Complement-independent retinal pathology produced by intravitreal injection of neuromyelitis optica immunoglobulin G

Aquaporin-4-IgG-seropositive neuromyelitis optica spectrum disorders: progress of experimental models based on disease pathogenesis

Neuromyelitis optica spectrum disorders are neuroinflammatory demyelinating disorders that lead to permanent visual loss and motor dysfunction. To date, no effective treatment exists as the exact causative mechanism remains unknown. Therefore, experimental models of neuromyelitis optica spectrum disorders are essential for exploring its pathogenesis and in screening for therapeutic targets. Since most patients with neuromyelitis optica spectrum disorders are seropositive for IgG autoantibodies against aquaporin-4, which is highly expressed on the membrane of astrocyte endfeet, most current experimental models are based on aquaporin-4-IgG that initially targets astrocytes. These experimental models have successfully simulated many pathological features of neuromyelitis optica spectrum disorders, such as aquaporin-4 loss, astrocytopathy, granulocyte and macrophage infiltration, complement activation, demyelination, and neuronal loss; however, they do not fully capture the pathological process of human neuromyelitis optica spectrum disorders. In this review, we summarize the currently known pathogenic mechanisms and the development of associated experimental models in vitro, ex vivo, and in vivo for neuromyelitis optica spectrum disorders, suggest potential pathogenic mechanisms for further investigation, and provide guidance on experimental model choices. In addition, this review summarizes the latest information on pathologies and therapies for neuromyelitis optica spectrum disorders based on experimental models of aquaporin-4-IgG-seropositive neuromyelitis optica spectrum disorders, offering further therapeutic targets and a theoretical basis for clinical trials.

Stage-dependent immunity orchestrates AQP4 antibody-guided NMOSD pathology: a role for netting neutrophils with resident memory T cells in situ

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune disease of the CNS characterized by the production of disease-specific autoantibodies against aquaporin-4 (AQP4) water channels. Animal model studies suggest that anti-AQP4 antibodies cause a loss of AQP4-expressing astrocytes, primarily via complement-dependent cytotoxicity. Nonetheless, several aspects of the disease remain unclear, including: how anti-AQP4 antibodies cross the blood-brain barrier from the periphery to the CNS; how NMOSD expands into longitudinally extensive transverse myelitis or optic neuritis; how multiphasic courses occur; and how to prevent attacks without depleting circulating anti-AQP4 antibodies, especially when employing B-cell-depleting therapies. To address these knowledge gaps, we conducted a comprehensive 'stage-dependent' investigation of immune cell elements in situ in human NMOSD lesions, based on neuropathological techniques for autopsied/biopsied CNS materials. The present study provided three major findings. First, activated or netting neutrophils and melanoma cell adhesion molecule-positive (MCAM+) helper T (TH) 17/cytotoxic T (TC) 17 cells are prominent, and the numbers of these correlate with the size of NMOSD lesions in the initial or early-active stages. Second, forkhead box P3-positive (FOXP3+) regulatory T (Treg) cells are recruited to NMOSD lesions during the initial, early-active or late-active stages, suggesting rapid suppression of proinflammatory autoimmune events in the active stages of NMOSD. Third, compartmentalized resident memory immune cells, including CD103+ tissue-resident memory T (TRM) cells with long-lasting inflammatory potential, are detected under "standby" conditions in all stages. Furthermore, CD103+ TRM cells express high levels of granzyme B/perforin-1 in the initial or early-active stages of NMOSD in situ. We infer that stage-dependent compartmentalized immune traits orchestrate the pathology of anti-AQP4 antibody-guided NMOSD in situ. Our work further suggests that targeting activated/netting neutrophils, MCAM+ TH17/TC17 cells, and CD103+ TRM cells, as well as promoting the expansion of FOXP3+ Treg cells, may be effective in treating and preventing relapses of NMOSD.

Retinal structural and microvascular deterioration independent of optic neuritis in aquaporin-4 antibody-positive neuromyelitis optica spectrum disorders: An optical coherence tomography angiography study

PURPOSE

To assess the retinal structural and microvascular change in aquaporin-4 antibody (AQP4) positive neuromyelitis optica spectrum disorder (NMOSD) patients and the correlation with clinical features.

METHODS

A cross-sectional study was performed with optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) to measure retinal structure and microvascular parameters in AQP4 positive NMOSD patients.

RESULTS

Sixty-two NMOSD patients (44 eyes with ON, NMOSD+ON; 77 eyes without ON, NMOSD-ON) and 62 healthy controls (HC, 124 eyes) were included. BCVA was worse in NMOSD patients compared to HC (p<0.001). Peripapillary retinal nerve fiber layer (pRNFL, p<0.001) and ganglion cell complex (GCC, p<0.001) was thinner in NMOSD+ON eyes compared to NMOSD-ON eyes and HC. Compared to HC, pRNFL (p = 0.002) and GCC (p = 0.001) was thinner in NMOSD-ON eyes. The vessel density (VD) in superficial capillary plexus (SCP, NMOSD+ON vs HC p<0.001, NMOSD-ON vs HC p = 0.002) and radial peripapillary capillary (RPC, NMOSD+ON vs HC p<0.001, NMOSD-ON vs HC p = 0.001) were also lower in NMOSD patients than HC independent of the history of ON. ON frequency and BCVA were correlated with the thickness of pRNFL and GCC, and VD in SCP and RPC (all p<0.001). EDSS was correlated with thickness of GCC (p = 0.008), and VD in SCP (p = 0.013), DCP (p<0.001) and RPC (p = 0.009).

CONCLUSIONS

Subclinical degradation of retinal structure and microvasculature was found in NMOSD patients before the occurrence of ON, and was correlated with clinical disability. Retinal parameter might be a tool to estimate the disease progression and investigate the pathogenesis of NMOSD.

hUC-MSCs-derived MFGE8 ameliorates locomotor dysfunction via inhibition of ITGB3/ NF-κB signaling in an NMO mouse model

Neuromyelitis optica (NMO) is a severe autoimmune inflammatory disease of the central nervous system that affects motor function and causes relapsing disability. Human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) have been used extensively in the treatment of various inflammatory diseases, due to their potent regulatory roles that can mitigate inflammation and repair damaged tissues. However, their use in NMO is currently limited, and the mechanism underlying the beneficial effects of hUC-MSCs on motor function in NMO remains unclear. In this study, we investigate the effects of hUC-MSCs on the recovery of motor function in an NMO systemic model. Our findings demonstrate that milk fat globule epidermal growth 8 (MFGE8), a key functional factor secreted by hUC-MSCs, plays a critical role in ameliorating motor impairments. We also elucidate that the MFGE8/Integrin αvβ3/NF-κB signaling pathway is partially responsible for structural and functional recovery, in addition to motor functional enhancements induced by hUC-MSC exposure. Taken together, these findings strongly support the involvement of MFGE8 in mediating hUC-MSCs-induced improvements in motor functional recovery in an NMO mouse model. In addition, this provides new insight on the therapeutic potential of hUC-MSCs and the mechanisms underlying their beneficial effects in NMO.

NMOSD IgG Impact Retinal Cells in Murine Retinal Explants

Neuromyelitis optica spectrum disorders (NMOSD) are chronic inflammatory diseases of the central nervous system, characterized by autoantibodies against aquaporin-4. The symptoms primarily involve severe optic neuritis and longitudinally extensive transverse myelitis. Although the disease progression is typically relapse-dependent, recent studies revealed retinal neuroaxonal degeneration unrelated to relapse activity, potentially due to anti-aquaporin-4-positive antibodies interacting with retinal glial cells such as Müller cells. In this exploratory study, we analysed the response of mouse retinal explants to NMOSD immunoglobulins (IgG). Mouse retinal explants were treated with purified IgG from patient or control sera for one and three days. We characterized tissue response patterns through morphological changes, chemokine secretion, and complement expression. Mouse retinal explants exhibited a basic proinflammatory response ex vivo, modified by IgG addition. NMOSD IgG, unlike control IgG, increased gliosis and decreased chemokine release (CCL2, CCL3, CCL4, and CXCL-10). Complement component expression by retinal cells remained unaltered by either IgG fraction. We conclude that human NMOSD IgG can possibly bind in the mouse retina, altering the local cellular environment. This intraretinal stress may contribute to retinal degeneration independent of relapse activity in NMOSD, suggesting a primary retinopathy.

Inhibition of complement C3 signaling ameliorates locomotor and visual dysfunction in autoimmune inflammatory diseases

Neuromyelitis optica (NMO) is an autoimmune inflammatory disease of the central nervous system (CNS) characterized by transverse myelitis and optic neuritis. The pathogenic serum IgG antibody against the aquaporin-4 (AQP4) on astrocytes triggers the activation of the complement cascade, causing astrocyte injury, followed by oligodendrocyte injury, demyelination, and neuronal loss. Complement C3 is positioned as a central player that relays upstream initiation signals to activate downstream effectors, potentially stimulating and amplifying host immune and inflammatory responses. However, whether targeting the inhibition of C3 signaling could ameliorate tissue injury, locomotor defects, and visual impairments in NMO remains to be investigated. In this study, using the targeted C3 inhibitor CR2-Crry led to a significant decrease in complement deposition and demyelination in both slice cultures and focal intracerebral injection models. Moreover, the treatment downregulated the expression of inflammatory cytokines and improved motor dysfunction in a systemic NMO mouse model. Similarly, employing serotype 2/9 adeno-associated virus (AAV2/9) to induce permanent expression of CR2-Crry resulted in a reduction in visual dysfunction by attenuating NMO-like lesions. Our findings reveal the therapeutic value of inhibiting the complement C3 signaling pathway in NMO.

Modeling MOG Antibody-Associated Disorder and Neuromyelitis Optica Spectrum Disorder in Animal Models: Visual System Manifestations

BACKGROUND AND OBJECTIVES

Mechanisms of visual impairment in aquaporin 4 antibody (AQP4-IgG) seropositive neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein antibody (MOG-IgG)-associated disorder (MOGAD) are incompletely understood. The respective impact of optic nerve demyelination and primary and secondary retinal neurodegeneration are yet to be investigated in animal models.

METHODS

Active MOG35-55 experimental autoimmune encephalomyelitis (EAE) was induced in C57BL/6Jrj mice, and monoclonal MOG-IgG (8-18C5, murine), recombinant AQP4-IgG (rAb-53, human), or isotype-matched control IgG (Iso-IgG, human) was administered 10 days postimmunization. Mobility impairment was scored daily. Visual acuity by optomotor reflex and ganglion cell complex thickness (GCC, 3 innermost retinal layers) by optical coherence tomography (OCT) were longitudinally assessed. Histopathology of optic nerve and retina was investigated during presymptomatic, acute, and chronic disease phases for immune cells, demyelination, complement deposition, natural killer (NK) cell, AQP4, and astrocyte involvement, retinal ganglion cells (RGCs), and Müller cell activation. Groups were compared by nonparametric tests with a p value <0.05 indicating statistical significance.

RESULTS

Visual acuity decreased from baseline to chronic phase in MOG-IgG (mean ± standard error of the mean: 0.54 ± 0.01 to 0.46 ± 0.02 cycles/degree, p < 0.05) and AQP4-IgG EAE (0.54 ± 0.01 to 0.43 ± 0.02, cycles/degree, p < 0.05). Immune cell infiltration of optic nerves started in presymptomatic AQP4-IgG, but not in MOG-IgG EAE (5.85 ± 2.26 vs 0.13 ± 0.10 macrophages/region of interest [ROI] and 1.88 ± 0.63 vs 0.15 ± 0.06 T cells/ROI, both p < 0.05). Few NK cells, no complement deposition, and stable glial fibrillary acid protein and AQP4 fluorescence intensity characterized all EAE optic nerves. Lower GCC thickness (Spearman correlation coefficient r = -0.44, p < 0.05) and RGC counts (r = -0.47, p < 0.05) correlated with higher mobility impairment. RGCs decreased from presymptomatic to chronic disease phase in MOG-IgG (1,705 ± 51 vs 1,412 ± 45, p < 0.05) and AQP4-IgG EAE (1,758 ± 14 vs 1,526 ± 48, p < 0.01). Müller cell activation was not observed in either model.

DISCUSSION

In a multimodal longitudinal characterization of visual outcome in animal models of MOGAD and NMOSD, differential retinal injury and optic nerve involvement were not conclusively clarified. Yet optic nerve inflammation was earlier in AQP4-IgG-associated pathophysiology. Retinal atrophy determined by GCC thickness (OCT) and RGC counts correlating with mobility impairment in the chronic phase of MOG-IgG and AQP4-IgG EAE may serve as a generalizable marker of neurodegeneration.

Active Transport and Ocular Distribution of Intravitreally Injected Liposomes

Purpose

Drug delivery to the retina remains a challenge due to ocular barriers and fast clearing mechanisms. Nanocarrier drug delivery systems (NDDSs) hold the promise of prolonging intraocular retention times and increasing drug concentrations in the retina.

Methods

Anionic and cationic PEGylated liposomes, loaded with oxaliplatin (OxPt) to be used as trace element, were prepared from dry lipid powders. The differently charged liposomes were intravitreally injected in C57BL/6JrJ mice; eyes were harvested 2 hours and 24 hours post-injection. To investigate active transport mechanisms in the eye, a subset of mice were pre-injected with chloroquine before injection with cationic liposomes. Eyes were dissected and the distribution of OxPt in different tissues were quantified by inductively coupled plasma mass spectrometry (ICP-MS).

Results

Both liposome formulations enhanced the retention time of OxPt in the vitreous over free OxPt. Surprisingly, when formulated in cationic liposomes, OxPt translocated through the retina and accumulated in the RPE-sclera. Pre-injection with chloroquine inhibited the transport of liposomal OxPt from the vitreous to the RPE-sclera.

Conclusions

We show that liposomes can enhance the retention time of small molecular drugs in the vitreous and that active transport mechanisms are involved in the trans retinal transport of NDDS after intravitreal injections.

Translational Relevance

These results highlight the need for understanding the dynamics of ocular transport mechanisms in living eyes when designing NDDS with the back of the eye as the target. Active transport of nanocarriers through the retina will limit the drug concentration in the neuronal retina but might be exploited for targeting the RPE.

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.

[Clinical phenotypes of optic nerve damage in patients with neuromyelitis optica spectrum disorder]

Neuromyelitis optica spectrum disorders (NMOSD) comprise a group of autoimmune inflammatory demyelinating diseases of the central nervous system that manifest as optic neuritis and transverse myelitis. Its manifestation in the form of optic neuritis makes early diagnosis difficult because neuroimaging of the spinal cord is not a part of the routine examination algorithm for such patients. This article presents the results of a comprehensive ophthalmological examination of 4 patients (8 eyes) diagnosed with NMSOD. Optic neuritis was the disease debut in 3 patients and had 1-2 relapses, in all cases partial optic atrophy with moderate to severe loss of visual function occurred. The clinical picture was characterized by a pronounced heterogeneity in terms of both ophthalmological symptoms, and accession of neurological disorders. Treatment of NMOSD requires differential diagnosis with multiple sclerosis, which depends on the awareness of specialists and the inclusion of antibody titers to aquaporin-4 and myelin oligodendrocyte glycoprotein into the examination algorithm of patients with optical neuritis.

Neuromyelitis Optica Spectrum Disorder: From Basic Research to Clinical Perspectives

Neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory disease of the central nervous system characterized by relapses and autoimmunity caused by antibodies against the astrocyte water channel protein aquaporin-4. Over the past decade, there have been significant advances in the biologic knowledge of NMOSD, which resulted in the IDENTIFICATION of variable disease phenotypes, biomarkers, and complex inflammatory cascades involved in disease pathogenesis. Ongoing clinical trials are looking at new treatments targeting NMOSD relapses. This review aims to provide an update on recent studies regarding issues related to NMOSD, including the pathophysiology of the disease, the potential use of serum and cerebrospinal fluid cytokines as disease biomarkers, the clinical utilization of ocular coherence tomography, and the comparison of different animal models of NMOSD.

Longitudinal retinal changes in MOGAD

OBJECTIVE

Patients with myelin oligodendrocyte glycoprotein antibody (MOG-IgG) associated disease (MOGAD) suffer from severe optic neuritis (ON) leading to retinal neuro-axonal loss, which can be quantified by optical coherence tomography (OCT). We assessed whether ON-independent retinal atrophy can be detected in MOGAD.

METHODS

Eighty MOGAD patients and 139 healthy controls (HC) were included. OCT data was acquired with 1) Spectralis spectral domain OCT (MOGAD (N=66) and HC (N=103)) and 2) Cirrus HD-OCT (MOGAD (N=14) and HC (N=36)). Macular combined ganglion cell and inner plexiform layer (GCIPL) and peripapillary retinal nerve fibre layer (pRNFL) were quantified.

RESULTS

At baseline, GCIPL and pRNFL were lower in MOGAD eyes with a history of ON (MOGAD-ON) compared with MOGAD eyes without a history of ON (MOGAD-NON) and HC (p<0.001). MOGAD-NON eyes had lower GCIPL volume compared to HC (p<0.001) in the Spectralis, but not in the Cirrus cohort. Longitudinally (follow-up up to 3 years), MOGAD-ON with ON within the last 6-12 months before baseline exhibited greater pRNFL thinning than MOGAD-ON with an ON >12 months ago (p<0.001). The overall MOGAD cohort did not exhibit faster GCIPL thinning compared with HC.

INTERPRETATION

Our study suggests the absence of attack-independent retinal damage in MOGAD. Yet, ongoing neuroaxonal damage or oedema resolution seems to occur for up to 12 months after ON, which is longer than what has been reported with other ON forms. These findings support that the pathomechanisms underlying optic nerve involvement and the evolution of OCT retinal changes after ON is distinct in MOGAD. This article is protected by copyright. All rights reserved.

Optical coherence tomography angiography (OCTA) in differential diagnosis of aquaporin-4 antibody seronegative NMOSD and multiple sclerosis

BACKROUND

Optic neuritis(ON) is a common feature of both relapsing-remitting multiple sclerosis(RRMS) and neuromyelitis optica spectrum disorders(NMOSD). It is crucial to early differentiate these two diseases, as they differ in pathophysiology and treatment.

OBJECTIVE

To compare NMOSD and RRMS patients using optical coherence tomography(OCT) and OCT angiography(OCTA) to assess retinal microvascular network differences.

METHODS

Fourteen RRMS (28 eyes) and 9 NMOSD patients(18 eyes), and 11 controls were enrolled. Seropositivity for aquaporin-4 antibody (anti-AQP4 Abs) was 44.4%. Peripapillary and macular retinal nerve fiber layer(RNFL) thickness, superficial peripapillary and macular vessel density(VD), area, perimeter and circularity of foveal avascular zone(FAZ) were analyzed.

RESULTS

OCTA showed reduction in peripapillary and macular VD and FAZ size in NMOSD+ON compared to RRMS+ON and controls (p = 0.001, p<0.001 and p = 0.010, p<0.001 respectively). Peripapillary VD was similar in RRMS +ON and controls. Peripapillary VD in monophasic seronegative NMOSD+ON eyes was significantly lower than monophasic RRMS+ON eyes (p = 0.030), which was no different from controls. FAZ area was smaller in unaffected eyes in NMOSD than RRMS and controls.

CONCLUSIONS

Both OCT and OCTA revealed considerable differences between RRMS and NMOSD patients, providing promising results in favor of clinical utility of OCTA in differential diagnosis of ON, particularly in anti-AQP4 antibody negative patients. OCTA might be a useful biomarker in differentiating NMOSD from MS.

Evidence for and against subclinical disease activity and progressive disease in MOG antibody disease and neuromyelitis optica spectrum disorder

Myelin oligodendrocyte glycoprotein antibody disease (MOGAD) and aquaporin-4 IgG seropositive neuromyelitis optica spectrum disorder (AQP4-IgG+ NMOSD) are generally considered to be relapsing disorders, without clinical progression or subclinical disease activity outside of clinical relapses, in contrast to multiple sclerosis (MS). With advances in the diagnosis and treatment of these conditions, prolonged periods of remission without relapses can be achieved, and the question of whether progressive disease courses can occur has re-emerged. In this review, we focus on studies exploring evidence for and against relapse-independent clinical progression and/or subclinical disease activity in patients with MOGAD and AQP4-IgG+ NMOSD.

Spectrum of sublytic astrocytopathy in neuromyelitis optica

Neuromyelitis optica is an autoimmune inflammatory disorder targeting aquaporin-4 water channels in CNS astrocytes. Histopathological descriptions of astrocytic lesions reported in neuromyelitis optica so far have emphasized a characteristic loss of aquaporin-4, with deposition of IgG and complement and lysis of astrocytes, but sublytic reactions have been underappreciated.

We performed a multi-modality study of 23 neuromyelitis optica autopsy cases (clinically and/or pathologically confirmed; 337 tissue blocks). By evaluating astrocytic morphology, immunohistochemistry and AQP4 RNA transcripts, and their associations with demyelinating activity, we documented a spectrum of astrocytopathy in addition to complement deposition, microglial reaction, granulocyte infiltration and regenerating activity.

Within advanced demyelinating lesions, and in periplaque areas, there was remarkable hypertrophic astrogliosis, more subtle than astrocytic lysis. A degenerative component was suggested by ‘dystrophic’ morphology, cytoplasmic vacuolation, Rosenthal fibres and associated stress protein markers. The abundance of AQP4 mRNA transcripts in sublytic reactive astrocytes devoid of aquaporin-4 protein supported in vivo restoration following IgG-induced aquaporin-4 endocytosis/degradation. Astrocytic alterations extending beyond demyelinating lesions speak to astrocytopathy being an early and primary event in the evolving neuromyelitis optica lesion. Focal astrocytopathy observed without aquaporin-4 loss or lytic complement component deposition verifies that astrocytic reactions in neuromyelitis optica are not solely dependent on IgG-mediated aquaporin-4 loss or lysis by complement or by IgG-dependent leucocyte mediators.

We conclude that neuromyelitis optica reflects a global astrocytopathy, initiated by binding of IgG to aquaporin-4 and not simply definable by demyelination and astrocytic lysis. The spectrum of astrocytic morphological changes in neuromyelitis optica attests to the complexity of factors influencing the range of astrocytic physiological responses to a targeted attack by aquaporin-4-specific IgG. Sublytic astrocytic reactions are no doubt an important determinant of the lesion’s evolution and potential for repair. Pharmacological manipulation of the astrocytic stress response may offer new avenues for therapeutic intervention.

Low Frequency Ultrasound With Injection of NMO-IgG and Complement Produces Lesions Different From Experimental Autoimmune Encephalomyelitis Mice

Neuromyelitis optica spectrum disorder (NMOSD), a relapsing autoimmune disease of the central nervous system, mainly targets the optic nerve and spinal cord. To date, all attempts at the establishment of NMOSD animal models have been based on neuromyelitis optica immunoglobulin G antibody (NMO-IgG) and mimic the disease in part. To solve this problem, we developed a rodent model by opening the blood-brain barrier (BBB) with low frequency ultrasound, followed by injection of NMO-IgG from NMOSD patients and complement to mice suffering pre-existing neuroinflammation produced by experimental autoimmune encephalomyelitis (EAE). In this study, we showed that ultrasound with NMO-IgG and complement caused marked inflammation and demyelination of both spinal cords and optic nerves compared to blank control group, as well as glial fibrillary acidic protein (GFAP) and aquaporin-4 (AQP4) loss of spinal cords and optic nerves compared to EAE mice and EAE mice with only BBB opening. In addition, magnetic resonance imaging (MRI) revealed optic neuritis with spinal cord lesions. We further demonstrated eye segregation defects in the dorsal lateral geniculate nucleus (dLGN) of these NMOSD mice.

Retinal Optical Coherence Tomography in Neuromyelitis Optica

Background and Objectives

To determine optic nerve and retinal damage in aquaporin-4 antibody (AQP4-IgG)-seropositive neuromyelitis optica spectrum disorders (NMOSD) in a large international cohort after previous studies have been limited by small and heterogeneous cohorts.

Methods

The cross-sectional Collaborative Retrospective Study on retinal optical coherence tomography (OCT) in neuromyelitis optica collected retrospective data from 22 centers. Of 653 screened participants, we included 283 AQP4-IgG–seropositive patients with NMOSD and 72 healthy controls (HCs). Participants underwent OCT with central reading including quality control and intraretinal segmentation. The primary outcome was thickness of combined ganglion cell and inner plexiform (GCIP) layer; secondary outcomes were thickness of peripapillary retinal nerve fiber layer (pRNFL) and visual acuity (VA).

Results

Eyes with ON (NMOSD-ON, N = 260) or without ON (NMOSD-NON, N = 241) were assessed compared with HCs (N = 136). In NMOSD-ON, GCIP layer (57.4 ± 12.2 μm) was reduced compared with HC (GCIP layer: 81.4 ± 5.7 μm, p < 0.001). GCIP layer loss (−22.7 μm) after the first ON was higher than after the next (−3.5 μm) and subsequent episodes. pRNFL observations were similar. NMOSD-NON exhibited reduced GCIP layer but not pRNFL compared with HC. VA was greatly reduced in NMOSD-ON compared with HC eyes, but did not differ between NMOSD-NON and HC.

Discussion

Our results emphasize that attack prevention is key to avoid severe neuroaxonal damage and vision loss caused by ON in NMOSD. Therapies ameliorating attack-related damage, especially during a first attack, are an unmet clinical need. Mild signs of neuroaxonal changes without apparent vision loss in ON-unaffected eyes might be solely due to contralateral ON attacks and do not suggest clinically relevant progression but need further investigation.

Optical Coherence Tomography Reveals Longitudinal Changes in Retinal Damage Under Different Treatments for Neuromyelitis Optica Spectrum Disorder

Background: Progressive retinal neuroaxonal damage after acute optic neuritis may occur in neuromyelitis optica spectrum disorder (NMOSD). However, it is unclear if treatments used to prevent attacks influence neurodegeneration.

Objectives: We aimed to investigate retinal damage in patients treated with disease-modifying drugs in a longitudinal study.

Methods: We retrospectively included 50 patients with aquaporin 4-antibody-seropositive NMOSD. Peripapillary retinal nerve fiber layer (pRNFL) thickness, macular ganglion cell complex (mGCC) thickness, total macular volume (TMV), and optic disc measures were acquired by spectral domain optical coherence tomography in patients treated with tocilizumab, rituximab, and azathioprine.

Results: Longitudinally, in eyes with a history of ON (NMOSD^ON+), we observed annual thinning of mGCC [tocilizumab: −1.77 (−3.44, −0.09) μm, p = 0.041; rituximab: −2.03 (−3.58, −0.48) μm, p = 0.017; azathioprine: −1.79 (−2.22, −1.37) μm, p < 0.001], and pRNFL [tocilizumab: −2.07 (−0.75, −3.39) μm, p = 0.005; rituximab: −2.18 (−0.36, −4.00) μm, p = 0.023; azathioprine: −2.37 (−0.98, −3.75) μm, p = 0.003], reduced TMV [tocilizumab: −0.12 (−0.22, −0.01) mm³, p = 0.028; rituximab: −0.15 (−0.21, −0.08) mm³, p = 0.001; azathioprine: −0.12 (−0.20, −0.04) mm³, p = 0.006], and increased cup area [tocilizumab: 0.08 (−0.01, 0.16) mm², p = 0.010; rituximab: 0.07 (0.01, 0.12) mm², p = 0.019; azathioprine: 0.14 (0.02, 0.26) mm², p = 0.023]. However, we detected no significant differences in annual changes in mGCC, pRNFL, TMV, and cup area between patients with tocilizumab, rituximab, and azathioprine in NMOSD^ON+ eyes. NMOSD^ON− eyes did not display mGCC or pRNFL thinning in patients treated with tocilizumab and rituximab. Intriguingly, we observed significant thinning of mGCC in patients treated with azathioprine compared with tocilizumab [−0.84 (−1.50, −0.18) μm vs. −0.19 (−0.87, 0.48) μm, p = 0.012] and rituximab [−0.84 (−1.50, −0.18) μm vs. −0.07 (−1.25, −2.51) μm, p = 0.015] in NMOSD^ON− eyes.

Conclusions: This study demonstrated that retinal ganglion cell loss is independent of ON attacks in NMOSD. Tocilizumab and rituximab may delay mGCC thinning in NMOSD^ON− eyes compared with azathioprine.

Aquaporin-4 Removal from the Plasma Membrane of Human Müller Cells by AQP4-IgG from Patients with Neuromyelitis Optica Induces Changes in Cell Volume Homeostasis: the First Step of Retinal Injury?

Aquaporin-4 (AQP4) is the target of the specific immunoglobulin G autoantibody (AQP4-IgG) produced in patients with neuromyelitis optica spectrum disorders (NMOSD). Previous studies demonstrated that AQP4-IgG binding to astrocytic AQP4 leads to cell-destructive lesions. However, the early physiopathological events in Müller cells in the retina are poorly understood. Here, we investigated the consequences of AQP4-IgG binding to AQP4 of Müller cells, previous to the inflammatory response, on two of AQP4's key functions, cell volume regulation response (RVD) and cell proliferation, a process closely associated with changes in cell volume. Experiments were performed in a human retinal Müller cell line (MIO-M1) exposed to complement-inactivated sera from healthy volunteers or AQP4-IgG positive NMOSD patients. We evaluated AQP4 expression (immunofluorescence and western blot), water permeability coefficient, RVD, intracellular calcium levels and membrane potential changes during hypotonic shock (fluorescence videomicroscopy) and cell proliferation (cell count and BrdU incorporation). Our results showed that AQP4-IgG binding to AQP4 induces its partial internalization, leading to the decrease of the plasma membrane water permeability, a reduction of swelling-induced increase of intracellular calcium levels and the impairment of RVD in Müller cells. The loss of AQP4 from the plasma membrane induced by AQP4-IgG positive sera delayed Müller cells' proliferation rate. We propose that Müller cell dysfunction after AQP4 removal from the plasma membrane by AQP4-IgG binding could be a non-inflammatory mechanism of retinal injury in vivo, altering cell volume homeostasis and cell proliferation and consequently, contributing to the physiopathology of NMOSD.

Foveal changes in aquaporin-4 antibody seropositive neuromyelitis optica spectrum disorder are independent of optic neuritis and not overtly progressive

BACKGROUND AND PURPOSE

Foveal changes were reported in aquaporin-4 antibody (AQP4-Ab) seropositive neuromyelitis optica spectrum disorder (NMOSD) patients; however, it is unclear whether they are independent of optic neuritis (ON), stem from subclinical ON or crossover from ON in fellow eyes. Fovea morphometry and a statistical classification approach were used to investigate if foveal changes in NMOSD are independent of ON and progressive.

METHODS

This was a retrospective longitudinal study of 27 AQP4-IgG + NMOSD patients (49 eyes; 15 ON eyes and 34 eyes without a history of ON [NON eyes]), follow-up median (first and third quartile) 2.32 (1.33-3.28), and 38 healthy controls (HCs) (76 eyes), follow-up median (first and third quartile) 1.95 (1.83-2.54). The peripapillary retinal nerve fibre layer thickness and the volume of combined ganglion cell and inner plexiform layer as measures of neuroaxonal damage from ON were determined by optical coherence tomography. Nineteen foveal morphometry parameters were extracted from macular optical coherence tomography volume scans. Data were analysed using orthogonal partial least squares discriminant analysis and linear mixed effects models.

RESULTS

At baseline, foveal shape was significantly altered in ON eyes and NON eyes compared to HCs. Discriminatory analysis showed 81% accuracy distinguishing ON vs. HCs and 68% accuracy in NON vs. HCs. NON eyes were distinguished from HCs by foveal shape parameters indicating widening. Orthogonal partial least squares discriminant analysis discriminated ON vs. NON with 76% accuracy. In a follow-up of 2.4 (20.85) years, no significant time-dependent foveal changes were found.

CONCLUSION

The parafoveal area is altered in AQP4-Ab seropositive NMOSD patients suggesting independent neuroaxonal damage from subclinical ON. Longer follow-ups are needed to confirm the stability of the parafoveal structure over time.

The Emerging Role of Microglia in Neuromyelitis Optica

Neuromyelitis optica (NMO) is an autoantibody-triggered neuro-inflammatory disease which preferentially attacks the spinal cord and optic nerve. Its defining autoantibody is specific for the water channel protein, aquaporin-4 (AQP4), which primarily is localized at the end-feet of astrocytes. Histopathology studies of early NMO lesions demonstrated prominent activation of microglia, the resident immune sentinels of the central nervous system (CNS). Significant microglial reactivity is also observed in NMO animal models induced by introducing AQP4-IgG into the CNS. Here we review the potential roles for microglial activation in human NMO patients as well as different animal models of NMO. We will focus primarily on the molecular mechanisms underlying microglial function and microglia-astrocyte interaction in NMO pathogenesis. Understanding the role of microglia in NMO pathology may yield novel therapeutic approaches for this disease.

Targeting the complement system in neuromyelitis optica spectrum disorder

INTRODUCTION

Neuromyelitis optica spectrum disorder (NMOSD) is characterized by central nervous system inflammation and demyelination. In AQP4-IgG seropositive NMOSD, circulating immunoglobulin G (IgG) autoantibodies against astrocyte water channel aquaporin-4 (AQP4) cause tissue injury. Compelling evidence supports a pathogenic role for complement activation following AQP4-IgG binding to AQP4. Clinical studies supported the approval of eculizumab, an inhibitor of C5 cleavage, in AQP4-IgG seropositive NMOSD.

AREAS COVERED

This review covers in vitro, animal models, and human evidence for complement-dependent and complement-independent tissue injury in AQP4-IgG seropositive NMOSD. Complement targets are discussed, including complement proteins, regulators and anaphylatoxin receptors, and corresponding drug candidates.

EXPERT OPINION

Though preclinical data support a central pathogenic role of complement activation in AQP4-IgG seropositive NMOSD, they do not resolve the relative contributions of complement-dependent vs. complement-independent disease mechanisms such as antibody-dependent cellular cytotoxicity, T cell effector mechanisms, and direct AQP4-IgG-induced cellular injury. The best evidence that complement-dependent mechanisms predominate in AQP4-IgG seropositive NMOSD comes from eculizumab clinical data. Various drug candidates targeting distinct complement effector mechanisms may offer improved safety and efficacy. However, notwithstanding the demonstrated efficacy of complement inhibition in AQP4-IgG seropositive NMOSD, the ultimate niche for complement inhibition is not clear given multiple drug options with alternative mechanisms of action.Abbreviations: AAV2, Adeno-associated virus 2; ADCC, antibody-dependent cellular cytotoxicity; ANCA, antineutrophilic cytoplasmic autoantibody; AQP4, aquaporin-4; AQP4-IgG, AQP4-immunoglobulin G; C1-INH, C1-esterase inhibitor; C3aR, C3a receptor; C4BP, C4 binding protein; C5aR, C5a receptor; CDC, complement-dependent cytotoxicity; CFHR1, complement factor H related 1; CNS, central nervous system; EAE, experimental autoimmune encephalomyelitis; EndoS, endoglycosidase S; FHL-1, factor-H-like protein 1; GFAP, glial fibrillary acidic protein; Iba-1, ionized calcium-binding adaptor protein-1; IgG, immunoglobulin G; IVIG, intravenous human immunoglobulin G; MAC, membrane attack complex; MBL, maltose-binding lectin; MBP, myelin basic protein; MOG, myelin oligodendrocyte glycoprotein; NK cell, natural killer cell; NMOSD, neuromyelitis optica spectrum disorder; OAP, orthogonal arrays of particles; PNH, paroxysmal nocturnal hemoglobinuria.

Astrocyte-microglia interaction drives evolving neuromyelitis optica lesion

Neuromyelitis optica (NMO) is a severe inflammatory autoimmune CNS disorder triggered by binding of an IgG autoantibody to the aquaporin 4 (AQP4) water channel on astrocytes. Activation of cytolytic complement has been implicated as the major effector of tissue destruction that secondarily involves myelin. We investigated early precytolytic events in the evolving pathophysiology of NMO in mice by continuously infusing IgG (NMO patient serum-derived or AQP4-specific mouse monoclonal), without exogenous complement, into the spinal subarachnoid space. Motor impairment and sublytic NMO-compatible immunopathology were IgG dose dependent, AQP4 dependent, and, unexpectedly, microglia dependent. In vivo spinal cord imaging revealed a striking physical interaction between microglia and astrocytes that required signaling from astrocytes by the C3a fragment of their upregulated complement C3 protein. Astrocytes remained viable but lost AQP4. Previously unappreciated crosstalk between astrocytes and microglia involving early-activated CNS-intrinsic complement components and microglial C3a receptor signaling appears to be a critical driver of the precytolytic phase in the evolving NMO lesion, including initial motor impairment. Our results indicate that microglia merit consideration as a potential target for NMO therapeutic intervention.

Neuromyelitis optica

Neuromyelitis optica (NMO; also known as Devic syndrome) is a clinical syndrome characterized by attacks of acute optic neuritis and transverse myelitis. In most patients, NMO is caused by pathogenetic serum IgG autoantibodies to aquaporin 4 (AQP4), the most abundant water-channel protein in the central nervous system. In a subset of patients negative for AQP4-IgG, pathogenetic serum IgG antibodies to myelin oligodendrocyte glycoprotein, an antigen in the outer myelin sheath of central nervous system neurons, are present. Other causes of NMO (such as paraneoplastic disorders and neurosarcoidosis) are rare. NMO was previously associated with a poor prognosis; however, treatment with steroids and plasma exchange for acute attacks and with immunosuppressants (in particular, B cell-depleting agents) for attack prevention has greatly improved the long-term outcomes. Recently, a number of randomized controlled trials have been completed and the first drugs, all therapeutic monoclonal antibodies, have been approved for the treatment of AQP4-IgG-positive NMO and its formes frustes.

AQP4-IgG and MOG-IgG Related Optic Neuritis-Prevalence, Optical Coherence Tomography Findings, and Visual Outcomes: A Systematic Review and Meta-Analysis

Background: Optic neuritis (ON) is a cardinal manifestation of multiple sclerosis (MS), aquaporin-4 (AQP4)-IgG-, and myelin oligodendrocyte glycoprotein (MOG)-IgG-associated disease. However, the prevalence of AQP4-IgG seropositivity and MOG-IgG seropositivity in isolated ON is unclear, and studies comparing visual outcomes and optical coherence tomography (OCT)-derived structural retinal measures between MS-ON, AQP4-ON, and MOG-ON eyes are limited by small sample sizes. Objectives: (1) To assess the prevalence of AQP4-IgG and MOG-IgG seropositivity among patients presenting with isolated ON; (2) to compare visual outcomes and OCT measures between AQP4-ON, MOG-ON, and MS-ON eyes. Methods: In this systematic review and meta-analysis, a total of 65 eligible studies were identified by PubMed search. Statistical analyses were performed with random effects models. Results: In adults with isolated ON, AQP4-IgG seroprevalence was 4% in non-Asian and 27% in Asian populations, whereas MOG-IgG seroprevalence was 8 and 20%, respectively. In children, AQP4-IgG seroprevalence was 0.4% in non-Asian and 15% in Asian populations, whereas MOG-IgG seroprevalence was 47 and 31%, respectively. AQP4-ON eyes had lower peri-papillary retinal nerve fiber layer (pRNFL; -11.7 μm, 95% CI: -15.2 to -8.3 μm) and macular ganglion cell + inner plexiform layer (GCIPL; -9.0 μm, 95% CI: -12.5 to -5.4 μm) thicknesses compared with MS-ON eyes. Similarly, pRNFL (-11.2 μm, 95% CI: -21.5 to -0.9 μm) and GCIPL (-6.1 μm, 95% CI: -10.8 to -1.3 μm) thicknesses were lower in MOG-ON compared to MS-ON eyes, but did not differ between AQP4-ON and MOG-ON eyes (pRNFL: -1.9 μm, 95% CI: -9.1 to 5.4 μm; GCIPL: -2.6 μm, 95% CI: -8.9 to 3.8 μm). Visual outcomes were worse in AQP4-ON compared to both MOG-ON (mean logMAR difference: 0.60, 95% CI: 0.39 to 0.81) and MS-ON eyes (mean logMAR difference: 0.68, 95% CI: 0.40 to 0.96) but were similar in MOG-ON and MS-ON eyes (mean logMAR difference: 0.04, 95% CI: -0.05 to 0.14). Conclusions: AQP4-IgG- and MOG-IgG-associated disease are important diagnostic considerations in adults presenting with isolated ON, especially in Asian populations. Furthermore, MOG-IgG seroprevalence is especially high in pediatric isolated ON, in both non-Asian and Asian populations. Despite a similar severity of GCIPL and pRNFL thinning in AQP4-ON and MOG-ON, AQP4-ON is associated with markedly worse visual outcomes.

Memantine ameliorates motor impairments and pathologies in a mouse model of neuromyelitis optica spectrum disorders

Background

Neuromyelitis optica spectrum disorders (NMOSD) are central nervous system (CNS) autoimmune inflammatory demyelinating diseases characterized by recurrent episodes of acute optic neuritis and transverse myelitis. Aquaporin-4 immunoglobulin G (AQP4-IgG) autoantibodies, which target the water channel aquaporin-4 (AQP4) on astrocytic membrane, are pathogenic in NMOSD. Glutamate excitotoxicity, which is triggered by internalization of AQP4-glutamate transporter complex after AQP4-IgG binding to astrocytes, is involved in early NMOSD pathophysiologies. We studied the effects of memantine, a N-methyl-D-aspartate (NMDA) receptor antagonist, on motor impairments and spinal cord pathologies in mice which received human AQP4-IgG.

Methods

Purified IgG from AQP4-IgG-seropositive NMOSD patients were passively transferred to adult C57BL/6 mice with disrupted blood-brain barrier. Memantine was administered by oral gavage. Motor impairments of the mice were assessed by beam walking test. Spinal cords of the mice were assessed by immunofluorescence and ELISA.

Results

Oral administration of memantine ameliorated the motor impairments induced by AQP4-IgG, no matter the treatment was initiated before (preventive) or after (therapeutic) disease flare. Memantine profoundly reduced AQP4 and astrocyte loss, and attenuated demyelination and axonal loss in the spinal cord of mice which had received AQP4-IgG. The protective effects of memantine were associated with inhibition of apoptosis and suppression of neuroinflammation, with decrease in microglia activation and neutrophil infiltration and reduction of increase in levels of proinflammatory cytokines including interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α). In addition, memantine elevated growth factors including brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), and vascular endothelial growth factor (VEGF) in the spinal cord.

Conclusions

Our findings support that glutamate excitotoxicity and neuroinflammation play important roles in complement-independent pathophysiology during early development of NMOSD lesions, and highlight the potential of oral memantine as a therapeutic agent in NMOSD acute attacks.

Altered fovea in AQP4-IgG-seropositive neuromyelitis optica spectrum disorders

Objective

To investigate disease-specific foveal shape changes in patients with neuromyelitis optica spectrum disorders (NMOSDs) using foveal morphometry.

Methods

This cross-sectional study included macular spectral domain optical coherence tomography scans of 52 eyes from 28 patients with aquaporin-4 immunoglobulin G (AQP4-IgG)-seropositive NMOSD, 116 eyes from 60 patients with MS, and 123 eyes from 62 healthy controls (HCs), retrospectively, and an independent confirmatory cohort comprised 33/33 patients with NMOSD/MS. The fovea was characterized using 3D foveal morphometry. We included peripapillary retinal nerve fiber layer (pRNFL) thickness and combined macular ganglion cell and inner plexiform layer (GCIPL) volume to account for optic neuritis (ON)-related neuroaxonal damage.

Results

Group comparison showed significant differences compared with HC in the majority of foveal shape parameters in NMOSD, but not MS. Pit flat disk area, average pit flat disk diameter, inner rim volume, and major slope disk length, as selected parameters, showed differences between NMOSD and MS (p value = 0.017, 0.002, 0.005, and 0.033, respectively). This effect was independent of ON. Area under the curve was between 0.7 and 0.8 (receiver operating characteristic curve) for discriminating between NMOSD and MS. Pit flat disk area and average pit flat disk diameter changes independent of ON were confirmed in an independent cohort.

Conclusions

Foveal morphometry reveals a wider and flatter fovea in NMOSD in comparison to MS and HC. Comparison to MS and accounting for ON suggest this effect to be at least in part independent of ON. This supports a primary retinopathy in AQP4-IgG–seropositive NMOSD.

Visualizing the Central Nervous System: Imaging Tools for Multiple Sclerosis and Neuromyelitis Optica Spectrum Disorders

Multiple sclerosis (MS) and neuromyelitis optica spectrum disorders (NMOSD) are autoimmune central nervous system conditions with increasing incidence and prevalence. While MS is the most frequent inflammatory CNS disorder in young adults, NMOSD is a rare disease, that is pathogenetically distinct from MS, and accounts for approximately 1% of demyelinating disorders, with the relative proportion within the demyelinating CNS diseases varying widely among different races and regions. Most immunomodulatory drugs used in MS are inefficacious or even harmful in NMOSD, emphasizing the need for a timely and accurate diagnosis and distinction from MS. Despite distinct immunopathology and differences in disease course and severity there might be considerable overlap in clinical and imaging findings, posing a diagnostic challenge for managing neurologists. Differential diagnosis is facilitated by positive serology for AQP4-antibodies (AQP4-ab) in NMOSD, but might be difficult in seronegative cases. Imaging of the brain, optic nerve, retina and spinal cord is of paramount importance when managing patients with autoimmune CNS conditions. Once a diagnosis has been established, imaging techniques are often deployed at regular intervals over the disease course as surrogate measures for disease activity and progression and to surveil treatment effects. While the application of some imaging modalities for monitoring of disease course was established decades ago in MS, the situation is unclear in NMOSD where work on longitudinal imaging findings and their association with clinical disability is scant. Moreover, as long-term disability is mostly attack-related in NMOSD and does not stem from insidious progression as in MS, regular follow-up imaging might not be useful in the absence of clinical events. However, with accumulating evidence for covert tissue alteration in NMOSD and with the advent of approved immunotherapies the role of imaging in the management of NMOSD may be reconsidered. By contrast, MS management still faces the challenge of implementing imaging techniques that are capable of monitoring progressive tissue loss in clinical trials and cohort studies into treatment algorithms for individual patients. This article reviews the current status of imaging research in MS and NMOSD with an emphasis on emerging modalities that have the potential to be implemented in clinical practice.

Optical coherence tomography reveals light-dependent retinal responses in Alzheimer's disease

Spectral-domain optical coherence tomography (SD-OCT) is an accessible clinical tool for measuring structural changes to the retina, and increasingly as a biomarker for brain-predominant neurodegenerative diseases like Alzheimer's. Information about retinal function can also be extracted from OCT images, but is under-studied, with literature examples often employing challenging protocols or requiring specialized hardware. The first goal of this study was to verify that functional retinal imaging was feasible with a commercially-available SD-OCT device and a clinically practical protocol. Inspired by methods from other functional imaging modalities, we acquired images while repeatedly cycling lights on and off, and spatially normalized retinas to facilitate intra- and inter-individual analyses. In eight healthy young adults, light-dependent increases in reflectivity were easily demonstrated at photoreceptor inner and outer segments, changing by ~7% in bright light and ~3% in dim light. Bright light elicited a subtle (~2%) but consistent light-dependent decrease in reflectivity through much of the rest of the retina, including the avascular outer nuclear layer (ONL). We speculated that some of these changes are influenced by glial function - as through water management - a topic of high interest in neurodegenerative diseases that may involve the glymphatic system. Functional abnormalities in patients with antibodies against aquaporin-4 (n ​= ​3) supported this interpretation. We next compared patients with early-onset Alzheimer's disease (n ​= ​14) to age-matched controls (n ​= ​14), revealing that patients had a relatively exaggerated light-induced change in ONL reflectivity (p ​< ​0.05). Because these measurements can be obtained within 30 ​min, regular use in research and limited clinical settings is feasible.

Experimental Models of Neuroimmunological Disorders: A Review

Immune-mediated inflammatory diseases of the central nervous system (CNS) are a group of neurological disorders in which inflammation and/or demyelination are induced by cellular and humoral immune responses specific to CNS antigens. They include diseases such as multiple sclerosis (MS), neuromyelitis optica spectrum disorders (NMOSD), acute disseminated encephalomyelitis (ADEM) and anti-NMDA receptor encephalitis (NMDAR encephalitis). Over the years, many in vivo and in vitro models were used to study clinical, pathological, physiological and immunological features of these neuroimmunological disorders. Nevertheless, there are important aspects of human diseases that are not fully reproduced in the experimental models due to their technical limitations. In this review, we describe the preclinical models of neuroimmune disorders, and how they contributed to the understanding of these disorders and explore potential treatments. We also describe the purpose and limitation of each one, as well as the recent advances in this field.

Binding patterns and functional properties of human antibodies to AQP4 and MOG on murine optic nerve and retina

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune-inflammatory CNS disease affecting spinal cord and optic nerves, mediated by autoantibodies against aquaporin-4 (AQP4) and myelin-oligodendrocyte-glycoprotein (MOG). Effects of those immunoglobulins (Ig) on retina and optic nerve are incompletely understood. We investigated AQP4-IgG and MOG-IgG sera on retina and optic nerve ex vivo and in 2D2 mice, which harbor a transgenic MOG-specific T-cell receptor. Some sera reacted with murine retina and optic nerve showing distinct binding patterns, suggesting different epitopes being targeted in both subgroups. Transfer of total IgG from a MOG-IgG positive patient to 2D2 mice did neither enhance disability nor induce functional or histological alterations in the retina.

The Detection of Retina Microvascular Density in Subclinical Aquaporin-4 Antibody Seropositive Neuromyelitis Optica Spectrum Disorders

Purpose: To use optical coherence tomography (OCT) and OCT angiography (OCT-A) to measure changes in the retinal structure and microvasculature of patients with aquaporin-4 antibody-positive, neuromyelitis optica spectrum disorder (NMOSD) with a history of optic neuritis (NMOSD+ON) and those without it (NMOSD–ON).

Methods: A total of 27 aquaporin-4 antibody-positive NMOSD patients and 31 age- and gender-matched healthy control (HC) participants were included. In 27 NMOSD patients, 19 of them had a history of optic neuritis (ON) and 8 of them had no history of ON. Peripapillary retinal nerve fiber layer (pRNFL) thickness and macular ganglion cell and inner plexiform layer (GCIPL) thickness were measured by OCT. Radial peripapillary capillary density (RPCD) and macular superficial vessel density (MSVD) were measured by OCT-A. Comparisons of retinal structural and microvascular parameters between the cohorts were performed using generalized estimating equation (GEE) models. Diagnostic accuracy was evaluated by the area under the receiver operating characteristics curve (AROC).

Results: In NMOSD+ON eyes, the GCIPL and pRNFL thicknesses, 48.6 ± 7.1 and 61.7 ± 25.1 μm, respectively, were significantly thinner than in HC eyes (P < 0.001 for both). However, in NMOSD–ON eyes, the GCIPL and pRNFL thicknesses were not significantly thinner than in HC eyes (P > 0.05 for both). In NMOSD+ON eyes, the RPCD and MSVD, 37.8 ± 7.1 and 36.7 ± 5.0%, respectively, were significantly less dense than HC eyes (P < 0.001 for both). Similarly, the RPCD and MSVD in NMOSD–ON eyes, 49.0 ± 2.8 and 43.9 ± 4.2%, respectively, were also less dense than in HC eyes (P < 0.029 for RPCD, P < 0.023 for MSVD). The highest AROC, 0.845 (sensitivity = 88.5%, specificity = 78.0%), was achieved by the logistic regression combination of all of the variables, i.e., pRNFL, GCIPL, RPCD, and MSVD.

Conclusions: Retinal microvascular changes were present in NMOSD–ON eyes. The combination of retinal structural and microvascular parameters might be helpful to discriminate NMOSD–ON eyes from HC eyes.

Retinal correlates of neurological disorders

Considering the retina as an extension of the brain provides a platform from which to study diseases of the nervous system. Taking advantage of the clear optical media of the eye and ever-increasing resolution of modern imaging techniques, retinal morphology can now be visualized at a cellular level in vivo. This has provided a multitude of possible biomarkers and investigative surrogates that may be used to identify, monitor and study diseases until now limited to the brain. In many neurodegenerative conditions, early diagnosis is often very challenging due to the lack of tests with high sensitivity and specificity, but, once made, opens the door to patients accessing the correct treatment that can potentially improve functional outcomes. Using retinal biomarkers in vivo as an additional diagnostic tool may help overcome the need for invasive tests and histological specimens, and offers the opportunity to longitudinally monitor individuals over time. This review aims to summarise retinal biomarkers associated with a range of neurological conditions including Alzheimer’s disease (AD), Parkinson’s disease (PD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS) and prion diseases from a clinical perspective. By comparing their similarities and differences according to primary pathological processes, we hope to show how retinal correlates can aid clinical decisions, and accelerate the study of this rapidly developing area of research.

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.

Optical coherence tomography in myelin-oligodendrocyte-glycoprotein antibody-seropositive patients: a longitudinal study

Background

Serum antibodies against myelin-oligodendrocyte-glycoprotein (MOG-IgG) are detectable in a proportion of patients with acute or relapsing neuroinflammation. It is unclear, if neuro-axonal damage occurs only in an attack-dependent manner or also progressively. Therefore, this study aimed to investigate longitudinally intra-retinal layer changes in eyes without new optic neuritis (ON) in MOG-IgG-seropositive patients.

Methods

We included 38 eyes of 24 patients without ON during follow-up (F/U) [median years (IQR)] 1.9 (1.0–2.2) and 56 eyes of 28 age- and sex-matched healthy controls (HC). The patient group’s eyes included 18 eyes without (Eye^ON-) and 20 eyes with history of ON (Eye^ON+). Using spectral domain optical coherence tomography (OCT), we acquired peripapillary retinal nerve fiber layer thickness (pRNFL) and volumes of combined ganglion cell and inner plexiform layer (GCIP), inner nuclear layer (INL), and macular volume (MV). High-contrast visual acuity (VA) was assessed at baseline.

Results

At baseline in Eye^ON-, pRNFL (94.3 ± 15.9 μm, p = 0.36), INL (0.26 ± 0.03 mm³, p = 0.11), and MV (2.34 ± 0.11 mm³, p = 0.29) were not reduced compared to HC; GCIP showed thinning (0.57 ± 0.07 mm³; p = 0.008), and VA was reduced (logMAR 0.05 ± 0.15 vs. − 0.09 ± 0.14, p = 0.008) in comparison to HC. Longitudinally, we observed pRNFL thinning in models including all patient eyes (annual reduction − 2.20 ± 4.29 μm vs. − 0.35 ± 1.17 μm, p = 0.009) in comparison to HC. Twelve Eye^ON- with other than ipsilateral ON attacks ≤ 6 months before baseline showed thicker pRNFL at baseline and more severe pRNFL thinning in comparison to 6 Eye^ON- without other clinical relapses.

Conclusions

We observed pRNFL thinning in patients with MOG-IgG during F/U, which was not accompanied by progressive GCIP reduction. This effect could be caused by a small number of Eye^ON- with other than ipsilateral ON attacks within 6 months before baseline. One possible interpretation could be a reduction of the swelling, which could mean that MOG-IgG patients show immune-related swelling in the CNS also outside of an attack’s target area.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1521-5) contains supplementary material, which is available to authorized users.

Cognitive Impairment in Neuromyelitis Optica Spectrum Disorders: A Review of Clinical and Neuroradiological Features

Neuromyelitis optica spectrum disorders (NMOSD) are mostly relapsing autoimmune inflammatory disorders of the central nervous system (CNS) with optic neuritis, myelitis, and brainstem syndromes as clinical hallmarks. With a reported prevalence of up to 70%, cognitive impairment is frequent, but often unrecognized and an insufficiently treated burden of the disease. The most common cognitive dysfunctions are decline in attention and memory performance. Magnetic resonance imaging can be used to access structural correlates of neuropsychological disorders. Cognitive impairment is not only a highly underestimated symptom in patients with NMOSD, but potentially also a clinical correlate of attack-independent changes in NMOSD, which are currently under debate. This article reviews cognitive impairment in NMOSD and discusses associations between structural changes of the CNS and cognitive deficits.

[Optical coherence tomography in neuromyelitis optica spectrum disorders]

Neuromyelitis optica spectrum disorders (NMOSD) are mostly relapsing inflammatory conditions of the central nervous system (CNS). In 55% of the cases of NMOSD optic neuritis (ON) is the most frequent first manifestation and can cause severe damage to the afferent visual system and the retina with resultant severe visual impairment. In recent years, investigations of the retina as part of the CNS by optical coherence tomography (OCT) has been shown to be a valid and efficient method for diagnostics and evaluation of the disease course in NMOSD. In addition, OCT not only shows severe damage of the afferent visual system due to multiple bouts of ON but also reveals NMOSD-specific intraretinal pathologies. The latter could be just as important for future differential diagnostics as for the evaluation of potential therapeutic targets. This article briefly reviews the principles of the OCT technique and describes its relevance for the diagnostics and assessment of disease course in NMOSD.

Mechanisms for lesion localization in neuromyelitis optica spectrum disorders

Purpose of review

Neuromyelitis optica spectrum disorders (NMOSD) are severe inflammatory diseases of the central nervous system (CNS), with the presence of aquaporin 4 (AQP4)-specific serum antibodies in the vast majority of patients, and with the presence of myelin oligodendrocyte glycoprotein (MOG)-specific antibodies in approximately 40% of all AQP4-antibody negative NMOSD patients. Despite differences in antigen recognition, the preferred sites of lesions are similar in both groups of patients: They localize to the spinal cord and to the anterior visual pathway including retina, optic nerves, chiasm, and optic tracts, and – to lesser extent – also to certain predilection sites in the brain.

Recent findings

The involvement of T cells in the formation of NMOSD lesions has been challenged for quite some time. However, several recent findings demonstrate the key role of T cells for lesion formation and localization. Studies on the evolution of lesions in the spinal cord of NMOSD patients revealed a striking similarity of early NMOSD lesions with those observed in corresponding T-cell-induced animal models, both in lesion formation and in lesion localization. Studies on retinal abnormalities in NMOSD patients and corresponding animals revealed the importance of T cells for the very early stages of retinal lesions which eventually culminate in damage to Müller cells and to the retinal nerve fiber layer. Finally, a study on cerebrospinal fluid (CSF) barrier pathology demonstrated that NMOSD immunopathology extends beyond perivascular astrocytic foot processes to include the pia, the ependyma, and the choroid plexus, and that diffusion of antibodies from the CSF could further influence lesion formation in NMOSD patients.

Summary

The pathological changes observed in AQP4-antibody positive and MOG-antibody positive NMOSD patients are strikingly similar to those found in corresponding animal models, and many mechanisms which determine lesion localization in experimental animals seem to closely reflect the human situation.

Circulating AQP4-specific auto-antibodies alone can induce neuromyelitis optica spectrum disorder in the rat

It is well established that the binding of pathogenic aquaporin-4 (AQP4)-specific autoantibodies to astrocytes may initiate a cascade of events culminating in the destruction of these cells and in the formation of large tissue-destructive lesions typical for patients with neuromyelitis optica spectrum disorders (NMOSD). To date, not a single experimental study has shown that the systemic presence of the antibody alone can induce any damage to the central nervous system (CNS), while pathological studies on brains of NMOSD patients suggested that there might be ways for antibody entry and subsequent tissue damage. Here, we systemically applied a highly pathogenic, monoclonal antibody with high affinity to AQP4 over prolonged period of time to rats, and show that AQP4-abs can enter the CNS on their own, via circumventricular organs and meningeal or parenchymal blood vessels, that these antibodies initiate the formation of radically different lesions with AQP4 loss, depending on their mode and site of entry, and that lesion formation is much more efficient in the presence of encephalitogenic T-cell responses. We further demonstrate that the established tissue-destructive lesions trigger the formation of additional lesions by short and far reaching effects on blood vessels and their branches, and that AQP4-abs have profound effects on the AQP4 expression in peripheral tissues which counter-act possible titer loss by antibody absorption outside the CNS. Cumulatively, these data indicate that directly induced pathological changes caused by AQP4-abs inside and outside the CNS are efficient drivers of disease evolution in seropositive organisms.

Evidence of Müller Glial Dysfunction in Patients with Aquaporin-4 Immunoglobulin G-Positive Neuromyelitis Optica Spectrum Disorder

PURPOSE

To compare functional and structural changes in the retina in patients with aquaporin-4 immunoglobulin G (AQP4-IgG)-positive neuromyelitis optica spectrum disorder (NMOSD) and multiple sclerosis (MS).

DESIGN

Cross-sectional study; biochemical study of human retinas.

PARTICIPANTS

A total of 181 participants, including 22 consecutive patients (44 eyes) with NMOSD, 131 patients (262 eyes) with multiple sclerosis (MS), and 28 normal subjects (56 eyes). In addition, 8 eyeballs from healthy donors were used for biochemical analysis.

METHODS

Full-field electroretinography (ERG) and spectral-domain OCT were performed in all the subjects. Topography of AQP4 expression and Müller glial distribution were analyzed using Western blotting and immunohistochemistry.

MAIN OUTCOME MEASURES

Full-field ERG parameters, including amplitudes and peak times. Tissue volume of each of the retinal layers at the fovea by OCT segmentation. Levels of AQP4 expression at different retinal regions.

RESULTS

The b-wave amplitude was significantly reduced in patients with AQP4-IgG+ NMOSD in scotopic ERGs (compared with AQP4-IgG- subjects, patients with MS, and normal controls) but not in photopic ERGs. Further analysis showed that this b-wave change was mainly caused by reduction of the slow PII component, suggesting specific Müller cell dysfunction. We also found thinning of specific retinal layers at the fovea in patients with AQP4-IgG+ NMOSD, in the Henle fiber outer nuclear layer (HFONL) and the inner segment (IS) layer, but not in the inner nuclear layer (INL), outer plexiform layer (OPL), or outer segment (OS) layer. Furthermore, there was a significant association between foveal HFONL-IS complex thinning and scotopic b-wave amplitude reduction (P = 0.005∼0.01, fixed-effects model). Western blotting demonstrated that Müller cell-specific AQP4 was expressed at a higher level at the fovea than the peripheral retina. Immunohistochemical studies revealed that the specific foveal thinning reflected the topography of AQP4 expression and Müller glial distribution in the human macula.

CONCLUSIONS

This study provides in vivo structural and functional evidence of Müller glial dysfunction in eyes of patients with AQP4-IgG+ NMOSD. Topography of retinal structural change is supported by distribution of Müller cells and patterns of AQP4 expression. The study suggests that visual electrophysiology and retinal imaging could be useful biomarkers to assess the potential retinal astrocytopathy in NMOSD.

Novel uses of retinal imaging with optical coherence tomography in multiple sclerosis

Introduction: Multiple Sclerosis (MS) is the most common chronic autoimmune neuroinflammatory condition in young adults. It is often accompanied by optic neuritis (ON) and retinal neuro-axonal damage causing visual disturbances. Optical coherence tomography (OCT) is a sensitive non-invasive method for quantifying intraretinal layer volumes. Recently, OCT not only showed to be a reliable marker for ON-associated damage, but also proved its high prognostic value for functional outcome and disability accrual in patients with MS. Consequently, OCT is discussed as a potential marker for monitoring disease severity and therapeutic response in individual patients. Areas covered: This article summarizes our current understanding of structural retinal changes in MS and describes the future potential of OCT for differential diagnosis, monitoring of the disease course and for clinical trials. Expert commentary: Today, OCT is used in clinical practice in specialized MS centers. Standardized parameters across devices are urgently needed for supporting clinical utility. Novel parameters are desirable to increase sensitivity and specificity in terms of MS.

Neuromyelitis optica spectrum disorder: Pathogenesis, treatment, and experimental models

Neuromyelitis optica (NMO) and NMO spectrum disorder (NMOSD) are inflammatory CNS syndromes mainly involving the optic nerve and/or spinal cord and characterized by the presence of serum aquaporin-4 immunoglobulin G antibodies (AQP4-IgG). The pathology of NMOSD is complicated, while therapies for NMOSD are limited and only partially effective in most cases. This review article focuses on the main pathology of NMOSD involving AQP4-IgG and lymphocyte function. We also review the existing therapeutic methods and potential new treatments. Experimental NMO animal models are crucial for further research into NMO pathology and treatment. However, no AQP4-IgG-immunized animals have been reported. The establishment of NMO models is therefore difficult and primarily depends on the generation of transgenic mice or transcranial manipulation using human or monoclonal mouse anti-AQP4 antibodies. Advantages and disadvantages of each model are discussed.

Comprehensive review of neuromyelitis optica and clinical characteristics of neuromyelitis optica patients in Puerto Rico

Neuromyelitis optica (NMO) is an immune-mediated inflammatory disorder of the central nervous system. It is characterized by concurrent inflammation and demyelination of the optic nerve (optic neuritis [ON]) and the spinal cord (myelitis). Multiple studies show variations in prevalence, clinical, and demographic features of NMO among different populations. In addition, ethnicity and race are known as important factors on disease phenotype and clinical outcomes. There are little data on information about NMO patients in underserved groups, including Puerto Rico (PR). In this research, we will provide a comprehensive overview of all aspects of NMO, including epidemiology, environmental risk factors, genetic factors, molecular mechanism, symptoms, comorbidities and clinical differentiation, diagnosis, treatment, its management, and prognosis. We will also evaluate the demographic features and clinical phenotype of NMO patients in PR. This will provide a better understanding of NMO and establish a basis of knowledge that can be used to improve care. Furthermore, this type of population-based study can distinguish the clinical features variation among NMO patients and will provide insight into the potential mechanisms that cause these variations.

Retinal ganglion cell loss in neuromyelitis optica: a longitudinal study

OBJECTIVES

Neuromyelitis optica spectrum disorders (NMOSD) are inflammatory conditions of the central nervous system and an important differential diagnosis of multiple sclerosis (MS). Unlike MS, the course is usually relapsing, and it is unclear, if progressive neurodegeneration contributes to disability. Therefore, we aimed to investigate if progressive retinal neuroaxonal damage occurs in aquaporin4-antibody-seropositive NMOSD.

METHODS

Out of 157 patients with NMOSD screened, 94 eyes of 51 patients without optic neuritis (ON) during follow-up (F/U) and 56 eyes of 28 age-matched and sex-matched healthy controls (HC) were included (median F/U 2.3 years). The NMOSD cohort included 60 eyes without (Eye^{ON -}) and 34 eyes with a history of ON prior to enrolment (Eye^ON+). Peripapillary retinal nerve fibre layer thickness (pRNFL), fovea thickness (FT), volumes of the combined ganglion cell and inner plexiform layer (GCIP) and the inner nuclear layer (INL) and total macular volume (TMV) were acquired by optical coherence tomography (OCT).

RESULTS

At baseline, GCIP, FT and TMV were reduced in Eye^ON+ (GCIP p<2e^-16; FT p=3.7e^-4; TMV p=3.7e^-12) and in Eye^{ON -} (GCIP p=0.002; FT p=0.040; TMV p=6.1e^-6) compared with HC. Longitudinally, we observed GCIP thinning in Eye^ON- (p=0.044) but not in Eye^ON+. Seven patients had attacks during F/U; they presented pRNFL thickening compared with patients without attacks (p=0.003).

CONCLUSION

This study clearly shows GCIP loss independent of ON attacks in aquaporin4-antibody-seropositive NMOSD. Potential explanations for progressive GCIP thinning include primary retinopathy, drug-induced neurodegeneration and retrograde neuroaxonal degeneration from lesions or optic neuropathy. pRNFL thickening in the patients presenting with attacks during F/U might be indicative of pRNFL susceptibility to inflammation.

Peripapillary and parafoveal vascular network assessment by optical coherence tomography angiography in aquaporin-4 antibody-positive neuromyelitis optica spectrum disorders

BACKGROUND/AIMS

Current understanding of the alterations in the retinal vascular network in neuromyelitis optica spectrum disorders (NMOSDs) is limited. We aim to assess the peripapillary and parafoveal vessel density in aquaporin-4 antibody-positive NMOSD patients by optical coherence tomography (OCT) angiography.

METHODS

A total of 55 aquaporin-4 antibody-positive NMOSD patients with or without a history of optic neuritis (ON) and 33 healthy controls underwent spectral domain OCT and OCT angiography. Clinical histories, Expanded Disability Status Scale score, visual functional system score (VFSS) and disease duration were collected.

RESULTS

Peripapillary and parafoveal vessel density was significantly decreased in NMOSD eyes with or without a history of ON. The decrease in retinal vessel density could occur before ON and retinal nerve fibre layer (RNFL) atrophy. Peripapillary vessel density correlated well with the spectral domain OCT measurements and VFSS in NMOSD eyes with a history of ON.

CONCLUSION

Subclinical primary retinal vasculopathy may occur in NMOSD prior to ON and RNFL atrophy. Peripapillary vessel density might be a sensitive predictor of visual outcomes in NMOSD patients with ON.

Aquaporin-4 Autoantibodies From Neuromyelitis Optica Spectrum Disorder Patients Induce Complement-Independent Immunopathologies in Mice

Neuromyelitis optica spectrum disorders (NMOSD) are central nervous system inflammatory disorders causing significant morbidities and mortality. The majority of NMOSD patients have autoimmunity against aquaporin-4 (AQP4), evidenced by seropositivity for autoantibodies against aquaporin-4 (AQP4–IgG). AQP4–IgG is pathogenic with neuroinflammation initiated upon binding of AQP4–IgG to astrocytic AQP4. Complement activation contributes to astrocytic cytotoxicity, neuroinflammation, and tissue necrosis in NMOSD, but the role of complement-independent mechanisms is uncertain. We studied the complement-independent pathogenic effects of AQP4–IgG by passive transfer of IgG from NMOSD patients to mice with breached blood–brain barrier (BBB). Mice, pretreated with bacterial proteins, received daily intraperitoneal injections of IgG purified from AQP4–IgG-seropositive NMOSD patients [IgG_(AQP4+)], or IgG from AQP4–IgG-seronegative patients [IgG_(AQP4−)] or healthy subjects [IgG_(Healthy)] for 8 days. Motor function was tested by walking across narrow beams, and spinal cords were collected for immunofluorescent analysis. We found that human IgG infiltrated into cord parenchyma of mice with breached BBB without deposition of complement activation products. Spinal cord of mice that received IgG_(AQP4+) demonstrated loss of AQP4 and glial fibrillary acidic protein (suggestive of astrocyte loss), decrease in excitatory amino acid transporter 2, microglial/macrophage activation, neutrophil infiltration, patchy demyelination, and loss in axonal integrity. Mice that received IgG_(AQP4+) required longer time with more paw slips to walk across narrow beams indicative of motor slowing and incoordination. Our findings suggest that AQP4–IgG induces complement-independent cord pathologies, including astrocytopathy, neuroinflammation, demyelination, and axonal injuries/loss, which are associated with subtle motor impairments. These complement-independent pathophysiologies likely contribute to early NMOSD lesion development.

Second regional plasmapheresis conference and workshop for Southeast Asia (SEA) on the immunomodulatory role of plasma exchange in central and peripheral nervous system disorders, Kuala Lumpur, Malaysia, 9th December 2017

In December 2017, 79 delegates attended the 2nd regional plasmapheresis conference and workshop for Southeast Asia (SEA) on the immunomodulatory role of plasma exchange in central and peripheral nervous system disorders in Kuala Lumpur, Malaysia. This meeting featured 6 plenary lectures, interactive sessions dedicated for experience sharing, case presentations, and a practical session for paramedics. Clinical experts and researchers from 7 SEA countries and India shared experience and challenges in treating autoimmune neurological disorders. While the spectrum of diseases and neurology practice remained largely similar, there was great disparities in accessibility of therapeutic plasma exchange (TPE) within SEA countries and between urban or rural settings. Costs, human resources, and healthcare policies are common challenges in providing sustainable TPE services. Novel techniques and innovative ideas in performing TPE were explored. A working consortium comprising of key opinion leaders was proposed to improve standards of TPE and enhance future research.