Detection Of IgG Autoantibodies Research Articles

Hope for patients with neuromyelitis optica spectrum disorders - from mechanisms to trials.

Neuromyelitis optica spectrum disorder (NMOSD) is a rare inflammatory CNS disease that primarily manifests as relapsing episodes of severe optic neuritis and myelitis. Diagnosis of NMOSD is supported by the detection of IgG autoantibodies that target the aquaporin 4 (AQP4) water channel, which, in the CNS, is an astrocyte-specific protein. AQP4 antibody binding leads to AQP4 internalization, complement-dependent and antibody-dependent cellular cytotoxicity, and water channel dysfunction. Cumulative attack-related injury causes disability in NMOSD, so the prevention of attacks is expected to prevent disability accrual. Until recently, no regulator-approved therapies were available for NMOSD. Traditional immunosuppressant therapies, including mycophenolate mofetil, azathioprine and rituximab, were widely used but their benefits have not been assessed in controlled studies. In 2019 and 2020, five phase II and III randomized placebo-controlled trials of four mechanism-based therapies for NMOSD were published and demonstrated that all four effectively prolonged the time to first relapse. All four drugs were monoclonal antibodies: the complement C5 antibody eculizumab, the IL-6 receptor antibody satralizumab, the B cell-depleting antibody inebilizumab, which targets CD19, and rituximab, which targets CD20. We review the pathophysiology of NMOSD, the rationale for the development of these mechanism-based drugs, the methodology and outcomes of the five trials, and the implications of these findings for the treatment of NMOSD.

IgE blockade in autoimmunity: Omalizumab induced remission of bullous pemphigoid

Bullous pemphigoid (BP) is a blistering dermopathy and a prototypic antibody-mediated autoimmune disease. Detection of IgG autoantibodies against hemidesmosomal proteins BP180 and/or BP230 are diagnostic and levels can correlate with disease activity. Therapies include corticosteroids and oral immunosuppressants, while intravenous immunoglobulin and rituximab are reserved for treatment resistant cases. Here we describe a patient with severe BP which was refractory to standard first line therapy, intravenous immunoglobulin and rituximab induced depletion of peripheral B cells. Use of the monoclonal anti-IgE antibody omalizumab resulted in rapid resolution of blistering despite ongoing high levels of anti-skin IgG antibodies. To our knowledge this is the first case of BP responsive to omalizumab after failure of rituximab to be reported. This case adds to emerging data on omalizumab as a novel BP treatment as well as providing new evidence of an independent role for autoreactive IgE-mediated inflammation in the formation of BP skin lesions.

P68: THE PATHOGENIC ROLE OF AUTOREACTIVE IGE IN BULLOUS PEMPHIGOID: A UNIQUE CASE SUPPORTING CONCLUSIONS FROM EXPERIMENTAL DATA

Bullous pemphigoid (BP), a blistering dermopathy, is a prototypic antibody‐mediated disease. Detection of IgG autoantibodies against hemidesmosomal proteins BP180 and/or BP230 are diagnostic and levels correlate with disease activity. Therapies include corticosteroids and oral immunosuppressants, while intravenous immunoglobulin (IVIG) and rituximab are reserved for resistant cases. These observations together support a central role for B cells and autoreactive IgG in BP pathogenesis. We describe a patient with persistent biopsy‐proven severe BP on a background of stable HIV infection with long‐term viral suppression and normal CD4 T cell counts, type 2 diabetes and chronic renal failure. The disease was widespread and refractory to standard first line therapy, IVIG and also rituximab, despite peripheral B cell depletion. Use of the monoclonal anti‐IgE antibody omalizumab resulted in a rapid resolution, within days, of pruritis and bullae formation. Disease remission has been maintained with ongoing Omalizumab therapy despite persistent high level junctional anti‐skin IgG antibodies. To our knowledge this is the first case of BP responsive to omalizumab after failure of rituximab to be described in the literature. Omalizumab does not currently have an established role in treatment of BP, although this case adds to previous case reports suggesting a role for omalizumab as a novel BP treatment. This is also supported by recent experimental data demonstrating a role for autoreactive IgE in bullous formation and correlation with disease activity. Selection of patients with BP who would benefit from anti‐IgE therapy remains to be defined, although given the speed of response and the low risk associated with its use, a therapeutic trial may be warranted in severe and/or resistant cases, particularly to reduce the side‐effects of standard therapies.

Response to ‘Serological diagnostics in the detection of IgG autoantibodies against human collagen VII in epidermolysis bullosa acquisita: a multicentre analysis’

In a recent retrospective serological study in 95 sera from epidermolysis bullosa acquisita (EBA) patients Schmidt et al. conclude that Col7A-NC1/NC2 ELISA (MBL, Japan) is superior to NC1 ELISA, Western blot and indirect immunofluorescence (IIF) on salt-split skin (SSS) with the highest sensitivity of 97.9%.(1) This sensitivity is an overestimation from a biased sample, since the sera had been preselected from patients with IgG reactivity fitting EBA by at least one of the immune serological assays indirect immunofluorescence, ELISA, and Western blot. The deficiency in study design with an incorrect reference standard creates a bias in estimated test accuracy. This article is protected by copyright. All rights reserved.

Serological diagnostics in the detection of IgG autoantibodies against human collagen VII in epidermolysis bullosa acquisita: a multicentre analysis

Epidermolysis bullosa acquisita (EBA) is a rare, potentially devastating autoimmune disease of the skin. IgG autoantibodies directed against type VII collagen (Col7), the major component of anchoring fibrils, induce skin fragility leading to cutaneous and mucocutaneous blister formation, which is mostly of a scarring phenotype. Thus, powerful and reproducible diagnostic assays are critical to establish the diagnosis of EBA early to avoid irreversible sequelae. The present international, retrospective multicentre study included a large cohort of patients with EBA and evaluated the diagnostic power of four different diagnostic assays for the detection of anti-Col7 IgG autoantibodies. Overall, 95 EBA sera and 200 control sera consisting of 100 bullous pemphigoid sera, 50 pemphigus vulgaris sera and 50 sera of healthy controls were tested for anti-Col7 IgG autoantibodies using indirect immunofluorescence (IIF), two commercial enzyme-linked immunosorbent assay (ELISA) systems and Western blot (WB) analysis. EBA sera were taken from patients with positive direct immunofluorescence and IgG reactivity in at least one of the immunoserological assays (IIF, ELISA, WB). A Col7-NC1/NC2 ELISA (MBL, Nagoya, Japan) showed the highest sensitivity (97·9%), followed by a Col7-NC1 ELISA (Euroimmun, Lübeck, Germany) (89·5%), WB with Col7-NC1 (85·3%), and IIF on saline-split human skin (74·7%). The specificities of both ELISA systems were comparable (NC1 98·7%, NC1/NC2 99·3%). Furthermore, WB was more sensitive than IIF, which was more specific. The two commercially available ELISA systems allow for a highly sensitive and specific diagnosis of EBA. The sensitivity of the Col7-NC1/NC2 ELISA is significantly higher compared with the ELISA based on the Col7-NC1 domain only.

Assessment of skin basement membrane zone antibodies in the urine of patients with acquired subepidermal immunobullous diseases.

In bullous pemphigoid (BP), cicatricial pemphigoid (CP) and linear IgA disease (LAD), autoantibodies to the basement membrane zone (BMZ) are found in skin and mucosa, blood and blister fluid. To assess whether BMZ antibodies might also be detected in urine. Urine and serum samples from 62 patients (32 with BP, 17 with CP and 13 with LAD) were analysed for antibody isotypes and subclasses by indirect immunofluorescence, and urine and serum samples from 40 patients (25 with BP, eight with CP and seven with LAD) were screened for target antigens using immunoblotting. Fourteen of 32 patients with BP had detectable levels of IgG BMZ autoantibodies in their urine, and all 32 had positive sera. Of these 14 BP patients, 13 had epidermal-binding serum autoantibodies at a titre > 1 : 160, and one had dermal-binding serum antibodies at a titre of 1 : 40. BMZ autoantibodies were not detected in the urine of the CP or LAD patients, but the corresponding sera were of low titre or negative. IgG subclasses (IgG1-4) were less frequently detected in urine than in serum. IgG4 was the predominant subgroup found (10 urine samples and all 14 sera), followed by IgG1 (two urine samples and 12 sera); IgG2 was detected in a single urine sample and three sera, and IgG3 was not detected. Eight of 25 BP and one of eight CP urine samples were positive on immunoblotting, and bound BP230 and/or BP180 with IgA and/or IgG autoantibodies. IgA autoantibodies were not detected in the urine of the seven LAD patients. The corresponding sera were often more positive, with 21 of 25 BP, five of eight CP and six of seven LAD sera immunoblotting the major BP antigens. The detection of IgG autoantibodies from urine samples using indirect immunofluorescence correlated with a high titre of IgG autoantibodies in the serum. IgG and IgA autoantibodies in the urine were detected by immunoblotting, although less frequently than in serum. The finding of BMZ antibodies in the urine of many BP patients may have clinical relevance, and may have a restricted application in the diagnosis of immunobullous disease.