IgG4:IgG RNA ratio differentiates active disease from remission in granulomatosis with polyangiitis: a new disease activity marker? A cross-sectional and longitudinal study

Coexistence of IgG4-related disease and ANCA-associated vasculitis: case report and review of the literature

IgG4-related disease (IgG4-RD) is a fibroinflammatory condition that is characterized by storiform fibrosis, infiltration of IgG4-positive lymphocytes, obliterative phlebitis, and high IgG4 levels. Since IgG4-RD affects a wide variety of organs, a differential diagnosis must include multiple conditions. IgG4-RD is also believed to coexist with certain diseases. In recent years, case reports and case series describing the co-occurrence of IgG4-RD and ANCA-associated vasculitis (AAV) have been published. We intended to evaluate patients with IgG4-RD and AAV overlap in the literature using a case similar to one that was diagnosed and monitored in our department. We searched the databases of Web of Science, Scopus, and Google Scholar as well as PubMed with the keywords ANCA, IgG4, IgG4-RD, granulomatosis with polyangiitis, Wegener's granulomatosis, microscopic polyangiitis, Eosinophilic granulomatosis with polyangiitis, and Churg-Strauss syndrome. Cases and Case series addressing the coexistence of IgG4-RD and AAV have been selected. Comprehensive diagnostic criteria are used to diagnose IgG4-RD. The Chapel Hill Consensus Conference nomenclature criteria were used for the inclusion of AAV. Out of a total of 910 publications, 20 articles, including 65 cases, were found to be eligible. Forty-seven cases with IgG4-RD were evaluated as definitive (71.2%), 10 cases as probable (15.1%), and 9 cases as possible IgG4-RD (13.6%). 26 patients were diagnosed with GPA, 1 patient with localized GPA, 23 patients with MPA, and 4 patients with EGPA. The aorta, lacrimal tissue, pancreas, and retroperitoneum are the sites of IgG4-RD rather than AAV. AAV and IgG4-RD might coexist in the same patient. IgG4-RD is mainly associated with GPA.

Antineutrophil Cytoplasmic Antibody-Associated Vasculitis With Immunoglobulin G4 Involvement in Lacrimal Sac Squamous Cell Carcinoma

Lacrimal sac squamous cell carcinoma is a rare but life-threatening disease that is often a delayed diagnosis secondary to difficulty in differentiating from other causes of dacrocystitis and acquired nasolacrimal duct obstruction. Chronic inflammation, including that of an underlying autoimmune disease, prior instrumentation, and poor wound healing, may be risk factors in the development to lacrimal sac squamous cell carcinoma. The authors present the first case of lacrimal sac squamous cell carcinoma associated with antineutrophil cytoplasmic antibody-associated vasculitis and immunoglobulin G4 positivity. Rather than an overlap syndrome between antineutrophil cytoplasmic antibody-associated vasculitis and immunoglobulin G4-related disease, high immunoglobulin G4 positivity may be considered an inflammatory marker of disease severity in the setting of antineutrophil cytoplasmic antibody-associated vasculitis and underlying malignancy. Inflammation-mediated tumorangiogenesis should be considered in the development of malignancy and red flags of chronic uncontrolled inflammation should warrant a lower threshold for further workup.

B Lineage Cells in ANCA-Associated Vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease that affects small sized blood vessels and can lead to serious complications in the lungs and kidneys. The prominent presence of ANCA autoantibodies in this disease implicates B cells in its pathogenesis, as these are the precursors of the ANCA-producing plasma cells (PCs). Further evidence supporting the potential role of B lineage cells in vasculitis are the increased B cell cytokine levels and the dysregulated B cell populations in patients. Confirmation of the contribution of B cells to pathology arose from the beneficial effect of anti-CD20 therapy (i.e., rituximab) in AAV patients. These anti-CD20 antibodies deplete circulating B cells, which results in amelioration of disease. However, not all patients respond completely, and this treatment does not target PCs, which can maintain ANCA production. Hence, it is important to develop more specific therapies for AAV patients. Intracellular signalling pathways may be potential therapeutic targets as they can show (disease-specific) alterations in certain B lineage cells, including pathogenic B cells, and contribute to differentiation and survival of PCs. Preliminary data on the inhibition of certain signalling molecules downstream of receptors specific for B lineage cells show promising therapeutic effects. In this narrative review, B cell specific receptors and their downstream signalling molecules that may contribute to pathology in AAV are discussed, including the potential to therapeutically target these pathways.

A case of eosinophilic granulomatosis with polyangiitis showing multiple white lichen lesions on the airway mucosa

A 70-year-old man, treated for asthma for 2 years and chronic sinusitis for several months, presented with fever, numbness in the lower limbs, heaviness in the head, gross hematuria, and black stools. He also had eosinophilia, elevated serum IgG4 levels, high levels of myeloperoxidase-anti-neutrophil cytoplasmic antibodies (MPO-ANCA), and pulmonary infiltrative shadows. Bronchoscopy revealed multiple white flattened lesions (white moss) on the airway mucosa, suggesting mycobacterial infection or malignancy. A biopsy from tracheal mucosa revealed airway inflammation with marked eosinophil infiltration. The patient was diagnosed with eosinophilic granulomatosis with polyangiitis (EGPA) and treated with steroids, and all findings improved. However, a year and a half after the initiation of treatment, eosinophils and IgE gradually increased; subjective symptoms, such as asthma symptoms and numbness in the lower limbs, worsened; and ANCA, which had been negative, turned positive. Therefore, we suspected disease relapse and anti-IL-5 antibody (mepolizumab) treatment was initiated. Thereafter, ANCA turned negative again, eosinophils and IgE normalized, and subjective symptoms decreased. The presence of airway mucosal lesions in EGPA is relatively rare, and we report this case as a valuable case owing to the interesting bronchoscopic findings that are worth comprehending as a respiratory physician.

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.

Update on IgG4-mediated autoimmune diseases: New insights and new family members

Antibodies of IgG4 subclass are exceptional players of the immune system, as they are considered to be immunologically inert and functionally monovalent, and as such may be part of classical tolerance mechanisms. IgG4 antibodies are found in a range of different diseases, including IgG4-related diseases, allergy, cancer, rheumatoid arthritis, helminth infection and IgG4 autoimmune diseases, where they may be pathogenic or protective. IgG4 autoimmune diseases are an emerging new group of diseases that are characterized by pathogenic, antigen-specific autoantibodies of IgG4 subclass, such as MuSK myasthenia gravis, pemphigus vulgaris and thrombotic thrombocytopenic purpura. The list of IgG4 autoantigens is rapidly growing and to date contains 29 candidate antigens. Interestingly, IgG4 autoimmune diseases are restricted to four distinct organs: 1) the central and peripheral nervous system, 2) the kidney, 3) the skin and mucous membranes and 4) the vascular system and soluble antigens in the blood circulation. The pathogenicity of IgG4 can be validated using our classification system, and is usually excerted by functional blocking of protein-protein interaction.