Importance of cryptic myelin basic protein epitopes in the pathogenicity of acute and recurrent anterior uveitis associated with EAE

Visual Dysfunction in Multiple Sclerosis and its Animal Model, Experimental Autoimmune Encephalomyelitis: a Review

Visual disabilities in central nervous system autoimmune diseases such as multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), are important symptoms. Past studies have focused on neuro-inflammatory changes and demyelination in the white matter of the brain and spinal cord. In MS, neuro-inflammatory lesions have been diagnosed in the visual pathway; the lesions may perturb visual function. Similarly, neuropathological changes in the retina and optic nerves have been found in animals with chronic EAE. Although the retina and optic nerves are immunologically privileged sites via the blood-retina barrier and blood-brain barrier, respectively, inflammation can occur via other routes, such as the uvea (e.g., iris and choroid) and cerebrospinal fluid in the meninges. This review primarily addresses the direct involvement of the blood-retina barrier and the blood-brain barrier in the development of retinitis and optic neuritis in EAE models. Additional routes, including pro-inflammatory mediator-filled choroidal and subarachnoid spaces, are also discussed with respect to their roles in EAE-induced visual disability and as analogues of MS in humans.

Preliminary evidence of the association between DNAm and orbital volumetry in GO

BACKGROUND

The pathogenesis underlying the alterations of orbital architecture in Graves' orbitopathy (GO) is not yet fully understood. The present study aimed to investigate the association of DNA methylation in peripheral blood and orbital volumetry in Chinese patients with GO.

METHODS

A total of 35 GO subjects (70 orbits) were subjected to computed tomography (CT) scan. The total cross-sectional area of the extraocular muscles (orbital muscles, OM), total orbit area (TOA), and the exophthalmometry were measured, and OM/TOA ratio was calculated. Targeted bisulfite sequencing was performed on seven candidate genes.

RESULTS

No significant correlation was established between the DNA methylation levels of these genes and exophthalmometry. The MBP methylation level was found to be correlated with OM/TOA ratio (P<0.05). Multiple linear regression analysis on parameters, including age, sex, TRAb, duration of GO, and DNA methylation levels of seven genes with OM/TOA ratio confirmed that MBP and OM/TOA ratio had a significant correlation (P<0.05). The partial least squares analysis showed that the top three genes with the highest loadings were MBP, BOLL, and BECN1, and OM/TOA ratio affected the DNA methylation block than exophthalmometry.

CONCLUSIONS

This study provided preliminary evidence that MBP is a potential gene associated with OM enlargement in GO patients according to the combination of DNA methylation sequencing and orbital CT measurement.

Biologic agents in experimental autoimmune uveitis

Experimental uveitis models were developed in an effort to elucidate the pathogenesis of human uveitis. The therapeutic effects of numerous anti-inflammatory agents including corticosteroids and immunomodulatory agents including biologic response modifiers have been investigated in both experimental and human uveitis. Monoclonal antibodies to tumor necrosis factor alpha and anti-interleukins, among others, demonstrate efficacy and are employed in the treatment of uveitis refractory to conventional immunomodulatory agents.

Calpain inhibition attenuates apoptosis of retinal ganglion cells in acute optic neuritis

PURPOSE

Optic neuritis (ON), inflammation of the optic nerve, is strongly associated with the pathogenesis of multiple sclerosis (MS) and is initiated by the attack of autoreactive T cells against self-myelin antigens, resulting in demyelination, degeneration of retinal ganglion cells (RGCs), and cumulative visual impairment.

METHODS

Experimental autoimmune encephalomyelitis (EAE) was induced in Lewis rats on day 0, and animals received daily intraperitoneal injections of calpain inhibitor (calpeptin) or vehicle from day 1 until killed. Retinal cell death was analyzed by DNA fragmentation, and surviving ganglion cells were quantified after double labeling of retinal tissue with TUNEL and Brn3a. The expression of apoptotic and inflammatory proteins was determined by Western blotting.

RESULTS

It was demonstrated that calpain inhibition downregulates expression of proapoptotic proteins and the proinflammatory molecule nuclear factor-kappa B (NF-κB) in the retina of Lewis rats with acute EAE. Immunofluorescent labeling revealed that apoptotic cells in the RGC layer of vehicle-treated EAE animals were Brn3a positive, and a moderate dose of calpeptin dramatically reduced the frequency of apoptotic RGCs.

CONCLUSIONS

These results suggest that calpain inhibition might be a useful supplement to immunomodulatory therapies such as corticosteroids in ON, due to its neuroprotective effect on RGCs.

Retinal antigens are recognized by antibodies present in sera of patients with multiple sclerosis

Multiple sclerosis (MS) is frequently accompanied by visual symptoms including those related to retinal disorders. Since they may be a consequence of an autoimmune reaction, we examined whether sera of patients with diagnosed MS and changes in visual-evoked potentials contain antibodies against retinal antigens (retAgs). Immunoblot analysis revealed that MS sera recognized mainly a 46-kD antigen, a 41-kD antigen, retinal arrestin, to a smaller extent also 70-, 56-, 43-, and 36-kD proteins. Patients whose sera showed the highest reactivity with 41- and 46-kD antigens had deficiencies in visual acuity, visual fields, ophthalmoscopy, and electroretinograms. Our observation suggests that antibodies to these retAgs may play a role in the origin of ophthalmologic impairment in MS.

Induction of autoimmune encephalomyelitis and uveitis in B6 and (B6 x SJL) mice by peptides derived from myelin/oligodendrocyte glycoprotein

Previous studies have shown that immunization of the Lewis rat with myelin basic protein (MBP), an encephalitogenic antigen derived from the myelin sheath of the CNS, induced both experimental autoimmune encephalomyelitis (EAE) and anterior uveitis (AU). In the current study, we show that a major peptide derived from another encephalitogenic myelin protein-the myelin/oligodendrocyte glycoprotein (MOG35-55)-induced both encephalomyelitis and uveitis in (B6 x SJL) F1 and wt-B6 mice. Pathological studies documented that an anterior uveitis was induced by MOG35-55. A similar disease pattern was induced by either active immunization with peptideMOG35-55 (pMOG35-55) or adoptive transfer of MOG35-55-specific T cells. The induced uveitis persisted for >60 days without remission. Our studies demonstrate for the first time that MOG is uveitogenic in mice that express the H-2(b) genetic background. This new experimental model should provide a useful tool for the study of the pathogenesis of chronic AU and determination of the pathogenic mechanisms by which a large portion of MS patients develops uveitis.

Cryptic MBP epitope 1-20 is inducing autoimmune anterior uveitis without EAE in Lewis rats

Lewis rats immunized with myelin basic protein (MBP) developed experimental autoimmune encephalomyelitis (EAE) and associated anterior uveitis (AU). Although several cryptic epitopes of MBP have strong encephalitogenic and uveitogenic properties, the peptide corresponding to the MBP residues 1-20 was uniquely capable of inducing AU without EAE. In this study, we showed that acetylation of the N-terminal amino acid did not produce encephalitogenicity, did not enhance uveitogenicity, and did not improve T cell proliferation in Lewis rats. The cytokine production profile induced by MBP(1-20) immunization was consistent with a Th1 response. In MBP-injected rats and in peptide-injected rats, the frequency of the IFN-gamma-secreting cells in MBP(69-89)-stimulated T cells was significantly higher than the frequency of IFN-gamma-secreting cells in MBP(1-20)-stimulated T cells. However, similar numbers of IFN-gamma-producing specific cells were found in the eyes of MBP(69-89) and MBP(1-20) immunized rats. In these rats, the iris-infiltrating cells consisted of a much higher percentage of CD4(+) T cells expressing L-selectin (CD62L) than did those cells found in the spinal cord. The results demonstrate that MBP(1-20) is immunogenic and uveitogenic, although it induced only weak proliferation and weak Th1 reaction. The fact that T cells with the same specificity have different effects on target organs suggested that, in the eye and spinal cord, a distinct mechanism might mediate the recruitment of cells to these organs.

Experimental autoimmune uveitides: multiple antigens, diverse diseases

Human autoimmune uveitides are diverse and complex. Animal models have been developed for studying the pathogenesis of uveitis because of the difficulties in obtaining tissues from a patient's inflamed eye for experiments. There are animal models for experimental uveitis that provoke inflammation of different tissues of the eye and represent different forms of uveitis. Since inflammatory cells can infiltrate any part of the uvea and spill over to nonuveal tissues, such as retina, various antigens have been used to induce uveitis. Most of those models that represent autoimmune forms of uveitis are induced with proteins specific for photoreceptor cells (S-antigen, IRBP, rhodopsin, recoverin, phosducin). Nonretinal antigens, including melanin-associated proteins and myelin basic protein, are also good inducers of uveitis in animals.