Epitope recognition and T cell receptors in recurrent autoimmune anterior uveitis in Lewis rats immunized with myelin basic protein

Local S100A8 Levels Correlate With Recurrence of Experimental Autoimmune Uveitis and Promote Pathogenic T Cell Activity

Purpose

To investigate the role of damage-associated molecular patterns (DAMPs) in recurrent experimental autoimmune uveitis (EAU).

Methods

Recurrent EAU was induced in Lewis rats by interphotoreceptor retinoid-binding protein (IRBP) R16-peptide specific T cells (tEAU). Aqueous humor and serum samples were kinetically collected and DAMPs examined by quantitative proteomics, Western blot analysis, and ELISA. tEAU rats were treated with S100 inhibitor paquinimod followed by disease evaluation. The functions of T effector cells and T regulatory cells (Tregs) were compared between treated and nontreated groups. The expression of costimulatory molecules on antigen-presenting cells was examined by flow cytometry.

Results

S100A8, but not high mobility group box 1 (HMGB1), in the eye was found to be correlated with intraocular inflammatory episodes. Administration of paquinimod significantly protected tEAU rats from recurrence. Treated tEAU rats had fewer R16-specific Th1 and Th17 cells, but increased numbers of Tregs. R16-specific T cells from treated tEAU rats into naïve recipients prevented induction of tEAU by R16-specific T cells from nontreated tEAU rats. Moreover, APCs from treated tEAU rats expressed higher levels of a negative costimulatory molecule, CD200R, and lower levels of CD80, CD86, and MHC class II molecules compared to APCs from nontreated tEAU rats. An opposite pattern of expression of these molecules was observed on APCs incubated in vitro with recombinant S100A8.

Conclusions

Our data demonstrate a link between local expression of DAMPs and autoimmune responses, and suggest that complete S100A8/A9 blockade may be a new therapeutic target in recurrent autoimmune uveitis.

Immunopathogenic Background of Pars Planitis

Pars planitis is defined as an intermediate uveitis of unknown background of systemic disease with characteristic formations such as vitreous snowballs, snowbanks and changes in peripheral retina. The incidence of pars planitis varies 2.4–15.4 % of the uveitis patients. The pathogenesis of the disease is to be determined in future. Clinical and histopathological findings suggest an autoimmune etiology, most likely as a reaction to endogenous antigen of unknown source, with T cells predominant in both vitreous and pars plana infiltrations. T cells subsets play an important role as a memory-effector peripheral cell. Snowbanks are formed as an effect of post inflammatory glial proliferation of fibrous astrocytes. There is also a genetic predisposition for pars planitis by human leukocyte antigen and several other genes. A coexistence of multiple sclerosis and optic neuritis has been described in numerous studies. Epiretinal membrane, cataract, cystoid macular edema, retinal detachment, retinal vasculitis, neovascularization, vitreous peripheral traction, peripheral hole formation, vitreous hemorrhage, disc edema are common complications observed in pars planitis. There is a need to expand the knowledge of the pathogenic and immunologic background of the pars planitis to create an accurate pharmacological treatment.

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.

Acute anterior uveitis and HLA-B27

Acute anterior uveitis is the most common form of uveitis. HLA-B27-associated acute anterior uveitis is a distinct clinical entity that has wide-ranging medical significance due to its ocular, systemic, immunologic, and genetic features. The association between HLA-B27 and the spectrum of HLA-B27-associated inflammatory diseases remains one of the strongest HLA-disease associations known to date. This review examines acute anterior uveitis with particular focus on HLA-B27-associated acute anterior uveitis, including the epidemiology, immunopathology, association with HLA-B27 and its subtypes, clinical features, complications, prognosis, and potential new therapies such as anti-TNFalpha therapy and oral HLA-B27-peptide tolerance. There have been substantial recent advances in both clinical and basic scientific research in this field, including studies of the various animal models of acute anterior uveitis and the HLA-B27 transgenic animals, and these are summarized in this review. To the ophthalmologist, HLA-B27-associated acute anterior uveitis is an important clinical entity that is common, afflicts relatively young patients in their most productive years, and is associated with significant ocular morbidity due to its typically recurrent attacks of inflammation and its potentially vision-threatening ocular complications. Furthermore, to the ophthalmologist and the internist, HLA-B27-associated acute anterior uveitis is also of systemic importance due to its significant association with extraocular inflammatory diseases.

Characterization of rat CD8+ uveitogenic T cells specific for interphotoreceptor retinal-binding protein 1177-1191

The uveitogenic T cells that mediate experimental autoimmune uveitis are commonly assumed to be exclusively CD4(+). In the present study, we showed that, although a panel of long-term cultured rat uveitogenic T cell lines specific for the interphotoreceptor retinal-binding protein peptide, R16, all expressed CD4, approximately 40% of the R16-specific uveitogenic T cells freshly prepared from Ag-immunized rats were CD8(+)alphabetaTCR(+), as demonstrated by CFSE staining. We showed that the expansion of these CD8(+)alphabetaTCR(+) T cells was Ag-specific and that highly purified CD8(+) R16-specific T cells were able to induce uveitis on transfusion into naive rats. Moreover, CD8(+) uveitogenic T cells more readily switched phenotype from, and to, TCR(-)CD8(-)CD4(-) during in vivo or in vitro activation compared with their CD4(+) counterparts. In a previous study, we showed that highly purified CD8(+) myelin oligodendrocyte glycoprotein-specific T cells induced more severe autoimmune encephalomyelitis than the corresponding CD4(+) T cells. In this study, we show that an interphotoreceptor retinal-binding protein peptide consistently activated a high proportion of CD8(+)alphabetaTCR(+) T cells, which were uveitogenic in Lewis rats.

Conversion of Monophasic to Recurrent Autoimmune Disease by Autoreactive T Cell Subsets

Autoimmune uveitis has been elicited in susceptible rodents by several ocular-specific Ags. In most of these animal models the induced uveitis is acute and monophasic. Because recurrent uveitis poses the highest risk for blinding ocular complications in human disease, a spontaneous relapsing animal model would be most helpful in understanding the disease pathogenesis. In our current study we have observed that the adoptive transfer of interphotoreceptor retinoid-binding protein residues 1177-1191-specific T cells to naive Lewis rats induced a chronic relapsing disease, in contrast to the monophasic disease induced by immunization with interphotoreceptor retinoid-binding protein residues 1177-1191 emulsified in CFA. The chronic relapsing uveitis induced by autoreactive T cell subsets is dependent on the number of autoreactive T cells generated as well as their activation status. Our study documented a spontaneous model of recurrent uveitis in the rat, which should assist us in the study of disease pathogenesis and the design of specific therapy.

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.

Oral tolerance for treating uveitis - new hope for an old immunological mechanism

Oral tolerance induction has evolved as an attractive approach for the treatment of autoimmune uveitis. This approach is effective and generally void of the side effects associated with conventional immunosuppression. Following uptake of soluble antigen via the gut mucosa a specific systemic tolerance is generated. Experimental autoimmune diseases such as uveitis can efficiently be treated when autoantigens are fed to animals. The immunological mechanisms of oral tolerance are not well understood but are thought to involve the recognition of tolerogenic epitopes, generation of suppressor T cells and altered regulation of selected cytokines. The dose, purity of the antigen (tissue extract vs. single peptide) and concomitant treatment with cytokines were evaluated with the aim to enhance oral tolerance. Immunomodulatory drugs can abrogate oral tolerance. This requires careful evaluation with respect to therapeutic approaches in patients. The first clinical trials for treatment of uveitis with oral retinal autoantigen or an HLA-peptide crossreactive with S-Antigen show a promising therapeutic effect and confirmed the safety of this approach.

Crucial role of CCL3/MIP-1alpha in the recurrence of autoimmune anterior uveitis induced with myelin basic protein in Lewis rats

In this study, we examined the role of CCL2/MCP-1, CCL3/MIP-1alpha, CCL4/MIP-1beta, and CCL5/RANTES during recurrent anterior uveitis (RAU). LEW rats injected with myelin basic protein (MBP) developed experimental autoimmune encephalomyelitis (EAE) and associated anterior uveitis (AU), which was mediated by CD4(+) T cells. After recovery, rats become resistant to EAE but developed RAU. Rats reinjected with MBP developed RAU without EAE. The chemokines tested were detected in the eye at RAU accelerated onset, increased as the disease progressed, and fell as clinical signs improved. At the same time, in the spinal cords of rats, these chemokines were still detected but at reduced levels. Administration of anti-MIP-1alpha neutralizing antibodies resulted in almost complete suppression of clinical RAU and significant reduction of inflammatory cell recruitment into the iris. Anti-MIP-1beta and anti-MCP-1 antibodies were effective in suppression of RAU but to lesser degree. Treatment with anti-RANTES antibodies was not effective in protecting against the recurrent development of the disease. In the eyes, the message for CCR1 and CCR5 was considerably elevated prior to the onset of AU and decreased after treatment with anti-chemokine antibodies. Our results suggest a crucial role of CCL3/MIP-1alpha in the development of RAU in Lewis rats. In addition, CCL2/MCP-1 and CCL4/MIP-1beta may also play a role in immunopathogenesis of RAU.

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.

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

Lewis rats immunized with myelin basic protein (MBP) develop experimental autoimmune encephalomyelitis (EAE) and associated anterior uveitis (AU), which can relapse without recurring of EAE. In this study, we analyzed the repertoire of MBP epitopes that play a role in acute and recurrent AU by injection of MBP synthetic peptides. In addition to the encephalitogenic epitopes 69-89 and 87-99, several cryptic epitopes were found to be strongly uveitogenic in Lewis rats upon immunization with synthetic peptides, including 100-120, 121-140 and 142-167. However, the peptide corresponding to the MBP residues 1-20 was uniquely capable of inducing AU without EAE. Immunization with intact MBP was not essential for the induction of the recurrence of AU. The responses of T cells from lymph nodes and spleens showed a dominant response to the original disease-induced epitope with responses to secondary epitopes. In conclusion, the analysis of pathogenic determinants important for the induction of uveitis provides further evidence that MBP-specific T cells also contribute to the pathogenesis of anterior uveitis. Moreover, this also suggests that a distinct immunoregulatory mechanism exists in the eye and spinal cord because of the uniqueness of the epitope 1-20 in AU but not EAE, and the capability of MBP-specific T cells of inducing AU without EAE.