Repertoire analysis and new pathogenic epitopes of IRBP in C57BL/6 (H-2b) and B10.RIII (H-2r) mice

4-Octyl Itaconate Inhibits Proinflammatory Cytokine Production in Behcet's Uveitis and Experimental Autoimmune Uveitis

4-octyl itaconate (4-OI) is an anti-inflammatory metabolite that activates the nuclear-factor-E2-related factor 2 (NRF2) signaling. In the current work, we investigated whether 4-OI could affect the production of proinflammatory cytokines in Behcet's uveitis (BU) and experimental autoimmune uveitis (EAU). Peripheral blood mononuclear cells (PBMCs) of active BU patients and healthy individuals with in vitro 4-OI treatment were performed to assess the influence of 4-OI on the proinflammatory cytokine production. EAU was induced and used for investigating the influence of 4-OI on the proinflammatory cytokine production in vivo. The flow cytometry, qPCR, and ELISA were performed to detect proinflammatory cytokine expression. NRF2 signaling activation was evaluated by qPCR and western blotting (WB). Splenic lymphocyte transcriptome was performed by RNA sequencing. The NRF2 expression by BU patients-derived PBMCs was lower than that by healthy individuals. After treatment with 4-OI, the proportion of Th17 cells, along with the expression of proinflammatory cytokines (IL-17, TNF-α, MCP-1, and IL-6) by PBMCs, were downregulated, and anti-inflammatory cytokine (IL-10) expression was upregulated, although IFN-γ expression was unaffected. The EAU severity was ameliorated by 4-OI in association with a lower splenic Th1/Th17 cell proportion and increased nuclear NRF2 expression. Additionally, 4-OI downregulated a set of 248 genes, which were enriched in pathways of positive regulation of immune responses. The present study shows an inhibitory effect of 4-OI on the proinflammatory cytokine production in active BU patients and EAU mice, possibly mediated through activating NRF2 signaling. These findings suggest that 4-OI could act as a potential therapeutic drug for the treatment and prevention of BU in the future study.

Comprehensive Grading System for Experimental Autoimmune Uveitis in Mice

Experimental autoimmune uveitis (EAU) is the most commonly used animal model to study the progression of chronic uveitis and to test various therapies to treat the disease. However, to accurately evaluate the effectiveness of such treatments, a grading system that combines the latest imaging techniques with definitive quantitative grading thresholds is required. This study aimed to develop a comprehensive grading system that objectively evaluates EAU progression in C57BL/6J mice. EAU was induced following immunisation with interphotoreceptor retinoid-binding protein (IRBP) and pertussis toxin. Weekly fundus and optical coherence tomography (OCT) images were acquired over 12 weeks using a Micron IV imaging system. Each mouse was graded (between 0 to 4) based on changes seen on both the fundus (optic disc, retinal blood vessels and retinal tissue) and OCT (vitreous and retinal layers) images. A total EAU response (with a maximum score of 48) was calculated for each mouse based on the sum of the individual scores each week. Analysis of the clinical scores depicted a gradual increase in inflammatory signs including optic disc and vascular swelling, leukocyte infiltration in the vitreous, lesions in the retina and formation of granulomas and hyper-reflective foci in the retinal layers in EAU mice, with most signs reaching a plateau towards the end of the study period. Development of these signs into sight-threatening complications such as optic disc atrophy, structural damage to the retina and subretinal oedema were noted in 80-90% of mice suggesting consistent disease induction. Overall, a comprehensive and objective grading system encompassing all pathologies occurring in EAU mice was developed to enhance the preclinical evaluation of novel uveitis treatments.

Apigenin Alleviates Autoimmune Uveitis by Inhibiting Microglia M1 Pro-Inflammatory Polarization

Purpose

Apigenin is a natural small molecule compound widely present in various vegetables and fruits. Recently, Apigenin was reported to inhibit lipopolysaccharide (LPS)-simulated microglial proinflammatory activation. Considering the important role of microglia in retinal disorders, we wonder whether Apigenin could exert a therapeutic effect on experimental autoimmune uveitis (EAU) through reprogramming retinal microglia to a beneficial subtype.

Methods

EAU was induced in C57BL/6J mice by immunization with interphotoreceptor retinoid-binding protein (IRBP)651-670, followed by intraperitoneal administration of Apigenin. Disease severity was assessed based on clinical and pathological scores. In vivo, Western blotting was used to quantify protein levels of classical inflammatory factors, microglial M1/M2 markers and the tight junction protein of the blood-retinal-barrier (BRB). Immunofluorescence was used to determine the Apigenin's efficacy on microglial phenotype. In vitro, Apigenin was added in LPS and IFN-γ stimulated human microglial cell line. Western blotting and Transwell assays were used to analyze the phenotype of microglia.

Results

In vivo, we found that Apigenin significantly reduced the clinical and pathological scores of EAU. The protein levels of inflammatory cytokines were significantly decreased in retina, and BRB disruption was ameliorated after Apigenin treatment. Meanwhile, Apigenin inhibited microglia M1 transition in EAU mice retina. In vitro functional studies showed that Apigenin decreased LPS and IFN-γ-induced microglial inflammatory factor production and M1-activation via the TLR4/MyD88 pathway.

Conclusions

Apigenin can ameliorate retinal inflammation in IRBP induced autoimmune uveitis through inhibiting microglia M1 pro-inflammatory polarization via TLR4/MyD88 pathway.

Optimization of determinant factors associated with the efficiency of experimental autoimmune uveitis induction in C57BL/6 mice

Background

Experimental autoimmune uveitis (EAU) is a widely used animal model for uveitis research. The C57BL/6 mouse strain is the most commonly used mouse strain in the research of genetic modification, but C57BL/6 mice are not sufficiently susceptible to EAU induction, partly due to experimental factors. This work aims to optimize relevant factors to improve the efficiency of EAU induction in C57BL/6 mice.

Methods

To induce EAU, mice were immunized via intraperitoneal injection with pertussis (PTX) and subcutaneous injection with interphotoreceptor retinoid-binding protein peptide 1-20 (IRBP_1-20) emulsified with complete Freund's adjuvant (CFA). The severity of inflammation was assessed using several approaches. The relevant experimental factors were evaluated, including methods of emulsification and doses of peptide and PTX.

Results

Uveitis occurred at 8-12 days after immunization and reached its peak at 18-20 days, while T helper type 17 (Th17) cells peaked earlier at 14-18 days after immunization. Based on clinical and histological scores, 500 µg of IRBP peptide was the optimal dose required to induce EAU. The PTX dose demonstrated no influence on EAU incidence, but potentially affected the severity of uveitis. A single injection of 1,000 ng of PTX induced the most severe EAU and the highest proportion of Th17 cells. Compared to extruded emulsion, sonicated emulsion produced a higher incidence, higher histological score, and a 2-day-earlier onset of EAU. Electron microscopy showed a significantly different microstructure between the 2 emulsions.

Conclusions

This work optimized the protocols of EAU induction and obtained a high and stable induction rate with severe inflammation in the C57BL/6 mouse strain. Our results facilitate future experimental research involving uveitis.

Combined Deficiency of the Melanocortin 5 Receptor and Adenosine 2A Receptor Unexpectedly Provides Resistance to Autoimmune Disease in a CD8+ T Cell-Dependent Manner

Regulatory immunity that provides resistance to relapse emerges during resolution of experimental autoimmune uveitis (EAU). This post-EAU regulatory immunity requires a melanocortin 5 receptor (MC5r)-dependent suppressor antigen presenting cell (APC), as shown using a MC5r single knock-out mouse. The MC5r-dependent APC activates an adenosine 2A receptor (A2Ar)-dependent regulatory Treg cell, as shown using an A2Ar single knock-out mouse. Unexpectedly, when MC5r^-/- post-EAU APC were used to activate A2Ar^-/- post-EAU T cells the combination of cells significantly suppressed EAU, when transferred to EAU mice. In contrast, transfer of the reciprocal activation scheme did not suppress EAU. In order to explain this finding, MC5r^-/-A2Ar^-/- double knock-out (DKO) mice were bred. Naïve DKO mice had no differences in the APC populations, or inflammatory T cell subsets, but did have significantly more Treg cells. When we examined the number of CD4 and CD8 T cell subsets, we found significantly fewer CD8 T cells in the DKO mice compared to WT and both single knock-out mice. DKO mice also had significantly reduced EAU severity and accelerated resolution. In order to determine if the CD8 T cell deficiency contributed to the resistance to EAU in the DKO mice, we transferred naïve CD8 T cells from WT mice, that were immunized for EAU. Susceptibility to EAU was restored in DKO mice that received a CD8 T cell transfer. While the mechanism that contributed to the CD8 T cell deficiency in the DKO mice remains to be determined, these observations indicate an importance of CD8 T cells in the initiation of EAU. The involvement of CD4 and CD8 T cells suggests that both class I and class II antigen presentation can trigger an autoimmune response, suggesting a much wider range of antigens may trigger autoimmune disease.

Changes in the Gut Microbiome Contribute to the Development of Behcet's Disease via Adjuvant Effects

Behcet’s disease (BD) is associated with considerable gut microbiome changes. However, it still remains unknown how the composition of the gut microbiome exactly affects the development of this disease. In this study, transplantation of stool samples from patients with active ocular BD to mice via oral gavage was performed. This resulted in decreases of three short chain fatty acids (SCFAs) including butyric acid, propionic acid and valeric acid in the feces of the BD-recipient group. Intestinal barrier integrity of mice receiving BD feces was damaged as shown by a decreased expression of tight junction proteins and was associated with the release of Lipopolysaccharides (LPS) in the circulation. The mice also showed a higher frequency of splenic neutrophils as well as an enrichment of genes associated with innate immune responses in the neutrophils and CD4 + T cells as identified by single cell RNA sequencing. Analysis of neutrophils and T cells functions in these mice showed an enhanced mesenteric lymph node and splenic Th1 and Th17 cell differentiation in association with activation of neutrophils. Transplantation of BD feces to mice and subsequent induction of experimental uveitis (EAU) or encephalomyelitis (EAE) led to an exacerbation of disease in both models, suggesting a microbial adjuvant effect. These findings suggest that the gut microbiome may regulate an autoimmune response via adjuvant effects including increased gut permeability and enhancement of innate immunity.

Mesenchymal stromal cells for the treatment of ocular autoimmune diseases

Mesenchymal stromal cells, commonly referred to as MSCs, have emerged as a promising cell-based therapy for a range of autoimmune diseases thanks to several therapeutic advantages. Key among these are: 1) the ability to modulate innate and adaptive immune responses and to promote tissue regeneration, 2) the ease of their isolation from readily accessible tissues and expansion at scale in culture, 3) their low immunogenicity enabling use as an allogeneic "off-the-shelf" product, and 4) MSC therapy's safety and feasibility in humans, as demonstrated in more than one thousand clinical trials. Evidence from preclinical studies and early clinical trials indicate the therapeutic potential of MSCs and their derivatives for efficacy in ocular autoimmune diseases such as autoimmune uveoretinitis and Sjögren's syndrome-related dry eye disease. In this review, we provide an overview of the current understanding of the therapeutic mechanisms of MSCs, and summarize the results from preclinical and clinical studies that have used MSCs or their derivatives for the treatment of ocular autoimmune diseases. We also discuss the challenges to the successful clinical application of MSC therapy, and suggest strategies for overcoming them.

A20 Inhibits Intraocular Inflammation in Mice by Regulating the Function of CD4+T Cells and RPE Cells

A20 is a negative regulator of inflammation and immunity and plays a role in several autoimmune and inflammatory diseases. Here, we demonstrate that A20 overexpression significantly ameliorates severity of EAU by inhibiting the infiltration of Th1 and Th17 cells, and by protecting integrity of the blood retinal barrier. In vitro studies showed that A20 silencing could promote CD4+T cells toward a Th1 and Th17 phenotype. A decreased expression of A20 in CD4+T cells was noticed in active BD patients but not in VKH patients. Furthermore, silencing of A20 in hRPE cells induced the production of IL-6, IL-8, and MCP-1 and downregulated ZO-1 and occludin expression which is mediated by inhibition of MAPK and NF-κB pathways. This study reveals a mechanism by which A20 prevents autoimmune uveitis.

AS101 ameliorates experimental autoimmune uveitis by regulating Th1 and Th17 responses and inducing Treg cells

AS101 is an organotellurium compound with multifaceted immunoregulatory properties that is remarkable for its lack of toxicity. We tested the therapeutic effect of AS101 in experimental autoimmune uveitis (EAU), a model for human autoimmune uveitis. Unexpectedly, treatment with AS101 elicited Treg generation in vivo in otherwise unmanipulated mice. Mice immunized for EAU with the retinal antigen IRBP and treated with AS101 developed attenuated disease, as did AS101-treated recipients of retina-specific T cells activated in vitro. In both settings, eye-infiltrating effector T cells were decreased, whereas regulatory T (Treg) cells in the spleen were increased. Mechanistic studies in vitro revealed that AS101 restricted polarization of retina-specific T cells towards Th1 or Th17 lineage by repressing activation of their respective lineage-specific transcription factors and downstream signals. Retina-specific T cells polarized in vitro towards Th1 or Th17 in the presence of AS101 had impaired ability to induce EAU in naïve recipients. Finally, AS101 promoted differentiation of retina-specific T cells to Tregs in vitro independently of TGF-β. We conclude that AS101 modulates autoimmune T cells by inhibiting acquisition and expression of effector function and by promoting Treg generation, and suggest that AS101 could be useful as a therapeutic approach for autoimmune uveitis.

Are Anti-Retinal Autoantibodies a Cause or a Consequence of Retinal Degeneration in Autoimmune Retinopathies?

Autoantibodies (AAbs) against various retinal proteins have been associated with vision loss in paraneoplastic and non-paraneoplastic autoimmune retinopathies (AR). There are two major paraneoplastic syndromes associated anti-retinal AAbs, cancer-associated retinopathy (CAR), and melanoma-associated retinopathy. Some people without a cancer diagnosis may present symptoms of CAR and have anti-retinal AAbs. The etiology and pathogenesis of those entities are not fully understood. In this review, we provide evidence for the role of AAbs in retinal death and degeneration. Studies of epitope mapping for anti-recoverin, anti-enolase, and anti-carbonic anhydrase II revealed that although patients' AAbs may recognize the same retinal protein as normal individuals they bind to different molecular domains, which allows distinguishing between normal and diseased AAbs. Given the great diversity of anti-retinal AAbs, it is likely some antibodies have greater pathogenic potential than others. Pathogenic, but not normal antibodies penetrate the target cell, reach their specific antigen, induce apoptosis, and impact retinal pathophysiology. Photoreceptors, dying by apoptosis, induced by other than immunologic mechanisms produce substantial amounts of metabolic debris, which consequently leads to autoimmunization and enhanced permeability of the blood-retinal barrier. AAbs that were made as a part of anti-cancer response are likely to be the cause of retinal degeneration, whereas others, generated against released antigens from damaged retina, contribute to the progression of retinopathy. Altogether, AAbs may trigger retinal degeneration and may also exacerbate the degenerative process in response to the release of sequestered antigens and influence disease progression.

Short chain fatty acids ameliorate immune-mediated uveitis partially by altering migration of lymphocytes from the intestine

Short chain fatty acids (SCFA) are metabolites of intestinal bacteria resulting from fermentation of dietary fiber. SCFA are protective in various animal models of inflammatory disease. We investigated the effects of exogenous administration of SFCAs, particularly propionate, on uveitis using an inducible model of experimental autoimmune uveitis (EAU). Oral SCFA administration attenuated uveitis severity in a mouse strain-dependent manner through regulatory T cell induction among lymphocytes in the intestinal lamina propria (LPL) and cervical lymph nodes (CLN). SCFA also suppressed effector T cell induction in the CLN and mesenteric lymph nodes (MLN). Alterations in intestinal morphology and gene expression demonstrated in the EAU model prior to the onset of uveitis were blunted by oral SCFA administration. Using a Kaede transgenic mouse, we demonstrated enhanced leukocyte trafficking between the intestine and the eye in EAU. Propionate suppressed T effector cell migration between the intestine and the spleen in EAU Kaede mice. In conclusion, our findings support exogenous administration of SCFAs as a potential treatment strategy for uveitis through the stabilization of subclinical intestinal alterations that occur in inflammatory diseases including uveitis, as well as prevention of trafficking of leukocytes between the gastrointestinal tract and extra-intestinal tissues.

An Ocular Commensal Protects against Corneal Infection by Driving an Interleukin-17 Response from Mucosal γδ T Cells

Mucosal sites such as the intestine, oral cavity, nasopharynx, and vagina all have associated commensal flora. The surface of the eye is also a mucosal site, but proof of a living, resident ocular microbiome remains elusive. Here, we used a mouse model of ocular surface disease to reveal that commensals were present in the ocular mucosa and had functional immunological consequences. We isolated one such candidate commensal, Corynebacterium mastitidis, and showed that this organism elicited a commensal-specific interleukin-17 response from γδ T cells in the ocular mucosa that was central to local immunity. The commensal-specific response drove neutrophil recruitment and the release of antimicrobials into the tears and protected the eye from pathogenic Candida albicans or Pseudomonas aeruginosa infection. Our findings provide direct evidence that a resident commensal microbiome exists on the ocular surface and identify the cellular mechanisms underlying its effects on ocular immune homeostasis and host defense.

Flow cytometric analysis of inflammatory and resident myeloid populations in mouse ocular inflammatory models

Myeloid cells make a pivotal contribution to tissue homeostasis during inflammation. Both tissue-specific resident populations and infiltrating myeloid cells can cause tissue injury through aberrant activation and/or dysregulated activity. Reliable identification and quantification of myeloid cells within diseased tissues is important to understand pathological inflammatory processes. Flow cytometry is a valuable technique for leukocyte analysis, but a standardized flow cytometric method for myeloid cell populations in the eye is lacking. Here, we validate a reproducible flow cytometry gating approach to characterize myeloid cells in several commonly used models of ocular inflammation. We profile and quantify myeloid subsets across these models, and highlight the value of this strategy in identifying phenotypic differences using Ccr2-deficient mice. This method will aid standardization in the field and facilitate future investigations into the roles of myeloid cells during ocular inflammation.

2-Methoxyestradiol Alleviates Experimental Autoimmune Uveitis by Inhibiting Lymphocytes Proliferation and T Cell Differentiation

Purpose. To investigate the effect of 2-Methoxyestradiol (2ME2) on experimental autoimmune uveitis (EAU) and the mechanism. Method. C57BL/6 male mice were used to establish the EAU model. 2ME2 was abdominal administrated in D0–D13, D0–D6, and D7–D13 and control group was given vehicle from D0–D13. At D14, pathological severity was scored. Lymphocyte reaction was measured using MTT assay. T cell differentiation in draining lymph nodes and eye-infiltrating cells was tested by flow cytometry. Proinflammatory cytokines production from lymphocytes was determined by ELISA. Result. The disease scores from 2ME2 D0–D13, 2ME2 D0–D6, 2ME2 D7–D13, and vehicle groups were 0.20 ± 0.12, 1.42 ± 0.24, 2.25 ± 0.32, and 2.42 ± 0.24. Cells from all 2ME2 treated groups responded weaker than control (p < 0.05). The inhibitory effect of 2ME2 on lymphocyte proliferation attenuated from 2ME2 D0–D13 to 2ME2 D0–D6 and to 2ME2 D7–D13 groups (p < 0.05). 2ME2 treated mice developed fewer Th1 and Th17 cells both in draining lymph nodes and in eyes than control (p < 0.05). Lymphocytes from 2ME2 group secreted less IFN-γ and IL-17A than those from control (p < 0.05). Conclusion. 2ME2 ameliorated EAU progression and presented a better effect at priming phase. The possible mechanism could be the inhibitory impact on IRBP specific lymphocyte proliferation and Th1 and Th17 cell differentiation.

Characterization of a New Epitope of IRBP That Induces Moderate to Severe Uveoretinitis in Mice With H-2b Haplotype

PURPOSE

Experimental autoimmune uveitis (EAU) induced in mice using the retinal antigen interphotoreceptor retinoid binding protein (IRBP) is an animal model for posterior uveitis in humans. However, EAU induced by native IRBP protein or its widely used epitope amino acid residues 1 to 20 of human IRBP (hIRBP1-20) is inconsistent, often showing low scores and incidence. We found an urgent need to identify a better pathogenic epitope for the C57BL/6 strain.

METHODS

Mice were immunized with uveitogenic peptides or with native bovine IRBP. Clinical and histological disease and associated immunological responses were evaluated. Truncated and substituted peptides, as well as bioinformatic analyses, were used to identify critical major histocompatibility complex (MHC)/T cell receptor (TCR) contact residues and the minimal core epitope.

RESULTS

The new uveitogenic epitope of IRBP, amino acid residues 651 to 670 of human IRBP (LAQGAYRTAVDLESLASQLT [hIRBP651-670]) is uveitogenic for mice of the H-2b haplotype and elicits EAU with a higher severity and incidence in C57BL/6 mice than the previously characterized hIRBP1-20 epitope. Using truncated and substituted peptides, as well as bioinformatic analysis, we identified the critical contact residues with MHC/TCR and defined the minimal core epitope. This made it possible to design MHC tetramers and use them to detect epitope-specific T cells in the uveitic eye and in lymphoid organs of hIRBP651-670-immunized mice.

CONCLUSIONS

Data suggest that hIRBP651-670 is an epitope naturally processed from a conserved region of native IRBP, potentially explaining its relatively high uveitogenicity. This epitope should be useful for basic and preclinical studies of uveitis in the C57BL/6 model and gives access to genetically engineered mice available on this background.

Complement anaphylatoxin receptors C3aR and C5aR are required in the pathogenesis of experimental autoimmune uveitis

Recent studies have suggested that reagents inhibiting complement activation could be effective in treating T cell mediated autoimmune diseases such as autoimmune uveitis. However, the precise role of the complement anaphylatoxin receptors (C3a and C5a receptors) in the pathogenesis of autoimmune uveitis remains elusive and controversial. We induced experimental autoimmune uveitis in mice deficient or sufficient in both C3a and C5a receptors and rigorously compared their retinal phenotype using various imaging techniques, including indirect ophthalmoscopy, confocal scanning laser ophthalmoscopy, spectral domain optical coherence tomography, topical endoscopic fundus imaging, and histopathological analysis. We also assessed retinal function using electroretinography. Moreover, we performed Ag-specific T cell recall assays and T cell adoptive transfer experiments to compare pathogenic T cell activity between wild-type and knockout mice with experimental autoimmune uveitis. These experiments showed that C3a receptor/C5a receptor-deficient mice developed much less severe uveitis than did control mice using all retinal examination methods and that these mice had reduced pathogenic T cell responses. Our data demonstrate that both complement anaphylatoxin receptors are important for the development of experimental autoimmune uveitis, suggesting that targeting these receptors could be a valid approach for treating patients with autoimmune uveitis.

A novel pathogenic RBP-3 peptide reveals epitope spreading in persistent experimental autoimmune uveoretinitis

Experimental autoimmune uveoretinitis (EAU) in the C57BL/6J mouse is a model of non-infectious posterior segment intraocular inflammation that parallels clinical features of the human disease. The purpose of this study was to analyse the immune response to the four murine subunits of retinol binding protein-3 (RBP-3) to identify pathogenic epitopes to investigate the presence of intramolecular epitope spreading during the persistent inflammation phase observed in this model of EAU. Recombinant murine subunits of the RBP-3 protein were purified and used to immunize C57BL/6J mice to induce EAU. An overlapping peptide library was used to screen RBP-3 subunit 3 for immunogenicity and pathogenicity. Disease phenotype and characterization of pathogenic subunits and peptides was undertaken by topical endoscopic fundal imaging, immunohistochemistry, proliferation assays and flow cytometry. RBP-3 subunits 1, 2 and 3 induced EAU in the C57BL/6J mice, with subunit 3 eliciting the most destructive clinical disease. Within subunit 3 we identified a novel uveitogenic epitope, 629-643. The disease induced by this peptide was comparable to that produced by the uveitogenic 1-20 peptide. Following immunization, peptide-specific responses by CD4(+) and CD8(+) T-cell subsets were detected, and cells from both populations were present in the retinal inflammatory infiltrate. Intramolecular epitope spreading between 629-643 and 1-20 was detected in mice with clinical signs of disease. The 629-643 RBP-3 peptide is a major uveitogenic peptide for the induction of EAU in C57BL/6J mice and the persistent clinical disease induced with one peptide leads to epitope spreading.

Environmental microbes and uveitis: is microbial exposure always bad?

The eye generally is considered to be an immune-privileged organ, but this notion is being increasingly challenged as ocular antigens can be expressed in the generative lymphoid organs, resulting in attainment of self-tolerance. What triggers a break in this tolerant state is a fundamental question in autoimmunity research. The general belief is that exposure to environmental microbes can break self-tolerance in genetically susceptible individuals, leading to the induction of autoimmune responses. The molecular mimicry hypothesis has been proposed as one major mechanistic, pathway through which microbes, by generating cross-reactive immune responses, can induce ocular damage of the kind that might occur in uveitis. However, our recent data suggest that exposure to microbial products containing mimicry epitopes for retinal antigens can potentially be beneficial to the host. In this review, we discuss the immune mechanisms with particular reference to the molecular mimicry hypothesis as it relates to immune-mediated uveitis.

In vivo multi-modal imaging of experimental autoimmune uveoretinitis in transgenic reporter mice reveals the dynamic nature of inflammatory changes during disease progression

Background

Experimental autoimmune uveoretinitis (EAU) is a widely used experimental animal model of human endogenous posterior uveoretinitis. In the present study, we performed in vivo imaging of the retina in transgenic reporter mice to investigate dynamic changes in exogenous inflammatory cells and endogenous immune cells during the disease process.

Methods

Transgenic mice (C57Bl/6 J Cx₃cr1^GFP/+, C57Bl/6 N CD11c-eYFP, and C57Bl/6 J LysM-eGFP) were used to visualize the dynamic changes of myeloid-derived cells, putative dendritic cells and neutrophils during EAU. Transgenic mice were monitored with multi-modal fundus imaging camera over five time points following disease induction with the retinal auto-antigen, interphotoreceptor retinoid binding protein (IRBP_1–20). Disease severity was quantified with both clinical and histopathological grading.

Results

In the normal C57Bl/6 J Cx₃cr1^GFP/+ mouse Cx₃cr1-expressing microglia were evenly distributed in the retina. In C57Bl/6 N CD11c-eYFP mice clusters of CD11c-expressing cells were noted in the retina and in C57Bl/6 J LysM-eGFP mice very low numbers of LysM-expressing neutrophils were observed in the fundus. Following immunization with IRBP_1–20, fundus examination revealed accumulations of Cx₃cr1-GFP⁺ myeloid cells, CD11c-eYFP⁺ cells and LysM-eGFP⁺ myelomonocytic cells around the optic nerve head and along retinal vessels as early as day 14 post-immunization. CD11c-eYFP⁺ cells appear to resolve marginally earlier (day 21 post-immunization) than Cx₃cr1-GFP⁺ and LysM-eGFP⁺ cells. The clinical grading of EAU in transgenic mice correlated closely with histopathological grading.

Conclusions

These results illustrate that in vivo fundus imaging of transgenic reporter mice allows direct visualization of various exogenously and endogenously derived leukocyte types during EAU progression. This approach acts as a valuable adjunct to other methods of studying the clinical course of EAU.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0235-6) contains supplementary material, which is available to authorized users.

Retinal antigen-specific regulatory T cells protect against spontaneous and induced autoimmunity and require local dendritic cells

BACKGROUND

We previously reported that the peripheral regulatory T cells (pTregs) generated 'on-demand' in the retina were crucial to retinal immune privilege, and in vitro analysis of retinal dendritic cells (DC) showed they possessed antigen presenting cell (APC) activity that promoted development of the Tregs and effector T cells (Teffs). Here, we expanded these findings by examining whether locally generated, locally acting pTregs were protective against spontaneous autoimmunity and autoimmunity mediated by interphotoreceptor retinoid-binding protein (IRBP). We also examined the APC capacity of retinal DC in vivo.

METHODS

Transgenic (Tg) mice expressing diphtheria toxin receptor (DTR) and/or green fluorescent protein (GFP) under control of the endogenous FoxP3 promoter (GFP only in FG mice, GFP and DTR in FDG mice) or the CD11c promoter (GFP and DTR in CDG mice) were used in conjunction with Tg mice expressing beta-galactosidase (βgal) as retinal neo-self antigen and βgal-specific TCR Tg mice (BG2). Retinal T cell responses were assayed by flow cytometry and retinal autoimmune disease assessed by histological examination.

RESULTS

Local depletion of the Tregs enhanced actively induced experimental autoimmune uveoretinitis to the highly expressed retinal self-antigen IRBP in FDG mice and spontaneous autoimmunity in βgal-FDG-BG2 mice, but not in mice lacking autoreactive T cells or their target antigen in the retina. The presence of retinal βgal downregulated the generation of antigen-specific Teffs and pTregs within the retina in response to local βgal challenge. Retinal DC depletion prevented generation of Tregs and Teffs within retina after βgal injection. Microglia remaining after DC depletion did not make up for loss of DC-dependent antigen presentation.

CONCLUSIONS

Our results suggest that local retinal Tregs protect against spontaneous organ-specific autoimmunity and that T cell responses within the retina require the presence of local DC.

Mimicry epitope from Ehrlichia canis for interphotoreceptor retinoid-binding protein 201-216 prevents autoimmune uveoretinitis by acting as altered peptide ligand

We report here identification of novel mimicry epitopes for interphotoreceptor retinoid-binding protein (IRBP) 201-216, a candidate ocular antigen that causes experimental autoimmune uveoretinitis (EAU) in A/J mice. One mimicry epitope from Ehrlichia canis (EHC), designated EHC 44-59, induced cross-reactive T cells for IRBP 201-216 capable of producing T helper (Th)1 and Th17 cytokines, but failed to induce EAU in A/J mice. In addition, animals first primed with suboptimal doses of IRBP 201-216 and subsequently immunized with EHC 44-59 did not develop EAU; rather, the mimicry epitope prevented the disease induced by IRBP 201-216. However, alteration in the composition of EHC 44-59 by substituting alanine with valine at position 49, similar to the composition of IRBP 201-216, enabled the mimicry epitope to acquire uveitogenicity. The data provide new insights as to how microbes containing mimicry sequences for retinal antigens can prevent ocular inflammation by acting as naturally occurring altered peptide ligands.

Uveitis in mouse and man

Uveitis is underappreciated as a sight-threatening cause of blindness. There are two broad causative classes of uveitis: infectious and non-infectious. Non-infectious uveitis is considered a prototypical autoimmune disorder based mainly on data from experimental models in the mouse. Several different experimental models exist that reflect the different types of uveitis in man (anterior, intermediate, and posterior uveitis). These models have demonstrated that uveitis is predominantly a Th1/Th17 mediated disease, although innate immune cells play a significant role both in induction of disease and in tissue damage. Most experimental models of uveitis rely on activation of the innate immune system by use of adjuvants that activate a range of pathogen recognition receptors (PRRs). This begs the question of the underlying role of initial and/or persistent infection, including latent infection, in immune-mediated uveitis in which active infection cannot be demonstrated. This further raises the possibility of pathogenic mechanisms such as antigenic cross-reactivity and molecular mimicry. Alternatively, residual/latent antigen from infectious agents may act as "endogenous" adjuvants for induction of immune reactions to damaged/altered self antigen, suggesting a commonality in pathogenesis for both infectious and non-infectious uveitis in man.

Retinal astrocytes pretreated with NOD2 and TLR2 ligands activate uveitogenic T cells

On entering the tissues, infiltrating autoreactive T cells must be reactivated locally to gain pathogenic activity. We have previously reported that, when activated by Toll-like receptor 3 (TLR3) and TLR4 ligands, retinal astrocytes (RACs) are able to function as antigen-presenting cells to re-activate uveitogenic T cells and allow responder T cells to induce uveitis in mice. In the present study, we found that, although the triggering of TLR2 or nucleotide-binding oligomerization domain receptor 2 (NOD2) alone did not activate RACs, their combined triggering induced RACs with the phenotypes required to efficiently re-activate interphotoreceptor retinoid-binding protein (IRBP)-specific T cells. The synergistic effect of TLR2 and NOD2 ligands on RAC activation might be explained by the observations that bacterial lipoprotein (BLP, a TLR2 ligand) was able to upregulate NOD2 expression and the combination of BLP and muramyldipeptide (MDP, a NOD2 ligand) enhanced the expression of RICK (Rip2), the signaling molecule of NOD2. Moreover, the synergistic effect of MDP and BLP on RACs was lost when the RACs were derived from NOD2 knockout mice or were pre-treated with Rip2 antagonist. Thus, our data suggest that exogenous or endogenous molecules acting on both TLR2 and NOD2 on RACs might have an enhancing effect on susceptibility to autoimmune uveitis.

Detection of an autoreactive T-cell population within the polyclonal repertoire that undergoes distinct autoimmune regulator (Aire)-mediated selection

The autoimmune regulator (Aire) plays a critical role in central tolerance by promoting the display of tissue-specific antigens in the thymus. To study the influence of Aire on thymic selection in a physiological setting, we used tetramer reagents to detect autoreactive T cells specific for the Aire-dependent tissue-specific antigen interphotoreceptor retinoid-binding protein (IRBP), in the polyclonal repertoire. Two class II tetramer reagents were designed to identify T cells specific for two different peptide epitopes of IRBP. Analyses of the polyclonal T-cell repertoire showed a high frequency of activated T cells specific for both IRBP tetramers in Aire(-/-) mice, but not in Aire(+/+) mice. Surprisingly, although one tetramer-binding T-cell population was efficiently deleted in the thymus in an Aire-dependent manner, the second tetramer-binding population was not deleted and could be detected in both the Aire(-/-) and Aire(+/+) T-cell repertoires. We found that Aire-dependent thymic deletion of IRBP-specific T cells relies on intercellular transfer of IRBP between thymic stroma and bone marrow-derived antigen-presenting cells. Furthermore, our data suggest that Aire-mediated deletion relies not only on thymic expression of IRBP, but also on proper antigen processing and presentation of IRBP by thymic antigen-presenting cells.

Low dose rapamycin exacerbates autoimmune experimental uveitis

Background

Rapamycin, a potent immune modulator, is used to treat transplant rejection and some autoimmune diseases. Uveitis is a potentially severe inflammatory eye disease, and 2 clinical trials of treating uveitis with rapamycin are under way. Unexpectedly, recent research has demonstrated that low dose rapamycin enhances the memory T cell population and function. However, it is unclear how low dose rapamycin influences the immune response in the setting of uveitis.

Design and Methods

B10.RIII mice were immunized to induce experimental autoimmune uveitis (EAU). Ocular inflammation of control and rapamycin-treated mice was compared based on histological change. ELISPOT and T cell proliferation assays were performed to assess splenocyte response to ocular antigen. In addition, we examined the effect of rapamycin on activation-induced cell death (AICD) using the MitoCapture assay and Annexin V staining.

Results

Administration of low dose rapamycin exacerbated EAU, whereas treating mice with high dose rapamycin attenuated ocular inflammation. The progression of EAU by low dose rapamycin coincided with the increased frequency of antigen-reactive lymphocytes. Lastly, fewer rapamycin-treated T cells underwent AICD, which might contribute to exaggerated ocular inflammation and the uveitogenic immune response.

Conclusion

These data reveal a paradoxical role for rapamycin in uveitis in a dose-dependent manner. This study has a potentially important clinical implication as rapamycin might cause unwanted consequences dependent on dosing and pharmacokinetics. Thus, more research is needed to further define the mechanism by which low dose rapamycin augments the immune response.

Mesenchymal stem cells induce functionally active T-regulatory lymphocytes in a paracrine fashion and ameliorate experimental autoimmune uveitis

PURPOSE

Mesenchymal stem/progenitor cells (MSCs) have regenerative and immunomodulatory properties, exerted by cell-cell contact and in a paracrine fashion. Part of their immunosuppressive activity has been ascribed to their ability to promote the induction of CD4+CD25+FoxP3+ T lymphocytes with regulatory functions (Treg). Here the authors studied the effect of MSCs on the induction of Treg and on the development of autoimmunity, and they examined the possibility that MSC-mediated Treg induction could be attributed to the secretion of soluble factors.

METHODS

The authors induced experimental autoimmune uveitis (EAU) in mice by immunization with the 1-20 peptide of the intraphotoreceptor binding protein. At the same time, some of the animals were treated intraperitoneally with syngeneic MSCs. The authors checked T-cell responses and in vitro Treg conversion by cell proliferation and blocking assays, in cell-cell contact and transwell settings. TGFβ and TGFβ receptor gene expression analyses were performed by real-time PCR.

RESULTS

The authors found that a single intraperitoneal injection of MSCs was able to significantly attenuate EAU and that a significantly higher percentage of adaptive Treg was present in MSC-treated mice than in MSC-untreated animals. In vitro blocking of antigen presentation by major histocompatibility complex class II precluded priming and clonal expansion of antigen-specific Treg, whereas blockade of TGFβ impaired the expression of FoxP3, preventing the conversion of CD4+ T cells into functionally active Treg.

CONCLUSIONS

The authors demonstrated that MSCs can inhibit EAU and that their immunomodulatory function is due at least in part to the induction of antigen-specific Treg in a paracrine fashion by secreting TGFβ.

Fertility comparison between wild type and transgenic mice by in vitro fertilization

Transgenic mice are increasingly used as animal models for studies of gene function and regulation of mammalian genes. Although there has been continuous and remarkable progress in the development of transgenic technology over several decades, many aspects of the resulting transgenic model's phenotype cannot be completely predicted. For example, it is well known that as a consequence of the random insertion of the injected DNA construct, several founder mice of the new line need to be analyzed for possible differences in phenotype secondary to different insertion sites. The Knock out technique for transgenic production disrupts a specific gene by insertion or homologous recombination creating a null expression or replacement of the gene with a marker to localize it expression. This modification could result in pleiotropic phenotype if the gene is also expressed in tissues other than the target organs. Although the future breeding performance of the newly created model is critical to many studies, it is rarely anticipated that the new integrations could modify the reproductive profile of the new transgenic line. To date, few studies have demonstrated the difference between the parent strain's reproductive performance and the newly developed transgenic model. This study was designed to determine whether a genetic modification, knock out (KO) or transgenics, not anticipated to affect reproductive performance could affect the resulting reproductive profile of the newly developed transgenic mouse. More specifically, this study is designed to study the impact of the genetic modification on the ability of gametes to be fertilized in vitro. We analyzed the reproductive performance of mice with different background strains: FVB/N, C57BL/6 (129Sv/J x C57Bl/6)F1 and outbred CD1((R)) and compared them to mice of the same strain carrying a transgene or KO which was not anticipated to affect fertility. In vitro Fertilization was used to analyze the fertility of the mice. Oocytes from superovulated females were inseminated with sperm of same background. Fertility rate was considered as the percentage of two cell embryos scored 24 h after insemination. The data collected from this study shows that the fertilization rate is affected (reduced to half fold) in some of the transgenic mice compared to the respective Wild Type (WT) mice. For the WT the average fertility rate ranged from 80% (C57BL/6), 90% (FVB/N), 45% (129Sv/J x C57Bl/6)F1 and 43% (CD1). For transgenic mice it was 52% (C57BL/6), 65% (FVB/N), 22% (129Sv/J x C57Bl/6)F1 and 25% (CD1).

Autoimmunity in the immune privileged eye: pathogenic and regulatory T cells

Experimental autoimmune uveitis (EAU) in animals serves as a model of human uveitis. EAU can be induced in mice by immunization with the retinal antigen interphotoreceptor retinoid binding protein (IRBP) in complete Freund's adjuvant (CFA) or by IRBP-pulsed mature dendritic cells, and can be driven either by a Th17 or a Th1 effector response, depending on the model. The direction of the response is affected by conditions present during the exposure to antigen, including the quality/quantity of innate receptor stimulation and/or type of APC. IL-17 and IFN-gamma production by innate cells such as NKT may also affect the disease process. If exposure to antigen is via a hydrodynamic DNA vaccination with an IRBP-encoding plasmid, the response is directed to a regulatory phenotype, and disease is ameliorated or prevented. Our data shed light on effector and regulatory responses in autoimmune disease, provide balance to the Th1/Th17 paradigm and help to explain the clinical heterogeneity of human uveitis, which occurs in the face of responses to the same ocular antigen(s).

Inhibitory peptide analogs derived from a major uveitogenic epitope protect from antiretinal autoimmunity by inducing type 2 and regulatory T cells

We identified inhibitory peptide analogs (IPAs), capable of immunomodulating experimental autoimmune uveitis (EAU), induced in B10.RIII mice by immunization with the retinal antigen interphotoreceptor-binding protein in CFA. Alanine-substituted peptides of the major pathogenic epitope, residues 161-180, were synthesized. They were tested for immunogenicity, cross-reactivity with the native 161-180 epitope, pathogenicity, and ability to prevent EAU when given in IFA before EAU challenge with native murine (m)161-180. Two peptides, 169A and 171A, were unable to elicit disease but cross-reacted with m161-180 by lymphocyte proliferation. Mice pretreated with either of the substituted peptides failed to develop EAU after challenge with the native epitope, m161-180, and had reduced cellular responses by lymphocyte proliferation and by delayed hypersensitivity. Their cytokine response profile to m161-180 showed reduced antigen-specific IFN-gamma and IL-17, whereas IL-4, IL-5, IL-10, and IL-13 from IPA-protected mice were increased, and serum antibody titers to m161-180 revealed reduced IgG2a and elevated IgG1 isotypes, suggesting a Th2 shift in the response. Protection was transferable with lymphoid cells from protected donors to naïve recipients, who were subsequently immunized for EAU. Thus, IPA pretreatment prevents induction of EAU by skewing the response to a subsequent uveitogenic challenge with the native peptide to a nonpathogenic phenotype, as well as by eliciting transferable regulatory cells.

Mouse models of experimental autoimmune uveitis

The mouse model of experimental autoimmune uveitis, induced by immunization of mice with the retinal protein IRBP, was developed in our laboratory 20 years ago and published in 1988. Since that time it has been adopted by many investigators and has given rise to many studies that helped elucidate genetic influences, dissect the basic mechanisms of pathogenesis and test novel immunotherapeutic paradigms. The current overview will summarize the salient features of the experimental autoimmune uveitis model and discuss its mechanisms.