Native and recombinant proteins to analyze auto-antibodies to myeloperoxidase in pauci-immune crescentic glomerulonephritis

Flexible Amperometric Immunosensor Based on Colloidal Quantum Dots for Detecting the Myeloperoxidase (MPO) Systemic Inflammation Biomarker

Myeloperoxidase (MPO) has been demonstrated to be a biomarker of neutrophilic inflammation in various diseases. Rapid detection and quantitative analysis of MPO are of great significance for human health. Herein, an MPO protein flexible amperometric immunosensor based on a colloidal quantum dot (CQD)-modified electrode was demonstrated. The remarkable surface activity of CQDs allows them to bind directly and stably to the surface of proteins and to convert antigen-antibody specific binding reactions into significant currents. The flexible amperometric immunosensor provides quantitative analysis of MPO protein with an ultra-low limit of detection (LOD) (31.6 fg mL^-1), as well as good reproducibility and stability. The detection method is expected to be applied in clinical examination, POCT (bedside test), community physical examination, home self-examination and other practical scenarios.

Detection of antineutrophil cytoplasmic antibodies (ANCAs): a multicentre European Vasculitis Study Group (EUVAS) evaluation of the value of indirect immunofluorescence (IIF) versus antigen-specific immunoassays

OBJECTIVE

This multicentre study was performed to evaluate the diagnostic accuracy of a wide spectrum of novel technologies nowadays available for detection of myeloperoxidase (MPO) and proteinase 3 (PR3)-antineutrophil cytoplasmic antibodies (ANCAs).

METHODS

Sera (obtained at the time of diagnosis) from 251 patients with ANCA-associated vasculitis (AAV), including granulomatosis with polyangiitis and microscopic polyangiitis, and from 924 disease controls were tested for the presence of cytoplasmic pattern/perinuclear pattern and atypical ANCA (A-ANCA) by indirect immunofluorescence (IIF) (at two sites) and for the presence of PR3-ANCA and MPO-ANCA by eight different immunoassays.

RESULTS

The area under the curve (AUC) of the receiver operating characteristic curve to discriminate AAV from controls was 0.923 (95% CI 0.902 to 0.944) and 0.843 (95% CI 0.814 to 0.871) for the two IIF methods. For the antigen-specific immunoassays, the AUC varied between 0.936 (95% CI 0.912 to 0.960) and 0.959 (95% CI 0.941 to 0.976), except for one immunoassay for which the AUC was 0.919 (95% CI 0.892 to 0.945).

CONCLUSIONS

Our comparison of various ANCA detection methods showed (i) large variability between the two IIF methods tested and (ii) a high diagnostic performance of PR3-ANCA and MPO-ANCA by immunoassay to discriminate AAV from disease controls. Consequently, dual IIF/antigen-specific immunoassay testing of each sample is not necessary for maximal diagnostic accuracy. These results indicate that the current international consensus on ANCA testing for AAV needs revision.

Diagnostic ANCA algorithms in daily clinical practice: evidence, experience, and effectiveness

Detection of antineutrophil cytoplasmic antibodies (ANCA) for ANCA-associated vasculitides (AAV) is based on indirect immunofluorescence (IIF) on ethanol-fixed neutrophils and reactivity toward myeloperoxidase (MPO) and proteinase 3 (PR3). According to the international consensus for ANCA testing, presence of ANCA should at least be screened for by IIF and, if positive, followed by antigen-specific immunoassays. Optimally, all samples are analyzed by both IIF and quantitative antigen-specific immunoassays. Since the establishment of this consensus many new technologies have become available and this has challenged the positioning of IIF in the testing algorithm for AAV. In the current paper, we summarize the novelties in ANCA diagnostics and discuss the possible implications of these developments for the different ANCA algorithms that are currently applied in routine diagnostic laboratories. Possible consequences of replacing ANCA assays by novel methods are illustrated by our data obtained in daily clinical practice. Eventually, it is questioned if there is a need to change the consensus, and if so, whether IIF can be discarded completely, or be used as a confirmation assay instead of a screening assay. Both alternative options require that ANCA requests for AAV can be separated from ANCA requests for gastrointestinal autoimmune diseases.

Performance of two strategies for urgent ANCA and anti-GBM analysis in vasculitis

BACKGROUND

In anti-neutrophil cytoplasmic antibodies (ANCA) associated small vessel vasculitis (AAV), rapid testing for ANCA and anti-glomerular basement membrane (GBM) antibodies may be beneficial for therapeutic purpose.

OBJECTIVE

We analysed the diagnostic performance of two rapid ANCA and anti-GBM test methods in 260 patients with suspected AAV.

METHODS

Between January 2004 and November 2010, we analysed 260 samples by qualitative Dotblot (Biomedical Diagnostics); retrospective analysis followed with directly coated highly sensitive automated Phadia ELiA and ELiA anti-GBM. Results were related to the final clinical diagnosis and compared with routine capture ELISA.

RESULTS

Seventy-four patients had a final diagnosis of AAV (n=62) or anti-GBM disease (n=12). Both Dotblot and ELiA detected all 12 cases of anti-GBM disease; 2 false positive results were found. Dotblot detected ANCA in 56 of 62 AAV patients (sensitivity 90%, NPV 97%), and showed 5 false positives (specificity 97%, PPV 90%). The Phadia ELiA anti-PR3(s) or anti-MPO(s) was positive in 57 of 62 AAV patients (sensitivity 92%, NPV 97%), and had 5 false positives (specificity 97%, PPV 88%). Routine capture ELISA was equally accurate (sensitivity 94%, specificity 97%, PPV 88%, NPV 98%).

CONCLUSION

The Dotblot and Phadia ELiA on anti-GBM, anti-PR3(s) and anti-MPO(s) performed excellently; results were almost identical to routine ELISA. When suspicion of AAV or anti-GBM disease is high and diagnosis is urgently needed, both tests are very powerful for rapid serological diagnosis. Further studies have to confirm the test performances in samples routinely presented for ANCA testing and in follow-up of positive patients.

Antineutrophil cytoplasmic autoantibodies: how are they detected and what is their use for diagnosis, classification and follow-up?

Antineutrophil cytoplasmic antibodies (ANCA) are traditionally detected by an indirect immunofluorescence technique. According to the international consensus on ANCA testing, ANCA should also be tested by antigen-specific tests for myeloperoxidase-ANCA and proteinase 3-ANCA. The direct noncompetitive enzyme-linked immunosorbent assay (ELISA) used to be the method of choice. Nowadays, these assays are called "first-generation" assays. Second-generation tests (capture ELISA) or third-generation tests (anchor ELISA) are more sensitive and specific for ANCA testing. We postulate that ANCA as detected by these newer ANCA tests may replace the need to perform indirect immunofluorescence-based assays. For classification of patients, ANCA serotype seems more important than classifying patients according to their clinical subtype, since genetics, clinical manifestations and response to therapy are more related to ANCA serotype than to clinical subtype. Detection of ANCA to monitor disease activity is still a controversial issue. Treatment based on ANCA levels is at present only experimentally performed in those patients who are treated with B-cell depletion therapy with rituximab. Future studies are needed to establish whether this way of monitoring patients is warranted.

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.

Evaluation of a new fluorescent-enzyme immuno-assay for diagnosis and follow-up of ANCA-associated vasculitis

In this study we have evaluated a new, fully automated fluorescent-enzyme immuno-assay (FEIA) for detection and quantification of anti-PR3 and anti-MPO ANCA in diagnosis and follow-up of ANCA-associated small vessel vasculitis (AAV). PR3- and MPO-ANCA were determined by FEIA technology in (1) sera of 87 consecutive patients with biopsy-proven, pauci-immune necrotizing crescentic glomerulonephritis (NCGN) and 72 controls; (2) 120 sera (60 patients with Wegener's granulomatosis and 60 controls) that were previously used in a multicentre comparison of direct and capture ELISAs for PR3-ANCA; (3) in samples preceding relapse in 23 PR3-AAV patients with and 23 matched PR3-AAV patients without relapse for prediction of relapses. PR3- and/or MPO-ANCA detection in pauci-immune NCGN by FEIA revealed an overall sensitivity of 82.8%. The FEIA specificity was 96% and 100% for PR3- and MPO-ANCA, respectively. The overall sensitivity of MPO- and PR3-ANCA could be increased to 88.5% by lowering the cut-off values without affecting the specificity (ROC-curve analysis), which is similar to a multistep ANCA procedure that combines indirect immunofluorescence with direct and capture ELISAs. The sensitivity for Wegener's granulomatosis (WG) of the PR3-ANCA FEIA (60%) was more comparable to direct ELISAs (64%) than to capture ELISAs (74%). A rise of 100% in ANCA level as measured by FEIA appeared optimal (ROC-curve) for prediction of relapses and such a rise was observed in 26 patients. In 18 of these 26 patients the rise was followed by a relapse (PPV 69%), whereas in 15 of the 20 patients without a rise no relapse was observed (NPV 75%). In conclusion, detection of PR3- and MPO-ANCA by FEIA has excellent performance in terms of diagnosis of AAV patients. Furthermore, detection of rises in PR3-ANCA by FEIA for prediction of relapses gives results comparable to other techniques.

Coexistence of Anti-Glomerular Basement Membrane Antibodies and Myeloperoxidase-ANCAs in Crescentic Glomerulonephritis

BACKGROUND

In a substantial proportion of patients with crescentic glomerulonephritis (CGN), both anti-glomerular basement membrane (GBM) antibodies and antineutrophil cytoplasmic antibodies (ANCAs) with specificity for myeloperoxidase (MPO-ANCA) are detected. In the present study, we questioned whether histological and clinical features of patients with both ANCA and anti-GBM antibodies differ from those of patients with either ANCA or anti-GBM alone.

METHODS

We reviewed the Limburg renal biopsy registry (1978 to 2003; n = 1,373) for cases of CGN. The presence of linear fluorescence on renal biopsy and the presence of ANCA and/or anti-GBM antibodies were measured. Subsequently, we assessed patient characteristics and follow-up and compared histological findings among the different groups.

RESULTS

We identified 46 MPO-ANCA-positive, 10 double-positive, and 13 anti-GBM-positive patients. Mean ages were 63, 64, and 52 years (P = 0.04), and serum creatinine levels were 5.0, 10.3, and 9.6 mg/dL (445, 910, and 850 micromol/L), respectively (P = 0.01). Granulomatous periglomerular inflammation was found in either MPO-ANCA- or double-positive patients, but not in anti-GBM-positive patients with CGN without MPO-ANCAs. Patient survival among the 3 groups was different, although not statistically significant (log rank P = 0.17, with 75%, 79%, and 100% alive at 1 year, respectively). Renal survival analysis showed significant differences among the 3 groups (P = 0.04, with 65%, 10%, and 15% off dialysis therapy at 1 year, respectively).

CONCLUSION

In patients with both anti-GBM antibodies and MPO-ANCAs, histological findings differ from those of patients with anti-GBM antibodies only. However, renal survival in these patients is not better than that in anti-GBM-positive patients and is worse compared with patients with MPO-ANCAs only.

Clinical applications of antineutrophil cytoplasmic antibody testing

PURPOSE OF REVIEW

Antineutrophil cytoplasmic antibodies are closely associated with Wegener granulomatosis, microscopic polyangiitis, and Churg-Strauss syndrome and have contributed to new pathogenetic concepts and improved nomenclature of systemic vasculitides (antineutrophil cytoplasmic antibody-associated vasculitides). However, the application of antineutrophil cytoplasmic antibody testing as a clinical diagnostic tool is still regarded as controversial. This review summarizes the most recent developments in the field, identifies areas of uncertainty, and gives practical guidelines.

RECENT FINDINGS

The problems of antineutrophil cytoplasmic antibody testing include the diversity of antineutrophil cytoplasmic antibody target antigens, assay standardization and performance, the application of antineutrophil cytoplasmic antibody testing in a clinical setting with a low pretest probability, and, finally, the widespread assumption that antineutrophil cytoplasmic antibody titers alone may closely reflect disease activity and therefore may be used to guide therapy.

SUMMARY

Recent findings demonstrate that the combined use of indirect immunofluorescence tests and solid phase assays to detect antineutrophil cytoplasmic antibody directed against myeloperoxidase and proteinase 3 can minimize the occurrence of false-positive antineutrophil cytoplasmic antibody results. Furthermore, the yield of antineutrophil cytoplasmic antibody testing can be improved by the use of a well-standardized test, adherence to published guidelines, and restricting the use of the tests to clinical situations with a rather high pretest probability for antineutrophil cytoplasmic antibody-associated vasculitides. However, treatment decisions should be based on the clinical presentation of the patient and histologic findings and not on the results of antineutrophil cytoplasmic antibody testing alone.

Recombinant autoantigens for diagnosis and therapy of autoimmune diseases

The characteristic of autoimmune diseases resides in the existence of T- and B-cell autoreactivity when directed against self-proteins. Thus autoantibodies are considered to be of diagnostic relevance. The advent of recombinant protein expression technology has made it possible to produce economically high-quality autoantigens for use in immunoassays for detecting autoantibodies in patients' sera. The intention of this short review is to give the reader a brief description of autoantigen production methodologies with their advantages, disadvantages and the limitations of these techniques in the diagnostics of autoimmune diseases. Further possible usage of recombinant autoantigens as tools in investigation and therapy of autoimmune diseases is discussed.

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.

Recombinant autoantigens

Autoimmune diseases frequently manifest themselves in fulminating immune reactions involving T and B cells that lead to the appearance of circulating autoantibodies. Such antibodies are considered to be of diagnostic relevance and may be pathognomonic for their associated autoimmune diseases. The advent of recombinant protein expression technology has made it possible to economically produce high quality autoantigens for use in immunoassays to detect autoantibodies in patients' sera. This short review is intended to give the reader a brief description of the various autoantigen production methodologies with their advantages and disadvantages, and the limitations of these techniques in the diagnostics of autoimmune diseases.