McCune, W. Joseph

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. image

Summary Anti-neutrophil cytoplasmic antibodies (ANCA) appear to play an important role in the pathogenesis of ANCA-associated vasculitis (AAV). However, ANCA alone are not sufficient to generate disease, and some evidence suggests that infectious triggers may serve as inciting events for AAV disease activity. Antibodies of the immunoglobulin (Ig)M isotype often serve as markers of recent infection, and IgM ANCA have been identified previously in patients with AAV, although the frequency and clinical relevance of IgM ANCA is not well established. We sought to characterize IgM ANCA more clearly by creating a novel enzyme-linked immunosorbent assay (ELISA) for IgM antibodies to proteinase 3 [IgM proteinase 3 (PR3)–ANCA], which we applied to two large, clinically well-characterized trial cohorts of patients with granulomatosis with polyangiitis and microscopic polyangiitis. In the first cohort, IgM PR3–ANCA occurred with a frequency of 15·0%, and were associated with a higher degree of disease severity and a trend towards a higher rate of alveolar haemorrhage (29·6 versus 15·7%, P = 0·10). Analysis of follow-up samples in this cohort showed that the presence of IgM PR3–ANCA was transient, but could recur. In the second cohort, IgM PR3–ANCA occurred with a frequency of 41·1%, and were also associated with a higher degree of disease severity. A higher rate of alveolar haemorrhage was observed among those with IgM PR3–ANCA (45·3 versus 15·8%; P < 0·001). The association of transient IgM PR3–ANCA with an acute respiratory manifestation of AAV suggests a possible link between an infectious trigger and AAV disease activity.

ObjectiveTo 1) describe the distribution of patient global assessment (PtGA) scores of disease activity in patients with granulomatosis with polyangiitis (GPA; Wegener's), 2) explore the discordance between PtGA scores and physician global assessment (PhGA) scores of disease activity, and 3) explore whether PtGA scores during disease remission are associated with future disease relapse.MethodsData from the Wegener's Granulomatosis Etanercept Trial (WGET) were used. PtGA and PhGA scores were assessed on 100‐mm visual analog scales (VAS). Presence of active disease was determined using the Birmingham Vasculitis Activity Score for WG (BVAS/WG), and remission was defined as a BVAS/WG score of 0. Disease relapse was defined as a BVAS/WG score of >0 after remission had been achieved. Discordance between PtGA and PhGA scores was defined as a difference of ≥20 points between the two measures. Mixed linear models were used in longitudinal analysis of PtGA scores.ResultsData were obtained from 180 patients in the WGET cohort, seen at a total of 1,719 study visits. The mean ± SD PtGA and PhGA disease activity scores (on 100‐mm VAS) at baseline were 64.2 ± 27.4 and 55.5 ± 23.4, respectively. PtGA–PhGA discordance occurred in 53% of patients at baseline, and this was inversely associated with newly diagnosed disease (as opposed to relapsing disease) at baseline (odds ratio 0.37, 95% confidence interval [95% CI] 0.20–0.68) but not with age, sex, or presence of renal or pulmonary disease. Patients were in disease remission during 62% of the study visits. The mean PtGA score during visits immediately prior to relapse was 4.52 points higher (95% CI 0.66–8.4) than that at other remission visits (P = 0.03).ConclusionPtGA–PhGA discordance is common in GPA. A rise in the PtGA disease activity score during times defined by physicians as periods of remission is associated with subsequent occurrence of disease relapse. These findings support the addition of PtGA as an outcome measure for GPA.