and granulomatosis with polyangiitis (GPA), the two major subtypes of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). The current standard therapy combining glucocorticoids (GC) and immunosuppressants has greatly improved the prognosis of AAV, however, issues such as side effects associated with GC use remain to be resolved. Avacopan suppresses priming of neutrophils induced by the complement component C5a, a process deeply involved in the pathogenesis of AAV. In pre-clinical studies, avacopan inhibited chemotaxis and priming of neutrophils induced by C5a-C5aR signaling. It also significantly suppressed nephritis and renal damage in an ANCA-induced glomerulonephritis mouse model. In the global phase 3 study "ADVOCATE", avacopan achieved both primary endpoints being 1) non-inferior to prednisone in inducing remission at week 26 and 2) superior in sustained remission at week 52 for MPA and GPA patients. Additionally, with avacopan, GC toxicity score was significantly lower and fewer adverse events possibly related to GC were observed. Furthermore, avacopan increased estimated glomerular filtration rate (eGFR) more than prednisone indicating improved renal function. Thus, the novel mechanism of avacopan targeting the complement system is a promising new therapeutic option for AAV with fewer GC-related side effects and better improvement of renal function.

Occurrence and localization of FOXP3 + cells in kidney biopsies in lupus nephritis and ANCA-associated vasculitis.

The study aims to increase the understanding regarding the role of regulatory T cells (Tregs) in lupus nephritis (LN) and ANCA-associated vasculitis (AAV) by comparing their localization in renal tissue and changes following immunosuppressive therapy. Kidney biopsies from 12 patients with LN and 7 patients with AAV were examined. Kidney biopsies had been performed both at active disease and following immunosuppressive treatment. Clinical data was collected at both biopsy occasions. Expression of Forkhead Box P 3 (Foxp3) in renal tissue was assessed by immunohistochemistry. An arbitrary scale was used to estimate the number of Foxp3+ cells. In LN, 8/12 (67%) had positive tissue staining for Foxp3 at baseline, most pronounced in inflammatory infiltrates, but also interstitially and in a peri-glomerular pattern. At second biopsies, after immunosuppressive treatment, 4/12 (33%) still had detectable Foxp3+ cells, found in persisting inflammatory infiltrates and some in the interstitium. Patients with a good clinical response to treatment had high grade of Foxp3+ cells in first biopsies. In AAV, only 2/7 (29%) had positive staining for Foxp3 at baseline, in inflammatory infiltrates and to a lesser extent in the interstitium, despite large areas of inflammatory infiltrates in all patients. At follow-up, 2/7 (29%) biopsies were positive for Foxp3. Our data show a higher presence of Foxp3+ cells in renal tissue from LN patients compared to AAV, suggesting that Tregs may be differently involved in the control of inflammatory mechanisms in these diseases. These findings could have further implication for therapeutic approaches aiming at restoring the immunological tolerance. Key Points • Foxp3+-cells are present in larger amount in renal tissue in lupus nephritis vs. ANCA-associated vasculitis. • Our data suggest that Foxp3+ regulatory T cells are involved in the control of inflammatory processes in lupus nephritis.

Image findings of anti-neutrophil cytoplasmic antibody-associated vasculitis involving the skull base.

AIM: To investigate computed tomography (CT) and magnetic resonance imaging (MRI) features of skull bases involving anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV). MATERIALS AND METHODS: A retrospective review was undertaken to identify an institutional historical cohort of 17 patients with confirmed AAV who underwent CT or MRI and had skull base involvement between 2002 and 2021. Two radiologists reviewed the extent and features of the lesions, bone changes, and other MRI findings. RESULTS: A total of 17 patients (12 men; mean age ± standard deviation, 46.5 ± 17.1 years) were selected. AAV presented as infiltrative lesions with involvement at various sites. Most cases involved the paranasal sinuses (PNS; 88%, 15/17), nasopharynx (88%, 15/17), pterygopalatine fossa (82%, 14/17), and parapharyngeal space (82%, 14/17), frequently accompanied by mucosal irregularity of the PNS and nasopharynx (71%, 12/17). Central skull base and temporal bone involvement were seen in 53% (9/17) and 38% (6/16) of cases, respectively. On T1-weighted imaging (WI) and T2WI MRI, all lesions (15/15) showed predominant signal iso-intensity to grey matter. CONCLUSIONS: Although radiological findings of AAV are non-specific and skull base involvement is less common, AAV may be considered if infiltrative lesions predominantly involving the PNS, nasopharynx, pterygopalatine fossa, and parapharyngeal space with combined bone changes of skull base are seen.

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.

Biomarkers of fibrosis, kidney tissue injury and inflammation may predict severity and outcome of renal ANCA - associated vasculitis.

Background: Activity and chronicity of kidney involvement in ANCA-associated vasculitis (AAV) can be currently reliably evaluated only by kidney biopsy. In this study, we measured a panel of serum and urinary biomarkers collected at the time of kidney biopsy and hypothesized that they could reflect specific histopathological parameters in the biopsy and help to predict prognosis. Methods: We examined a cohort of 45 patients with AAV and 10 healthy controls. Biomarker levels (DKK-3, CD163, EGF, PRO-C6 and C3M) were measured in this study by ELISA. Biopsies were scored with a scoring system for AAV (focal x crescentic x sclerotic x mixed class) and interstitial fibrosis was quantified. Results: Levels of urinary DKK-3, CD163, EGF, PRO-C6 and C3M significantly differed among biopsy classes in AAV, with urinary DKK-3 and PRO-C6 levels being highest in the sclerotic class and lowest in the focal class, urinary CD163 levels highest in the crescentic class and urinary C3M levels highest in the focal class. Moreover, the urinary biomarkers were able to discriminate focal biopsy class from the other classes. Urinary DKK-3, EGF, PRO-C6 and C3M levels measured at the time of biopsy were also significantly related to the extent of fibrosis and to the final kidney function at the end of follow-up. Conclusions: This small pilot study suggests that selected urinary biomarkers of fibrosis and inflammation may reflect changes in the kidney biopsy and be prognostic of kidney outcome in patients with AAV.

Interstitial Lung Disease and Anti-Neutrophil Cytoplasmic Antibody-Associated Vasculitis: A Review.

Interstitial lung disease is a common complication of anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV). It is seen most commonly in microscopic polyangiitis owing to the pathogenic effect of myeloperoxidase in the lung. Oxidative stress, neutrophil elastase release, and expression of inflammatory proteins by neutrophil extracellular traps result in fibroblast proliferation and differentiation and therefore fibrosis. Usually, interstitial pneumonia pattern fibrosis is common and associated with poor survival. Treatment for patients with AAV and interstitial lung disease lacks evidence, and those with vasculitis are treated with immunosuppression, whereas those with progressive fibrosis may well benefit from antifibrotic therapy.

The role of anti-eosinophilic therapies in eosinophilic granulomatosis with polyangiitis: a systematic review.

Eosinophilic granulomatosis with polyangiitis (EGPA) is an antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, mostly affecting small-sized arteries and usually occurring in patients with an allergic background. Eosinophils seem to play a significant role in the pathogenesis of the disease and, therefore, biologics targeting interleukin 5 (IL5), a cytokine tightly linked to eosinophils, have emerged as a promising therapeutic tool. A systematic review of Medline was conducted from 2007 to 2022 to search for data regarding the use of anti-IL5 therapies in patients with EGPA. Ongoing or unpublished trials were also searched in ClinicalTrials.gov and the World Health Organization trials portal. The efficacy and safety of mepolizumab, an anti-IL5 monoclonal antibody (mAb), was confirmed by a randomized controlled trial (RCT), although a significant proportion of patients did not respond to this treatment. Other studies showed that both doses of 100 mg and 300 mg of mepolizumab are almost equally effective in EGPA. Benralizumab, an anti-IL5 receptor mAb has preliminary promising results and an RCT is planned to be conducted. Apart from their clinical efficacy in EGPA, anti-IL5 therapies may have steroid-sparing properties. Anti-IL5 therapies seem to be effective and safe in patients with refractory/relapsing EGPA and can be used as a steroid-sparing treatment. Nevertheless, more research is needed to clarify the pathophysiology of the disease; this may potentially lead to the identification of biomarkers to pinpoint patients most likely to respond to anti-IL5-blockade.

A modified renal risk score for Chinese patients with antineutrophil cytoplasmic antibody-associated vasculitis.

BACKGROUND: The renal risk score (RRS) is a useful tool to predict end-stage renal disease (ESRD) in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). The current study aimed to validate the predictive performance of RRS and to further modify this model in Chinese AAV patients. METHODS: Two hundred and seventy-two patients diagnosed with AAV confirmed by renal biopsies were retrospectively enrolled from a single center. The RRS was calculated based on 3 categorical variables, i.e., the proportion of normal glomeruli, the proportion of interstitial fibrosis and tubular atrophy (IF/TA), and eGFR at biopsy, classifying these patients into low-, medium-, and high-risk groups. In addition, a modified model was developed based on the RRS and was further validated in another independent cohort of 117 AAV patients. The predictive performance of each model was evaluated according to discrimination and calibration. RESULTS: Patients were classified by the RRS into low- (26.5%), medium- (46.7%), and high-risk (26.8%) groups, with 120-month renal survival rates of 93.3%, 57.2%, and 18.4%, respectively (P < 0.001). The RRS showed good discrimination but less satisfactory calibration. Therefore, a modified model with improved discrimination and calibration was developed in Chinese AAV patients, with eGFR, proportion of normal glomeruli (both as continuous variables), and IF/TA (< 25%, 25-50%, > 50%) included. Internal and external validation of the modified model were performed. Finally, an online risk prediction tool was developed based on the modified model. CONCLUSIONS: The RRS was an independent predictor of ESRD of AAV patients. The modified model could predict the probability of ESRD for AAV patients with improved performance in Chinese AAV patients.

Association between Loss of Immune Checkpoint Programmed Cell Death Protein 1 and Active ANCA-Associated Renal Vasculitis.

Immune checkpoint inhibitors (ICIs) have made an important contribution to the survival of patients with certain cancers. ICIs interrupt co-inhibitory signaling pathways mediated by programmed cell death protein 1 (PD-1), programmed cell death protein ligand 1 (PD-L1) and cytotoxic T lymphocyte-associated antigen (CTLA-4) that result in the elimination of cancer cells by stimulating the immune system. However, immune-related adverse events have also been described and attributed to an enhanced immune system activation. Recent observations have suggested a dysregulation of immune checkpoints in active antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). We here analyzed intrarenal PD-1 and PD-L1 by immunostaining in a total of 15 kidney biopsies with ANCA-associated renal vasculitis in correlation with glomerular and tubulointerstitial lesions. For independent validation, publicly available datasets were analyzed for PD-1 expression (encoded by PDCD1). We here observed a predominant tubulointerstitial expression of PD-1 that is decreased in ANCA-associated renal vasculitis. Moreover, loss of tubulointerstitial PD-1 correlated with active ANCA-associated renal vasculitis. Consistent with the observed association with active glomerular and tubulointerstitial lesions, we identified that interstitial PD-1 correlated with tubular and/or glomerular PD-L1 positivity. Finally, PD-1 was associated with decreased local synthesis of complement factor B. Interestingly, we did not observe a correlation between PD-1 and complement C5 or its C5a receptor. Combined with our observations, this may implicate a link between impaired PD-1/PD-L1 signaling, complement factor B and active ANCA-associated renal vasculitis. These findings could be of relevance because experimental data have already described that PD-1 agonism can be used therapeutically to attenuate autoimmunity in multiple disease models. Furthermore, targeted therapy against a complement C5/C5a receptor and factor B are both available and currently evolving in the treatment of AAV. Therefore, this pilot study expands our current knowledge and describes a potential interplay between immune checkpoints and the alternative complement pathway in active ANCA-associated renal vasculitis.

C-Reactive Protein Levels Are Associated with Complement C4 Deposits and Interstitial Arteritis in ANCA-Associated Renal Vasculitis.

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a potentially life-threatening systemic small-vessel vasculitis that is characterized by pauci-immune glomerulonephritis in case of kidney involvement, representing a major denominator of AAV mortality. Innate immunity with complement system activation is increasingly recognized in the pathogenesis of AAV and as an attractive therapeutic target. Although C-reactive protein (CRP) was thought to be a passive, nonspecific marker of inflammation, recent studies indicate that CRP plays a key role in the innate immune system by recognizing pathogens and altered self-determinants. Elevated baseline CRP at disease onset of AAV has already been described as a determinant of poor long-term outcomes. However, its clinical implications at disease onset of AAV, with respect to vasculitis manifestations and complement system activation that might also affect long-term outcomes, remain elusive. CRP levels were retrospectively analyzed in 53 kidney-biopsy-confirmed cases of ANCA-associated renal vasculitis; a total of 138 disease controls were also evaluated. Univariate and multivariate regression analysis was performed on clinicopathological parameters associated with CRP levels in ANCA-associated renal vasculitis. Results: Compared to disease controls, CRP elevation was common in ANCA-associated renal vasculitis and associated with de novo disease (p = 0.0169), critical illness (p = 0.0346), and severe deterioration of kidney function (p = 0.0167), independent of extrarenal disease manifestations. As confirmed by multiple regression analysis, CRP levels were correlated with active lesions predominated by interstitial arteritis in renal vasculitis, specifically with MPO-ANCA seropositivity (p = 0.0017). Based on analysis of systemic complement system activation and intrarenal complement deposits, CRP elevation was correlated specifically with complement C4 deposits in interstitial arteries in the subgroup with myeloperoxidase (MPO)-ANCA seropositivity (p = 0.039). Finally, this association was independent of systemic complement system activation, as reflected by the consumption of respective complement components. Here, we expand our current understanding of CRP in ANCA-associated renal vasculitis not only as an inflammatory marker, but potentially also as being involved in the pathogenesis of kidney injury by interaction with the complement system.

Selective deficiency of UCP-1 and adropin may lead to different subtypes of anti-neutrophil cytoplasmic antibody-associated vasculitis.

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease that is prone to respiratory and renal failures. Its major target antigens are serine protease 3 (PR3) and myeloperoxidase (MPO), but the determinants of PR3 and MPO subtypes are still unclear. Uncoupling protein-1 (UCP-1) and adropin (Adr) regulate mutually and play an important role in endothelial cell injury. In this study, adropin and UCP-1 knockout (AdrKO and UCP-1-KO) models were established on the basis of C57BL/6 J mice. The results showed that UCP-1-KO and AdrKO mice similar to AAV: significant inflammatory cell infiltration, vascular wall damage, and erythrocyte extravasation. The pathological basis of AdrKO was that endothelial cells adhered and activated neutrophils to release MPO, and the core gene was peroxisome proliferator-activated receptor gamma (PPARG). However, UCP-1-KO induced PR3 release, and the accumulation and expression of tissue factor on the vascular wall, and the core gene was peroxisome proliferator-activated receptor delta (PPARD). The present study verified that the subtypes of AAV may be genetically different diseases and it also provide novel experimental evidence for clinical differentiation of the two subtypes.