Functional characterization of aquaporin-4 specific T cells: towards a model for neuromyelitis optica

The immunological processes behind aquaporin 4-antibody seropositive neuromyelitis optica spectrum disorders

Ever since the discovery of pathogenic aquaporin 4-specific antibodies in the serum of patients with neuromyelitis optica spectrum disorders current knowledge about clinical observations and diagnosis, and about the underlying pathology and resulting therapies have been put forward in excellent reviews and primary publications. However, in order to further develop novel strategies for the treatment of this disease, there is an urgent need to understand the immunological processes associated with the formation of the pathogenic antibodies, and with aberrant immune responses observed in affected patients. In this review, we will highlight and evaluate important studies on these processes.

Immune Repertoires in Various Dermatologic and Autoimmune Diseases

The immune repertoire (IR) is a term that defines the combined unique genetic rearrangements of antigen receptors expressed by B and T lymphocytes. The IR determines the ability of the immune system to identify and respond to foreign antigens while preserving tolerance to host antigens. When immune tolerance is disrupted, development of autoimmune diseases can occur due to the attack of self-antigens. Recent technical advances in immune profiling allowed identification of common patterns and shared antigen-binding sequences unique to diverse array of diseases. However, there is no current literature to date evaluates IR findings in autoimmune and skin inflammatory conditions. In this review, we provide an overview of the past and current research findings of IR in various autoimmune and dermatologic conditions. Enriching our understanding of IRs in these conditions is critical for understanding the pathophysiology behind autoimmune skin disease onset and progression. Furthermore, understanding B-cell and T-cell IR will help devise therapeutic treatments in the hopes of restoring immune tolerance and preventing disease onset and progression.

Delimiting MOGAD as a disease entity using translational imaging

The first formal consensus diagnostic criteria for myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) were recently proposed. Yet, the distinction of MOGAD-defining characteristics from characteristics of its important differential diagnoses such as multiple sclerosis (MS) and aquaporin-4 antibody seropositive neuromyelitis optica spectrum disorder (NMOSD) is still obstructed. In preclinical research, MOG antibody-based animal models were used for decades to derive knowledge about MS. In clinical research, people with MOGAD have been combined into cohorts with other diagnoses. Thus, it remains unclear to which extent the generated knowledge is specifically applicable to MOGAD. Translational research can contribute to identifying MOGAD characteristic features by establishing imaging methods and outcome parameters on proven pathophysiological grounds. This article reviews suitable animal models for translational MOGAD research and the current state and prospect of translational imaging in MOGAD.

Modelling MOG antibody-associated disorder and neuromyelitis optica spectrum disorder in animal models: Spinal cord manifestations

Antibodies to myelin oligodendrocyte glycoprotein (MOG-IgG) or aquaporin 4 (AQP4-IgG) are associated with CNS inflammatory disorders. We directly compared MOG35-55-induced experimental autoimmune encephalomyelitis exacerbated by MOG- and AQP4-IgG (versus isotype IgG, Iso-IgG). Disease severity was highest after MOG-IgG application. MOG- and AQP4-IgG administration increased disease incidence compared to Iso-IgG. Inflammatory lesions appeared earlier and with distinct localizations after AQP4-IgG administration. AQP4 intensity was more reduced after AQP4- than MOG-IgG administration at acute disease phase. The described models are suitable for comparative analyses of pathological features associated with MOG- and AQP4-IgG and the investigation of therapeutic interventions.

T cell deletional tolerance restricts AQP4 but not MOG CNS autoimmunity

Aquaporin-4 (AQP4)-specific Th17 cells are thought to have a central role in neuromyelitis optica (NMO) pathogenesis. When modeling NMO, only AQP4-reactive Th17 cells from AQP4-deficient (AQP4-/-), but not wild-type (WT) mice, caused CNS autoimmunity in recipient WT mice, indicating that a tightly regulated mechanism normally ensures tolerance to AQP4. Here, we found that pathogenic AQP4 T cell epitopes bind MHC II with exceptionally high affinity. Examination of T cell receptor (TCR) α/β usage revealed that AQP4-specific T cells from AQP4-/- mice employed a distinct TCR repertoire and exhibited clonal expansion. Selective thymic AQP4 deficiency did not fully restore AQP4-reactive T cells, demonstrating that thymic negative selection alone did not account for AQP4-specific tolerance in WT mice. Indeed, AQP4-specific Th17 cells caused paralysis in recipient WT or B cell-deficient mice, which was followed by complete recovery that was associated with apoptosis of donor T cells. However, donor AQP4-reactive T cells survived and caused persistent paralysis in recipient mice deficient in both T and B cells or mice lacking T cells only. Thus, AQP4 CNS autoimmunity was limited by T cell-dependent deletion of AQP4-reactive T cells. In contrast, myelin oligodendrocyte glycoprotein (MOG)-specific T cells survived and caused sustained disease in WT mice. These findings underscore the importance of peripheral T cell deletional tolerance to AQP4, which may be relevant to understanding the balance of AQP4-reactive T cells in health and in NMO. T cell tolerance to AQP4, expressed in multiple tissues, is distinct from tolerance to MOG, an autoantigen restricted in its expression.

Intradermal AQP4 peptide immunization induces clinical features of neuromyelitis optica spectrum disorder in mice

We challenged to create a mouse model of neuromyelitis optica spectrum disorder (NMOSD) induced by AQP4 peptide immunization. Intradermal immunization with AQP4 p201-220 peptide induced paralysis in C57BL/6J mice, but not in AQP4 KO mice. AQP4 peptide-immunized mice showed pathological features similar to NMOSD. Administration of anti-IL-6 receptor antibody (MR16-1) inhibited the induction of clinical signs and prevented the loss of GFAP/AQP4 and deposition of complement factors in AQP4 peptide-immunized mice. This novel experimental model may contribute to further understanding the pathogenesis of NMOSD, elucidating the mechanism of action of therapeutic agents, and developing new therapeutic approaches.

T follicular helper cells contribute to pathophysiology in a model of neuromyelitis optica spectrum disorders

Neuromyelitis optica spectrum disorders (NMOSD) are inflammatory autoimmune disorders of the CNS. IgG autoantibodies targeting the aquaporin-4 water channel (AQP4-IgGs) are the pathogenic effector of NMOSD. Dysregulated T follicular helper (Tfh) cells have been implicated in loss of B cell tolerance in autoimmune diseases. The contribution of Tfh cells to disease activity and therapeutic potential of targeting these cells in NMOSD remain unclear. Here, we established an autoimmune model of NMOSD by immunizing mice against AQP4 via in vivo electroporation. After AQP4 immunization, mice displayed AQP4 autoantibodies in blood circulation, blood-brain barrier disruption, and IgG infiltration in spinal cord parenchyma. Moreover, AQP4 immunization induced motor impairments and NMOSD-like pathologies, including astrocytopathy, demyelination, axonal loss, and microglia activation. These were associated with increased splenic Tfh, Th1, and Th17 cells; memory B cells; and plasma cells. Aqp4-deficient mice did not display motor impairments and NMOSD-like pathologies after AQP4 immunization. Importantly, abrogating ICOS/ICOS-L signaling using anti-ICOS-L antibody depleted Tfh cells and suppressed the response of Th1 and Th17 cells, memory B cells, and plasma cells in AQP4-immunized mice. These findings were associated with ameliorated motor impairments and spinal cord pathologies. This study suggests a role of Tfh cells in the pathophysiology of NMOSD in a mouse model with AQP4 autoimmunity and provides an animal model for investigating the immunological mechanisms underlying AQP4 autoimmunity and developing therapeutic interventions targeting autoimmune reactions in NMOSD.

Anti-aquaporin-4 immunoglobulin G colorimetric detection by silver nanoparticles

Neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory and autoimmune disease whose biomarker is the anti-AQP4-IgG autoantibody that binds to aquaporin-4 (AQP4) protein. We introduced a nanosensor with a sensitivity of 84.6%, higher than the CBA's 76.5%. Using silver nanoparticles (AgNPs), we detected not only seropositive but also some false-negative patients previously classified with CBA. It consisted of AgNPs coated with one of a panel of 5 AQP4 epitopes. The ability in detecting the anti-AQP4-IgG in NMOSD patients depended on the epitope and synergy could be obtained by combining different epitopes. We demonstrated that NMOSD patients could easily be distinguished from healthy subjects and patients with multiple sclerosis. Using the most sensitive AQP4_61-70 peptide, we established a calibration curve to estimate the concentration of anti-AQP4-IgG in seropositive NMOSD patients. The ability to enhance the accuracy of the diagnosis may improve the prognosis of 10-27% of anti-AQP4-IgG seronegative patients worldwide.

Relationship between the Clinical Characteristics in Patients with Neuromyelitis Optica Spectrum Disorders and Clinical Immune Indicators: A Retrospective Study

Objective: T lymphocytes, complement, and immunoglobulin play an important role in neuromyelitis optica spectrum disorders (NMOSD). As common clinical examination indicators, they have been used as routine indicators in many hospitals, which is convenient for being carried out in clinical work, but there are few articles of guiding significance for clinical practice. The purpose of this study was to study the relationship between commonly used immune indicators and clinical characteristics in patients with NMOSD. Methods: We compared clinical characteristics and clinical immune indicators in 258 patients with NMOSD and 200 healthy controls (HCs). We used multiple linear regression to study the relationship between immunotherapy, disease phase, sex, age, AQP4-IgG, and immune indicators. In addition, lymphocyte subsets were compared before and after immunotherapy in 24 of the 258 patients. We explored the influencing factors and predictors of severe motor disability. Results: The percentages of CD3 ratio (71.4% vs. 73.8%, p = 0.013), CD4 ratio (38.8% vs. 42.2%, p < 0.001), and CD4/CD8 ratio (1.43 vs. 1.66, p < 0.001) in NMOSD patients were significantly lower than those in the HC group. In addition, complement C4 (0.177 g/L vs. 0.221 g/L, p < 0.001) and peripheral blood IgG (10.95 g/L vs. 11.80 g/L, p = 0.026) in NMOSD patients were significantly lower than those in the HC group. CD3 percentage was correlated with blood collection age and disease stage; CD8 percentage was correlated with blood collection age, disease stage, and treatment; CD4/CD8 percentage was correlated with blood collection age and treatment; complement C4 was correlated with blood collection age and sex; and IgG was correlated with disease stage and treatment. Twenty-four patients before and after treatment showed that the percentages of CD3 ratio (74.8% vs. 66.7%, p = 0.001) and CD8 ratio (32.4% vs. 26.2%, p < 0.001) after treatment in NMOSD patients were significantly increased, and the percentage of CD3 before treatment was moderately negatively correlated with ARR (r = −0.507, p = 0.011). Binary logistic regression analysis showed that peripheral blood complement C3 is a serious influencing factor for severe motor disability (EDSS score ≥ 6 points). Peripheral blood complement C3 and C4 are predictors of severe motor disability (p < 0.05). Conclusion: Our results suggest that peripheral blood T lymphocytes, C3, C4 and immunoglobulin are convenient and routine clinical indicators that are convenient for implementation in clinical work. They have certain reference values for disease staging, recurrence, drug efficacy, and motor disability. They have improved our understanding of clinical immune indicators for NMOSD patients, but whether they can be used as biomarkers for clinical prognosis remains to be further studied.

Comparative Analysis of T-Cell Responses to Aquaporin-4 and Myelin Oligodendrocyte Glycoprotein in Inflammatory Demyelinating Central Nervous System Diseases

Autoantibodies against aquaporin-4 (AQP4-Ab) and myelin oligodendrocyte glycoprotein (MOG-Ab) are associated with rare central nervous system inflammatory demyelinating diseases like neuromyelitis optica spectrum disorders (NMOSD). Previous studies have shown that not only antibodies, but also autoreactive T-cell responses against AQP4 are present in NMOSD. However, no study has yet analyzed the presence of MOG reactive T-cells in patients with MOG antibodies. Therefore, we compared AQP4 and MOG specific peripheral T-cell response in individuals with AQP4-Ab (n = 8), MOG-Ab (n = 10), multiple sclerosis (MS, n = 8), and healthy controls (HC, n = 14). Peripheral blood mononuclear cell cultures were stimulated with eight AQP4 and nine MOG peptides selected from previous studies and a tetanus toxoid peptide mix as a positive control. Antigen-specific T-cell responses were assessed using the carboxyfluorescein diacetate succinimidyl ester proliferation assay and the detection of granulocyte macrophage colony-stimulating factor (GM-CSF), interferon (IFN)-ɤ and interleukin (IL)-4, IL-6, and IL-17A in cell culture supernatants. Additionally, human leukocyte antigen (HLA)-DQ and HLA-DR genotyping of all participants was performed. We classified a T-cell response as positive if proliferation (measured by a cell division index ≥3) was confirmed by the secretion of at least one cytokine. Reactivity against AQP4 peptides was observed in many groups, but the T-cell response against AQP4 p156-170 was present only in patients with AQP4-Ab (4/8, 50%) and absent in patients with MOG-Ab, MS and HC (corrected p = 0.02). This AQP4 p156-170 peptide specific T-cell response was significantly increased in participants with AQP4-Ab compared to those without [Odds ratio (OR) = 59.00, 95% confidence interval-CI 2.70–1,290.86]. Moreover, T-cell responses against at least one AQP4 peptide were also more frequent in participants with AQP4-Ab (OR = 11.45, 95% CI 1.24–106.05). We did not observe any significant differences for the other AQP4 peptides or any MOG peptide. AQP4-Ab were associated with HLA DQB1^*02 (OR = 5.71, 95% CI 1.09–30.07), DRB1^*01 (OR = 9.33, 95% CI 1.50–58.02) and DRB1^*03 (OR = 6.75, 95% CI = 1.19–38.41). Furthermore, HLA DRB1^*01 was also associated with the presence of AQP4 p156-170 reactive T-cells (OR = 31.67, 95% CI 1.30–772.98). To summarize, our findings suggest a role of AQP4-specific, but not MOG-specific T-cells, in NMOSD.

Experimental animal models of aquaporin-4-IgG-seropositive neuromyelitis optica spectrum disorders: progress and shortcomings

Neuromyelitis optica spectrum disorders (NMOSD) is a heterogeneous group of neuroinflammatory conditions associated with demyelination primarily in spinal cord and optic nerve, and to a lesser extent in brain. Most NMOSD patients are seropositive for IgG autoantibodies against aquaporin-4 (AQP4-IgG), the principal water channel in astrocytes. There has been interest in establishing experimental animal models of seropositive NMOSD (herein referred to as NMO) in order to elucidate NMO pathogenesis mechanisms and to evaluate drug candidates. An important outcome of early NMO animal models was evidence for a pathogenic role of AQP4-IgG. However, available animal models of NMO, based largely on passive transfer to rodents of AQP4-IgG or transfer of AQP4-sensitized T cells, often together with pro-inflammatory maneuvers, only partially recapitulate the clinical and pathological features of human NMO, and are inherently biased toward humoral or cellular immune mechanisms. This review summarizes current progress and shortcomings in experimental animal models of seropositive NMOSD, and opines on the import of advancing animal models.

Foxp3+ regulatory T cells expression in neuromyelitis optica spectrum disorders

BACKGROUND

Alterations in the frequency or function of regulatory T cells (Tregs), which play a critical role in the maintenance of peripheral immune tolerance, are known to be involved in the pathogenesis of several autoimmune diseases. Neuromyelitis optica spectrum disorders (NMOSD) are autoimmune inflammatory diseases of the central nervous system (CNS), of which the etiology and mechanisms underlying its development are not completely understood. Although there is increasing evidence for the involvement of effector T cells in NMOSD, no data are available regarding the role of Tregs in its pathogenesis.

AIM

The aim of this study was to investigate the mRNA expression level of regulatory T cell genes in NMOSD.

METHODS

We used gene expression array and RT-PCR analysis to study Treg cell genes in NMOSD RESULTS: A distinctive Treg gene signature in the peripheral blood of NMOSD patients is described, as well as significantly decreased FoxP3 mRNA expression in the peripheral blood mononuclear cells (PBMCs) of the patients vs that in the healthy controls (HCs) (NMOSD,1.8RQ vs HC, 6.8RQ, p = 0.01).

CONCLUSIONS

The present study shows downregulation at the mRNA expression level of a Treg key transcription factor FoxP3, in NMOSD. Exploration of Tregs function and interconnections in the peripheral immune system should advance our understanding of NMOSD pathogenesis.

Reduced expression of the IL7Ra signaling pathway in Neuromyelitis optica

Neuromyelitis optica (NMO) is a chronic inflammatory demyelinating autoimmune disease of the central nervous system that most commonly affects the optic nerves and spinal cord. To characterize the immunological pathways involved in NMO, whole blood RNA expression array was performed using Nanostring nCounter technology. Two major clusters of genes were found associated with NMO: T cell-associated genes and the TNF/NF-kB signaling pathway. Analysis of the genes within the first cluster confirmed significantly reduced expression of IL7Ra (CD127) in the peripheral blood of NMO patients vs that in healthy controls. IL7Ra upstream transcription factors and its downstream survival signaling pathway were also markedly reduced. In line with the essential role of IL7Ra in T cell maturation and survival, a significantly lower number of naïve T cells, and reduced T cell survival signaling mediated by increased BID (BH3-interacting domain death agonist) expression and increased apoptosis was observed. Cumulatively, these findings indicate that the IL7Ra signaling pathway may play a role in the autoimmune process in NMO.

Infections in neuromyelitis optica spectrum disorder

Neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory astrocytopathy that has both genetic and environmental causes. A growing body of evidence suggests that the presence of several infectious agents correlates with the development of NMOSD. In this review, we summarize studies that either support or present evidence against the hypothesized association between infection and NMOSD. We will also present an overview of potential mechanisms underlying the pathogenesis of NMOSD. Finally, we provide some beneficial properties that infectious elements may have based on "hygiene hypothesis". It is of great clinical significance to further investigate the complex mechanisms by which infections may affect autoimmune diseases to develop better strategies to prevent and treat them, although so far no causal link between infectious agents and NMOSD has been established.

Induction of Paralysis and Visual System Injury in Mice by T Cells Specific for Neuromyelitis Optica Autoantigen Aquaporin-4

While it is recognized that aquaporin-4 (AQP4)-specific T cells and antibodies participate in the pathogenesis of neuromyelitis optica (NMO), a human central nervous system (CNS) autoimmune demyelinating disease, creation of an AQP4-targeted model with both clinical and histologic manifestations of CNS autoimmunity has proven challenging. Immunization of wild-type (WT) mice with AQP4 peptides elicited T cell proliferation, although those T cells could not transfer disease to naïve recipient mice. Recently, two novel AQP4 T cell epitopes, peptide (p) 135-153 and p201-220, were identified when studying immune responses to AQP4 in AQP4-deficient (AQP4^-/-) mice, suggesting T cell reactivity to these epitopes is normally controlled by thymic negative selection. AQP4^-/- Th17 polarized T cells primed to either p135-153 or p201-220 induced paralysis in recipient WT mice, that was associated with predominantly leptomeningeal inflammation of the spinal cord and optic nerves. Inflammation surrounding optic nerves and involvement of the inner retinal layers (IRL) were manifested by changes in serial optical coherence tomography (OCT). Here, we illustrate the approaches used to create this new in vivo model of AQP4-targeted CNS autoimmunity (ATCA), which can now be employed to study mechanisms that permit development of pathogenic AQP4-specific T cells and how they may cooperate with B cells in NMO pathogenesis.

T cells targeting neuromyelitis optica autoantigen aquaporin-4 cause paralysis and visual system injury

Aquaporin-4 (AQP4)-specific antibodies are instrumental in promoting central nervous system (CNS) tissue injury in neuromyelitis optica (NMO), yet evidence indicates that AQP4-specific T cells also have a pivotal role in NMO pathogenesis. Although considerable effort has been devoted to creation of animal models to study how AQP4-specific T cells and antibodies may cooperate in development of both clinical and histologic opticospinal inflammatory disease, the initial attempts were unsuccessful. Recently, it was discovered that T cells from AQP4-deficient (AQP4^-/-) mice recognize distinct AQP4 epitopes that were not identified previously in wild-type (WT) mice, and that donor Th17 cells from AQP4^-/- mice that target those novel epitopes could cause paralysis and visual system injury associated with opticospinal inflammation in WT recipient mice. These observations indicate that the pathogenic AQP4-specific T cell repertoire is normally controlled by negative selection. Here, we describe the advances leading to development of an animal model for aquaporin-targeted CNS autoimmunity (ATCA). This new model provides a foundation to investigate immune mechanisms that may participate in NMO pathogenesis. It should also permit preclinical testing of agents considered for treatment of NMO.

Deletional tolerance prevents AQP4-directed autoimmunity in mice

Neuromyelitis optica (NMO) is an autoimmune disorder of the central nervous system (CNS) mediated by antibodies to the water channel protein AQP4 expressed in astrocytes. The contribution of AQP4‐specific T cells to the class switch recombination of pathogenic AQP4‐specific antibodies and the inflammation of the blood–brain barrier is incompletely understood, as immunogenic naturally processed T‐cell epitopes of AQP4 are unknown. By immunizing Aqp4^−/− mice with full‐length murine AQP4 protein followed by recall with overlapping peptides, we here identify AQP4(201‐220) as the major immunogenic IA^b‐restricted epitope of AQP4. We show that WT mice do not harbor AQP4(201–220)‐specific T‐cell clones in their natural repertoire due to deletional tolerance. However, immunization with AQP4(201–220) of Rag1^−/− mice reconstituted with the mature T‐cell repertoire of Aqp4^−/− mice elicits an encephalomyelitic syndrome. Similarly to the T‐cell repertoire, the B‐cell repertoire of WT mice is “purged” of AQP4‐specific B cells, and robust serum responses to AQP4 are only mounted in Aqp4^−/− mice. While AQP4(201–220)‐specific T cells alone induce encephalomyelitis, NMO‐specific lesional patterns in the CNS and the retina only occur in the additional presence of anti‐AQP4 antibodies. Thus, failure of deletional T‐cell and B‐cell tolerance against AQP4 is a prerequisite for clinically manifest NMO.

Müller cells and retinal axons can be primary targets in experimental neuromyelitis optica spectrum disorder

Recent work from our laboratory, using different models of experimental neuromyelitis optica spectrum disorder (NMOSD), has led to a number of observations that might be highly relevant for NMOSD patients. For example: (i) in the presence of neuromyelitis optica immunoglobulin G, astrocyte‐destructive lesions can be initiated by CD4+ T cells when these cells recognize aquaporin 4 (AQP4), but also when they recognize other antigens of the central nervous system. The only important prerequisite is that the T cells have to be activated within the central nervous system by “their” specific antigen. Recently activated CD4+ T cells with yet unknown antigen specificity are also found in human NMOSD lesions. (ii) The normal immune repertoire might contain AQP4‐specific T cells, which are highly encephalitogenic on activation. (iii) The retina might be a primary target of AQP4‐specific T cells and neuromyelitis optica immunoglobulin G: AQP4‐specific T cells alone are sufficient to cause retinitis with low‐grade axonal pathology in the retinal nerve fiber/ganglionic cell layer. A thinning of these layers is also observed in NMOSD patients, where it is thought to be a consequence of optic neuritis. Neuromyelitis optica immunoglobulin G might target cellular processes of Müller cells and cause their loss of AQP4 reactivity, when AQP4‐specific T cells open the blood–retina barrier in the outer plexiform layer. Patchy loss of AQP4 reactivity on Müller cells of NMOSD patients has been recently described. Cumulatively, our findings in experimental NMOSD suggest that both CD4+ T cell and antibody responses directed against AQP4 might play an important role in the pathogenesis of tissue destruction seen in NMOSD.

Variants of Interleukin-7/Interleukin-7 Receptor Alpha are Associated with Both Neuromyelitis Optica and Multiple Sclerosis Among Chinese Han Population in Southeastern China

BACKGROUND

Neuromyelitis optica (NMO) and multiple sclerosis (MS) are autoimmune demyelinating diseases of the central nerve system. Interleukin-7 (IL-7) and interleukin-7 receptor alpha (IL-7Rα) were proved to be important in the pathogenesis of both diseases because of the roles they played in the differentiations of autoimmune lymphocytes. The variants of both genes had been identified to be associated with MS susceptibility in Caucasian, Japanese and Korean populations. However, the association of these variants with NMO and MS has not been well studied in Chinese Southeastern Han population. Here, we aimed to evaluate the association of six IL-7 variants (rs1520333, rs1545298, rs4739140, rs6993386, rs7816065, and rs2887502) and one variant of IL-7RA (rs6897932) with NMO and MS among Chinese Han population in southeastern China.

METHODS

Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MassARRAY system) and Sanger sequencing were used to determine the variants of IL-7 and IL-7RA in 167 NMO patients, 159 MS patients and 479 healthy controls among Chinese Han population in southeastern China. Samples were excluded if the genotyping success rate <90%.

RESULTS

Statistical differences were observed in the genotypes of IL-7 rs1520333 in MS patients and IL-7RA rs6897932 in NMO patients, compared with healthy controls (P = 0.035 and 0.034, respectively). There was a statistically significant difference in the genotypes of IL-7 rs2887502 between MS and NMO patients (P = 0.014). And there were statistically significant differences in the rs6897932 genotypes (P = 0.004) and alleles (P = 0.042) between NMO-IgG positive patients and healthy controls.

CONCLUSIONS

The study suggested that among Chinese Han population in southeastern China, the variant of IL-7RA (rs6897932) was associated with NMO especially NMO-IgG positive patients while the variant of IL-7 (rs1520333) with MS patients. And the genotypic differences of IL-7 rs2887502 between MS and NMO indicated the different genetic backgrounds of these two diseases.

Tolerance checkpoint bypass permits emergence of pathogenic T cells to neuromyelitis optica autoantigen aquaporin-4

Aquaporin-4 (AQP4)-specific T cells are expanded in neuromyelitis optica (NMO) patients and exhibit Th17 polarization. However, their pathogenic role in CNS autoimmune inflammatory disease is unclear. Although multiple AQP4 T-cell epitopes have been identified in WT C57BL/6 mice, we observed that neither immunization with those determinants nor transfer of donor T cells targeting them caused CNS autoimmune disease in recipient mice. In contrast, robust proliferation was observed following immunization of AQP4-deficient (AQP4^-/-) mice with AQP4 peptide (p) 135-153 or p201-220, peptides predicted to contain I-A^b-restricted T-cell epitopes but not identified in WT mice. In comparison with WT mice, AQP4^-/- mice used unique T-cell receptor repertoires for recognition of these two AQP4 epitopes. Donor T cells specific for either determinant from AQP4^-/-, but not WT, mice induced paralysis in recipient WT and B-cell-deficient mice. AQP4-specific Th17-polarized cells induced more severe disease than Th1-polarized cells. Clinical signs were associated with opticospinal infiltrates of T cells and monocytes. Fluorescent-labeled donor T cells were detected in CNS lesions. Visual system involvement was evident by changes in optical coherence tomography. Fine mapping of AQP4 p201-220 and p135-153 epitopes identified peptides within p201-220 but not p135-153, which induced clinical disease in 40% of WT mice by direct immunization. Our results provide a foundation to evaluate how AQP4-specific T cells contribute to AQP4-targeted CNS autoimmunity (ATCA) and suggest that pathogenic AQP4-specific T-cell responses are normally restrained by central tolerance, which may be relevant to understanding development of AQP4-reactive T cells in NMO.

A Single Amino Acid Substitution Prevents Recognition of a Dominant Human Aquaporin-4 Determinant in the Context of HLA-DRB1*03:01 by a Murine TCR

Background

Aquaporin 4 (AQP4) is considered a putative autoantigen in patients with Neuromyelitis optica (NMO), an autoinflammatory disorder of the central nervous system (CNS). HLA haplotype analyses of patients with NMO suggest a positive association with HLA-DRB1* 03:01. We previously showed that the human (h) AQP4 peptide 281–300 is the dominant immunogenic determinant of hAQP4 in the context of HLA-DRB1*03:01. This immunogenic peptide stimulates a strong Th₁ and Th₁₇ immune response. AQP4_281-300-specific encephalitogenic CD4⁺ T cells should initiate CNS inflammation that results in a clinical phenotype in HLA-DRB1*03:01 transgenic mice.

Methods

Controlled study with humanized experimental animals. HLA-DRB1*03:01 transgenic mice were immunized with hAQP4_281-300, or whole-length hAQP4 protein emulsified in complete Freund’s adjuvant. Humoral immune responses to both antigens were assessed longitudinally. In vivo T cell frequencies were assessed by tetramer staining. Mice were followed clinically, and the anterior visual pathway was tested by pupillometry. CNS tissue was examined histologically post-mortem. Flow cytometry was utilized for MHC binding assays and to immunophenotype T cells, and T cell frequencies were determined by ELISpot assay.

Results

Immunization with hAQP4_281-300 resulted in an in vivo expansion of antigen-specific CD4⁺ T cells, and an immunoglobulin isotype switch. HLA-DRB1*03:01 TG mice actively immunized with hAQP4_281-300, or with whole-length hAQP4 protein were resistant to developing a neurological disease that resembles NMO. Experimental mice show no histological evidence of CNS inflammation, nor change in pupillary responses. Subsequent analysis reveals that a single amino acid substitution from aspartic acid in hAQP4 to glutamic acid in murine (m)AQP4 at position 290 prevents the recognition of hAQP4_281-300 by the murine T cell receptor (TCR).

Conclusion

Induction of a CNS inflammatory autoimmune disorder by active immunization of HLA-DRB1*03:01 TG mice with human hAQP4_281-300 will be complex due to a single amino acid substitution. The pathogenic role of T cells in this disorder remains critical despite these observations.

T-cell responses to distinct AQP4 peptides in patients with neuromyelitis optica (NMO)

BACKGROUND

Although antibodies to aquaporin-4(AQP4) are strongly associated with Neuromyelitis optica (NMO), the sole transfer of these antibodies is not sufficient to induce an NMO-like disease in experimental animals and T-cells and complement are also needed. Initial data indicating the presence of T-cell responses to AQP4 in patients with NMO, have beeen recently reported.

OBJECTIVE

To evaluate the T-cell responses to specific AQP4 peptides/epitopes in patients with NMO and multiple sclerosis (MS).

METHODS

Peripheral blood mononuclear cells (PBMCs) were obtained from 14 patients fulfilling the criteria for definite NMO and the proliferation responses to one of 15 distinct pentadecapeptides of AQP4, spanning the whole protein (except of its transmembrane parts) were tested by a standard [H3]-thymidine uptake assay and compared with those of 9 healthy controls and 7 MS patients. A cytometric bead array assay (CBA) and flow cytometry were used to evaluate cytokine (IFNγ, IL17, IL2, IL4, IL5, IL10 and TNFα) and chemokine (CXCL8, CCL5, CXCL10, CXCL9, CCL2) secretion by PHA-stimulated PBMCs and AQP4-specific T-cell lines.

RESULTS

Four main immunodominant epitopes of the AQP4 protein (p137-151, p222-236, p217-231 and the p269-283) were identified in the NMO group. The first two epitopes (assigned as peptides 3 and 9) showed the highest sensitivity (~60% positivity), whereas the latter two (assigned as peptides 8 and 11), the higher specificity. Longitudinal follow up of 5 patients revealed changes in the epitope-specificities during the course of NMO. T-cell lines specific for the AQP4 peptides, produced from NMO patients (but not healthy donors) secreted mainly IL-17 and IL-10 and less IFNγ.

CONCLUSIONS

Our findings indicate that T-cells bearing characteristics of both Th1 and Th17 T-cells and targeting specific immunodominant epitopes of the AQP4 protein might be involved in the pathogenesis of NMO.

Highly encephalitogenic aquaporin 4-specific T cells and NMO-IgG jointly orchestrate lesion location and tissue damage in the CNS

In neuromyelitis optica (NMO), astrocytes become targets for pathogenic aquaporin 4 (AQP4)-specific antibodies which gain access to the central nervous system (CNS) in the course of inflammatory processes. Since these antibodies belong to a T cell-dependent subgroup of immunoglobulins, and since NMO lesions contain activated CD4⁺ T cells, the question arose whether AQP4-specific T cells might not only provide T cell help for antibody production, but also play an important role in the induction of NMO lesions. We show here that highly pathogenic, AQP4-peptide-specific T cells exist in Lewis rats, which recognize AQP4_268–285 as their specific antigen and cause severe panencephalitis. These T cells are re-activated behind the blood–brain barrier and deeply infiltrate the CNS parenchyma of the optic nerves, the brain, and the spinal cord, while T cells with other AQP4-peptide specificities are essentially confined to the meninges. Although AQP4_268–285-specific T cells are found throughout the entire neuraxis, they have NMO-typical “hotspots” for infiltration, i.e. periventricular and periaqueductal regions, hypothalamus, medulla, the dorsal horns of spinal cord, and the optic nerves. Most remarkably, together with NMO-IgG, they initiate large astrocyte-destructive lesions which are located predominantly in spinal cord gray matter. We conclude that the processing of AQP4 by antigen presenting cells in Lewis rats produces a highly encephalitogenic AQP4 epitope (AQP4_268–285), that T cells specific for this epitope are found in the immune repertoire of normal Lewis rats and can be readily expanded, and that AQP4_268–285-specific T cells produce NMO-like lesions in the presence of NMO-IgG.

Change in autoantibody and cytokine responses during the evolution of neuromyelitis optica in patients with systemic lupus erythematosus: A preliminary study

BACKGROUND

Neuromyelitis optica (NMO)-systemic lupus erythematosus (SLE) association is a rare condition characterized by multiple autoantibodies.

OBJECTIVE

To examine if, during the evolution of NMO, anti-AQP4 responses are part of polyclonal B cell activation, and if T cell responses contribute.

METHODS

In 19 samples of six patients who developed NMO during SLE, we examined the correlation of AQP4-IgG1 and IgM with (i) anti-MOG IgG and IgM, (ii) anti-nuclear, anti-nucleosome and anti-dsDNA IgG antibodies, (iii) cytokines and chemokines in the serum and (iv) longitudinal relation to NMO relapses/remission.

RESULTS

AQP4-IgG1 was present 1-2-5 years before the first NMO relapse. During relapse, AQP4-IgG1, ANA, anti-dsDNA and anti-nucleosome antibodies were elevated. Anti-MOG IgG/IgM and AQP4-IgM antibodies were not detected. AQP4-IgG1 antibodies correlated with concentration of anti-nucleosome, IFN-γ,interferon-gamma-induced CCL10/IP-10 and CCL17/TARC (p<0.05, respectively). CCL17/TARC correlated with levels of anti-nucleosome and anti-dsDNA (p<0.05, respectively). Compared to healthy subjects, concentration of IFN-γ and CCL17/TARC was higher in NMO/SLE (p<0.05).

CONCLUSIONS

AQP4-IgG1 antibodies are present in the sera years before the first NMO attack in patients with SLE; elevation of anti-AQP4 is part of a polyclonal B cell response during NMO relapses; in spite of multiple autoantibodies in the serum, MOG antibodies were not present; Th1 responses accompany autoantibody responses in NMO/SLE.

Experimental models of neuromyelitis optica: current status, challenges and future directions

Neuromyelitis optica (NMO) is a recurrent inflammatory disease that predominantly attacks the opticnerves and spinal cord. NMO-IgG, the specific autoantibody present in the vast majority of NMO patients, targets the astrocytic water channel protein aquaporin 4 (AQP4), and differentiates NMO from multiple sclerosis. The growing clinical and research interest in NMO makes it urgent to produce an animal model of NMO. The pathogenic effect of anti-AQP4 antibodies derived from the serum of patients paves the way to generating an experimental model based on the anti-AQP4-mediated astrocyte damage. In this review, we discuss the contribution of experimental models to the understanding of the pathogenesis of the disease and drug development. Key questions raised by the existing models are also discussed.

Epidemiological, clinical, and immunological characteristics of neuromyelitis optica: A review

The aim of this study was to review the epidemiological and clinical characteristics of neuromyelitis optica (NMO) and the immunopathological mechanisms involved in the neuronal damage. NMO is an inflammatory demyelinating autoimmune disease of the central nervous system that most commonly affects the optic nerves and spinal cord. NMO is thought to be more prevalent among non-Caucasians and where multiple sclerosis (MS) prevalence is low. NMO follows a relapsing course in more than 80-90% of cases, which is more commonly in women. It is a complex disease with an interaction between host genetic and environmental factors and the main immunological feature is the presence of anti-aquaporin 4 (AQP4) antibodies in a subset of patients. NMO is frequently associated with multiple other autoantibodies and there is a strong association between NMO with other systemic autoimmune diseases. AQP4-IgG can cause antibody-dependent cellular cytotoxicity (ADCC) when effector cells are present and complement-dependent cytotoxicity (CDC) when complement is present. Acute therapies, including corticosteroids and plasma exchange, are designed to minimize injury and accelerate recovery. Several aspects of NMO pathogenesis remain unclear. More advances in the understanding of NMO disease mechanisms are needed in order to identify more specific biomarkers to NMO diagnosis.

Pathogenic aquaporin-4 reactive T cells are sufficient to induce mouse model of neuromyelitis optica

Introduction

Neuromyelitis Optica (NMO) is an autoimmune disease primarily targeting the spinal cord and optic nerve leading to paralysis and blindness. The discovery of an antibody against the astrocytic water channel, aquaporin-4 (AQP4), in the majority of patients, has led to the presumption that the antibody was necessary for disease pathogenesis. The potential role of T cells in the central nervous system, however, has not been thoroughly examined.

Results

We generated an anti-AQP4 antibody seronegative model of NMO using pathogenic AQP4-reactive T cells in mice by immunizing AQP4 null mice with peptides corresponding to the second extracellular loop of AQP4, loop C. When polarized to a Th17 phenotype and transferred to wild-type mice, these cells caused tail and limb weakness. Histology showed demyelination and T cell infiltration in the spinal cord, optic nerve and brain. Animals receiving cells re-stimulated in culture with non-specific proteins resulted in no behavioral disease, indicating that specific targeting of AQP4 is essential for this phenotype.

Conclusions

In summary, we show that AQP4-reactive T cells are sufficient to trigger an NMO-like disease in mice, independent of antibodies, indicating that pathogenic AQP4-reactive T cells may play a similar role in humans.

Experimental models of neuromyelitis optica

For a long time, the most important inflammatory demyelinating diseases of the central nervous system (CNS), for example, multiple sclerosis (MS) and neuromyelitis optica (NMO), were extremely hard to differentiate, often with severe consequences for affected patients. This changed with the discovery of NMO‐immunoglobulin G (IgG), a specific autoantibody which was detected in the vast majority of NMO patients, and with the demonstration that this autoantibody targets aquaporin 4 (AQP4), a water channel found on astrocytes in the CNS. These findings paved the way for the generation of experimental models of NMO. This chapter will discuss the contribution of experimental models to NMO research and what key questions remain to be addressed.

Neuromyelitis optica: clinical features, immunopathogenesis and treatment

The term 'neuromyelitis optica' ('Devic's syndrome', NMO) refers to a syndrome characterized by optic neuritis and myelitis. In recent years, the condition has raised enormous interest among scientists and clinical neurologists, fuelled by the detection of a specific serum immunoglobulin (Ig)G reactivity (NMO-IgG) in up to 80% of patients with NMO. These autoantibodies were later shown to target aquaporin-4 (AQP4), the most abundant water channel in the central nervous system (CNS). Here we give an up-to-date overview of the clinical and paraclinical features, immunopathogenesis and treatment of NMO. We discuss the widening clinical spectrum of AQP4-related autoimmunity, the role of magnetic resonance imaging (MRI) and new diagnostic means such as optical coherence tomography in the diagnosis of NMO, the role of NMO-IgG, T cells and granulocytes in the pathophysiology of NMO, and outline prospects for new and emerging therapies for this rare, but often devastating condition.

Immunopathogenesis of neuromyelitis optica

Neuromyelitis optica (NMO, Devic's syndrome) is a clinical syndrome characterized by optic neuritis and (mostly longitudinally extensive) myelitis. If untreated, NMO usually takes a relapsing course and often results in blindness and tetra- or paraparesis. The discovery of autoantibodies to aquaporin-4, the most abundant water channel in the CNS, in 70-80% of patients with NMO (termed NMO-IgG or AQP4-Ab) and subsequent investigations into the pathogenic impact of this new reactivity have led to the recognition of NMO as an autoimmune condition and as a disease entity in its own right, distinct from classic multiple sclerosis. Here, we comprehensively review the current knowledge on the role of NMO-IgG/AQP4-Ab, B cells, T cells, and the innate immune system in the pathogenesis of NMO.

Early loss of oligodendrocytes in human and experimental neuromyelitis optica lesions

Neuromyelitis optica (NMO) is a chronic, mostly relapsing inflammatory demyelinating disease of the CNS characterized by serum anti-aquaporin 4 (AQP4) antibodies in the majority of patients. Anti-AQP4 antibodies derived from NMO patients target and deplete astrocytes in experimental models when co-injected with complement. However, the time course and mechanisms of oligodendrocyte loss and demyelination and the fate of oligodendrocyte precursor cells (OPC) have not been examined in detail. Also, no studies regarding astrocyte repopulation of experimental NMO lesions have been reported. We utilized two rat models using either systemic transfer or focal intracerebral injection of recombinant human anti-AQP4 antibodies to generate NMO-like lesions. Time-course experiments were performed to examine oligodendroglial and astroglial damage and repair. In addition, oligodendrocyte pathology was studied in early human NMO lesions. Apart from early complement-mediated astrocyte destruction, we observed a prominent, very early loss of oligodendrocytes and oligodendrocyte precursor cells (OPCs) as well as a delayed loss of myelin. Astrocyte repopulation of focal NMO lesions was already substantial after 1 week. Olig2-positive OPCs reappeared before NogoA-positive, mature oligodendrocytes. Thus, using two experimental models that closely mimic the human disease, our study demonstrates that oligodendrocyte and OPC loss is an extremely early feature in the formation of human and experimental NMO lesions and leads to subsequent, delayed demyelination, highlighting an important difference in the pathogenesis of MS and NMO.

Autoimmune profiling with protein microarrays in clinical applications

In recent years, knowledge about immune-related disorders has substantially increased, especially in the field of central nervous system (CNS) disorders. Recent innovations in protein-related microarray technology have enabled the analysis of interactions between numerous samples and up to 20,000 targets. Antibodies directed against ion channels, receptors and other synaptic proteins have been identified, and their causative roles in different disorders have been identified. Knowledge about immunological disorders is likely to expand further as more antibody targets are discovered. Therefore, protein microarrays may become an established tool for routine diagnostic procedures in the future. The identification of relevant target proteins requires the development of new strategies to handle and process vast quantities of data so that these data can be evaluated and correlated with relevant clinical issues, such as disease progression, clinical manifestations and prognostic factors. This review will mainly focus on new protein array technologies, which allow the processing of a large number of samples, and their various applications with a deeper insight into their potential use as diagnostic tools in neurodegenerative diseases and other diseases. This article is part of a Special Issue entitled: Biomarkers: A Proteomic Challenge.

Update on the diagnosis and treatment of neuromyelitis optica: recommendations of the Neuromyelitis Optica Study Group (NEMOS)

Neuromyelitis optica (NMO, Devic’s syndrome), long considered a clinical variant of multiple sclerosis, is now regarded as a distinct disease entity. Major progress has been made in the diagnosis and treatment of NMO since aquaporin-4 antibodies (AQP4-Ab; also termed NMO-IgG) were first described in 2004. In this review, the Neuromyelitis Optica Study Group (NEMOS) summarizes recently obtained knowledge on NMO and highlights new developments in its diagnosis and treatment, based on current guidelines, the published literature and expert discussion at regular NEMOS meetings. Testing of AQP4-Ab is essential and is the most important test in the diagnostic work-up of suspected NMO, and helps to distinguish NMO from other autoimmune diseases. Furthermore, AQP4-Ab testing has expanded our knowledge of the clinical presentation of NMO spectrum disorders (NMOSD). In addition, imaging techniques, particularly magnetic resonance imaging of the brain and spinal cord, are obligatory in the diagnostic workup. It is important to note that brain lesions in NMO and NMOSD are not uncommon, do not rule out the diagnosis, and show characteristic patterns. Other imaging modalities such as optical coherence tomography are proposed as useful tools in the assessment of retinal damage. Therapy of NMO should be initiated early. Azathioprine and rituximab are suggested as first-line treatments, the latter being increasingly regarded as an established therapy with long-term efficacy and an acceptable safety profile in NMO patients. Other immunosuppressive drugs, such as methotrexate, mycophenolate mofetil and mitoxantrone, are recommended as second-line treatments. Promising new therapies are emerging in the form of anti-IL6 receptor, anti-complement or anti-AQP4-Ab biologicals.

Aquaporin 4 molecular mimicry and implications for neuromyelitis optica

Neuromyelitis optica (NMO) is associated with antibodies to aquaporin 4 (AQP4). We hypothesized that antibodies to AQP4 can be triggered by exposure to environmental proteins. We compared human AQP4 to plant and bacterial proteins to investigate the occurrence of significantly similar structures and sequences. High similarity to a known epitope for NMO-IgG, AQP4(207-232), was observed for corn ZmTIP4-1. NMO and non-NMO sera were assessed for reactivity to AQP4(207-232) and the corn peptide. NMO patient serum showed reactivity to both peptides as well as to plant tissue. These findings warrant further investigation into the role of the environment in NMO etiology.

Immunology of neuromyelitis optica: a T cell-B cell collaboration

Neuromyelitis optica (NMO) is a debilitating autoimmune inflammatory disease of the central nervous system (CNS) that is distinct from multiple sclerosis (MS). The discovery of NMO-immunoglobulin G (IgG) in the serum of NMO-but not MS-patients was a breakthrough in defining diagnostic criteria for NMO. NMO-IgG is an antibody directed against the astrocytic water channel protein aquaporin-4 (AQP4). While there is evidence that NMO-IgG is also involved in mediating tissue damage in the CNS, many aspects of the pathogenic cascade in NMO remain to be determined. It is clear that antigen-specific T cells contribute to the generation of NMO-IgG in the peripheral immune compartment, as well as to the development of NMO lesions in the CNS. T helper 17 (Th17) cells, equipped both in providing B cell help and inducing tissue inflammation, may be involved in NMO development and pathogenesis. Here, we review immunologic aspects of NMO, placing recent findings in the biology of T-B cell cooperation into perspective with autoimmunity of the CNS.

Myelin oligodendrocyte glycoprotein induces aquaporin-4 autoantibodies in mouse experimental autoimmune encephalomyelitis

To investigate whether AQP4 autoantibodies (AQP4-Ab) are causative for neuromyelitis optica (NMO), the production of AQP4-Ab and clinical experimental autoimmune encephalomyelitis (EAE) was investigated in mice administered with mouse AQP4 antigen or myelin oligodendrocyte glycoprotein (MOG35-55) alone, and in combination. Eight- to twelve-week-old female C57BL/6 mice were randomly immunized with encephalitogenic mixture containing 300 μg of MOG35-55 or AQP4 antigen alone, and in combination in complete Freund's adjuvant supplemented with H37Ra M. tuberculosis. The incidence of EAE, Weaver 15 scores, and body weight was evaluated. ELISA was used to detect serum mouse AQP4-Ab. Mice injected with MOG35-55 and MOG33-35 plus AQP4 antigen began to show EAE symptoms 12 days after immunization. The incidence of EAE was 91.6%, and 62.5%, for MOG35-55 alone and MOG33-35 plus AQP4 antigen groups, respectively, while AQP4 antigen alone didn't develop EAE. In all but the control group, serum AQP4-Ab levels were increased, and correlated positively with Weaver 15 score (rs=0.713, p=0.000) and negatively with body weight changes (rs=-0.415, p=0.011). Injection of human NMO sera positive for AQP4-Ab exacerbated MOG-induced EAE. Our results suggest that AQP4-Ab can be produced in MOG-induced MS model, and itself is not sufficient for the development of EAE, implying that NMO might be a subtype or transition from MS.

Epigallocatechin-3-gallate: a useful, effective and safe clinical approach for targeted prevention and individualised treatment of neurological diseases?

Neurodegenerative disorders show an increasing prevalence in a number of highly developed countries. Often, these diseases require life-long treatment mostly with drugs which are costly and mostly accompanied by more or less serious side-effects. Their heterogeneous manifestation, severity and outcome pose the need for individualised treatment options. There is an intensive search for new strategies not only for treating but also for preventing these diseases. Green tea and green tea extracts seem to be such a promising and safe alternative. However, data regarding the beneficial effects and possible underlying mechanism, specifically in clinical trials, are rare and rather controversial or non-conclusive. This review outlines the existing evidence from preclinical studies (cell and tissue cultures and animal models) and clinical trials regarding preventive and therapeutic effects of epigallcatechin-3-gallate in neurodegenerative diseases and considers antioxidative vs. pro-oxidative properties of the tea catechin important for dosage recommendations.

Human aquaporin 4281-300 is the immunodominant linear determinant in the context of HLA-DRB1*03:01: relevance for diagnosing and monitoring patients with neuromyelitis optica

OBJECTIVE To identify linear determinants of human aquaporin 4 (hAQP4) in the context of HLA-DRB1*03:01. DESIGN In this controlled study with humanized experimental animals, HLA-DRB1*03:01 transgenic mice were immunized with whole-protein hAQP4 emulsified in complete Freund adjuvant. To test T-cell responses, lymph node cells and splenocytes were cultured in vitro with synthetic peptides 20 amino acids long that overlap by 10 amino acids across the entirety of hAQP4. The frequency of interferon γ, interleukin (IL) 17, granulocyte-macrophage colony-stimulating factor, and IL-5-secreting CD4+ T cells was determined by the enzyme-linked immunosorbent sport assay. Quantitative immunofluorescence microscopy was performed to determine whether hAQP4281-300 inhibits the binding of anti-hAQP4 recombinant antibody to surface full-length hAQP4. SETTING Academic neuroimmunology laboratories. SUBJECTS Humanized HLA-DRB1*03:01+/+ H-2b-/- transgenic mice on a B10 background. RESULTS Peptide hAQP4281-300 generated a significantly (P &lt;.01) greater TH1 and TH17 immune response than any of the other linear peptides screened. This 20mer peptide contains 2 dominant immunogenic 15mer peptides. hAQP4284-298 induced predominantly an IL-17 and granulocyte-macrophage colony-stimulating factor TH cell phenotype, whereas hAQP4285-299 resulted in a higher frequency of TH1 cells. hAQP4281-300 did not interfere with recombinant AQP4 autoantibody binding. CONCLUSIONS hAQP4281-330 is the dominant linear immunogenic determinant of hAQP4 in the context of HLA-DRB1*03:01. Within hAQP4281-330 are 2 dominant immunogenic determinants that induce differential TH phenotypes. hAQP4 determinants identified in this study can serve as diagnostic biomarkers in patients with neuromyelitis optica and may facilitate the monitoring of treatment responses to pharmacotherapies.

Pathogenic and physiological autoantibodies in the central nervous system

In this article, we review the current knowledge on pathological and physiological autoantibodies directed toward structures in the central nervous system (CNS) with an emphasis on their regulation and origin. Pathological autoantibodies in the CNS that are associated with autoimmunity often lead to severe neurological deficits via inflammatory processes such as encephalitis. In some instances, however, autoantibodies function as a marker for diagnostic purposes without contributing to the pathological process and/or disease progression. The existence of naturally occurring physiological autoantibodies has been known for a long time, and their role in maintaining homeostasis is well established. Within the brain, naturally occurring autoantibodies targeting aggregated proteins have been detected and might be promising candidates for new therapeutic approaches for neurodegenerative disorders. Further evidence has demonstrated the existence of naturally occurring antibodies targeting antigens on neurons and oligodendrocytes that promote axonal outgrowth and remyelination. The numerous actions of physiological autoantibodies as well as their regulation and origin are summarized in this review.

Review of Animal Models of Neuromyelitis Optica

Neuromyelitis optica (NMO) is a recurrent neuroinflammatory disease of the optic nerves and spinal cord associated with the anti-aquaporin-4 (AQP4) antibody biomarker, NMO-IgG. As clinical and scientific research interest in NMO grows, the need for an animal model becomes more urgent. Over the past few years, several groups have developed rodent models that partially represent human NMO disease. Passive transfer of the NMO-IgG is not pathogenic alone, but in certain contexts can recruit granulocytes and lead to increased inflammation. Studies of the cellular immune response against AQP4 have also shed light on the roles of B and T cells in NMO, especially focusing on the role of Th17 T helper cells. This review discusses the contribution of the available NMO animal models to the understanding of NMO disease pathogenesis.

Identifying autoantigens in demyelinating diseases: valuable clues to diagnosis and treatment?

PURPOSE OF REVIEW

Identification of autoantigens in demyelinating diseases is essential for the understanding of the pathogenesis. Immune responses against these antigens could be used as biomarkers for diagnosis, prognosis and treatment responses. Knowledge of antigen-specific immune responses in individual patients is also a prerequisite for antigen-based therapies.

RECENT FINDINGS

A proportion of patients with demyelinating disease have antibodies to aquaporin 4 (AQP4) or myelin oligodendrocyte glycoprotein (MOG). Patients with anti-AQP4 have the distinct clinical presentation of neuromyelitis optica (NMO), and these patients often also harbour other autoimmune responses. In contrast, anti-MOG is seen in patients with different disease entities such as childhood multiple sclerosis (MS), acute demyelinating encephalomyelitis (ADEM), anti-AQP4 negative NMO, and optic neuritis, but hardly in adult MS. A number of new candidate autoantigens have been identified and await validation. Antigen-based therapies are mainly aimed at tolerizing T-cell responses against myelin basic protein (MBP) and have shown only modest or no clinical benefit so far.

SUMMARY

Currently, only few patients with demyelinating diseases can be characterized based on their autoantibody profile. The most prominent antigens in this respect are MOG and AQP4. Further research has to focus on the validation of newly discovered antigens as biomarkers.

Aquaporin 4-specific T cells in neuromyelitis optica exhibit a Th17 bias and recognize Clostridium ABC transporter

OBJECTIVE

Aquaporin 4 (AQP4)-specific autoantibodies in neuromyelitis optica (NMO) are immunoglobulin (Ig)G1, a T cell-dependent Ig subclass, indicating that AQP4-specific T cells participate in NMO pathogenesis. Our goal was to identify and characterize AQP4-specific T cells in NMO patients and healthy controls (HC).

METHODS

Peripheral blood T cells from NMO patients and HC were examined for recognition of AQP4 and production of proinflammatory cytokines. Monocytes were evaluated for production of T cell-polarizing cytokines and expression of costimulatory molecules.

RESULTS

T cells from NMO patients and HC proliferated to intact AQP4 or AQP4 peptides (p11-30, p21-40, p61-80, p131-150, p156-170, p211-230, and p261-280). T cells from NMO patients demonstrated greater proliferation to AQP4 than those from HC, and responded most vigorously to p61-80, a naturally processed immunodominant determinant of intact AQP4. T cells were CD4(+), and corresponding to association of NMO with human leukocyte antigen (HLA)-DRB1*0301 and DRB3, AQP4 p61-80-specific T cells were HLA-DR restricted. The T-cell epitope within AQP4 p61-80 was mapped to 63-76, which contains 10 residues with 90% homology to a sequence within Clostridium perfringens adenosine triphosphate-binding cassette (ABC) transporter permease. T cells from NMO patients proliferated to this homologous bacterial sequence, and cross-reactivity between it and self-AQP4 was observed, supporting molecular mimicry. In NMO, AQP4 p61-80-specific T cells exhibited Th17 polarization, and furthermore, monocytes produced more interleukin 6, a Th17-polarizing cytokine, and expressed elevated CD40 and CD80 costimulatory molecules, suggesting innate immunologic dysfunction.

INTERPRETATION

AQP4-specific T-cell responses are amplified in NMO, exhibit a Th17 bias, and display cross-reactivity to a protein of an indigenous intestinal bacterium, providing new perspectives for investigating NMO pathogenesis.

Quantitative assays for anti-aquaporin-4 antibody with subclass analysis in neuromyelitis optica

BACKGROUND

To clarify the clinical relevance of anti-aquaporin-4 (anti-AQP4) antibody titers and immunoglobulin (IgG) subclass.

METHODS

Using a bridging enzyme-linked immunosorbent assay (ELISA), a flow cytometric assay (FCMA) and an immunofluorescence assay (IFA) for anti-AQP4 antibodies, sera from 142 patients with multiple sclerosis (MS) as defined by the McDonald criteria (2005), 29 with neuromyelitis optica (NMO) who fulfilled the 1999 criteria, 19 with recurrent and/or longitudinally extensive myelitis (RM/LM), 86 with other non-inflammatory neurological diseases (OND) and 28 healthy controls (HC) were studied.

RESULTS

Anti-AQP4 antibody positivity rates by IFA, FCMA, and ELISA were 41.4%, 51.7% and 48.3%, respectively, in NMO (1999) patients, and 0% in the OND and HC groups. Twenty-six MS patients (18.3%) were positive for the antibody; 17 met the 2006 NMO criteria, including positivity for anti-AQP4 antibody, and five had longitudinally extensive myelitis (LM). Among the cases with anti-AQP4 antibody detected by FCMA, IgG1, 2, 3, and 4 anti-AQP4 antibodies were found in 97.8%, 37.0%, 6.5% and 6.5% respectively. There was no association of either antibody positivity or level of anti-AQP4 antibody IgG subclasses with clinical parameters after adjustment of p values for multiple comparisons.

CONCLUSIONS

FCMA and bridging ELISA are useful for detecting and quantifying anti-AQP4 antibodies.

Where Do AQP4 Antibodies Fit in the Pathogenesis of NMO?

Recent advances in the field of neuromyelitis optica (NMO) research provided convincing evidence that anti-AQP4 antibody (AQP4-Ab) not only serves as a highly specific disease marker, but also plays an essential role in the pathogenesis of the disease. Although it is now widely recognized that AQP4-Ab induces astrocytic necrosis in a complement-dependent manner, additional triggers are also suspected as a prerequisite for the development of the disease. Unraveling these unresolved aspects of the disease will provide substantial insight into still controversial issues in the pathogenesis of NMO.

New insights into neuromyelitis optica

Neuromyelitis optica (NMO) is an idiopathic inflammatory disorder of the central nervous system (CNS) that preferentially affects the optic nerves and spinal cord. In Asia, NMO has long been considered a subtype of multiple sclerosis (MS). However, recent clinical, pathological, immunological, and imaging studies have suggested that NMO is distinct from MS. This reconsideration of NMO was initially prompted by the discovery of a specific antibody for NMO (NMO-IgG) in 2004. NMO-IgG is an autoantibody that targets aquaporin-4 (AQP4), the most abundant water channel in the CNS; hence, it was named anti-AQP4 antibody. Since it demonstrated reasonable sensitivity and high specificity, anti-AQP4 antibody was incorporated into new diagnostic criteria for NMO.The spectrum of NMO is now known to be wider than was previously recognized and includes a proportion of patients with recurrent, isolated, longitudinally extensive myelitis or optic neuritis, and longitudinally extensive myelitis or optic neuritis associated with systemic autoimmune disease or with brain lesions typical of NMO. In this context, a new concept of "NMO spectrum disorders" was recently introduced. Furthermore, seropositivity for NMO-IgG predicts future relapses and is recognized as a prognostic marker for NMO spectrum disorders. Humoral immune mechanisms, including the activation of B-cells and the complement pathway, are considered to play important roles in NMO pathogenesis. This notion is supported by recent studies showing the potential pathogenic role of NMO-IgG as an initiator of NMO lesions. However, a demonstration of the involvement of NMO-IgG by the development of active immunization and passive transfer in animal models is still needed. This review focuses on the new concepts of NMO based on its pathophysiology and clinical characteristics. Potential management strategies for NMO in light of its pathomechanism are also discussed.

Pathogenic T cell responses against aquaporin 4

Inflammatory lesions in the central nervous system of patients with neuromyelitis optica are characterized by infiltration of T cells and deposition of aquaporin-4-specific antibodies and complement on astrocytes at the glia limitans. Although the contribution of aquaporin-4-specific autoantibodies to the disease process has been recently elucidated, a potential role of aquaporin-4-specific T cells in lesion formation is unresolved. To address this issue, we raised aquaporin-4-specific T cell lines in Lewis rats and characterized their pathogenic potential in the presence and absence of aquaporin-4-specific autoantibodies of neuromyelitis optica patients. We show that aquaporin-4-specific T cells induce brain inflammation with particular targeting of the astrocytic glia limitans and permit the entry of pathogenic anti-aquaporin-4-specific antibodies to induce NMO-like lesions in spinal cord and brain. In addition, transfer of aquaporin-4-specific T cells provoked mild (subclinical) myositis and interstitial nephritis. We further show that the expression of the conformational epitope, recognized by NMO patient-derived aquaporin-4-specific antibodies is induced in kidney cells by the pro-inflammatory cytokine gamma-interferon. Our data provide further support for the view that NMO lesions may be induced by a complex interplay of T cell mediated and humoral immune responses against aquaporin-4.