Some patients with anti-myeloperoxidase autoantibodies have a C-ANCA pattern

The role of ANCA in the management of cocaine-induced midline destructive lesions or ENT pseudo-granulomatosis with polyangiitis: a London multicentre case series

OBJECTIVE

In this multicentric study involving three London hospitals, we compared ANCA-positive and ANCA-negative cocaine-induced midline destructive lesions (CIMDL) patients to assess how presence of antineutrophil cytoplasmic antibodies (ANCA) may correlate with disease severity. Our secondary aims are to better classify etiology centered around ANCA positivity and, consequently, better disease management.

METHODS

A retrospective review was performed to identify patients with CIMDL seen between January 2019 and December 2022. Population data including age, sex, presentation, endoscopic findings, duration of cocaine use and active use of cocaine, type of treatment, laboratory (including ANCA serology), radiological, and histological findings were collected.

RESULTS

Forty CIMDL patients (25 male, median age of 42 years) were identified. The majority of them (72.5%) presented with either a septal perforation, a saddle nose deformity (22.5%), and/or a palatal fistula (20.0%). ANCA was positive in 71.1% of cases (66.7% p-ANCA). No statistically significant differences in the general characteristics, type of treatment, laboratory results, radiological or histological findings were observed when comparing ANCA-positive and ANCA-negative CIMDL patients or when comparing p-ANCA and c-ANCA patients. Similarly, no statistically significant difference was obtained when comparing the pattern of distribution of lesions between the two groups.

CONCLUSIONS

A large percentage of CIMDL patients showed positive ANCA test (71.1%) and in the majority of the cases a p-ANCA pattern specifically targeting PR3 (p-ANCA, PR3 + MPO-). However, ANCA positivity or presence of a specific ANCA pattern was not associated with more severe presentation or more aggressive disease. Given its similarities to granulomatosis with polyangiitis (GPA), we recommend the use of the term "cocaine-induced ENT pseudo-GPA" instead of CIMDL.

LEVEL OF EVIDENCE

IV Laryngoscope, 134:2609-2616, 2024.

The Role of Neutrophils in ANCA-Associated Vasculitis: The Pathogenic Role and Diagnostic Utility of Autoantibodies

Recent years have brought progress in understanding the role of the neutrophil, dispelling the dogma of homogeneous cells mainly involved in the prime defence against pathogens, shedding light on their pathogenic role in inflammatory diseases and on the importance of antineutrophil-cytoplasmic antibodies' pathogenic role in ANCA-associated vasculitides vasculitis (AAV). Myeloperoxidase (MPO) and proteinase 3 (PR3) expressed in neutrophil granulocytes are the most common targets for ANCAs and contribute to the formation of MPO-ANCAs and PR3-ANCAs which, released to the bloodstream, become an excellent diagnostic tool for AAV. In this study, we focus on increasing the clinical and experimental evidence that supports the pathogenic role of ANCAs in AAV. Additionally, we discuss the diagnostic utility of ANCAs for disease activity and prognosis in AAV. Understanding the central role of ANCAs in AAV is crucial for advancing our knowledge of these complex disorders and developing targeted therapeutic strategies in the era of personalized medicine.

ANCA-associated vasculitis and IgG4-related disease overlap syndrome: a case report and literature review

Anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitides are infrequent autoimmune diseases characterized by inflammation of the walls of small vessels leading to tissue and endothelial damage. On the other hand, IgG4-related disease is a fibroinflammatory disease characterized histologically by lymphoplasmacytic infiltrates with IgG4+ plasma cells, storiform fibrosis, and obliterative phlebitis that may affect nearly every organ of the body. There are similarities in clinical, serological, radiological, and histopathological features between both diseases, and hence, they usually mimic each other complicating the differential diagnosis. Furthermore, reports of patients with the coexistence of both conditions (overlap syndrome) have been reported. We herein report a patient with an unequivocal diagnosis of ANCA-associated vasculitis, specifically granulomatosis with polyangiitis (posterior uveitis, polyneuropathy, pauci-immune glomerulonephritis with crescent formation and granulomas, and MPO-ANCA positivity) and IgG4-related disease (thoracic aortitis, tubulointerstitial nephritis with prominent IgG4+ plasma cell infiltration, fibrosis, and obliterative arteritis, high levels of serum IgG4, and eosinophilia) overlap syndrome.

The biology, pathogenetic role, clinical implications, and open issues of serum anti-neutrophil cytoplasmic antibodies

Anti-neutrophil cytoplasmic antibodies (ANCA) are a group of autoantibodies, predominantly IgG, involved in the pathogenesis of several autoimmune disorders, detected either through indirect immunofluorescence or enzyme-linked immunosorbent assay. By means of indirect immunofluorescence, the main patterns are C-ANCA (cytoplasmic) and P-ANCA (perinuclear), while proteinase 3 (PR3) and myeloperoxidase (MPO) represent the main autoantigens in granulomatosis with polyangiitis and microscopic polyangiitis, both belonging to the family of ANCA-associated vasculitis (AAV). While several experiments established the pathogenicity of MPO-ANCA, evidence remains elusive for PR3-ANCA and an additional target antigen, i.e. LAMP2, has been postulated with specific clinical relevance. The presence of a subset of AAV without ANCA may be explained by the presence of further target antigens or the presence of molecules in blood which make ANCA undetectable. A rise in ANCA titers is not necessarily predictive of a flare of disease in AAV if not accompanied by clinical manifestations. ANCA may develop through variable mechanisms, such as autoantigen complementarity, apoptosis impairment, neutrophil extracellular traps dysfunction and molecular mimicry. We will provide herein a comprehensive review of the available evidence on the biological mechanisms, pathogenetic role, and clinical implications of ANCA testing and disease management. Further, we will address the remaining open challenges in the field, including the role of ANCA in inflammatory bowel disease and in cocaine-induced vasculitis.

Comparison between enzyme-linked immunosorbent assay and indirect immunofluorescence for detection of antineutrophil cytoplasmic antibodies

Objective

To evaluate the performance of enzyme-linked immunosorbent assay and indirect immunofluorescence methods for the detection of antineutrophil cytoplasmic antibodies in a routine clinical laboratory setting.

Methods

A total of 227 samples were tested by indirect immunofluorescence and enzyme-linked immunosorbent assay with antigen specificity for antiproteinase 3 and antimyeloperoxidase. The proportions of positive samples were compared by McNemar hypotheses and agreement was described by Cohen’s Kappa coefficient.

Results

The agreement of the tests was 96.5%, and the Kappa coefficient obtained was 0.70 (95%CI: 0.50-0.90; p<0.001). Considering indirect immunofluorescence as the gold standard, the sensitivity of the enzyme-linked immunosorbent assay was 0.62 and the specificity was 0.99, with diagnostic accuracy in 96% of cases. Some samples were negative in enzyme-linked immunosorbent assay and positive in indirect immunofluorescence. This situation occurred in all immunofluorescence patterns, but particularly in atypical patterns. Two samples with antiproteinase 3 positivity were considered negative in indirect immunofluorescence.

Conclusion

The enzyme-linked immunosorbent assay had high specificity but lower sensitivity. The performance of indirect immunofluorescence increases diagnostic sensitivity, while the search for antiproteinase 3 by enzyme-linked immunosorbent assay may also add diagnostic power.

A Case of Diffuse Alveolar Hemorrhage Associated with High-Titer of MPO-ANCA Demonstrating Cytoplasmic Staining Pattern

Diffuse alveolar hemorrhage (DAH) is a life-threatening complication of ANCA-associated vasculitis (AAV) that requires urgent recognition and treatment. A presumptive diagnosis is often rendered without histopathology if concordant positivity of ANCA by indirect immunofluorescence (IIF) and ELISA assays, i.e., P-ANCA+/myeloperoxidase (MPO) Ab+ or C-ANCA+/proteinase-3 (PR3) Ab+, is documented in the context of pulmonary-renal syndrome or rapidly progressive glomerulonephritis. In this respect, the discordance between IIF and ELISA assays poses a diagnostic challenge in the absence of convincing histopathology and involves the risks of delaying the implementation of timely immunosuppressive therapy. Here, we report a 74-year-old woman who developed DAH and was found to have a high titer of MPO-ANCA exhibiting cytoplasmic staining on IIF, i.e., MPO-C-ANCA. The literature suggests that the availability of distinct epitopes on the MPO molecule dictates the perinuclear versus cytoplasmic staining pattern, which potentially explains the discordance between ELISA and IIF assays. Her DAH was controlled in association with seven sessions of plasmapheresis, methylprednisolone 1 gram daily for 3 days followed by 1 mg/kg/day, and rituximab. This case exemplifies the importance of consideration of pretest probability of suspected diagnosis that would realize a plausible interpretation of seemingly inconsistent serological profile and its effective incorporation into the diagnostic reasoning.

A challenging diagnosis of MPO-C-ANCA EGPA

Eosinophilic granulomatosis with polyangiitis (EGPA) is a multisystemic small-vessel vasculitic disease that can present with positive MPO-P-ANCA (myeloperoxidase-perinuclear-anti-neutrophil cytoplasmic antibody). It is a rare condition that is difficult to diagnose. We present the case of a 64-year-old man with late-onset adult asthma and treated nasopharyngeal carcinoma who initially presented to us with proximal myopathy. Thereafter, he developed a constellation of fleeting symptoms which included rhinosinusitis, mononeuritis multiplex, skin vasculitis and arthritis. Blood investigations showed that he had eosinophilia, and skin biopsy demonstrated dermal vasculitis with eosinophils. He was found to be MPO-C-ANCA positive, and although initially thought to have granulomatosis with polyangiitis, the diagnosis was later revised to EGPA. This case highlights the diagnostic challenges with atypical presentations of EGPA and also presents a rare case of positive MPO-C-ANCA that has never been described in EGPA before.

MPO-C-ANCA-associated necrotising and crescentic glomerulonephritis

The patterns of ANCA staining usually relate closely to antibodies against myeloperoxidase and proteinase-3. C-ANCA is mainly antibodies to proteinase-3 and P-ANCA is antibodies to myeloperoxidase. C-ANCA with antibodies to MPO with clinical sequelae is unusual.

Utility of immunologic testing in suspected rheumatologic disease

The use of diagnostic testing in the clinical practice of medicine has been a shifting landscape from the time that the first blood test was utilized. This is no different in the field of immunology and in particular rheumatology. As the field of immunology is relatively young, the clinical tests are not well established and therefore guidelines for use are still under debate. In this review, we seek to look at some of the key autoantibodies, as well as other tests that are available to diagnose suspected rheumatologic disease, and examine how to best use these tests in the clinic. In particular, we will focus on the anti-nuclear antibodies, anti-neutrophil cytoplasmic antibodies, complement, cryoglobulins, rheumatoid factor, and anti-citrullinated protein antibodies.

Myeloperoxidase-antineutrophil Cytoplasmic Antibodies with Cytoplasmic Fluorescence Pattern

We report here two rare cases of myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA)-positive Wegener's granulomatosis (limited variant) which deceptively produced a cytoplasmic (C-ANCA) pattern on indirect immunofluorescence.

Natural autoantibodies to myeloperoxidase, proteinase 3, and the glomerular basement membrane are present in normal individuals

Anti-neutrophil cytoplasmic antibodies (ANCAs) have a pathogenic role in ANCA-associated vasculitis. The origin of ANCAs and anti-glomerular basement membrane (GBM) antibodies, however, is unknown. In this study, we determined whether natural autoantibodies against myeloperoxidase (MPO), proteinase 3 (PR3), and GBM were present in each of 10 healthy Chinese and Swedish individuals, negative for all three antigens by routine ELISA. Antibodies were purified from isolated IgG by antigen-specific affinity columns. Natural anti-GBM autoantibodies gave a linear staining pattern along the GBM of human renal sections. On ethanol-fixed granulocytes, both natural anti-MPO and anti-PR3 autoantibodies gave cytoplasmic staining. The titers of natural anti-MPO/PR3 autoantibodies were significantly lower than those from patients with vasculitis. In competition ELISA, the binding of natural anti-MPO autoantibodies could be inhibited by MPO, but not by PR3 or noncollagenous domains from type IV collagen. The same specificity results were found for natural anti-PR3 and anti-GBM autoantibodies. Overall, individuals of the Chinese origin had more natural autoantibodies than did those of the Swedish origin, but no other differences were found. Hence, our study shows that healthy individuals have masked circulating, noncross-reactive, antigen-specific natural autoantibodies against MPO, PR3, and GBM in their serum and IgG fractions. Further studies are needed to determine their role if any in the etiology of ANCA-associated vasculitis and anti-GBM disease.

Clinical and pathophysiological significance of anti-neutrophil cytoplasmic autoantibodies in vasculitis syndromes

Necrotizing vasculitis of small blood vessels is a rare condition, but when it affects important organs it can lead to life-threatening organ damage and death. Thus, recognizing these conditions at an early stage before they spread to become systemic is a constant challenge to clinical medicine. The objectives of this review are: to give advice on clinical indications for ANCA diagnostics and laboratory procedures for highly specifically detecting the most important ANCA; to provide some data on the autoantigens involved in ANCA reactivity in small vessel vasculitides; and to discuss at the occurrence of ANCA in different vasculitic populations and at different stages of disease. One important task for the near future will be to standardize the assays used for ANCA detection/quantification and to harmonize the results given to clinicians by ensuring that international reference reagents are used by laboratories and the diagnostic industry. Finally, the author has attempted to summarize the role that ANCA are currently believed to play in the immuno-inflammatory events that take place in tissues and that affect small vessels in idiopathic vasculitis. The review concludes that the presence of ANCA is likely to become an important criterion for diagnosing idiopathic small vessel vasculitis.

Antineutrophil cytoplasmic autoantibodies: how should the biologist manage them?

Antineutrophil cytoplasmic antibodies (ANCA) are directed against enzymes found in the granules of the polymorphonuclear (PMN) leukocytes. They are detected by indirect immunofluorescence microscopy assays on human ethanol fixed neutrophils. Three different fluorescence patterns can be distinguished: a cytoplasmic pattern (cANCA), a perinuclear pattern (pANCA), and an atypical pattern (aANCA). The use of other fixatives, e.g., formalin and methanol, allows differentiation between the pANCA and the antinuclear antibodies. ANCA specificity is determined by solid phase assays (ELISA, immunodot, and multiplex assay). ANCA with high titres and defined specificities (antiproteinase 3 [PR 3] or antimyeloperoxidase [MPO]) are proven to be good serological markers of active primary systemic vasculitis: c/PR 3-ANCA for Wegener's granulomatosis and p/MPO-ANCA for microscopic polyangiitis. The former have higher sensitivity and specificity for Wegener's granulomatosis than the latter for microscopic polyangiitis. ANCA with low titres and unknown specificity have been detected in a wide range of inflammatory and infectious diseases leading to a critical reappraisal of the diagnostic significance of ANCA testing. Physicians must keep in mind the possible occurrence of infectious diseases like subacute endocarditis that could be dramatically worsened by irrelevant immunosuppressive therapy. ANCA findings in certain manifestations, such as the pulmonary-renal syndrome in which massive pulmonary hemorrhage can quickly be life-threatening, warrant ANCA testing as an emergency test for patient care.

Prevalence and clinical significance of antineutrophil cytoplasmic antibodies in Churg-Strauss syndrome

OBJECTIVE

Churg-Strauss syndrome (CSS) is classified among the so-called antineutrophil cytoplasmic antibody-associated systemic vasculitides (AASVs) because of its clinicopathologic features that overlap with the other AASVs. However, while antineutrophil cytoplasmic antibodies (ANCAs) are consistently found in 75-95% of patients with Wegener's granulomatosis or microscopic polyangiitis, their prevalence in CSS varies widely and their clinical significance remains uncertain. We undertook this study to examine the prevalence and antigen specificity of ANCAs in a large cohort of patients with CSS. Moreover, we evaluated the relationship between ANCA positivity and clinicopathologic features.

METHODS

Immunofluorescence and enzyme-linked immunosorbent assay were used to determine the presence or absence of ANCAs in 93 consecutive patients at the time of diagnosis. The main clinical and pathologic data, obtained by retrospective analysis, were correlated with ANCA status.

RESULTS

ANCAs were present by immunofluorescence in 35 of 93 patients (37.6%). A perinuclear ANCA (pANCA) pattern was found in 26 of 35 patients (74.3%), with specificity for myeloperoxidase (MPO) in 24 patients, while a cytoplasmic ANCA pattern, with specificity for proteinase 3, was found in 3 of 35 patients (8.6%). Atypical patterns were found in 6 of 30 patients with anti-MPO antibodies (20.0%). ANCA positivity was associated with higher prevalences of renal disease (51.4% versus 12.1%; P < 0.001) and pulmonary hemorrhage (20.0% versus 0.0%; P = 0.001) and, to a lesser extent, with other organ system manifestations (purpura and mononeuritis multiplex), but with lower frequencies of lung disease (34.3% versus 60.3%; P = 0.019) and heart disease (5.7% versus 22.4%; P = 0.042).

CONCLUSION

ANCAs are present in approximately 40% of patients with CSS. A pANCA pattern with specificity for MPO is found in most ANCA-positive patients. ANCA positivity is mainly associated with glomerular and alveolar capillaritis.

Increased monocyte transcription of the proteinase 3 gene in small vessel vasculitis

Proteinase 3 (PR3) is a pleiotropic and destructive serine protease and it is also a major target for autoantibodies in systemic small vessel vasculitis. We have shown recently that patients in stable remission have increased circulating levels of PR3, independent of autoantibody titre, inflammation, neutrophil degranulation and renal function. Here we explore the possibility of increased PR3 gene transcription. RNA was purified from peripheral blood monocytes from vasculitis patients and controls. Specific mRNA was measured by TaqMan real-time polymerase chain reaction (PCR). The monocyte-like cell lines THP-1 and U937 and human peripheral blod monocytes from healthy controls were stimulated with cytokines and lipopolysaccharide (LPS) for different time periods. PR3 protein was measured in plasma with enzyme-linked immunosorbent assay (ELISA). The median result for PR3 mRNA was 9.6 (1.8-680) for 22 patients, compared to 1 (0.1-2.8) for the 15 healthy controls. Elastase expression was also significantly increased, whereas myeloperoxidase and interleukin-8 were not. Stimulation of monocytes with tumour necrosis factor (TNF)-alpha, interferon (IFN)-gamma or LPS did not result in any increase of PR3 or elastase transcription, whereas interleukin (IL)-8 transcription was increased 10-fold. Circulating monocytes from patients with systemic vasculitis display increased PR3 gene transcription compared to healthy controls and patients with sytemic lupus erythematosus (SLE). This may be important for the development of vasculitis. Our results do not favour a role for cytokines, antineutrophil cytoplasmic antibodies (ANCA) or immunosuppressive medication in the upregulation of PR3 transcription in vasculitis.

Monitoring proteinase 3 antineutrophil cytoplasmic antibodies for detection of relapses in small vessel vasculitis

The clinical usefulness of antineutrophil cytoplasmic antibodies (ANCAs) in the monitoring of patients treated for small vessel vasculitis is debated. A capture enzyme-linked immunosorbent assay (ELISA) based on anti-proteinase 3 (anti-PR3) monoclonal antibody 4A3 has previously been proven to be superior to indirect immunofluorescence (IIF) and standard ELISA for the diagnosis of vasculitis. The present study compared the effectiveness of the capture ELISA for the detection of disease relapse. Samples from patients with relapses and remissions (relapse and remission samples, respectively) were identified through the database of the Glomerular Disease Collaborate Network. Twenty-one relapse samples and 49 remission samples were analyzed by the capture PR3-ANCA ELISA from Wieslab AB, the standard PR3-ANCA ELISA from Inova, and IIF. A Medline search was performed to identify published data on ANCA status at relapse. The capture ELISA was positive for 21 instances of relapses in 14 patients, while the standard ELISA and IIF each failed to detect 2 relapses (P was not significant). By using a higher cutoff value, the capture ELISA correctly categorized 84% of the remission samples and 81% of the relapse samples. Similar degrees of discrimination could be achieved by IIF but not by the standard ELISA. In previously published series, the median proportions of patients positive at relapse were 100% by IIF (range, 75 to 100%) and 86% by standard ELISA (range, 38 to 100%). The corresponding values for a rise that accompanied or preceded a relapse were 75% (range, 20 to 100%) for IIF and 50% (range, 25 to 81%) for ELISA. The capture PR3-ANCA ELISA is a sensitive tool for the detection of relapses. Larger studies are needed to detect differences between methods. Negative results by tests for ANCAs are rare during relapses.

Immunofluorescent patterns produced by antineutrophil cytoplasmic antibodies (ANCA) vary depending on neutrophil substrate and conjugate

BACKGROUND

The "International consensus statement on testing and reporting antineutrophil cytoplasmic antibodies (ANCA)" advocates screening by indirect immunofluorescence (IIF), but external quality assessment programmes often demonstrate different IIF patterns for a single serum.

AIM

To determine whether the variation in IIF patterns can be attributed solely to errors in interpretation.

METHODS

This study compared the IIF patterns produced by four sera (two with cytoplasmic or C-ANCA; one with perinuclear or P-ANCA with myeloperoxidase (MPO) specificity; and one P-ANCA without MPO specificity) that were tested in 11 different laboratories. The sera were examined according to individual laboratory protocols at dilutions of 1/10 to 1/40 using P1 (n = 4), P2 (n = 2), P3 (n = 2), or in house (n=3) neutrophil preparations and conjugates from manufacturers C1 (n = 3), C2 (n = 1), C3 (n = 2), C4 (n = 1), C5 (n = 2), and C6 (n = 2). The IIF patterns were noted in each laboratory, the testing repeated, and the fluorescent patterns photographed and subsequently discussed at a meeting of the Australian ANCA study group.

RESULTS

All IIF patterns described in individual laboratories were confirmed on retesting and by the ANCA study group. Neutrophil substrates produced commercially or in house varied in their ability to demonstrate cytoplasmic granularity and interlobular accentuation, which distinguish between "C-ANCA" and "C-ANCA (atypical)". All commercial and in house neutrophil substrates demonstrated neutrophil nuclear extension of P-ANCA fluorescence, which correlates with MPO specificity. However, eight assays (eight of 43) from eight laboratories resulted in IIF patterns different from those usually seen. One of these produced a C-ANCA (atypical) rather than a C-ANCA pattern. The other seven resulted in at least some cytoplasmic fluorescence when the consensus pattern was P-ANCA with (n = 4) or without (n = 3) MPO specificity. These assays used three different commercial and one in house neutrophil substrate, and six different conjugates, with anti-IgG, anti-(Fab)'(2), anti-Ig (heavy and light chain), and anti-G, A, and M activity. Four of the seven assays tested on commercial substrates had used the manufacturer's conjugates.

CONCLUSIONS

This study indicates that the variation in IIF patterns seen with ANCA positive sera tested in different laboratories does not necessarily result from errors in the interpretation of patterns and cannot be attributed solely to the use of a particular neutrophil substrate or conjugate, or to the use of substrate from one manufacturer and conjugate from another.

Clinical use of serological tests for antineutrophil cytoplasmic antibodies. What do the studies say?

Trustworthy and clinically useful laboratory test results depend on high quality laboratory knowledge and performance and on close collaboration with experienced clinicians. Just like a diagnosis can only be made by contrasting it to a number of differential diagnoses, a prototype autoantibody profile can only be recognized if autoantibodies that partially mimic the former are just as well-known. In antineutrophil cytoplasmic antibody (ANCA)-associated small vessel vasculitides the characteristic autoantibody profile can only be demonstrated by use of at least two different methodologies and an assay-specific cut-off selection that clearly distinguishes between strongly positive and disease control low positive to negative values. Local serum banks containing samples from patients with well-characterized chronic immunoinflammatory diseases and ANCA-associated vasculitides are needed for such important studies whether in-house or commercial assays are used.

Apolipoprotein H, a new mediator in the inflammatory changes ensuring in jeopardised human myocardium

AIM

To investigate the presence of membrane "flip flop" in ischaemic human myocardium, we assessed depositions of apolipoprotein H (apoH; beta 2-glycoprotein 1) in ischaemic myocardium. Serum protein apoH can bind to negatively charged phospholipids and can also inhibit blood coagulation in vitro. We hypothesised that, because of its affinity for phosphatidyl serine, apoH might bind to "flip flopped" cells and would therefore be useful as a marker for membrane flip flop in vivo.

METHODS

Myocardial tissue specimens were obtained from patients who had died within 14 days of acute myocardial infarction.

RESULTS

Immunohistochemical analysis of these specimens revealed that apoH was selectively deposited in infarcted areas of human myocardium of at least one day's duration. Depositions of apoH were not found in non-ischaemic myocardial tissue samples obtained from patients who died from other (extracardial) causes. In vitro experiments with the human leukaemia T cell line Jurkat, subjected to apoptosis by etoposide, showed that apoH was bound to the membrane of apoptotic cells. However, these experiments also indicated that flip flop itself is not sufficient for apoH binding. In addition, Jurkat cells that bound apoH were positive for activated complement complexes, as was also found in the human heart.

CONCLUSIONS

These results suggest that apoH is involved in the inflammatory processes that occur in ischaemic myocardium.

Antineutrophil cytoplasmic antibodies (ANCA) and systemic vasculitis: update of assays, immunopathogenesis, controversies, and report of a novel de novo ANCA-associated vasculitis after kidney transplantation

OBJECTIVES

To characterize antineutrophil cytoplasmic antibodies (ANCA), their major autoantigens, disease associations, and pathophysiology in systemic vasculitides. To describe a patient with a novel de novo ANCA-associated vasculitis after kidney transplantation.

METHODS

We reviewed and compiled the literature on ANCA-related topics and systemic vasculitis. Laboratory and clinical data from a cadaveric kidney transplant patient who developed necrotizing vasculitis involving glomerular capillaries, with crescent formation associated with P-ANCA and myeloperoxidase, were analyzed.

RESULTS

Large-scale multi-center testing of patient and normal sera by the European ANCA Assay Standardization Project using immunofluorescence assays and enzyme immunoassays indicate the assays have good sensitivity and specificity, and diagnostic utility for ANCA-associated vasculitis. A few investigations covering basic and clinical research with ANCA remain controversial: whether endothelial cells do or do not express a 29-kd neutral serine protease termed proteinase-3 (PR-3), the target of ANCA in most individuals with Wegener's granulomatosis, and whether anti-myeloperoxidase (MPO) ANCAs recognize a restricted number of epitopes on MPO. This issue has relevance for using monoclonal antibodies to treat patients with vasculitis who have adverse effects from immunosuppressive drugs. The two allelic forms of FcgammaRIIa (H131/R131) and the two of FcgammaRIIlb (NA1/NA2) are discussed as possible inheritable genetic elements for vasculitic disorders and for signaling responses. Stimulatory and costimulatory molecules, and cytokine profiles of T lymphocytes are characterized to show that these cells are actively involved in the ANCA-associated vasculitides. The patient described had a de novo ANCA associated small vessel vasculitis which developed after renal transplantation.

CONCLUSIONS

There have been significant advances in the development of sensitive and specific ANCA assays. The immunopathogenetic mechanism of ANCA involves the constitutive FcgammaRs, ligands, and signaling responses to activate cytokine-primed neutrophils. This may lead to the generation of reactive oxygen intermediates, degranulation, and secretion of intracellular granule contents, and ultimately inflammation and vasculitis.

IgM anti-myeloperoxidase antibody-secreting lymphocytes are present in the peripheral repertoire of lupus mice but rarely differentiate into IgG-producing cells

Two IgM, kappa anti-myeloperoxidase (MPO) monoclonal antibodies, 6D6 and 9B5, bound to MPO in a solid-phase enzyme-linked immunosorbent assay were derived from the splenocytes of (NZB x NZW) F1 and MRL/lpr-lpr mice, respectively. 6D6 gave a characteristic perinuclear immunofluorescence staining pattern on ethanol-fixed human neutrophils, bound to the native form of MPO by immunoblotting and had a high constant affinity for MPO as demonstrated by real-time specific interaction. 9B5 produced a cytoplasmic immunofluorescence staining pattern, reacted with the heavy chain of MPO and had a low constant affinity for MPO. The heavy-and light-chain variable region genes of monoclonal antibodies (mAb) 6D6 and 9B5 were sequenced and found to be highly homologous to germline genes and to contain negatively charged amino acids in the complementarity determining regions. IgM MPO-binding activity was observed in most BW and MRL/lpr-lpr mouse sera, which may correspond to polyclonal activation of B cells, whereas IgG anti-MPO antibodies could be rarely detected. Thus, this study indicates that (i) BW and MRL/lpr-lpr mice do not delete IgM anti-MPO secreting B cells, do not maintain these B cells in a state of anergy, but most individuals are not able to spontaneously induce the class-switching of this autoantibody population; (ii) IgM anti-MPO antibodies can recognize different epitopes on MPO and produce different immunofluorescence staining pattern on ethanol-fixed human neutrophils, as demonstrated by the immunochemical properties of the two lupus-mouse derived mAb.

A comparison of commercial and in-house ELISAs for antineutrophil cytoplasmic antibodies directed against proteinase 3 and myeloperoxidase

This study compares the concordance of results in different ELISAs for antineutrophil cytoplasmic antibodies (ANCA) directed against proteinase 3 (PR3) or myeloperoxidase (MPO). Sera were considered "true positives" if they were positive according to the manufacturer's criteria in a least three of the five PR3-ANCA ELISAs, or in at least four of the six MPO-ANCA ELISAs. Of the 26 sera that demonstrated cytoplasmic fluorescence (C-ANCA), 23 (89%) contained PR3-ANCA and three (11%) had MPO-ANCA. Two sera that were negative by indirect immunofluorescence (IIF) contained PR3-ANCA. Of the 26 sera with perinuclear fluorescence (P-ANCA), 19 (73%) contained MPO-ANCA, and one (4%) had PR3-ANCA. Six sera with P-ANCA did not have PR3- or MPO-ANCA. No serum that was negative by IIF contained MPO-ANCA. For the different PR3-ANCA ELISAs, sensitivities ranged from 88 to 100%, and specificities from 91 to 100%. For the MPO-ANCA ELISAs, sensitivities varied from 59 to 100% and specificities from 83 to 100%. The highest sensitivity and specificity for both the PR3- and MPO-ANCA ELISAs were obtained with the IBL and Eurodiagnostica assays. The in-house PR3-ANCA ELISA performed slightly less well than the commercial assays, but the performance of the in-house MPO-ANCA assay was comparable or better.

A review of immunofluorescent patterns associated with antineutrophil cytoplasmic antibodies (ANCA) and their differentiation from other antibodies

AIM

To describe the neutrophil fluorescent patterns produced by antineutrophil cytoplasmic antibodies (ANCA) with different antigen specificities, and by other auto- and alloantibodies.

BACKGROUND

Most sera from patients with active generalised Wegener's granulomatosis result in diffusely granular cytoplasmic neutrophil fluorescence with internuclear accentuation (cANCA) and proteinase 3 (PR3) specificity. About 80% of the sera from patients with microscopic polyangiitis result in perinuclear neutrophil fluorescence with nuclear extension (pANCA) and myeloperoxidase (MPO) specificity, or a cANCA pattern with PR3 specificity. However, many different neutrophil fluorescence patterns are noted on testing for ANCA in routine immunodiagnostic laboratories.

METHODS

Sera sent for ANCA testing, or containing a variety of auto- and alloantibodies, were studied. They were examined by indirect immunofluorescence according to the recommendations of the first international ANCA workshop, and for PR3 and MPO specificity in commercial and in-house enzyme linked immunosorbent assays (ELISA).

RESULTS

Sera with typical cANCA accounted for only half of all neutrophil cytoplasmic fluorescence. Other sera had "flatter" fluorescence without internuclear accentuation, and the corresponding antigens included MPO and bactericidal/permeability increasing protein (BPI), but were usually unknown. Peripheral nuclear fluorescence without nuclear extension occurred typically when the antigens were BPI, lactoferrin, lysozyme, elastase, or cathepsin G. Most types of ANA were evident on ethanol fixed neutrophil nuclei. AntidsDNA, antiRo, and antilamin antibodies resembled pANCA. Antimicrobial and antiribosomal antibodies produced cytoplasmic fluorescence, and antiGolgi antibodies, a pANCA. Sera from patients with anti-smooth muscle antibodies were associated with cytoplasmic fluorescence. There was no neutrophil fluorescence with anti-skeletal muscle and anti-heart muscle antibodies, anti-liver/kidney microsomal, antithyroid microsomal, or antiadrenal antibodies. Alloantibodies such as antiNB1 typically resulted in cytoplasmic fluorescence of only a subpopulation of the neutrophils.

CONCLUSIONS

The ability to distinguish between different neutrophil fluorescence patterns, and the patterns seen with other auto- and alloantibodies is helpful diagnostically. However, the demonstration of MPO or PR3 specificity by ELISA will indicate that the neutrophil fluorescence is probably clinically significant, and that the diagnosis is likely to be Wegener's granulomatosis or microscopic polyangiitis.

Anti-neutrophil cytoplasm autoantibodies (ANCA). The need for specific and sensitive assays

Anti-neutrophil cytoplasm antibodies (ANCA) are a group of autoantibodies primarily associated with systemic vasculitis. Hitherto, the method of choice for ANCA detection has been indirect immunofluorescence (IIF). By this method two major patterns can be seen: a cytoplasmic pattern (cANCA) or a perinuclear pattern (pANCA). The cANCA pattern is most often caused by antibodies directed against proteinase-3 (PR3) and in rare cases it is caused by anti-myeloperoixdase (MPO) antibodies. The pANCA pattern can de caused by antibodies directed against a large group of proteins i.e. MPO, lactofenin and bactericidal/permeability-increasing protein. Often there is a discrepancy between the results obtained by IIF and those reported from the use of assays with purified antigens. This causes confusion. Until now only anti-PR3 and anti-MPO have been found of any clinical value. Therefore, it would be more proper to use assays with these highly purified antigens instead of an unspecific method like IIF.

Clinical evaluation of a capture ELISA for detection of proteinase-3 antineutrophil cytoplasmic antibody

Detection of antineutrophil cytoplasmic antibodies (ANCA) has become a useful tool in the diagnosis of Wegener's granulomatosis and microscopic polyangiitis. However, the results obtained with indirect immunofluorescence (IIF) and by ELISA for ANCA demonstration do not always correlate. A possible explanation for this finding could be that proteins are denatured during the process of antigen purification or during coating onto the solid phase. To avoid this possibility, a monoclonal antibody to PR3 that is precoated on the plate can be used. In the present study we have used the monoclonal antibody (MoAb) 4A3 for the capture of PR3 in an ELISA, and a clinical evaluation of the diagnostic properties of the new capture ELISA has been made. The sensitivity of the capture PR3-ANCA ELISA was 85% in a material of c-ANCA positive sera. A specificity of 90% was obtained in analyses from patients having various forms of glomerulonephritis. There was a significantly higher diagnostic sensitivity of the capture PR3-ANCA ELISA (85%) compared to c-ANCA by IIF (58%) in patients with Wegener's granulomatosis with renal involvement. Capture PR3-ANCA and direct ELISA for MPO-ANCA together gave a diagnostic sensitivity of 98%, versus 75% using IIF. In conclusion, the capture PR3-ANCA ELISA seems to be a valuable tool in the diagnosis of Wegener's granulomatosis with renal involvement. Preliminary data suggest that the technique may have an advantage over direct ELISA for PR3-ANCA, as well as in the follow-up of c-/PR3-ANCA associated vasculitides. However, further prospective studies are needed to clarify this premise.

Anticytokeratins are a potential source of false-positive indirect immunofluorescence assays for C-ANCA

Antibodies to neutrophil cytoplasmic antigens (ANCA) targeted toward granule enzymes have been recognized as a valuable diagnostic tool in the detection of Wegener's granulomatosis and systemic vasculitides. However, the most commonly used method of detection, the indirect immunofluorescence assay, is prone to false-positive results due to antibodies of different pathological significance either targeted to, or cross-reacting with, similarly distributed epitopes. Using double immunofluorescence, the present study demonstrates that anticytokeratin antibodies are able to produce false-positive C-ANCA immunofluorescence assays. In addition, a case of natural appearance of cytokeratin-reactive antibodies causing a false-positive "pseudo-ANCA" staining pattern in a patient presenting with sepsis is reported. Since the expression of cytokeratins is almost exclusively confined to epithelial cells, the most plausible explanation for both phenomena is a crossreaction of anticytokeratin antibodies with granule associated epitopes. Due to the natural appearance of anticytokeratin antibodies in association with a variety of other pathologic entities, it is of crucial importance for the diagnostic significance of the C-ANCA immunofluorescence assay to exclude anticytokeratin caused false-positive results. It is shown that supplementary indirect immunofluorescence tests performed on cultured human epithelial cells readily distinguish anticytokeratin caused "pseudo-ANCA" from true C-ANCA.

Antineutrophil cytoplasmic antibodies: major autoantigens, pathophysiology, and disease associations

Antineutrophil cytoplasmic antibodies (ANCA) are important serological markers for the primary systemic vasculitides, including microscopic polyarteritis and necrotizing crescentic glomerulonephritis. Numerous reports have established the clinical utility of ANCA titer in monitoring disease activity, relapses, and response to treatment. ANCA, detected by indirect immunofluorescence (IIF) assays using patient's serum and ethanol-fixed human neutrophils, produce two common fluorescent staining patterns: cytoplasmic (C-ANCA), involving a 29-kD neutral serine protease termed proteinase 3 (PR3), and perinuclear (P-ANCA), the result mainly of myeloperoxidase (MPO), but occasionally by other components of the azurophilic granules including lysozyme, elastase, cathepsins, and lactoferrin. Some sera contain granulocyte-specific antinuclear antibodies (GS-ANA), which require formaldehyde fixation of neutrophils to cross link cytoplasmic antigens for distinguishing between ANCA and the GS-ANA by IIF. Positive IIF is confirmed by Western blot analysis or specific enzyme-linked immunosorbent assay for PR3, MPO, and other neutrophil granule antigens. The C-ANCA pattern is highly specific for Wegener's granulomatosis, a disease characterized by granulomatous inflammation, necrotizing and crescentic glomerulonephritis, and vasculitis; P-ANCA is found in sera of individuals with vasculitis, glomerulonephritis, and several other diseases. ANCA are predominantly immunoglobulin (Ig)G isotype, but may be IgM and IgA. Various pathophysiologic mechanisms have been proposed involving ANCA-mediated neutrophil activation in a hypothetical model of vasculitic diseases: positive signals via the FcgammaRII (CD32) receptor after IgG-ANCA binding to membrane-associated PR3, relevant cytokines, production of adhesion molecules on both activated neutrophils and endothelial cells, and the release of neutrophil reactive oxygen species and degranulation causing endothelial cell damage. Interference of C-ANCA with PR3 proteolysis and PR3 inhibition physiologically by the alpha1-proteinase inhibitor may have a pathogenic role. No convincing data have been reported for the existence of autoreactive T lymphocytes reactive to any degree with the neutrophil azurophilic enzymes. Studies of various drug- and infectious agent-related diseases and ANCA may contribute to understanding the mechanism(s) involved in some vasculitides.

Screening for anti-neutrophil cytoplasmic antibodies (ANCA): is indirect immunofluorescence the method of choice?

Detection of ANCA has become an important tool for the diagnosis and monitoring of disease activity in Wegener's granulomatosis (WG). Unfortunately, a group of sera positive by the standard method for ANCA detection, indirect immunofluorescence (IIF), are negative when more specific tests with purified proteins are used. In order to examine this discrepancy we examined groups of sera selected for being (i) C-ANCA-positive by IIF; (ii) positive in proteinase 3 (PR3)-ANCA ELISA; and (iii) from 24 patients with WG. The following assays were used: IIF, PR3-ANCA ELISA and capture PR3-ANCA ELISA using MoAbs against PR3. Furthermore, since granule enzymes are released during coagulation, we also measured ANCA in complex with PR3. To test if granule enzyme release had any influence on ANCA detection, both serum and EDTA-plasma were collected from a patient with active WG. No difference, however, was found. In the IIF-positive group (n = 60) 68% of the sera were positive in PR3-ANCA ELISA, 86% in capture PR3-ANCA ELISA and 80% were positive for the PR3/IgG-ANCA complex. In the PR3-ANCA ELISA group (n = 105) 88% of the sera were positive by IIF, 98% in capture PR3-ANCA ELISA and 53% in the PR3/IgG-ANCA assay. To evaluate the tests clinically sera from 24 patients with WG were examined. In the remission group (n = 10) two patients were positive by IIF, four in the PR3-ANCA ELISA, and five in the capture PR3-ANCA ELISA. Fourteen had active disease, and in this group 11/14 were positive by IIF, 10/14 in PR3-ANCA ELISA and 12/14 by capture-ELISA. The correlation between IIF and capture PR3-ANCA ELISA titre (r = 0.72, P = 0.0095) was better than between PR3-ANCA ELISA and IIF (r = 0.56, P = 0.043). It is concluded that the capture PR3-ANCA ELISA is more sensitive than PR3-ANCA ELISA, and that the capture ELISA can be used for screening of PR3-ANCA.