A new M23-based ELISA assay for anti-aquaporin 4 autoantibodies: diagnostic accuracy and clinical correlation

AQP4-DARPin1: A Chimeric Antigen Based on Scaffold Protein DARPin for Efficient Detection of AQP4-IgG in NMOSD

AQP4-IgG is an autoantibody associated with neuromyelitis optica spectroscopic disorder (NMOSD), a central nervous system inflammatory disease that requires early diagnosis and treatment. We designed two fusion proteins, AQP4-DARPin1 and AQP4-DARPin2, comprising the complete antigenic epitopes of aquaporin-4 (AQP4) and the constant region of the scaffold protein DARPin. These fusion proteins were expressed and purified from Escherichia coli and coated on microplates to develop an efficient method for detecting AQP4-IgG. Molecular dynamics simulation revealed that the fusion of AQP4 extracellular epitopes with DARPin did not alter the main structure of DARPin. The purified AQP4-DARPins bound recombinant antibody rAb-53 (AQP4-IgG) with affinities of 135 and 285 nM, respectively. Enzyme-linked immunosorbent assay (ELISA) and immunoprecipitation demonstrated that AQP4-DARPin1 specifically recognized AQP4-IgG in the NMOSD patient serum. AQP4-DARPin1 as a coated antigen showed higher ELISA signal and end point dilution ratio than full-length AQP4. Our AQP4-DARPin1-coated AQP4-IgG ELISA had 100% specificity and 90% sensitivity. These results indicate that AQP4-DARPin1, compared to existing detection strategies that use full-length or extracellular loop peptides of AQP4, provides a new and more effective approach to the ELISA detection of NMOSD.

Chimeric AQP4-based immunosorbent for highly-specific removal of AQP4-IgG from blood

Anti-aquaporin-4 autoantibodies (AQP4-IgG) are implicated in the pathogenesis of neuromyelitis optica spectrum disorders (NMOSD), and their removal from the blood circulation is considered to be an effective method for acute treatment. An ideal extracorporeal AQP4-IgG removal system should have high specificity, which means that it can selectively remove AQP4-IgG without affecting normal immunoglobulins. However, the conventional tryptophan immobilized column lacks sufficient specificity and cannot achieve this goal. In this study, we successfully prepared a fusion protein chimeric AQP4, which consists of the complete antigenic epitopes of human AQP4 and the constant region of scaffold protein DARPin. Chimeric AQP4 was expressed and purified from Escherichia coli, and then immobilized on agarose gel as a ligand for selective capture of AQP4-IgG immunosorbent. The prepared immunosorbent had a theoretical maximum adsorption capacity of 20.48 mg/g gel estimated by Langmuir isotherm. In vitro plasma perfusion tests demonstrated that the chimeric AQP4 coupled adsorbent had remarkable adsorption performance, and could eliminate more than 85 % of AQP4-IgG under the gel-to-plasma ratio of 1:50. Moreover, it exhibited high specificity because other human plasma proteins were not adsorbed in the dynamic adsorption experiment. These results suggest that the chimeric AQP4 coupled immunosorbent can provide a new approach for specific immunoadsorption (IA) treatment of NMOSD.

Different immunological mechanisms between AQP4 antibody-positive and MOG antibody-positive optic neuritis based on RNA sequencing analysis of whole blood

Purpose

To compare the different immunological mechanisms between aquaporin 4 antibody-associated optic neuritis (AQP4-ON) and myelin oligodendrocyte glycoprotein antibody-associated optic neuritis (MOG-ON) based on RNA sequencing (RNA-seq) of whole blood.

Methods

Whole blood was collected from seven healthy volunteers, 6 patients with AQP4-ON and 8 patients with MOG-ON, and used for RNA-seq analysis. An examination of immune cell infiltration was performed using the CIBERSORTx algorithm to identify infiltrated immune cells.

Results

RNA-seq analysis showed that the inflammatory signaling was mainly activated by TLR2, TLR5, TLR8 and TLR10 in AQP4-ON patients, while which was mainly activated by TLR1, TLR2, TLR4, TLR5 and TLR8 in MOG-ON patients. Biological function identification of differentially expressed genes (DEGs) based on Gene Ontology (GO) term and Kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analysis, as well as Disease Ontology (DO) analysis, showed that the inflammation in AQP4-ON was likely mediated by damage-associated molecular pattern (DAMP), while which in MOG-ON was likely mediated by pathogen-associated molecular pattern (PAMP). Analysis of immune cell infiltration showed that the proportion of immune cell infiltration was related to patients' vision. The infiltration ratios of monocytes (rs=0.69, P=0.006) and M0 macrophages (rs=0.66, P=0.01) were positively correlated with the BCVA (LogMAR), and the infiltration ratio of neutrophils was negatively correlated with the BCVA (LogMAR) (rs=0.65, P=0.01).

Conclusion

This study reveals different immunological mechanisms between AQP4-ON and MOG-ON based on transcriptomics analysis of patients' whole blood, which may expand the current knowledge regarding optic neuritis.

Update on glial antibody-mediated optic neuritis

Optic neuritis (ON) refers to inflammatory demyelinating lesions of the optic nerve, which can cause acute or subacute vision loss and is a major cause of vision loss in young adults. Much of our understanding of typical ON is from the Optic Neuritis Treatment Trial. Glial autoantibodies to aquaporin-4 immunoglobulin (AQP4-IgG) and myelin oligodendrocyte glycoprotein immunoglobulin (MOG-IgG) are recently established biomarkers of ON that have revolutionized our understanding of atypical ON. The detection of glial antibodies is helpful in the diagnosis, treatment, and follow-up of patients with different types of ON. AQP4-IgG and MOG-IgG screening is strongly recommended for patients with atypical ON. Research on the pathogenesis of NMOSD and MOGAD will promote the development and marketing of targeted immunotherapies. The application of new and efficient drugs, such as the selective complement C5 inhibitor, IL-6 receptor inhibitor, B cell-depleting agents, and drugs against other monoclonal antibodies, provides additional medical evidence. This review provides information on the diagnosis and management of glial antibody-mediated ON.

The role of autophagy-related proteins in the pathogenesis of neuromyelitis optica spectrum disorders

This study aimed to investigate the expression of autophagy-related proteins in a mouse model of neuromyelitis optica (NMO). Mice were assigned to one of four groups: an animal experimental model group (NMO-EAE group, given with exogenous IL-17A), Interleukin-17 monoclonal antibody intervention group (NMO-EAE_0IL17inb), No exogenous interleukin-17 enhanced immune intervention group (NMO-EAE_0IL17), and a control group. Behavioral scores were assessed in each group, and the protein expressions of sequestosome 1 (P62), Beclin-1, the mammalian target of rapamycin (mTOR), phosphoinositide 3-kinase (PI3K-I), and LC3II/LC3I were detected using Western blotting. In the NMO-EAE_0IL17 group, the expression of Beclin-1 decreased, the LC3II/LC3I ratio was lower, and the expressions of P62, mTOR, and PI3K-I increased; after administration of IL-17A inhibitor into the brain tissue, however, the expression of Beclin-1 increased significantly, along with the LC3II/LC3I ratio, while the expressions of P62, mTOR and PI3K-I protein decreased significantly. In terms of behavioral scores, the scores of optic neuritis and myelitis were more serious, onset occurred earlier and the progress was faster, after the administration of IL-17A. In the mechanism of NMO animal model, IL-17A may regulate autophagy and affect the disease process through the activation of the PI3K-mTOR signaling pathway.

Are Zika virus cross-reactive antibodies against aquaporin-4 associated to Neuromyelitis Optica Spectrum Disorder?

Zika virus (ZIKV) infection has been associated with the development of Neuromyelitis Optica Spectrum Disorder (NMOSD). ZIKV-induced antibodies that putatively cross-react to aquaporin-4 (AQP4) protein are suggested to cause inflammation of the optic nerve. A region of similarity between AQP4 and the ZIKV NS2B protein was identified. Our data showed that ZIKV-associated NMOSD patients develop anti-AQP4 antibodies, but not anti-ZIKV NS2B antibodies, revealing that cross-reacting antibodies are not the underlying cause of this phenotype. ZIKV infection in mice showed persistent viral replication in the eye tissue, suggesting that NMOSD symptoms are consequence of viral infection of the optic nerve cells.

Association of Circulating T Follicular Helper Cells With Idiopathic Optic Neuritis and Neuromyelitis Optica Spectrum Disorders

Background: T follicular helper cells (Tfh cells) play an important role in activating B lymphocytes and may associate with idiopathic Optic Neuritis (ON) and Neuromyelitis Optica Spectrum Disorders (NMOSD).

Objective: This study aimed to examine the potential role of Tfh cells in pathogenesis of idiopathic ON and NMOSD.

Methods: Circulating CD4⁺CXCR5⁺ and CD4⁺CXCR5⁺PD-1⁺ cells in 46 idiopathic ON and 68 NMOSD patients as well as 28 healthy controls were examined by flow cytometry before treatment. Serum AQP4 antibody, Expended Disability Status Scale (EDSS) and Visual Outcome Scale (VOS) were detected before and after treatment.

Results: The percentages of circulating CD4⁺CXCR5⁺ and CD4⁺CXCR5⁺PD-1⁺Tfh cells in CD4⁺ cells (%) were significantly increased in idiopathic ON and NMOSD compared with those of healthy controls (p < 0.01). No significant difference of Tfh cells in blood and cerebral spinal fluid (CSF) was found between ON and NMOSD patients. The percentages of CSF, CD4⁺, CXCR5⁺, and CD4⁺CXCR5⁺PD-1⁺ cells in CD4⁺ cells (%) were positively correlated with those of the blood (r = 0.5781, r = 0.6079, p = 0.0076, and p = 0.0045, respectively). EDSS scores of NMOSD group were higher than those of ON group and the time course of NMOSD patients was longer than that of ON patients (p < 0.01). After methylprednisolone treatment, both EDSS and VOS scores were significantly decreased at discharge compared with before treatment (p < 0.01). There was no significant correlation among Tfh cell percentages in CD4⁺ cells, CSF leukocytes, CSF protein, annual recurrence rate, EDSS and VOS scores between two groups (p > 0.05).

Conclusion: The Circulating T follicular helper cells were increased in both idiopathic ON and NMOSD.

Aquaporin-4 Autoantibody Detection by ELISA: A Retrospective Characterization of a Commonly Used Assay

Objective

Aquaporin-4 (AQP4) serum autoantibodies are detected by a variety of methods. The highest sensitivity is achieved with cell-based assays, but the enzyme-linked immunosorbent assay (ELISA) is still commonly utilized by clinicians worldwide.

Methods

We performed a retrospective review to identify all patients at the University of Utah who had AQP4 ELISA testing at ARUP Laboratories from 2010 to 2017. We then reviewed their diagnostic evaluation and final diagnosis based on the ELISA titer result.

Results

A total of 750 tests for the AQP4 ELISA were analyzed, and 47 unique patients with positive titers were identified. Less than half of these patients (49%) met the clinical criteria for neuromyelitis optica spectrum disorder (NMOSD). In cases of low positive titers (3.0–7.9 U/mL, n = 19), the most common final diagnosis was multiple sclerosis (52.6%). In the moderate positive cohort (8.0–79.9 U/mL, n = 14), only a little more than half the cohort (64.3%) had NMOSD. In cases with high positives (80–160 U/mL, n = 14), 100% of patients met clinical criteria for NMOSD.

Conclusions

Our data illustrates diagnostic uncertainty associated with the AQP4 ELISA, an assay that is still commonly ordered by clinicians despite the availability of more sensitive and specific tests to detect AQP4 autoantibodies in patients suspected of having NMOSD. In particular, low positive titer AQP4 ELISA results are particularly nonspecific for the diagnosis of NMOSD. The importance of accessibility to both sensitive and specific AQP4 testing cannot be overemphasized in clinical practice.

Severe orthostatic hypotension associated with lesions of the area postraema in neuromyelitis optica spectrum disorder

Hiccups, nausea and vomiting are known as the clinical manifestations of neuromyelitis optica spectrum disorder (NMOSD) linked to lesions of the area postraema in the medullary tegmentum. Here, we describe a 74-year-old male patient with NMOSD who presented with recurrent syncope due to severe orthostatic hypotension (OH) following symptoms of hiccups, nausea and vomiting. Brain magnetic resonance imaging revealed the lesion of the area postraema and it could be responsible for the symptom of OH. Considering the numerous related reports, we suspect that the prevalence of OH is underreported in the patients with NMOSD. OH may transition into more serious conditions, so it should be evaluated carefully in all patients with NMOSD, particularly when there is a lesion of the area postraema.

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The area postraema is frequently affected in Neuromyelitis optica spectrum disorder.

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A Neuromyelitis optica spectrum disorder patient presented orthostatic hypotension.

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The lesion of the area postraema could be responsible for orthostatic hypotension.