Agreement of anti-neutrophil cytoplasmic antibody measurements obtained from serum and plasma

Clair EW, Ytterberg SR, Stone JH, Robinson WH, Specks U. Activation of a Latent Epitope Causing Differential Binding of Antineutrophil Cytoplasmic Antibodies to Proteinase 3

OBJECTIVE

Proteinase 3 (PR3) is the major antigen for antineutrophil cytoplasmic antibodies (ANCAs) in the systemic autoimmune vasculitis, granulomatosis with polyangiitis (GPA). PR3-targeting ANCAs (PR3-ANCAs) recognize different epitopes on PR3. This study was undertaken to study the effect of mutations on PR3 antigenicity.

METHODS

The recombinant PR3 variants, iPR3 (clinically used to detect PR3-ANCAs) and iHm5 (containing 3 point mutations in epitopes 1 and 5 generated for epitope mapping studies) immunoassays and serum samples from patients enrolled in ANCA-associated vasculitis (AAV) trials were used to screen for differential PR3-ANCA binding. A patient-derived monoclonal ANCA 518 (moANCA518) that selectively binds to iHm5 within the mutation-free epitope 3 and is distant from the point mutations of iHm5 was used as a gauge for remote epitope activation. Selective binding was determined using inhibition experiments.

RESULTS

Rather than reduced binding of PR3-ANCAs to iHm5, we found substantially increased binding of the majority of PR3-ANCAs to iHm5 compared to iPR3. This differential binding of PR3-ANCA to iHm5 is similar to the selective moANCA518 binding to iHm5. Binding of iPR3 to monoclonal antibody MCPR3-2 also induced recognition by moANCA518.

CONCLUSION

The preferential binding of PR3-ANCAs from patients, such as the selective binding of moANCA518 to iHm5, is conferred by increased antigenicity of epitope 3 on iHm5. This can also be induced on iPR3 when captured by monoclonal antibody MCPR2. This previously unrecognized characteristic of PR3-ANCA interactions with its target antigen has implications for studying antibody-mediated autoimmune diseases, understanding variable performance characteristics of immunoassays, and design of potential novel treatment approaches.

The comparison of real world and core laboratory antiphospholipid antibody ELISA results from antiphospholipid syndrome alliance for clinical trials & international networking (APS ACTION) clinical database and repository analysis

BACKGROUND

The APS ACTION International Clinical Database and Repository includes a secure web-based data capture system storing patient information including demographics, antiphospholipid antibodies (aPL)-related medical history, and aPL tests. Despite efforts at harmonization, inter-assay variability remains a problem in aPL testing. As a clinical repository open to researchers, ensuring comparability between assays and consistency in results between APS ACTION laboratories is essential to the validity of studies emerging from this network.

OBJECTIVE

To assess the level of agreement between an aPL-registry inclusion and core laboratory (core lab) anticardiolipin antibody (aCL) and anti-β₂-glycoprotein-I antibody (aβ₂GPI) ELISA testing results.

METHODS

Patients are recruited from 25 international centers based on positive aPL tests at inclusion. All samples are retested at the corresponding national APS ACTION core lab to confirm aPL positivity based on standard validated protocols. We analysed the categorical agreement, degree of linear association, and correlation between inclusion (local laboratory) and core lab aPL tests. Samples were included in this study only if results of aPL testing with ELISA at baseline were available.

RESULTS

497 registry samples underwent confirmatory aPL tests. Categorical agreement between the inclusion and core lab values, as expressed by Cohen's kappa coefficients, ranged between 0.61 and 0.80 (as substantial agreement). The correlation between quantitative results in the aCL and aβ₂GPI was better for IgM and IgA compared to IgG (Spearman rho 0.789 and 0.666 vs. 0.600 for aCL and rho 0.892 and 0.744 vs. 0.432 for aβ₂GPI).

CONCLUSIONS

The results of inclusion for aCL and aβ₂GPI tests used for recruitment into the registry were in agreement to the results obtained by the APS ACTION core laboratories; aCL and aβ₂GPI results showed very good categorical agreement. This agreement increased when considering high titer (>40 units) samples. APS ACTION is a reliable and useful research resource for APS.

The presentation and management of granulomatosis with polyangiitis (Wegener's Granulomatosis) in the pediatric airway

OBJECTIVE

Granulomatosis with polyangiitis (GPA) is a necrotizing inflammatory disease that can affect the airway. The purpose of this study was to present a case of pediatric laryngotracheal GPA and provide management recommendations based on a thorough review of the literature.

DATA SOURCES

Retrospective chart and literature review REVIEW METHODS: A pediatric patient with laryngotracheal and pulmonary manifestations of GPA who underwent chemotherapy and intralesional corticosteroid injection is described. An extensive literature review of pediatric GPA affecting the larynx/trachea was also performed.

RESULTS

A pediatric patient presented with acute respiratory distress. Flexible laryngoscopy revealed a laryngeal mass. Magnetic resonance imaging showed circumferential subglottic stenosis, and chest computed tomography demonstrated multiple pulmonary nodules. Laryngeal and tracheal biopsy revealed granulation tissue and primary vasculitis. Labs demonstrated positive cytoplasmic antineutrophil cytoplasmic antibody, consistent with GPA. Methylprednisone, rituximab, cyclophosphamide, and intralesional steroid injection resulted in remission after 12 weeks. Review of the literature revealed two pediatric cases series and 10 case reports of GPA affecting the larynx or trachea.

CONCLUSIONS

There is a higher prevalence of GPA of the airway in children when compared to adults. Biopsy of the airway lesion may not be necessary and has lower diagnostic yield compared to other GPA subsites. Medical management includes induction therapy followed by maintenance therapy once the disease is in remission. Most patients will require a surgical intervention to maintain the airway.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:233-240, 2017.

Non-malignant central airway obstruction

The most common causes of non-malignant central airway obstruction are post-intubation and post-tracheostomytracheal stenosis, followed by the presence of foreign bodies, benign endobronchial tumours and tracheobronchomalacia. Other causes, such as infectious processes or systemic diseases, are less frequent. Despite the existence of numerous classification systems, a consensus has not been reached on the use of any one of them in particular. A better understanding of the pathophysiology of this entity has allowed us to improve diagnosis and treatment. For the correct diagnosis of nonspecific clinical symptoms, pulmonary function tests, radiological studies and, more importantly, bronchoscopy must be performed. Treatment must be multidisciplinary and tailored to each patient, and will require surgery or endoscopic intervention using thermoablative and mechanical techniques.

Discrimination and variable impact of ANCA binding to different surface epitopes on proteinase 3, the Wegener's autoantigen

Proteinase 3 (PR3)-specific antineutrophil cytoplasmic antibodies (ANCA) are highly specific for the autoimmune small vessel vasculitis, Wegener's granulomatosis (WG). PR3-ANCA have proven diagnostic value but their pathogenic potential and utility as a biomarker for disease activity remain unclear. PR3-ANCA recognize conformational epitopes, and epitope-specific PR3-ANCA subsets with variable impact on biological functions of PR3 have been postulated. The aims of this study were to identify specific PR3 surface epitopes recognized by monoclonal antibodies (moAbs) and to determine whether the findings can be used to measure the functional impact of epitope-specific PR3-ANCA and their potential relationship to disease activity. We used a novel flow cytometry assay based on TALON-beads coated with recombinant human (H) and murine (M) PR3 and 10 custom-designed chimeric human/mouse rPR3-variants (Hm1-5/Mh1-5) identifying 5 separate non-conserved PR3 surface epitopes. Anti-PR3 moAbs recognize 4 major surface epitopes, and we identified the specific surface location of 3 of these with the chimeric rPR3-variants. The ability of PR3-ANCA to inhibit the enzymatic activity of PR3 was measured indirectly using a capture-ELISA system based on the different epitopes recognized by capturing moAbs. Epitope-specific PR3-ANCA capture-ELISA results obtained from patient plasma (n=27) correlated with the inhibition of enzymatic activity of PR3 by paired IgG preparations (r=0.7, P<0.01). The capture-ELISA results also seem to reflect disease activity. In conclusion, insights about epitopes recognized by anti-PR3 moAbs can be applied to separate PR3-ANCA subsets with predictable functional qualities. The ability of PR3-ANCA to inhibit the enzymatic activity of PR3, a property linked to disease activity, can now be gauged using a simple epitope-based capture-ELISA system.

An approach to the diagnosis and management of systemic vasculitis

The systemic vasculitides are a complex and often serious group of disorders which, while uncommon, require careful management in order to ensure optimal outcome. In most cases there is no known cause. Multi-system disease is likely to be fatal without judicious use of immunosuppression. A prompt diagnosis is necessary to preserve organ function. Comprehensive and repeated disease assessment is a necessary basis for planning therapy and modification of treatment protocols according to response. Therapies typically include glucocorticoids and, especially for small and medium vessel vasculitis, an effective immunosuppressive agent. Cyclophosphamide is currently the standard therapy for small vessel multi-system vasculitis, but other agents are now being evaluated in large randomized trials. Comorbidity is common in patients with vasculitis, including the cumulative effects of potentially toxic therapy. Long-term evaluation of patients is important in order to detect and manage relapses.

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.

Wegener's granulomatosis: an update on diagnosis and therapy

Wegener's granulomatosis (WG) is a unique clinicopathological disease characterized by necrotizing granulomatous vasculitis of the respiratory tract, pauci-immune necrotizing glomerulonephritis and small-vessel vasculitis. Owing to its wide range of clinical manifestations, WG has a broad spectrum of severity that includes the potential for alveolar hemorrhage or rapidly progressive glomerulonephritis, which are immediately life threatening. WG is associated with the presence of circulating antineutrophil cytoplasm antibodies (c-ANCAs). The most widely accepted pathogenetic model suggests that c-ANCA-activated cytokine-primed neutrophils induce microvascular damage and a rapid escalation of inflammation with recruitment of mononuclear cells. The diagnosis of WG is made on the basis of typical clinical and radiologic findings, by biopsy of involved organ, the presence of c-ANCA and exclusion of all other small-vessel vasculitis. Currently, a regimen consisting of daily cyclophosphamide and corticosteroids is considered standard therapy. A number of trials have evaluated the efficacy of less-toxic immunosuppressants and antibacterials for treating patients with WG, resulting in the identification of effective alternative regimens to induce or maintain remission in certain subpopulations of patients. Recent investigation has focused on other immunomodulatory agents (e.g., TNF-alpha inhibitors and anti-CD20 antibodies), intravenous immunoglobulins and antithymocyte globulins for treating patients with resistant WG.