Circulating immune profile in granulomatosis with polyangiitis reveals distinct patterns related to disease activity

Granulomatosis with polyangiitis (GPA) is an autoimmune disorder characterized by recurrent relapses that can cause severe tissue damage and life-threatening organ dysfunction. Multiple immune cells and cytokines/chemokines are involved in the different stages of the disease. Immune profiling of patients may be useful for tracking disease activity, however, reliable immune signatures for GPA activity are lacking. In this study, we examined circulating immune profiles in GPA patients during active and remission disease states to identify potential immune patterns associated with disease activity. The distribution and phenotypic characteristics of major circulating immune cells, and the profiles of circulating cytokines/chemokines, were studied on cryopreserved peripheral blood mononuclear cells from GPA patients (active, n = 20; remission, n = 20) and healthy controls (n = 20) leveraging a 40-color optimized multicolor immunofluorescence panel (OMIP-69) and in serum using a 46-plex Luminex multiplex assay, respectively. Deep phenotyping uncovered a distinct composition of major circulating immune cells in active GPA and GPA in remission, with the most significant findings emerging within the monocyte compartment. Our detailed analysis revealed circulating monocyte diversity beyond the conventional monocyte subsets. We identified eight classical monocyte populations, two intermediate monocyte populations, and one non-classical monocyte population. Notably, active GPA had a higher frequency of CD45RA+CCR5+CCR6-CCR7+/lowCD127-HLA-DR+CD2- classical monocytes and a lower frequency of CD45RA-CCR5-/lowCCR6-CCR7-CD127-HLA-DR+CD2+/- classical monocytes, which both strongly correlated with disease activity. Furthermore, serum levels of CXCL1, CXCL2, and CCL20, all linked to monocyte biology, were elevated in active GPA and correlated strongly with disease activity. These findings shed light on the circulating immune profile of GPA and may lead to immune signature profiles for assessing disease activity. Monocytes in particular may be studied further as potential markers for monitoring GPA.

OP0091 EXPANSION OF MYELOPEROXIDASE (MPO)-SPECIFIC IgM B CELLS IN ANTI-NEUTROPHIL CYTOPLASMIC ANTIBODY (ANCA)-ASSOCIATED VASCULITIS

Background

ANCA-associated vasculitides (AAV) are characterized by recurrent, chronic small vessel inflammation and deleterious organ damage. The main targets of ANCA are myeloperoxidase (MPO) and proteinase 3 (PR3). ANCA, B cells and the complement system are crucial to AAV pathogenesis, as evidenced by the clinical benefit of B cell depletion with rituximab and, more recently, the C5a receptor antagonist avacopan. While ANCA in serum have been studied extensively, phenotypic and functional characteristics of the underlying B cell responses remain largely unknown.

Objectives

To develop a flow cytometry-based technique for identifying MPO-specific B cells in the circulation of MPO-positive AAV patients in order to characterize this B cell response and its potential contribution to disease pathogenesis.

Methods

Human neutrophil-derived MPO was conjugated to two different fluorochromes and used to identify MPO-specific B cells by flow cytometry. An antigen-specific staining protocol was developed and validated using MPO- and PR3-specific hybridoma cells. MPO-specific B cells were phenotypically characterized and isolated from the peripheral blood of AAV patients by fluorescence activated cell sorting (FACS) and cultured as single cells. MPO-specificity was confirmed by ELISA on culture supernatants. B cell receptor (BCR) sequences were obtained from MPO-positive clones by full length ARTISAN-PCR and Sanger sequencing. MPO-specific IgG and IgM monoclonal antibodies (mAb) were produced to validate specificity and to examine their ability to activate complement. Finally, MPO-positive AAV patient plasma and plasma depleted of IgG or IgM was tested in in vitro complement assays.

Results

The newly developed, differential antigen labelling approach successfully identified MPO-specific but not PR3-specific hybridoma cells. Subsequently, we detected MPO-specific B cells in the circulation of MPO-positive AAV patients at a frequency of up to 1:1000 B cells. FACS sorting and single cell culture yielded an enrichment of MPO-specificity of ~80%. Notably, the majority of isolated, MPO-specific B cells (60-95%) displayed an IgM memory phenotype, which corresponded to the presence of anti-MPO IgM in plasma. The remainder of the MPO-specific cells were mainly IgG memory B cells and few naive cells. BCR sequencing revealed a polyclonal IgM response with diverse V-gene usage, consisting of both germline and highly mutated clones. Generation of mAb (n=5) confirmed MPO specificity by inhibition ELISA for both germline and somatically mutated clones. Interestingly, anti-MPO IgM mAb showed a high capacity for complement factor deposition upon MPO binding. MPO-specific complement assays with IgG- and IgM-depleted patient plasma showed that anti-MPO IgM activated complement much more efficiently than anti-MPO IgG.

Conclusion

We demonstrate the direct ex-vivo identification, isolation and characterization of MPO-specific B cells in human AAV. Intriguingly, we observed a remarkable expansion of MPO-specific, IgM-expressing memory B cells in patients. This so far unrecognized, active IgM-compartment may be clinically relevant, as both mAb and plasma-derived polyclonal MPO-specific IgM strongly activated complement, a pathway thought to play a central role in AAV. Next to these novel insights into autoreactive B cell biology in AAV, our findings now provide new opportunities for studying auto-reactive B cell responses in different clinical phases of AAV, amongst which active disease, remission and (imminent) flares.

Disclosure of Interests

None declared.

POS0249 FIBROBLAST ACTIVATION PROTEIN AS A LINK BETWEEN INFLAMMATION AND VASCULAR REMODELING IN GIANT CELL ARTERITIS

Background

Giant cell arteritis (GCA) can present with serious complications such as blindness, stroke and aortic aneurysm that are related to both inflammation and remodeling of the vessel wall. GCA frequently overlaps with polymyalgia rheumatica (PMR). The pathogenesis of GCA starts in the adventitia where fibroblasts are the major stromal cell population. A preliminary study [1] reported the migration of adventitial fibroblasts to the intima, contributing to intimal hyperplasia in GCA. Fibroblast activation protein (FAP) is a non-classical serine protease which can be present in both a membrane-bound form and a soluble form and has been demonstrated to promote inflammation and fibrosis in coronary artery disease and rheumatoid arthritis [2-3]. We hypothesize that FAP is involved in GCA vasculopathy due to its pro-inflammatory and pro-fibrotic effects.

Objectives

As a first step to unravel the contribution of FAP to the vasculopathy in GCA, we determined FAP plasma levels and FAP protein expression at the site of vascular inflammation in GCA.

Methods

In our prospective cohort of GCA, PMR and healthy elderly (GPS), we measured the plasma FAP levels with ELISA in new-onset, treatment-naïve GCA (N=62), and PMR (N=63) patients and 42 age-matched healthy controls (HC). In addition, we measured the plasma FAP levels at follow-up (3-months, 1-year, 1.5-year and treatment-free remission (TFR)). Temporal artery biopsies (TAB) from treatment-naïve GCA patients (n=9) and non-GCA patients (n=9), aorta samples from GCA-related aneurysm (n=9) and atherosclerosis (n=11) were stained for FAP using immunohistochemistry. Immunofluorescence staining for CD90, CD68, αSMA and FAP was performed to detect FAP expression in fibroblasts, macrophages and vascular smooth muscle cells (VSMC), respectively.

Results

Baseline plasma FAP levels were significantly lower in GCA patients (52.72±2.93 ng/ml) than in PMR patients (66.42±2.86 ng/ml) and HC (80.47±3.38 ng/ml). FAP levels at baseline correlated inversely with C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), interleukin (IL)-6, macrophage-associated protein YKL-40 (Chitinase 3-like 1/CHI3L1) levels and monocyte counts. Plasma FAP levels in GCA patients decreased even further at 3 months (37.23±2.10 ng/ml) upon glucocorticoid-induced remission, and gradually increased to the level of HC (76.84±5.43 ng/ml) when patients were in TFR. Increased FAP expression in GCA TAB (adventitia, media, intima) and aorta (media) compared with tissues from non-GCA was documented. FAP was abundantly expressed in fibroblast- and macrophage-rich areas but not in VSMC-rich areas in TAB and aorta of GCA patients.

Conclusion

FAP expression is clearly modulated both in plasma and at the site of vascular inflammation in GCA and may represent a pathogenic link between the inflammatory and remodeling processes in GCA. As such, FAP may have utility as a biomarker and should be further investigated as target for therapeutic intervention.

References

[1]Parreau Simon VN, Regent Alexis, et al. (2019). Adventitial fibroblast, an important player in giant cell arteritis. Annual European Congress of Rheumatology, EULAR 2019: Annals of the Rheumatic Diseases), pp. 434.2-5.

[2]Brokopp CE, Schoenauer R, Richards P, et al. Fibroblast activation protein is induced by inflammation and degrades type I collagen in thin-cap fibroatheromata. Eur Heart J. 2011; 32: 2713-22.

[3]Croft AP, Campos J, Jansen K, et al. Distinct fibroblast subsets drive inflammation and damage in arthritis. Nature. 2019; 570: 246-51.

Acknowledgements

No.

Disclosure of Interests

None declared

OP0015 PROINFLAMMATORY MONOCYTES AND MACROPHAGES IN SYNOVIAL FLUID AND BURSAL TISSUE OF PATIENTS WITH POLYMYALGIA RHEUMATICA: POTENT PRODUCERS OF IL-6 AND GM-CSF

Background

Polymyalgia rheumatica (PMR) is a common, rheumatic inflammatory disease. Inflammation of bursae and tendon sheaths is a characteristic finding in patients with PMR. Glucocorticoid treatment remains the mainstay treatment for PMR. A study published in 1996 reported that macrophages dominate the inflammatory infiltrates in the glenohumeral synovium of PMR patients1, suggesting the importance of these cells in the immunopathology of PMR. However, the functional and phenotypical heterogeneity of the tissue-infiltrating macrophages in PMR remains obscure. Although treatment with anti-IL-6 receptor (tocilizumab) has shown promising results2, it is unclear whether macrophages contribute to IL-6 production in PMR. Additionally, anti-GM-CSF receptor therapy (mavrilimumab), recently shown to be efficacious in the closely related disease giant cell arteritis3, may also be useful for the treatment of PMR. Knowledge on the functional heterogeneity of monocytes/macrophages in PMR may aid in identifying novel therapeutic targets for this condition.

Objectives

To determine the phenotype of monocyte/macrophages in peripheral blood, bursal/tenosynovial fluid and bursal tissue of patients with PMR.

Methods

Paired peripheral blood (PB), bursal/tenosynovial fluid (SF) and bursal tissue biopsy samples from 11 PMR patients were included in our study. Bursal and tenosynovial samples were obtained from the shoulder. Distribution of the monocyte subsets (classical, intermediate and non-classical monocytes) was determined based on the level of CD14 and CD16 expression by flow cytometry. To study monocyte activation status, markers of ‘M1’ like (CD80 and CD64) and ‘M2’ like (CD206 and FRβ) macrophage polarization were included in the flow cytometry analysis. Immunohistochemistry of bursal tissue biopsies was focused on macrophage markers (CD68, CD86, CD64, CD206 and FRβ) andproinflammatory cytokines (IL-6 and GM-CSF), which were scored semi-quantitatively. Double immunofluorescence stainings were performed to determine the expression of IL-6 and GM-CSF by tissue-infiltrating macrophages in bursal tissue.

Results

Monocytes were detected in the SF of PMR patients. The proportion of classical monocytes was significantly lowered (p=0.001) in SF versus PB, while the proportion of intermediate monocytes was significantly elevated (p=0.001). The expression of CD206 was significantly elevated (p=0.001) but not FRβ in SF monocytes, suggesting GM-CSF skewed phenotype. In bursal tissue, macrophages displayed mixed ‘M1’/’M2’ traits with high expression of all macrophage polarization markers. Proinflammatory cytokines IL-6 and GM-CSF were highly expressed throughout the bursal tissue biopsies. Double immunofluorescence staining confirmed the expression of IL-6 and GM-CSF by the infiltrating macrophages.

Conclusion

SF monocytes and bursal tissue macrophages show a pro-inflammatory phenotype in PMR. Moreover, tissue-infiltrating macrophages show a prominent IL-6 and GM-CSF response in PMR. Our data add to the rationale of targeting IL-6 and GM-CSF as treatment options in PMR.

References

[1]Meliconi R, Pulsatelli L, Uguccioni M, et al. Leukocyte infiltration in synovial tissue from the shoulder of patients with polymyalgia rheumatica. Quantitative analysis and influence of corticosteroid treatment. Arthritis Rheum. 1996;39(7):1199-1207.

[2]Devauchelle-Pensec V, Berthelot JM, Cornec D, et al. Efficacy of first-line tocilizumab therapy in early polymyalgia rheumatica: a prospective longitudinal study. Ann Rheum Dis. 2016;75(8):1506-1510.

[3]Cid MC, Unizoni S, Pupim L, et al. Mavrilimumab (anti GM-CSF Receptor α Monoclonal Antibody) Reduces Time to Flare and Increases Sustained Remission in a Phase 2 Trial of Patients with Giant Cell Arteritis [Abstract]. Arthritis Rheumatol. 2020; 72 (suppl 10).

Acknowledgements

This work was supported by a research grant from FOREUM Foundation for Research in Rheumatology. The PMR Research On disease Mechanisms In Synovium (PROMIS) study was also funded by the Rheumatology Grant (Dutch Society for Rheumatology) and Mandema Stipend (University Medical Center Groningen).

Disclosure of Interests

William Febry Jiemy: None declared, Rosanne Reitsema: None declared, Anqi Zhang: None declared, Maria Sandovici: None declared, Annemieke Boots: None declared, Peter Heeringa: None declared, Elisabeth Brouwer Speakers bureau: E. Brouwer reports speaker and consulting fees from Roche in 2017-2018, outside the submitted work, Consultant of: E. Brouwer reports speaker and consulting fees from Roche in 2017-2018, outside the submitted work, Kornelis van der Geest Consultant of: K. van der Geest reports personal fees from Roche, outside the submitted work.

The Nasal Microbiome in ANCA-Associated Vasculitis: Picking the Nose for Clues on Disease Pathogenesis

PURPOSE OF REVIEW

The onset and progression of small vessel vasculitis associated with anti-neutrophil cytoplasmic antibodies has been linked to microbial infections. Here, we provide a brief overview of the association of nasal colonization of Staphylococcus aureus with ANCA-associated vasculitis (AAV) and discuss several recent studies mapping the nasal microbiome in AAV patients in particular.

RECENT FINDINGS

Nasal microbiome studies revealed dysbiosis as a common trait in active AAV which tends to normalize upon immunosuppressive treatment and quiescent disease. However, due to differences in study design, patient selection, and methodology, the reported microbiome profiles differ considerably precluding conclusions on causal relationships. The microbiome is an emerging area of research in AAV warranting further investigation. Ideally, such studies should be combined with mechanistic studies to unravel key elements related to host-microbe interactions and their relevance for AAV pathogenesis.

OP0066 METABOLIC PROFILE AND COMORBIDITIES IN GIANT CELL ARTERITIS AND POLYMYALGIA RHEUMATICA PATIENTS BEFORE AND AFTER TREATMENT

Background:

Giant cell arteritis (GCA) is a granulomatous vasculitis that affects the large vessels, occurring in people over 50 years of age. GCA frequently overlaps with polymyalgia rheumatica (PMR), which affects the proximal joints in the shoulders and hips. Both GCA and PMR patients require long-term treatment with glucocorticoids (GCs). Investigation of new treatment options is required because many GCA and PMR patients experience GC-related adverse events. These include hypercholesterolemia, hypertension, diabetes mellitus, cataract, and infections.(1) Previous studies suggest that unhealthy metabolic features and a higher Body Mass Index (BMI) might be protective in the development of GCA (2). However, data are limited.

Objectives:

We aimed to elaborate more-in depth on the metabolic features, BMI and prevalence of comorbidities of GCA and PMR patients at the time of diagnosis and during treatment, to characterize patients for improved treatment options.

Methods:

This study included two independent cohorts: the GPS (Groningen) cohort, and the Aarhus cohort for validation of baseline data (Table 1). Patients in the GPS cohort were prospectively followed with visits at 3 months, 1, 2, and 5 years. Laboratory measurements, metabolic co-morbidities were assessed at every visit. At baseline, we assessed whether comorbidities and BMI predicted the duration of GC treatment.

Table 1.

Baseline characteristics. P-values were calculated with Mann-Whitney U test and Fischer Exact test. Numbers in bold: significance between HC and GCA/PMR patients from GPS cohort. *: significance between GCA and PMR of GPS cohort. a: significance between two cohorts.

GCAGPS cohort (n=50)PMRGPS cohort (n=44)HCsGPS cohort (n=65)GCA Aarhus cohort(n=52)PMR Aarhus cohort(n=25)Age, median7173706768Female, %3526433213Follow-up duration in months, median4240NANANABMI, median24.326.625.42426.4Systolic BP (mmHg), median140140145135143Diastolic BP (mmHg), median79.5*808076.583HbA1c (mmol/mol), median4340394340CRP (mg/L), median544247653ESR (mm/h), median94*5797751Diabetes mellitus, %122312158Hypercholesterolemia, %2214171524Hypertension, %66a55603836Cataract, %141634NANA

Results:

Frequencies of metabolic features in GCA/PMR patients from the GPS cohort were not significantly different in comparison to healthy controls (HCs). Higher HbA1c levels were detected in GCA patients than in HCs. Data on metabolic features from the Aarhus cohort compared well with the GPS cohort data and thus validated these findings (Table 1). Next, the effect of co-existing co-morbidities on the clinical manifestations was investigated. GCA patients with cataract had reduced CRP and ESR whereas PMR patients with cataract had a higher ESR than patients without cataract (p=0,034). Analysis of GC treatment effect on co-morbidities revealed a significant increase in prevalence of diabetes (after 3 months) and cataract (after 5 years) compared to baseline. BMI was significantly higher after one year and five years of GC treatment. PMR patients with cataract at baseline required longer treatment with GCs (p=0.023). Presence of other metabolic features at the time of GCA or PMR diagnosis did not affect the treatment duration (Figure 1).

Conclusion:

Newly-diagnosed GCA and PMR patients did not appear to have a healthier metabolic profile than HCs. As expected, GC treatment resulted in the development of an unhealthier metabolic profile in GCA patients. In PMR patients, the presence of cataract at baseline was predictive for a prolonged treatment period which could be explained by higher ESR levels in PMR patients with cataract. Together, our findings emphasize the importance of novel GC sparing therapeutic agents and personalized medicine in GCA and PMR.

References:

[1]Buttgereit F,et al. Prevention of glucocorticoid morbidity in giant cell arteritis. Rheumatol (United Kingdom). 2018.

[2]Ungprasert P, et al. Lower body mass index is associated with a higher risk of giant cell arteritis: A systematic review and meta-analysis. Ann Transl Med. 2015.

Disclosure of Interests:

Idil Esen: None declared, Philip Therkildsen: None declared, Berit Dalsgaard NIelsen: None declared, Anna van ‘t Ende: None declared, Annemieke Boots Consultant of: Grunenthal, Peter Heeringa: None declared, Ellen-Margrethe Hauge: None declared, Elisabeth Brouwer Speakers bureau: Roche, fees paid to UMCG, Yannick van Sleen: None declared

POS0112 CD8+ T-CELL INFILTRATION IS ASSOCIATED WITH LESIONAL GM-CSF OVEREXPRESSION IN GCA

Background:

Giant cell arteritis (GCA) is a large-vessel vasculitis characterized by granulomatous T cell- and macrophage infiltration. Granulocyte-macrophage colony stimulating factor (GM-CSF) is present in GCA-affected vessels where it may be involved in skewing of tissue destructive macrophages (1). Furthermore, a recent phase 2 clinical trial demonstrated that GM-CSF receptor blockade was superior to placebo at 26 weeks in GCA. However, the cellular source of GM-CSF in GCA is still unclear.

Objectives:

As T cells have been identified as a major source of GM-CSF in other immune-mediated diseases such as multiple sclerosis, we investigated whether T cells are GM-CSF producers in GCA patients, both systemically and locally.

Methods:

GM-CSF production capacity by PMA-stimulated PBMCs from newly diagnosed, untreated GCA patients and HCs (N=10 each) was assessed using flow cytometry. Temporal artery biopsies (TABs, N=5) were immunohistochemically stained for CD3, CD8 and GM-CSF. Colocalization of these markers was assessed with immunofluorescence.

Results:

Proportions of CD4+ (median GCA=3.1%; HCs=2.76%) and CD8+ (median GCA=5.8%; HCs=5.8%) T cells produced GM-CSF after in vitro stimulation, but no significant differences were found between the groups. Immunofluorescence staining confirmed that CD3+ T cells (both CD8+ and CD8-) were positive for GM-CSF in TABs. Interestingly, GM-CSF positivity in TABs correlated strongly with the extent of CD8+ T-cell infiltration (r=0.74, p<0.01), but not with CD3+ T-cell infiltration (r=0.38, p=0.16).

Conclusion:

Our data imply that T cells are an important source of GM-CSF in GCA lesions. The correlation of the extent of CD8+ T-cell infiltration with GM-CSF positivity suggests that CD8+ T cells are the major source of local GM-CSF overexpression in tissue.

References:

[1]W.F. Jiemy, Y. Sleen, K.S. Geest, H.A. Berge, W.H. Abdulahad, M. Sandovici, A.M. Boots, P. Heeringa, E. Brouwer, Distinct macrophage phenotypes skewed by local granulocyte macrophage colony stimulating factor (GM-CSF) and macrophage colony stimulating factor (M-CSF) are associated with tissue destruction and intimal hyperplasia in giant cell arteritis, Clin. Transl. Immunol. 9 (2020).

Disclosure of Interests:

William Febry Jiemy: None declared, Rosanne Reitsema: None declared, Ayla Kwant: None declared, Wayel Abdulahad: None declared, Annemieke Boots Consultant of: Grünenthal Gmbh until 2017, Peter Heeringa: None declared, Elisabeth Brouwer Speakers bureau: Roche, paid to the UMCG

POS0809 A BIOMARKER PROFILE AIDING AN EARLY DIAGNOSIS OF GIANT CELL ARTERITIS

Background:

Diagnosing patients with giant cell arteritis (GCA) remains difficult. Due to its non-specific symptoms, it is challenging to identify GCA in patients presenting with polymyalgia rheumatica (PMR), which is a more common disease (1). In addition, commonly used acute-phase markers fail to discriminate between GCA patients and (infectious) mimicry patients.

Objectives:

To investigate a selection of biomarkers for their utility in the accurate diagnosis of GCA in two cohorts.

Methods:

Treatment-naïve GCA patients participated in the Aarhus GCA/PMR cohort (N=52) and the Groningen GPS cohort (N=48). Symptoms and biomarker levels were compared to patients presenting phenotypically as isolated PMR, disease controls and healthy controls (HCs). Diagnosis or exclusion of diagnosis of GCA was based on clinical assessment and in the majority of cases aided by imaging. Serum/plasma levels of 12 biomarkers were measured by ELISA or Luminex.

Results:

In both the Aarhus and the GPS cohort, we found that weight loss, elevated erythrocyte sedimentation rate (ESR) and higher angiopoietin-2/-1 ratios but lower matrix metalloproteinase (MMP)-3 levels identify concomitant GCA in PMR patients (Figure 1). In addition, we confirmed (1) that elevated platelet counts are characteristic of GCA but not of GCA look-alikes, and that low MMP-3 and proteinase 3 (PR3) levels may help to discriminate GCA from other diseases (Figure 1). Multiple biomarkers of inflammation were found elevated in patient and disease control groups when compared to HCs.

Conclusion:

This study, performed in two independent cohorts, consistently shows the potential of angiopoietin-2/-1 ratios and MMP-3 levels to identify GCA in patients presenting with PMR. These biomarkers may be used to select which PMR patients require further diagnostic workup. Platelet counts may be used to discriminate GCA from GCA look-alike patients.

Figure 1.

Summary of the most important and consistent findings in both cohorts. A shows the four factors that perform best in discriminating GCA/PMR patients overlap from isolated PMR patients in both cohorts. B shows the four factors that perform best in discriminate GCA patients from GCA look-alike patients in both cohorts. Cut-off values for the biomarkers are calculated by the Youden index.

References:

[1]van der Geest, KSM, Sandovici M, Brouwer E, Mackie SL. Diagnostic accuracy of symptoms, physical signs, and laboratory tests for giant cell arteritis: A systematic review and meta-analysis. JAMA internal medicine. 2020.

Disclosure of Interests:

Yannick van Sleen: None declared, Philip Therkildsen: None declared, Annemieke Boots: None declared, Berit Dalsgaard NIelsen: None declared, Kornelis van der Geest: None declared, Peter Heeringa: None declared, Minke G. Huitema: None declared, M.D. Posthumus: None declared, Maria Sandovici: None declared, Erik Toonen Employee of: Is an employee of Hycult Biotech, Jannik Zijlstra: None declared, Ellen-Margrethe Hauge: None declared, Elisabeth Brouwer: None declared

OP0062 CYTOKINE PRODUCING B CELLS SKEW MACROPHAGES TOWARDS A PRO-INFLAMMATORY PHENOTYPE IN GIANT CELL ARTERITIS

Background:

Giant cell arteritis (GCA) is the most frequent form of systemic vasculitis affecting the temporal artery (TA) and the aorta. Macrophages and T cells are well recognized players in the pathogenesis of GCA while B cells are often not taken into account. Recently, changes in the circulating B cell compartment were documented in GCA and B cells were found to organize into tertiary lymphoid organs at the site of vascular inflammation (TA and aorta).1,2 The exact role of B cells in GCA is still unknown as no disease-specific antibodies have been defined. However, beside their role in humoral immunity, B cells can also produce various cytokines. In GCA, peripheral B cells of treated GCA patients, showed an enhanced capacity to produce pro-inflammatory cytokine Interleukin (IL)63 which is nowadays an important target of treatment in GCA.4 We hypothesize that B cells help shape the inflammatory response in GCA by producing effector and regulatory cytokines.

Objectives:

We aimed to assess the cytokine profile of circulating and lesional B cells in GCA and studied the effects on macrophage skewing.

Methods:

To assess B cells with the capacity to produce cytokines, cryopreserved peripheral blood mononuclear cells of 11 untreated GCA patients and 15 age- and sex-matched healthy controls (HC) were cultured for 3 days in the presence of CpG-ODN 2006. During the last 5 hours phorbol myristate acetate and Calcium Ionophore were added. Thereafter, intracellular effector (IL6, TNFa, IFNy, LTb) and regulatory B cell-related cytokines (IL10) were measured with flow cytometry. To assess potential skewing of macrophages by B cell products, THP-1 cells were differentiated into macrophages and stimulated for 24 hours with supernatant from stimulated B cells (n=6). Expression of IL23, IL6, IL1b, TNFa, MMP9 and YKL40 was assessed on mRNA level with qPCR. To assess local cytokine production, TA (n=11) and aorta tissue samples (n=10) of histologically-proven GCA patients were stained to detect CD20, IL6, TNFa, IFNy, LTb, and IL10 expression. For comparison, 14 aorta tissues samples of patients with an atherosclerosis-related aortic aneurysm were included.

Results:

In vitro stimulated B cells from untreated GCA patients showed an enhanced percentage of IL6+ B cells (median (IQR); 44 (41-52)) and of IL6+TNFa+ B cells (12 (8-24)) compared to stimulated B cells from HC (IL6+: 28 (23-39), IL6+TNFa+: 6 (4-24)). In addition, soluble factors, secreted by GCA derived and stimulated B cells, skewed macrophages towards a pro-inflammatory phenotype with enhanced expression of IL23, IL6, IL1b, and TNFa. Furthermore, these macrophages also showed higher expression of the tissue remodelling factor MMP9 and the pro-angiogenic factor YKL40. At the site of vascular inflammation, B cells were detected in the regions with clear TNFa, IL6, IFNY, LTb and IL10 expression in both the TA and aorta of GCA patients.

Conclusion:

This study demonstrates that circulating B cells of patients with GCA have the capacity to express pro-inflammatory cytokines (IL6 and TNFa) which can influence other cellular players in GCA. Specifically, B cell secreted soluble factors were able to skew macrophages towards a pro-inflammatory phenotype. In addition, this study provides evidence for an active role of B cells in shaping the cytokine milieu at the site of inflammation thereby revealing the B cell as a new target of intervention in GCA.

References:

[1]Ciccia, F. et al. Ectopic expression of CXCL13, BAFF, April and LT-β is associated with artery tertiary lymphoid organs in giant cell arteritis. Ann. Rheum. Dis.76, 235–243 (2017)

[2]Graver, JC. et al. Massive B cell Infiltration and Organization Into Artery Tertiary Lymphoid Organs in the Aorta of Large Vessel Giant Cell Arteritis. Front. Immunol.10, 83 (2019)

[3]Van Der Geest, KSM. et al. Disturbed B cell homeostasis in newly diagnosed giant cell arteritis and polymyalgia rheumatica. Arthritis Rheumatol.66, 1927–1938 (2014)

[4]Stone, JH. et al. Trial of tocilizumab in giant-cell arteritis. N. Engl. J. Med.377, 317–328 (2017)

Disclosure of Interests:

Jacoba Carolien Graver: None declared, William Febry Jiemy: None declared, Dania Altulea: None declared, Annemieke Boots Consultant of: Grunenthal, Peter Heeringa: None declared, Wayel Abdulahad: None declared, Elisabeth Brouwer Speakers bureau: Roche, fees paid to UMCG, Maria Sandovici: None declared

AB0041 CD8+ T CELLS HAVE AN ELEVATED PROLIFERATIVE CAPACITY IN GIANT CELL ARTERITIS

Background:

Giant cell arteritis (GCA) is the most frequent form of systemic vasculitis affecting the large- and medium-sized vessels. The involvement of innate immune cells and CD4+ T cells in the pathogenesis of GCA has been extensively studied. Interestingly, recent findings suggest a role for CD8+ T cells in disease development (1). However, CD8+ subsets and their functional capacities have not yet been studied in detail.

Objectives:

This study aims to characterize the phenotype and proliferative capacity of CD8+ T cells in newly diagnosed GCA patients and GCA patients in remission compared to healthy age- and sex- matched controls.

Methods:

To determine the phenotype of CD8+ T cells in GCA, newly diagnosed, untreated GCA patients (baseline, n=14), GCA patients in stable glucocorticoid-free remission (GC-FR, n=10) and age- and sex-matched healthy controls (HCs, n=18) were enrolled. Peripheral blood mononuclear cells (PBMCs) were stained with fluorochrome-conjugated antibodies directed against CD3, CD4, CD8, CCR7, CD45RO, Ki-67, CD69 and CD25 and analyzed by flow cytometry. The following differentiation subsets were defined: CD8+ T naive (CD45RO-CCR7+), central memory (TCM, CD45RO+CCR7+), effector memory (TEM, CD45RO+CCR7-) and effector memory re-expressing CD45RA (TEMRA, CD45RO-CCR7-) cells. Secondly, the proliferative capacity of CD8+ T cells was determined in isolated CD3+ T cells of 10 GCA baseline, 10 GCA GC-FR patients and 19 HCs after 5 days of stimulation with plate-bound anti-CD3 or anti-CD3 plus soluble anti-CD28 using a dye-based proliferation assay.

Results:

A reduced frequency of CD8+ TEMcells was found in GCA baseline patients compared to HCs (p=0.025). Furthermore, a higher frequency of Ki-67+ cells was detected among CD8+ TEMcells in GCA baseline patients than in HCs (p=0.0007), suggesting a higher proliferative activityin vivo.In addition,in vitrostimulation with anti-CD3 and anti-CD3+anti-CD28 led to higher percentages of divided CD8+ T cells in GCA baseline and GC-FR patients than in HCs (p<0.05). Moreover, the frequencies of CD8+ TEMRAcells and the percentage of divided CD8+ T cells upon CD3 stimulation strongly correlated in GCA baseline patients (R=0.79, p=0.009) and GCA GC-FR patients (R=0.67, p=0.039) but not in HCs (R=0.31, p=0.25).

Conclusion:

GCA baseline patients demonstrate a higher frequency of proliferating circulating CD8+ TEMcells, defined by Ki-67 expression, than HCs. In addition, functional data on induced proliferative capacity suggest that CD8+ T cells from GCA baseline patients are more rapidly activated by crosslinking CD3 and CD3+CD28, suggesting either reduced regulation in these patients or more intrinsic threshold changes. Furthermore, the induced proliferative capacity is also elevated in patients in stable glucocorticoid-free remission. Whether the increased proliferative capacity of total CD8+ T cells in GCA patients is causally linked to the increased frequencies of CD8+ TEMRAcells in these patients requires further investigation.

References:

[1]Samson M, Ly KH, Tournier B, Janikashvili N, Trad M, Ciudad M, et al. Involvement and prognosis value of CD8+ T cells in giant cell arteritis. J Autoimmun. 2016;72:73–83.

Disclosure of Interests:

Rosanne Reitsema: None declared, Rebeca Hid Cadena: None declared, Wayel Abdulahad: None declared, Annemieke Boots Consultant of: Grünenthal Gmbh until 2017, Peter Heeringa: None declared, Elisabeth Brouwer Consultant of: Roche (consultancy fee 2017 and 2018 paid to the UMCG), Speakers bureau: Roche (2017 and 2018 paid to the UMCG)

THU0323 MYELOID BIOMARKERS IN GIANT CELL ARTERITIS AND POLYMYALGIA RHEUMATICA – TWO INDEPENDENT COHORTS

Background:

Giant cell arteritis (GCA) commonly overlaps with polymyalgia rheumatica (PMR). The incidence of GCA among PMR patients is between 16 and 21%, and both diseases are treated with long-term glucocorticoids (GCs). Patients with GCA suffer from inflammation of their large-sized arteries, whereas PMR is characterized by synovial inflammation. A key question for every physician dealing with a PMR patient is whether or not the patient also has GCA. Symptoms of GCA are often non-specific and difficult to identify. Compared to healthy controls (HCs), newly-diagnosed GCA and PMR patients display a change in leukocyte composition with a shift towards the myeloid lineage, evidenced by elevated monocyte and neutrophil counts. Persistence of this myeloid bias (during and after treatment) is in congruence with mounting evidence that GCs do not sufficiently suppress the vascular/synovial inflammation, contributing to a relapsing disease course. Yet, it may be difficult to readily identify the myeloid bias in the blood, and therefore easily detectable biomarkers are required to monitor this myeloid bias in GCA and PMR patients.

Objectives:

The first objective of this study is to identify disease specific biomarkers for GCA and for PMR using myeloid serum/plasma markers. Next, we assessed whether (a profile of) these markers could be used to reflect the persistent myeloid profile.

Methods:

Biomarkers were measured in two independent cohorts: Groningen, the Netherlands (GPS cohort) and Aarhus Denmark (Aarhus cohort). Both cohorts included treatment-naive GCA and PMR patients, supplemented with age- and sex matched HCs (Table 1). Along with the GPS cohort, age-matched inflammatory controls were included. GCA-lookalike patients were added in the measurements for the Aarhus cohort. All patients started treatment with GCs, and follow-up samples were measured at 8 weeks for GCA patients. All measurements were performed by ELISA: sCD206, calprotectin, A1AT and elastase in serum samples, whereas PR3 and MPO were measured in plasma samples.

Table 1.

Baseline characteristics of the two cohorts

GPS cohortAarhus CohortGCAPMRHCInfectionGCAPMRHCGCA-lookalikeN4839501652252018PET-CT:positive/ negative/not done32 5 110 29 10NANA48 4 00 25 0NA0 13 5CRP, median (mg/L)52352707435154

Results:

Analyses of biomarkers in the two cohorts had mostly equivalent results. Compared to HCs, levels of sCD206, calprotectin, PR3 and A1AT were elevated in GCA, PMR and infection/GCA-lookalike patients. GCA patients had higher levels of sCD206 than PMR patients, but only in the Aarhus cohort this reached statistical significance (Aarhus: p=0.02, GPS: p=0.17). Treatment with GCs substantially affected the biomarker levels: in GCA patients of both cohorts, calprotectin and A1AT levels dropped, sCD206 levels remained high (unchanged), and elastase and PR3 levels increased. Next, we assessed whether the biomarkers correlated with inflammation and the myeloid bias in the GPS cohort. Particularly in GCA patients, A1AT levels correlated with inflammatory marker CRP. Elastase correlated significantly with neutrophil counts in both GCA (R=0.42) and PMR (R=0.57). Calprotectin correlated with neutrophil counts in both GCA and PMR, and with monocyte counts in GCA.

Conclusion:

This is one of the first studies in GCA and PMR patients to study biomarkers in two independent cohorts. We consistently showed elevated levels of monocyte/macrophage and neutrophil products in both cohorts. Levels of sCD206 may help in discriminating GCA from PMR patients. The myeloid bias may be monitored using a combination of calprotectin and elastase levels. Additionally, sCD206 or calprotectin may serve as tissue inflammation markers under the cover of GC treatment, a notion to be further investigated using follow-up imaging data.

Disclosure of Interests:

Yannick van Sleen: None declared, Philip Therkildsen: None declared, Berit Dalsgaard NIelsen: None declared, Minke G. Huitema: None declared, Erik Toonen Employee of: Employed by Hycult Biotech, Annemieke Boots Consultant of: Grünenthal Gmbh until 2017, Peter Heeringa: None declared, Ellen-Margrethe Hauge Speakers bureau: Fees for speaking/consulting: MSD, AbbVie, UCB and Sobi; research funding to Aarhus University Hospital: Roche and Novartis (not related to the submitted work)., Elisabeth Brouwer Consultant of: Roche (consultancy fee 2017 and 2018 paid to the UMCG), Speakers bureau: Roche (2017 and 2018 paid to the UMCG)

AB0471 ELEVATED EXPRESSION OF PYRUVATE KINASE M2 IN GIANT CELL ARTERITIS

Background:

Giant Cell Arteritis (GCA) is an inflammatory disease of large and medium vessels. In GCA, expression of interleukin-6 (IL-6), a systemic marker of inflammation, is elevated and it has been shown that treatment with IL-6 receptor blockade (Tocilizumab) is beneficial for GCA patients.1To investigate the role of the IL-6 signaling pathway in GCA pathogenesis in more depth, we focused on the metabolic enzyme Pyruvate Kinase M2 (PKM2). PKM2 may exist as a tetramer, a dimer and/or a monomer in the cell. Tetrameric PKM2 acts as a glycolytic enzyme and catalyzes the last steps of glycolysis by converting phosphoenolpyruvate (PEP) to pyruvate and ATP. On the other hand, dimeric PKM2 translocates to the nucleus and mediates gene regulation via its non-canonical protein kinase activity. Dimeric PKM2 regulates hypoxia, IL-1β expression and, phosphorylates signal transducer and activator of transcription 3 (STAT3) which functions downstream of the IL-6 signaling pathway.2

Objectives:

To investigate the role of PKM2 in GCA diagnosis and pathogenesis.

Methods:

Immunohistochemical staining for PKM2 was performed on inflamed (n=8) and non-inflamed (n=4) temporal artery biopsies (TAB) from GCA patients and on TAB from non-GCA (n=9) patients. To detect soluble, dimeric PKM2 in plasma commercially available dimeric PKM2 specific ELISA kit was used. To determine the modulation of dimeric PKM2 by treatment, samples of GCA patients at baseline (n=44), at 6 weeks (n=32) and at 1 year (n=31) after treatment were compared to samples from age- and sex-matched healthy controls (HC, n=45) As a positive control, samples from melanoma patients (n =8) were used. To investigate the role of dimeric PKM2 in the pathogenesis of GCA, we correlated PKM2 plasma levels with markers of inflammation (CRP, IL-6) and markers of angiogenesis (Angpt2, VEGF, YKL40). Statistical analysis included the Mann-Whitney U test for comparing different groups while the Wilcoxon rank test was used for paired samples. Correlations were assessed by Spearman’s rank correlation coefficient.

Results:

High expression of PKM2 was found in inflamed and non-inflamed TABs of GCA patients, while in non-GCA TABs PKM2 was sparsely expressed. Circulating levels of dimeric PKM2 were found elevated in melanoma and in GCA patients at baseline/active disease compared to those in healthy controls. Analysis of 6 weeks and 1 year follow up plasma samples showed that plasma levels of dimeric PKM2 significantly decreased upon treatment. Dimeric PKM2 weakly correlated with CRP at baseline (r=0.399, p=0.048) but not with angiogenesis markers.

Conclusion:

Dimeric PKM2 plasma levels were found elevated in GCA patients at baseline. PKM2 plasma levels were down modulated by treatment. PKM2 plasma levels weakly correlated with inflammation marker CRP. The data suggest that PKM2 as a marker of glycolysis may have relevance in GCA at diagnosis and for monitoring disease activity. Future studies should aim to validate PKM2 in an independent cohort. Additional studies are needed to determine the molecular mechanism underlying the increase in elevated dimeric PKM2 levels and how this may contribute to IL-6 signaling.

References:

[1]Samson M, Corbera-Bellalta M, Audia S, Planas-Rigol E, Martin L, Cid MC, Bonnotte B. Recent advances in our understanding of giant cell arteritis pathogenesis. Autoimmunity reviews. 2017;16(8):833-44.

[2]Alquraishi M, Puckett DL, Alani DS, Humidat AS, Frankel VD, Donohoe DR, Whelan J, Bettaieb A. Pyruvate kinase M2: A simple molecule with complex functions. Free Radical Biology and Medicine.2019;143:176-192.

Acknowledgments:

This project received funding from the EU Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement 754425.

Disclosure of Interests:

Idil Esen: None declared, Yannick van Sleen: None declared, Peter Heeringa: None declared, Annemieke Boots Consultant of: Grünenthal Gmbh until 2017, Elisabeth Brouwer Consultant of: Roche (consultancy fee 2017 and 2018 paid to the UMCG), Speakers bureau: Roche (2017 and 2018 paid to the UMCG)

OP0134 MACROPHAGES SKEWED BY GM-CSF PRODUCE YKL-40, INSTIGATING ANGIOGENESIS IN GIANT CELL ARTERITIS

Background:

Giant cell arteritis (GCA) is an inflammatory disease affecting the medium- and large-sized arteries. The pathology of GCA is characterized by an infiltrate of mainly CD4+ T-cells and macrophages. These macrophages release a wide range of inflammatory, tissue destructive and proangiogenic proteins, including YKL-40. Previously, we demonstrated that macrophage populations in the vessel wall of GCA patients are heterogeneous; one such macrophage subset highly expressed CD206 and MMP-9, and was located in or near the media layer. Cancer studies have implicated YKL-40 production by tumor-associated macrophages in various inflammatory and tissue remodeling processes, including angiogenesis. Less is known about the role of YKL-40 in inflammatory diseases such as GCA.

Objectives:

Our objective was to investigate the cellular source and the pro-angiogenic function of YKL-40 in GCA patients.

Methods:

For this study we performed immunohistochemistry (IHC) and cell culture experiments. IHC for YKL-40 and CD206 was performed on GCA positive temporal artery biopsies (TABs; n=12) and GCA positive aortas (n=10) of treatment-naive patients. Expression of YKL-40 by macrophages was confirmed by double staining with macrophage transcription factor PU.1. Additionally, the TABs were stained for IL-13Rα2, recently described as the receptor for YKL-40. The effect of skewing signals on YKL-40 production was assessed by cell culture of monocyte-derived macrophages of GCA patients with either M-CSF or GM-CSF (n=8). Subsequently, the supernatant was assayed by ELISA. Finally, the angiogenic potential of YKL-40 was investigated by tube formation experiments using human microvascular endothelial cells (HMVECs).

Results:

YKL-40 is produced by a distinct subset of macrophages in GCA TABs and aortas, usually located in or near the media (Figure 1 shows representative stainings in consecutive slides of a GCA TAB). We here show YKL-40 to be expressed by CD206+/MMP-9+ macrophages in all GCA TABs and aortas. In vitro, macrophages were found to produce YKL-40 (Figure 2 shows an increasing YKL-40 production during the maturation of monocytes towards macrophages over 8 days of culture). GM-CSF stimulation, which is known to upregulate CD206 expression in macrophages, gave rise to higher YKL-40 production by GCA macrophages, when compared to M-CSF stimulated macrophages from GCA patients (p=0.038). In addition, YKL-40 stimulation of HMVECs induced more tube formation compared to unstimulated HMVECs. Finally, we showed, by IHC, abundant expression of the YKL-40 receptor IL-13Rα2 in TABs of GCA patients.

Figure 1Figure 2

Conclusion:

Taken together, we show here that a distinct subset of macrophages, skewed by GM-CSF and highly positive for CD206, is responsible for the production of YKL-40 in GCA. The results are in line with previous reports demonstrating that CD206 expression distinguishes YKL-40 positive macrophages from YKL-40 negative macrophages (1). Thus, YKL-40 production by CD206+ macrophages may be involved in angiogenesis in GCA tissues, a process important for the continuation of the inflammatory process.

References:

[1]Bonneh-Barkay, D. et al., 2012. Astrocyte and macrophage regulation of YKL-40 expression and cellular response in neuroinflammation. Brain Path. 22: 530-546

Disclosure of Interests:

Yannick van Sleen: None declared, William Febry Jiemy: None declared, Sarah A. Pringle: None declared, Wayel Abdulahad: None declared, Kornelis van der Geest Speakers bureau: Roche (2019), Maria Sandovici: None declared, Peter Heeringa: None declared, Elisabeth Brouwer Consultant of: Roche (consultancy fee 2017 and 2018 paid to the UMCG), Speakers bureau: Roche (2017 and 2018 paid to the UMCG), Annemieke Boots Consultant of: Grünenthal Gmbh until 2017

Autoantibodies to box A of high mobility group box 1 in systemic lupus erythematosus

Autoantibodies to nuclear structures are a hallmark of systemic lupus erythematosus (SLE), including autoantibodies to nuclear protein high mobility group box 1 (HMGB1). HMGB1 consists of three separate domains: box A, box B and an acidic tail. Recombinant box A acts as a competitive antagonist for HMGB1 and might be an interesting treatment option in SLE. However, antibodies to box A might interfere. Therefore, levels of anti-box A were examined in SLE patients in association with disease activity and clinical parameters. Serum anti-box A was measured in 86 SLE patients and 44 age- and sex-matched healthy controls (HC). Serum samples of 28 patients with primary Sjögren's syndrome and 32 patients with rheumatoid arthritis were included as disease controls. Anti-HMGB1 and anti-box B levels were also measured by enzyme-linked immunosorbent assay during quiescent disease [SLE Disease Activity Index (SLEDAI) ≤ 4, n = 47] and active disease (SLEDAI ≥ 5, n = 39). Anti-box A levels in active SLE patients were higher compared to quiescent patients, and were increased significantly compared to HC and disease controls. Anti-box A levels correlated positively with SLEDAI and anti-dsDNA levels and negatively with complement C3 levels. Increased levels of anti-box A antibodies were present in the majority of patients with nephritic (73%) and non-nephritic exacerbations (71%). Antibodies to the box A domain of HMGB1 might be an interesting new biomarker, as these had a high specificity for SLE and were associated with disease activity. Longitudinal studies should be performed to evaluate whether these antibodies perform better in predicting an exacerbation, especially non-nephritic exacerbations.

MicroRNA-126 contributes to renal microvascular heterogeneity of VCAM-1 protein expression in acute inflammation

Endothelial cells in different microvascular segments of the kidney have diverse functions and exhibit differential responsiveness to disease stimuli. The responsible molecular mechanisms are largely unknown. We previously showed that during hemorrhagic shock, VCAM-1 protein was expressed primarily in extraglomerular compartments of the kidney, while E-selectin protein was highly induced in glomeruli only (van Meurs M, Wulfert FM, Knol AJ, de Haes A, Houwertjes M, Aarts LPHJ, Molema G. Shock 29: 291–299, 2008). Here, we investigated the molecular control of expression of these endothelial cell adhesion molecules in mouse models of renal inflammation. Microvascular segment-specific responses to the induction of anti-glomerular basement membrane (anti-GBM), glomerulonephritis and systemic TNF-α treatment showed that E-selectin expression was transcriptionally regulated, with high E-selectin mRNA and protein levels preferentially expressed in the glomerular compartment. In contrast, VCAM-1 mRNA expression was increased in both arterioles and glomeruli, while VCAM-1 protein expression was limited in the glomeruli. These high VCAM-1 mRNA/low VCAM-1 protein levels were accompanied by high local microRNA (miR)-126 and Egfl7 levels, as well as higher Ets1 levels compared with arteriolar expression levels. Using miR-reporter constructs, the functional activity of miR-126 in glomerular endothelial cells could be demonstrated. Moreover, in vivo knockdown of miR-126 function unleashed VCAM-1 protein expression in the glomeruli upon inflammatory challenge. These data imply that miR-126 has a major role in the segmental, heterogenic response of renal microvascular endothelial cells to systemic inflammatory stimuli.

Inhibition of neutrophil-mediated production of reactive oxygen species (ROS) by endothelial cells is not impaired in anti-neutrophil cytoplasmic autoantibodies (ANCA)-associated vasculitis patients

Leucocyte transendothelial migration is strictly regulated to prevent undesired inflammation and collateral damage of endothelial cells by activated neutrophils/monocytes. We hypothesized that in anti-neutrophil cytoplasmic autoantibodies (ANCA)-associated vasculitis (AAV) patients' dysregulation of this process might underlie vascular inflammation. Peripheral blood mononuclear cells (PBMC) and neutrophils from AAV patients (n = 12) and healthy controls (HC, n = 12) were isolated. The influence of human umbilical vein endothelial cells (HUVEC) on neutrophil/monocytes function was tested by N-formyl-methionyl-leucyl-phenyl-alanine (fMLP)- and phorbol 12-myristate 13-acetate (PMA)-mediated ROS production, degranulation and interleukin (IL)-8 production. In addition, the ability of lipopolysaccharide (LPS)-stimulated PBMC to produce tumour necrosis factor (TNF)-alpha in the presence or absence of HUVEC was tested. HUVEC inhibited ROS production dose-dependently by fMLP-stimulated neutrophils but did not influence degranulation. No differences between neutrophils from HC and AAV were found. However, in only one active patient was degranulation inhibited significantly by HUVEC only before cyclophosphamide treatment, but not 6 weeks later. Co-cultures of HUVEC with LPS-stimulated neutrophils/monocytes increased IL-8 production while TNF-alpha production was inhibited significantly. There was no apparent difference between AAV patients and HC in this respect. Our findings demonstrate that HUVEC are able to inhibit ROS and modulate cytokine production upon stimulation of neutrophils or monocytes. Our data do not support the hypothesis that endothelial cells inhibit ROS production of neutrophils from AAV patients inadequately. Impaired neutrophil degranulation may exist in active patients, but this finding needs to be confirmed.

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.

Anti-oxLDL antibody isotype levels, as potential markers for progressive atherosclerosis in APOE and APOECD40L mice

In humans and animal models of atherosclerosis, antibodies against oxidized LDL have been associated with atherosclerotic lesion development. It has been suggested that IgM anti-oxLDL antibodies are anti-atherogenic, whereas IgG anti-oxLDL antibodies are pro-atherogenic. In this study, we examined the relation between IgM and IgG antibody levels and atherosclerosis severity in APOE(-/-)CD40L(-/-) mice, which are deficient for IgG and develop moderate advanced atherosclerosis, and compared results with mice developing severe (APOE(-/-)) or no atherosclerosis (C57Bl/6). Mice were followed in time for anti-oxLDL antibodies while on high-fat diet or normal chow. Anti-oxLDL antibody levels were determined by ELISA. Results revealed that 24-week-old APOE(-/-)CD40L(-/-) mice had enhanced IgM anti-oxLDL antibody levels when compared with wild-type mice, but similar levels to those of APOE(-/-) mice. As expected, IgG anti-oxLDL antibody levels were almost absent in APOE(-/-)CD40L(-/-) mice. The transition from early to advanced lesions in APOE(-/-) mice was reflected by elevated IgM anti-oxLDL antibody levels. IgM anti-oxLDL levels did not further increase during progression to more advanced lesions. No relation was found between IgG anti-oxLDL levels and atherosclerosis severity. In conclusion, the severity of advanced atherosclerosis in mice is not reflected by IgM and/or IgG anti-oxLDL antibody levels. Furthermore, less advanced atherosclerotic lesion development in APOE(-/-)CD40L(-/-) mice does not seem to be the result of higher levels of protective IgM anti-oxLDL antibodies. Therefore, our study does not support the idea that the previously observed inconsistency in the relation between anti-oxLDL and atherosclerosis severity is due to differences in antibody isotypes.

Myeloperoxidase modulates lung epithelial responses to pro-inflammatory agents

During extensive inflammation, neutrophils undergo secondary necrosis causing myeloperoxidase (MPO) release that may damage resident lung cells. Recent observations suggest that MPO has pro-inflammatory properties, independent of its enzymatic activity. The aims of the present study were to characterise MPO internalisation by lung epithelial cells and to investigate the effect of MPO on oxidative stress, DNA damage and cytokine production by lung epithelial cells. Human alveolar and bronchial epithelial cells were stimulated with MPO, with or without priming the cells with pro-inflammatory stimuli. MPO protein was detected in the cell cytoplasm. Expression of haemoxygenase (HO)-1 and DNA strand breakage were determined. The production of interleukin (IL)-8 and -6 were measured. Analyses of MPO-stimulated cells demonstrated MPO presence in the cells. HO-1 expression was increased after MPO stimulation and increased further when cells were primed before MPO stimulation. MPO exposure also induced DNA strand breakage. Interestingly, MPO inhibited IL-8 production in bronchial, but not alveolar epithelium. In conclusion, alveolar and bronchial epithelial cells can internalise myeloperoxidase. Stimulation with myeloperoxidase increases haemoxygenase-1 expression and DNA strand breakage, suggesting cell damaging capacity of myeloperoxidase. In addition, myeloperoxidase inhibited interleukin-8 production by bronchial epithelial cells, indicating a negative feedback loop for neutrophil recruitment.

Inhibition of complement factor C5 protects against anti-myeloperoxidase antibody-mediated glomerulonephritis in mice

In mice, administration of murine anti-myeloperoxidase (MPO) IgG induces pauci-immune necrotizing crescentic glomerulonephritis. Recent studies in this model indicate a crucial role for complement activation in disease induction. Here, we investigated the effect of pretreatment or intervention with a C5-inhibiting monoclonal antibody (BB5.1) in the mouse model of anti-MPO IgG-induced glomerulonephritis. Mice received BB5.1 8 h before or 1 day after disease induction with anti-MPO IgG and lipopolysaccharide. Mice were killed after 1 or 7 days. Control antibody-pretreated mice developed hematuria, leukocyturia and albuminuria, and glomerulonephritis with a mean of 21.0+/-8.8% glomerular crescents and 12.8+/-5.5% glomerular capillary necrosis. BB5.1 pretreatment prevented disease development, as evidenced by the absence of urinary abnormalities, a marked reduction in glomerular neutrophil influx at day 1 and normal renal morphology at day 7. Importantly, BB5.1 administration 1 day after disease induction also resulted in a marked attenuation of urinary abnormalities and a more than 80% reduction in glomerular crescent formation. In conclusion, inhibition of C5 activation attenuates disease development in a mouse model of anti-MPO IgG-induced glomerulonephritis. These results favor further investigations into the role of complement activation in human MPO-anti-neutrophil cytoplasmic autoantibody-mediated glomerulonephritis, and indicate that inhibition of C5 activation is a potential therapeutic approach in this disease.

Mechanisms of vasculitis: how pauci-immune is ANCA-associated renal vasculitis?

Both the innate and the acquired immune system are involved in the pathophysiology of renal vasculitis. However, anti-neutrophil cytoplasmic antibody (ANCA)-associated renal vasculitis is characterized by a 'pauci-immune' pattern of immunofluorescence during kidney biopsy, indicating the relative lack of immunoglobulin and complement deposition within the kidney. On the other hand, evidence is accumulating that ANCA, autoantibodies against constituents of primary granules of neutrophils and the lysosomes of monocytes, play a pathogenic role in renal vasculitis. In this review we will discuss both in vitro and in vivo experimental data providing compelling evidence that ANCA are a primary pathogenic factor in renal vasculitis, mainly by augmenting leukocyte-endothelial interactions. We will also address novel data, pointing at the role of, in addition to ANCA, non-specific proinflammatory signals. Finally, we propose a working hypothesis of the pathogenesis of ANCA-associated renal vasculitis.

Leukocyte CD40L deficiency affects the CD25+ CD4 T cell population but does not affect atherosclerosis

Inhibition of CD40-CD40L interactions results in a reduction of innate regulatory T cells (Tregs) in CD40(-/-) mice and induces a stable plaque phenotype in atherosclerosis-prone mouse strains. Here we investigated the effects of leukocyte CD40L on the Treg population and on atherosclerosis. LDLR(-/-) mice were reconstituted with wild-type or CD40L(-/-) bone marrow (BM). These BM chimeras were analysed by flow cytometry for the presence of innate Tregs (CD45RB(low) CD25(+) CD4) in lymphoid organs and peripheral blood. As in CD40(-/-) mice, the CD45RB(high):CD45RB(low) CD4 T cell ratio significantly increased and the CD25(+) CD4(+) subpopulation significantly decreased in LDLR(-/-) mice receiving CD40L(-/-) BM compared to LDLR(-/-) mice receiving wild-type BM. However, atherosclerotic plaque progression and plaque phenotype did not change in LDLR(-/-) mice reconstituted with CD40L(-/-) BM. In conclusion, the present study shows that CD40-CD40L interactions on leukocytes are essential for the size of the CD45RB(low) CD25(+) CD4 Treg subpopulation. Nevertheless, CD40L deficiency on hemopoietic cells did not affect atherosclerosis, implying that CD40L expressing leukocytes alone are not responsible for the stable plaque phenotype observed after total CD40L blockade.

Dendritic cells overexpressing Fas-ligand induce pulmonary vasculitis in mice

Dendritic cells (DC) genetically engineered to express Fas (CD95) ligand (FasL-DC) have been proposed as immunotherapeutic tools to induce tolerance to allografts. However, we and others recently showed that FasL-DC elicit a vigorous inflammatory response involving granulocytes and can promote Th1-type CD4+ and cytotoxic CD8+ T lymphocytes. This prompted us to evaluate the pathology induced by intravenous injection of FasL-DC in mice. We observed that FasL-DC obtained after retroviral gene transfer of bone marrow precursors derived from Fas-deficient C57Bl/6 mice induce massive pulmonary inflammation and pleuritis one day after a single intravenous injection in C57Bl/6 mice. Two months later, all mice presented granulomatous vasculitis of small to medium sized vessels, alveolar haemorrhage and pleuritis. In these lesions, apoptotic bodies were found in large number. Anti-neutrophilic cytoplasmic and anti-myeloperoxidase autoantibodies were not detected. This study documents that intravenous injection of FasL-DC causes severe lung granulomatous vasculitis. This new animal model for vasculitis is inducible, highly reproducible and shares many features with human Wegener granulomatosis. This model may be an appropriate tool to further investigate the pathogenesis of vasculitis and test new therapeutic strategies. Moreover, our findings highlight the potential severe complications of FasL-DC-based immunotherapy.

Pathophysiology of ANCA-associated vasculitides: Are ANCA really pathogenic?

The strong association of antineutrophil cytoplasmic autoantibodies (ANCA) with certain forms of small vessel vasculitis suggests a pathogenic role of these autoantibodies in the disease process. In vitro, ANCA can activate neutrophils and monocytes to produce reactive oxygen intermediates, to release lysosomal enzymes, and to secrete proinflammatory cytokines. More recently, it was demonstrated that antimyeloperoxidase ANCA can induce systemic vasculitis and glomerulonephritis in mice. Taken together, these data provide convincing evidence that ANCA are indeed pathogenic.

Pathophysiology of ANCA-associated vasculitides: are ANCA really pathogenic?

The strong relation between antineutrophil cytoplasmic autoantibodies (ANCA) and primary vasculitic syndromes suggests a pathophysiological role for ANCA. Experimental evidence for the pathogenic potential of ANCA has been derived from in vitro studies that demonstrate that ANCA can activate tumour necrosis factor alpha primed neutrophils, monocytes and/or endothelial cells. The binding of ANCA to primed neutrophils results in activation of these cells by a process that is largely dependent on engagement of beta-2 integrins and on the interaction of the Fc portion of ANCA. An Fc-independent mechanism is, however, also operative. In experimental animal models, it has been demonstrated that immunisation with myeloperoxidase (MPO) induces MPO-ANCA. The induction of ANCA, however, is not sufficient to induce vasculitis in rats since immune complexes first have to be deposited along the vessel wall before lesions develop. When MPO-deficient mice are, however, immunised with murine MPO, anti-MPO immunoglobulins are purified and subsequently injected into mice that are not deficient for MPO, systemic vasculitis and glomerulonephritis is induced. These experiments suggest that ANCA indeed induces vasculitis. Risk factors for breaking self-tolerance to ANCA antigens are genetic factors, drugs, chemical substances and/or infectious agents.

The role of myeloperoxidase in the pathogenesis of systemic vasculitis

Wegener's granulomatosis, microscopic polyangiitis, Churg-Strauss syndrome and idiopathic pauci-immune necrotizing crescentic glomerulonephritis are strongly associated with the presence of anti-neutrophil cytoplasmic antibodies (ANCA). These ANCA-associated vasculitides can serologically be separated into myeloperoxidase (MPO)-ANCA and proteinase 3 (PR3)-ANCA positive patients. The unique properties of the antigen targeted by the anti-MPO antibodies could help to explain the specific characteristics of MPO-ANCA associated disease. Recently, an animal model has been developed that proves that anti-mouse MPO immunoglobulins alone are capable of causing disease similar to that in humans. Also, the in vitro pathologic effects of binding of MPO-ANCA to MPO are better understood. MPO-ANCA can activate (primed) neutrophils directly causing extensive reactive oxygen species formation and degranulation of neutrophil constituents, including MPO, resulting in a destructive inflammatory response towards the vessel wall. MPO-ANCA can prevent the clearing and inactivation of MPO by ceruloplasmin as well, resulting in increased myeloperoxidase activity. Myeloperoxidase produces not only the strong oxidant bleach (hypochlorous acid) out of hydrogen peroxide and chloride ions but also oxidizes LDL into a macrophage high-uptake form, inactivates protease inhibitors, and consumes nitric oxide. These may contribute to endothelial dysfunction and add to the chronic renal lesions observed in patients with MPO-ANCA. MPO levels are influenced by genetic factors including two, MPO463 and MPO129, single nucleotide polymorphisms. The MPO 463 polymorphism has been associated with an increased risk of development of MPO-ANCA associated disease.

ANCA and anti-GBM antibodies in diagnosis and follow-up of vasculitic disease

In the last decade, serological detection of anti-neutrophil cytoplasmic antibodies (ANCA) and of anti-glomerular basement membrane (GBM) antibodies has tremendously facilitated the diagnosis of small vessel vasculitides. Once diagnosed, these diseases have proven to be treatable. However, in contrast to anti-GBM disease, ANCA-associated vasculitides are chronic diseases with a high relapse rate. Since morbidity in ANCA-associated vasculitides is dictated by the frequency and severity of relapses, much health benefit would be achieved if a relapse could be prevented or early treatment started. Increases in ANCA titers and persistently high ANCA levels indicate a high risk of relapse and warrant clinical evaluation of the patient for signs of relapse. This review will focus on the value of ANCA and anti-GBM antibody testing in diagnosis and on the importance of these tests in follow-up of disease.

Increased expression of inducible nitric oxide synthase in circulating monocytes from patients with active inflammatory bowel disease

BACKGROUND

Inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) synthesis are increased in epithelial cells and in tissue macrophages of the inflamed mucosa from patients with inflammatory bowel disease (IBD). Since tissue macrophages are derived from circulating monocytes, we studied iNOS expression in circulating monocytes and related this expression to disease activity. In view of the possible role of NO in monocyte function, we also studied iNOS expression in relation to markers of monocyte activation.

METHODS

The expression of iNOS in circulating monocytes from 15 patients with active IBD, 6 patients who went into remission and 18 healthy controls was quantified by flow cytometry and correlated with surface markers (CD63, CD11b, HLA-DR) for monocyte activation. In addition, iNOS expression in circulating monocytes was assessed by Western blotting, immunocytochemistry and measurement of the NO metabolites nitrite and nitrate in plasma.

RESULTS

The expression of iNOS in circulating monocytes and the percentage of iNOS-positive monocytes were increased in patients with active IBD compared to healthy controls (fluorescence index: 1.3 (0.1-6.3) versus 0.8 (0.0-1.8); P < 0.05: percentage of iNOS positive monocytes: 37.3 (1.0-77.0)% versus 5.3 (0.0-43.3)%; P<0.01). The six patients who went into remission all had a marked reduction of iNOS expression. iNOS expression was confirmed by Western blotting and immunocytochemistry. Plasma nitrite and nitrate levels were elevated in three patients with active 1BD. The surface markers for monocyte activation, CD63 and CD11b, were not elevated. HLA-DR expression was decreased on circulating monocytes from patients with active ulcerative colitis.

CONCLUSIONS

iNOS is increased in circulating monocytes from patients with active IBD and this increased expression correlates with disease activity. Considering the decreased HLA-DR expression and absence of monocyte activation markers, NO produced by iNOS may have a function in suppressing systemic monocyte activation.

Nitric oxide inhibition enhances platelet aggregation in experimental anti-Thy-1 nephritis

In the present paper we studied the role of nitric oxide radicals (NO) on platelet aggregation, fibrinogen deposition, superoxide formation, peroxynitrite formation, hemodynamics, and leukocyte migration in the Thy-1 model of glomerulonephritis. To first study the baseline kinetics of these parameters, groups of anti-Thy-1-treated rats were sacrificed at 1 h, 4 h, 24 h, 3 days, 7 days, and 14 days and compared to controls. Urinary protein excretion was significantly elevated in Thy-1 nephritis at 3 and 7 days. Glomerular macrophages, PMNs, and superoxide anion-positive cells were significantly increased in Thy-1 nephritis. Nitrotyrosine immunoreactivity was absent during the entire study period. Glomerular platelet aggregation was significantly increased in anti-Thy-1 injected rats at 1 h, 4 h, 24 h, and 3 days. Glomerular fibrinogen deposition was significantly elevated at all time points. To elucidate the role of NO in this process, additional groups of anti-Thy-1-injected rats were treated with the NOS inhibitor l-NAME and studied at 24 h. Urinary protein excretion was significantly higher in l-NAME treated Thy-1 rats compared to nontreated Thy-1 rats. Plasma and urine nitrite/nitrate levels were significantly lower in l-NAME-treated Thy-1 rats compared to nontreated Thy-1 rats. Compared to nontreated Thy-1 rats, there were no differences in intraglomerular leukocyte accumulation after treatment with l-NAME. In contrast, we observed a marked increase in platelet aggregation following l-NAME treatment. From these data we conclude that the inflammatory infiltrate in Thy-1 nephritis develops independent of NO radical production, whereas NO radicals prevent the accumulation of platelet aggregates.

Internalization of proteinase 3 is concomitant with endothelial cell apoptosis and internalization of myeloperoxidase with generation of intracellular oxidants

The important issue addressed by the studies presented here is the mechanism of neutrophil-mediated damage to endothelial and epithelial cells during inflammation. Binding of neutrophil-released granule proteins to endothelial cells may be involved in vascular damage in patients with inflammatory vascular diseases. We have determined whether granule proteins proteinase 3(PR3) and/or myeloperoxidase (MPO) are internalized into endothelial cells, as examined by UV light, confocal, and electron microscopy. Coincident induction of apoptosis and/or the generation of intracellular oxidants were monitored. The results indicate that human endothelial cells (human umbilical vein endothelial cells, human umbilical arterial endothelial cells, human lung microvascular endothelial cells) internalize both PR3 and MPO, which are detected on the cell surface, in the cytoplasm, and possibly nuclear. Epithelial cells (small airway epithelial cells) internalized MPO but not PR3, implying that the mechanism of PR3 internalization may be cell-type specific and different from that of MPO. Internalization of PR3, but not MPO, correlated with activation of apoptosis. Internalization of MPO correlated with an increase in intracellular oxidant radicals. The requirement for the proteolytic activity of PR3 for the induction of apoptosis was examined by generating PR3-truncated fragments that did not contain the components of the catalytic triad. An apoptotic function was localized to the C-terminal portion of PR3. These studies reveal novel mechanisms by which the neutrophil granule proteins PR3 and MPO contribute to tissue injury at sites of inflammation.

Renal expression of endothelial and inducible nitric oxide synthase, and formation of peroxynitrite-modified proteins and reactive oxygen species in Wegener's granulomatosis

To investigate the role of nitric oxide (NO) in glomerular inflammation, the expression of endothelial NO synthase (eNOS) and inducible NOS (iNOS) was studied in conjunction with inflammatory cell influx, H2O2 production, and the formation of nitrotyrosines in renal biopsies from patients with Wegener's granulomatosis (WG). Renal cryostat sections from patients with WG (n=15) were stained by immunohistochemistry for eNOS, iNOS, endothelial cells (CD31), nitrotyrosines, polymorphonuclear cells (PMNs, CD15), and monocytes/macrophages (CD14, CD68). Production of H2O2 was identified by enzyme cytochemistry using diaminobenzidine. In control tissues, strong staining for eNOS was found in glomerular and interstitial tubular capillaries and cortical vessels. A significant reduction in eNOS expression was found in WG biopsies, which was associated with a reduction in CD31 expression. Expression of iNOS was found in infiltrating inflammatory cells, mainly located in the interstitium. H2O2-producing cells were detected in glomeruli and were abundantly present in the interstitium. Nitrotyrosine-positive cells, however, were almost exclusively found in the interstitium. It is concluded that renal inflammation in WG is associated with the induction of iNOS in inflammatory cells and the formation of nitrotyrosines. Expression of eNOS in glomerular capillaries is lost, most likely due to endothelial cell damage. These results suggest that decreased NO production by endothelial cells, in conjunction with increased NO production by iNOS-positive inflammatory cells, is involved in renal tissue injury in WG.

Antimyeloperoxidase-associated lung disease. An experimental model

The lung is a common target in systemic vasculitides associated with antineutrophil cytoplasmic antibodies (ANCA). In the present study, we tested the hypothesis that the presence of antibodies directed against myeloperoxidase (MPO) induces pulmonary (vasculitic) lesions when neutrophils release lysosomal enzymes. Brown Norway (BN) rats were immunized with human MPO in complete Freund's adjuvant (CFA) or with CFA alone. Two weeks after immunization, rats had developed antibodies to human and rat MPO. Next, isolated single left lung perfusion was performed with human neutrophil lysosomal extract containing MPO and proteolytic enzymes. Rats were killed at 15 min, 4 h, and 10 d after perfusion. Tissue samples from the left and right lung were examined for vasculitic lesions and inflammatory cell infiltrates. At 15 min and 4 h, left lungs from control and MPO-immunized rats showed a mild influx of polymorphonuclear cells. At 10 d, patchy inflammatory cell infiltrates, consisting predominantly of polymorphonuclear leukocytes (PMNs) and monocytes, were observed throughout the parenchyma of the left lung in MPO-immunized rats. Occasionally, granuloma-like lesions, giant cells, and foci of alveolar hemorrhage were observed as well. Far less severe lesions were seen in control immunized rats. Strikingly, at 10 d after perfusion, severe pulmonary tissue injury was observed also in right lungs from MPO-immunized rats whereas right lungs from control immunized rats appeared normal. The lesions were characterized by influx of PMNs and monocytes and, in some rats, foci of alveolar hemorrhage. These studies suggest that the presence of an anti-MPO directed autoimmune response contributes to generalized pulmonary tissue injury after local release of products of activated neutrophils, which supports a pathogenic role of MPO-ANCA.

Reduction in glomerular heparan sulfate correlates with complement deposition and albuminuria in active Heymann nephritis

In a time-study of active Heymann nephritis, the expression of agrin, the main heparan sulfate proteoglycan in the glomerular basement membrane, was analyzed in relation to deposition of IgG and complement in the glomerular capillary wall and the development of albuminuria. Binding of IgG autoantibodies to the glomerular capillary wall could be detected from 2 wk onward, followed by activation of complement after 6 wk. Progressive albuminuria developed from 6 wk onward to a level of 274+/-68 mg/18 h at week 12. The staining intensity for the agrin core protein decreased slightly, and the staining intensity for the heparan sulfate stubs that were still attached to the core protein after heparitinase digestion remained normal. From week 6 onward, however, a progressive decrease was seen in the staining of two monoclonal antibodies (mAb) directed against different epitopes on the heparan sulfate polysaccharide side chain of agrin (to 35 and 30% of the control level, respectively, at week 12, both mAb P = 0.016). Moreover, albuminuria was inversely correlated with heparan sulfate staining as revealed by these antibodies (r(s) = -0.82 and r(s) = -0.75, respectively, both mAb P < 0.0001). This decrease in heparan sulfate staining was due to a progressive reduction of glomerular heparan sulfate content to 46 and 32% of control level at week 10 and week 12 of the disease, respectively, as measured biochemically. It is speculated that the observed decrease in glomerular heparan sulfate in active Heymann nephritis is due to complement-mediated cleavage of heparan sulfate, resulting in an increased permeability of the glomerular basement membrane to macromolecules.

Pathogenesis of vasculitis

This review discusses current thoughts on the pathogenesis of vasculitis. Secondary vasculitides, frequently associated with infections or systemic autoimmune diseases, are, in most cases, characterized by immune deposits in the vessel wall, which probably underlies the development of lesions. In the primary vasculitides, immune deposits are generally absent. A group of primary vasculitides is, however, strongly associated with anti-neutrophil cytoplasmic autoantibodies (ANCA). Various in vitro and in vivo experimental data suggest that those ANCA are involved in the pathogenesis of lesions in the associated disorders.

Expression of iNOS, eNOS, and peroxynitrite-modified proteins in experimental anti-myeloperoxidase associated crescentic glomerulonephritis

Nitric oxide radicals are recognized as important mediators in various physiological and pathophysiological processes. During inflammation, increased amounts of nitric oxide (NO) are produced, but it is unclear whether NO radicals are either protective or harmful. To obtain more insight into the role of NO in glomerular inflammation, we studied the temporal expression of endothelial NO synthase (eNOS) and inducible NOS (iNOS) in conjunction with platelet aggregation, inflammatory cell influx, superoxide anion production cells, and nitrotyrosine formation in an experimental model of anti-myeloperoxidase (MPO) associated necrotizing crescentic glomerulonephritis (NCGN). Brown Norway rats were immunized with MPO in complete Freund's adjuvant (CFA) or CFA alone. After two weeks, the left kidney was perfused with a neutrophil lysosomal extract and H2O2. Rats were sacrificed at 24 hours, four days, and 10 days after perfusion. Kidney sections were stained by immunohistochemistry for eNOS, iNOS, platelets, nitrotyrosines, polymorphonuclear cells (PMN), monocytes, and T-cells. Superoxide anion producing cells were identified by enzyme cytochemistry using diaminobenzidine. Strong staining for eNOS was found in glomerular capillaries and interstitial tubular capillaries and larger vessels from non-perfused kidneys. At 24 hours after perfusion, glomerular and interstitial eNOS staining was greatly reduced, which was associated with massive platelet aggregation. At later time points, eNOS expression was absent in severely damaged glomeruli. Inducible NOS expression was found at all time points in infiltrating inflammatory cells, which by double labeling studies were identified as PMNs and monocytes. The peak in iNOS expression was observed at four days after perfusion but declined thereafter. Superoxide anion and nitrotyrosine generating cells were also found at all time points, but were most abundantly present at four days after perfusion, coinciding with the peak in iNOS expression. Double labeling experiments revealed that most nitrotyrosine generating cells also produced superoxide anions and expressed iNOS. In conclusion, these studies suggest that during the course of anti-MPO associated NCGN, loss of NO production by eNOS in conjunction with NO radical production by iNOS contribute to tissue injury. This is compatible with a protective role for eNOS contrasting with the possibly harmful effects of iNOS in anti-MPO associated NCGN.

Recombinant proteinase 3 (Wegener's antigen) expressed in Pichia pastoris is functionally active and is recognized by patient sera

The open reading frame of human proteinase 3 (PR3) without the prepro-peptide was cloned and expressed in Escherichia coli (rcPR3) and in Pichia pastoris (rpPR3). The 6-histidine tagged rpPR3 was efficiently secreted into culture supernatant from which it could be purified by immobilized metal chelate chromatography. Purified rpPR3 migrated as a single 32-kD band on SDS-PAGE and harboured protease activity that could be inhibited with inhibitors specific for serine-proteases. By indirect antigen-capture ELISA using rpPR3, 60% of sera from patients with Wegener's granulomatosis bound to the recombinant product, although it was not recognized in ELISA with directly coated rpPR3.

Systemic injection of products of activated neutrophils and H2O2 in myeloperoxidase-immunized rats leads to necrotizing vasculitis in the lungs and gut

The strong association of anti-neutrophil cytoplasmic antibodies with various forms of systemic vasculitis suggests a role for these autoantibodies in the pathophysiology of systemic vasculitis. In the present study, we tested the hypothesis that release of neutrophil lysosomal enzymes in the presence of an anti-myeloperoxidase (anti-MPO) immune response may underlie the development of systemic vasculitis. Brown Norway rats were immunized with MPO in complete Freund's adjuvant or complete Freund's adjuvant alone. Two weeks after immunization, rats bad developed antibodies to human and rat MPO as measured by enzyme-linked immunosorbent assay. Next, rats were intravenously infused with 400 micrograms of a human neutrophil lysosomal extract containing 200 micrograms of MPO followed by 0.5 ml of a 1 mmol/L solution of H2O2 through a cannula inserted into the right jugular vein. Rats were sacrificed at 4 hours, 24 hours, 7 days, or 14 days, and several organs (lungs, heart, liver, spleen, gut, and kidneys) were examined for vasculitic lesions and inflammatory cell infiltrates. Macroscopically, patchy hemorrhagic spots were observed in the lungs and gut of MPO-immunized rats at days 7 and 14 after systemic infection of the neutrophil lysosomal extract and H2O2. Such changes were not observed at earlier time points or in control immunized rats. Histologically, the lungs of MPO-immunized rats sacrificed at days 7 and 14 showed patchy inflammatory cell infiltrates associated with vasculitis, granuloma formation, giant cells, and foci of hemorrhage. At 14 days, early signs of fibrosis were found with deposition of collagen and proliferation of fibroblasts. Furthermore, a prominent leukocytoclastic vasculitis was found in the small intestine of these rats characterized by fibrinoid necrosis and an extensive neutrophilic infiltrate. No inflammatory changes were found in the other organs studied (heart, liver, spleen, and kidneys). Control immunized rats, sacrificed at days 7 and 14 showed only some small foci of inflammatory infiltrates in the lungs whereas no inflammatory changes were found in the gastrointestinal tract. These studies show that release of products from activated neutrophils in the presence of anti-MPO autoantibodies may be relevant to the pathogenesis of anti-MPO-associated vasculitides.