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.

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.

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.

Coexpression of CD177 and membrane proteinase 3 on neutrophils in antineutrophil cytoplasmic autoantibody-associated systemic vasculitis: anti-proteinase 3-mediated neutrophil activation is independent of the role of CD177-expressing neutrophils.

OBJECTIVE: Wegener's granulomatosis (WG) is strongly associated with antineutrophil cytoplasmic autoantibodies (ANCAs) directed against proteinase 3 (PR3). Recent studies have shown that membrane-bound PR3 (mPR3) is differentially expressed and colocalizes with CD177/NB1 on circulating neutrophils. We undertook this study to assess the differential expression of CD177 on neutrophils from patients with ANCA-associated systemic vasculitis (ASV) in comparison with patients with systemic lupus erythematosus (SLE), patients with rheumatoid arthritis (RA), and healthy individuals, and to investigate whether colocalization of mPR3 and CD177 affects anti-PR3-mediated neutrophil activation. METHODS: Expression of CD177 and mPR3 was analyzed by flow cytometry on isolated neutrophils from patients with ASV (n=53), those with SLE (n=30), those with RA (n=26), and healthy controls (n=31). Neutrophil activation mediated by anti-PR3 antibodies was assessed by measuring the oxidative burst with a dihydrorhodamine assay. RESULTS: Percentages of CD177-expressing neutrophils were significantly higher in patients with ASV and those with SLE than in healthy controls. In 3 healthy donors, CD177 expression was not detected. After priming with tumor necrosis factor alpha, neutrophils remained negative for CD177 while mPR3 expression was induced. Neutrophils from CD177-negative donors or CD177- neutrophils sorted from donors with bimodal expression were susceptible to anti-PR3-mediated oxidative burst. Variation in the extent of anti-PR3-mediated neutrophil activation among different donors occurred independent of the percentage of CD177-expressing neutrophils. CONCLUSION: Membrane expression of CD177 on circulating neutrophils is increased in patients with ASV and in those with SLE, but not in RA patients. However, primed neutrophils from CD177-negative individuals also express mPR3 and are susceptible to anti-PR3-mediated oxidative burst, suggesting that recruitment of CD177-independent mPR3 is involved in anti-PR3-induced neutrophil activation.

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.

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.

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.

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.