Immunoglobulin (Ig)M antibodies to proteinase 3 in granulomatosis with polyangiitis and microscopic polyangiitis

Fc receptors gone wrong: A comprehensive review of their roles in autoimmune and inflammatory diseases

Systemic autoimmune and inflammatory diseases have a complex and only partially known pathophysiology with various abnormalities involving all the components of the immune system. Among these components, antibodies, and especially autoantibodies are key elements contributing to autoimmunity. The interaction of antibody fragment crystallisable (Fc) and several distinct receptors, namely Fc receptors (FcRs), have gained much attention during the recent years, with possible major therapeutic perspectives for the future. The aim of this review is to comprehensively describe the known roles for FcRs (activating and inhibitory FcγRs, neonatal FcR [FcRn], FcαRI, FcεRs, Ro52/tripartite motif containing 21 [Ro52/TRIM21], FcδR, and the novel Fc receptor-like [FcRL] family) in systemic autoimmune and inflammatory disorders, namely rheumatoid arthritis, Sjögren's syndrome, systemic lupus erythematosus, systemic sclerosis, idiopathic inflammatory myopathies, mixed connective tissue disease, Crohn's disease, ulcerative colitis, immunoglobulin (Ig) A vasculitis, Behçet's disease, Kawasaki disease, IgG4-related disease, immune thrombocytopenia, autoimmune hemolytic anemia, antiphospholipid syndrome and heparin-induced thrombocytopenia.

Pathogenicity of Proteinase 3-Anti-Neutrophil Cytoplasmic Antibody in Granulomatosis With Polyangiitis: Implications as Biomarker and Future Therapies

Granulomatosis with polyangiitis (GPA) is a rare but serious necrotizing auto-immune vasculitis. GPA is mostly associated with the presence of Anti-Neutrophil Cytoplasmic Antibody (ANCA) targeting proteinase 3 (PR3-ANCA), a serine protease contained in neutrophil granules but also exposed at the membrane. PR3-ANCAs have a proven fundamental role in GPA: they bind neutrophils allowing their auto-immune activation responsible for vasculitis lesions. PR3-ANCAs bind neutrophil surface on the one hand by their Fab binding PR3 and on the other by their Fc binding Fc gamma receptors. Despite current therapies, GPA is still a serious disease with an important mortality and a high risk of relapse. Furthermore, although PR3-ANCAs are a consistent biomarker for GPA diagnosis, relapse management currently based on their level is inconsistent. Indeed, PR3-ANCA level is not correlated with disease activity in 25% of patients suggesting that not all PR3-ANCAs are pathogenic. Therefore, the development of new biomarkers to evaluate disease activity and predict relapse and new therapies is necessary. Understanding factors influencing PR3-ANCA pathogenicity, i.e. their potential to induce auto-immune activation of neutrophils, offers interesting perspectives in order to improve GPA management. Most relevant factors influencing PR3-ANCA pathogenicity are involved in their interaction with neutrophils: level of PR3 autoantigen at neutrophil surface, epitope of PR3 recognized by PR3-ANCA, isotype and glycosylation of PR3-ANCA. We detailed in this review the advances in understanding these factors influencing PR3-ANCA pathogenicity in order to use them as biomarkers and develop new therapies in GPA as part of a personalized approach.

Antineutrophil cytoplasmic antibodies (ANCA) - their role in pathogenesis, diagnosis, and treatment monitoring of ANCA-associated vasculitis

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) constitutes a group of rare diseases characterized by necrotizing inflammation of small blood vessels and the presence of ANCA. Increasing clinical and experimental evidences support their pathogenic role in AAV, but the exact mechanism is not fully understood. Recently, the important role of neutrophil extracellular traps (NETs) in pathogenesis of AAV is underlined. There is an indication that NETs can be a source for the formation of ANCA. The most common ANCA target antigens are myeloperoxidase (MPO) and proteinase 3 (PR3). Though the mechanism of action of ANCA is still under exploration, ANCA serology is being increasingly used for classification of AAV and revealed as kenner in defining various disease subsets associated with different genetic background, clinical features, treatment response, and prognosis. Controversy exists regarding the utility of serial measurements of ANCA in patients with AAV to monitor treatment and predict disease relapse.

IgM ANCA in healthy individuals and in patients with ANCA-associated vasculitis

Low levels of IgM auto-antibodies have been reported in health and disease. IgM anti-neutrophil cytoplasmic antibodies (ANCA) have been reported in patients with ANCA-associated vasculitis (AAV). We sought to investigate if healthy individuals may have IgM ANCA in their sera. The first aim of the study was to determine whether IgM ANCA was present in healthy individuals and in patients with ANCA-associated vasculitis. The second aim was to determine what happens to IgM ANCA levels over time. The third aim was to determine whether bacterial infections affected IgM ANCA levels in non-AAV patients. Sera from healthy individuals and patients with AAV were tested for IgM ANCA by immunofluorescence on fixed neutrophils, immunoprecipitation, Western blot and ELISA. Peripheral blood mononuclear cells were isolated and tested by ELISpot for circulating IgM ANCA B cells. To determine whether infection affected IgM ANCA levels, we studied non-AAV patients with bacterial endocarditis or Staphylococcus aureus bacteraemia and measured IgM ANCA levels over time. IgM ANCA is detectable in both healthy individuals and patients with AAV and the titres decreased with increasing age. Circulating IgM ANCA B cells were identified by ELISpot. In the presence of infection, we could not find a significant change in IgM ANCA levels. We report the presence of low-level specific IgM ANCA in the sera of healthy individuals and in patients with ANCA-associated vasculitis. Bacterial infection did not affect the level of IgM ANCA in this small study.

In situ detection of PR3-ANCA+ B cells and alterations in the variable region of immunoglobulin genes support a role of inflamed tissue in the emergence of auto-reactivity in granulomatosis with polyangiitis

Circulating anti-neutrophilic cytoplasmic autoantibodies targeting proteinase 3 (PR3-ANCA) are a diagnostic and pathogenic hallmark of granulomatosis with polyangiitis (GPA). It is, however, incompletely understood if inflamed tissue supports presence or emergence of PR3-ANCA⁺ B cells. In search of such cells in inflamed tissue of GPA, immunofluorescence staining for IgG and a common PR3-ANCA idiotype (5/7 Id) was undertaken. Few 5/7 Id⁺/IgG⁺ B cells were detected in respiratory and kidney tissue of GPA. To gain more insight into surrogate markers possibly indicative of an anti-PR3-response, a meta-analysis comprising IGVH and IGVL genes derived from respiratory tract tissue of GPA (231 clones) was performed. Next generation sequencing-based IGHV genes derived from peripheral blood of healthy donors (244.353 clones) and previously published IGLV genes (148 clones) served as controls. Additionally, Ig genes of three murine and five known human monoclonal anti-PR3 antibodies were analyzed. Primary and probably secondary rearrangements led to altered VDJ usage and an extended complementarity determining region 3 (CDR3) of IGHV clones from GPA tissue. Selection against amino acid exchanges was prominent in the framework region of IGHV clones from GPA tissue. The comparison of V(D)J rearrangements and deduced amino acid sequences of the CDR3 yielded no identities and few similarities between clones derived from respiratory tissue of GPA and anti-PR3 antibodies, arguing against a presence of B cells that carry PR3-ANCA-prone Ig genes among the clones. In line with the scarcity of 5/7 Id⁺ B lymphocytes in GPA tissue, the results suggest that with respect to a local anti-PR3 response, methods detecting rare clones are required.

Pathogenetic and Clinical Aspects of Anti-Neutrophil Cytoplasmic Autoantibody-Associated Vasculitides

Anti-neutrophil cytoplasmic autoantibodies (ANCA) targeting proteinase 3 (PR3) and myeloperoxidase expressed by innate immune cells (neutrophils and monocytes) are salient diagnostic and pathogenic features of small vessel vasculitis, comprising granulomatosis with polyangiitis (GPA), microscopic polyangiitis, and eosinophilic GPA. Genetic studies suggest that ANCA-associated vasculitides (AAV) constitute separate diseases, which share common immunological and pathological features, but are otherwise heterogeneous. The successful therapeutic use of anti-CD20 antibodies emphasizes the prominent role of ANCA and possibly other autoantibodies in the pathogenesis of AAV. However, to elucidate causal effects in AAV, a better understanding of the complex interplay leading to the emergence of B lymphocytes that produce pathogenic ANCA remains a challenge. Different scenarios seem possible; e.g., the break of tolerance induced by a shift from non-pathogenic toward pathogenic autoantigen epitopes in inflamed tissue. This review gives a brief overview on current knowledge about genetic and epigenetic factors, barrier dysfunction and chronic non-resolving inflammation, necro-inflammatory auto-amplification of cellular death and inflammation, altered autoantigen presentation, alternative complement pathway activation, alterations within peripheral and inflamed tissue-residing T- and B-cell populations, ectopic lymphoid tissue neoformation, the characterization of PR3-specific T-cells, properties of ANCA, links between autoimmune disease and infection-triggered pathology, and animal models in AAV.

Analysis of Antineutrophil Cytoplasm Antibody from 118 730 Patients in Tertiary Hospitals in Jiangxi Province, China

BACKGROUND The discovery of antineutrophil cytoplasm antibody (ANCA) makes the early diagnosis of primary vasculitis possible, and also has important guiding significance for the diagnosis and treatment of secondary vasculitis. This study aimed to investigate the clinical significance of ANCA. MATERIAL AND METHODS ANCA was detected by indirect immunofluorescence assay (IIF), and anti-myeloperoxidase (MPO) antibody, and anti-proteinase 3 (PR3) antibody were detected by ELISA. The results were analyzed retrospectively. RESULTS Among 118 730 patients, a total of 5853 (4.93%) were positive for ANCA. In the positive cases, 3.98% were male and 6.33% were female, with significant differences (χ²=123.38, P<0.01). For ANCA, the department with the highest positive rate (15.06%) was the Department of Rheumatology, followed by 7.78% in the Department of Dermatology, 6.79% in the Department of Nephrology, and 5.72% in the Department of Traditional Chinese Medicine (TCM). Anti-PR3 and cANCA were highly specific in primary vasculitis (P<0.01). Anti-MPO and pANCA had high specificity for other autoimmune diseases (P<0.01). CONCLUSIONS ANCA has important guiding significance for vasculitis-related diseases. Therefore, it is important in the diagnosis and treatment of this disease and has value in clinical practice.