Recruitment of antigen-nonspecific cells plays a pivotal role in the pathogenesis of a T cell-mediated organ-specific autoimmune disease, experimental autoimmune uveoretinitis

Comparative models of uveitis

Several clinical subtypes of uveitis exist yet specific immunopathogenic mechanisms involved remain unclear. Ex vivo studies are limited by lack of fresh retinal biopsies and studies have relied on aqueous humour or peripheral blood, which may not directly reflect disease. The aim of this review is to compare the various in vivo models and review their contributions to our understanding of disease processes. These models, although unable to reflect all clinical signs, have provided insight into the contribution of genes and molecules, characterisation of effector T-cells, cell trafficking into retinal tissues, the contribution of tissue-resident myeloid cells and the mechanism(s) of action of several anti-inflammatory compounds. In vivo uveitis models have provided an excellent resource with which to study the molecular and cellular processes involved. Recent refinements in models, improved imaging, and the application of omics have greatly increased the number of readouts and translational opportunities. Future approaches with in vitro models will also be discussed.

Unveiling Differential Responses of Granulocytes to Distinct Immunostimulants with Implications in Autoimmune Uveitis

The perception of circulating granulocytes as cells with a predetermined immune response mainly triggered by pathogens is evolving, recognizing their functional heterogeneity and adaptability, particularly within the neutrophil subset. The involvement of these cells in the pathophysiology of autoimmune uveitis has become increasingly clear, yet their exact role remains elusive. We used an equine model for autoimmune-mediated recurrent pan-uveitis to investigate early responses of granulocytes in different inflammatory environments. For this purpose, we performed differential proteomics on granulocytes from healthy and diseased horses stimulated with IL8, LPS, or PMA. Compared to healthy horses, granulocytes from the recurrent uveitis model significantly changed the cellular abundance of 384 proteins, with a considerable number of specific changes for each stimulant. To gain more insight into the functional impact of these stimulant-specific proteome changes in ERU pathogenesis, we used Ingenuity Pathway Analysis for pathway enrichment. This resulted in specific reaction patterns for each stimulant, with IL8 predominantly promoting Class I MHC-mediated antigen processing and presentation, LPS enhancing processes in phospholipid biosynthesis, and PMA, clearly inducing neutrophil degranulation. These findings shed light on the remarkably differentiated responses of neutrophils, offering valuable insights into their functional heterogeneity in a T-cell-driven disease. Raw data are available via ProteomeXchange with identifier PXD013648.

Pre-Activated Granulocytes from an Autoimmune Uveitis Model Show Divergent Pathway Activation Profiles upon IL8 Stimulation In Vitro

In the pathophysiology of autoimmune-mediated uveitis, granulocytes have emerged as possible disease mediators and were shown to be pre-activated in equine recurrent uveitis (ERU), a spontaneous disease model. We therefore used granulocytes from ERU horses to identify early molecular mechanisms involved in this dysregulated innate immune response. Primary granulocytes from healthy and ERU horses were stimulated with IL8, and cellular response was analyzed with differential proteomics, which revealed significant differences in protein abundance of 170 proteins in ERU. Subsequent ingenuity pathway analysis identified three activated canonical pathways “PKA signaling”, “PTEN signaling” and “leukocyte extravasation”. Clustered to the leukocyte extravasation pathway, we found the membrane-type GPI-anchored protease MMP25, which was increased in IL8 stimulated ERU granulocytes. These findings point to MMP25 as a possible regulator of granulocyte extravasation in uveitis and a role of this molecule in the impaired integrity of the blood-retina-barrier. In conclusion, our analyses show a clearly divergent reaction profile of pre-activated granulocytes upon IL8 stimulation and provide basic information for further in-depth studies on early granulocyte activation in non-infectious ocular diseases. This may be of interest for the development of new approaches in uveitis diagnostics and therapy. Raw data are available via ProteomeXchange with identifier PXD013648.

Hydroxychloroquine Alleviates EAU by Inhibiting Uveitogenic T Cells and Ameliorating Retinal Vascular Endothelial Cells Dysfunction

Purpose

Inflammation triggers the activation of CD4⁺T cells and the breakdown of blood–retinal barrier, thus contributing to the pathology of experimental autoimmune uveitis (EAU). We explored the anti-inflammatory effect of hydroxychloroquine (HCQ) on EAU and the potential mechanisms active in T cells and retinal vascular endothelial cells (RVECs).

Methods

C57BL/6J mice were immunized with interphotoreceptor retinoid binding protein 1-20 (IRBP_1–20) to induce EAU and then treated with the vehicle or HCQ (100 mg/kg/day). On day 7, 14, 21, 30 and 60 after immunization, clinical scores were evaluated. On day 14, histopathological scores were assessed, and retinas, spleens, and lymph nodes were collected for quantitative polymerase chain reaction or flow cytometry analysis. RVEC dysfunction was induced by tumor necrosis factor α (TNF-α) stimulation. The expression of cytokines, chemokines, adhesion molecules, and lectin-like oxidized LDL receptor-1 (LOX-1)/nuclear factor κB (NF-κB) was measured in RVECs with or without HCQ.

Results

HCQ treatment protected mice from uveitis, evidenced by reduced expression of inflammatory factors, chemokines, and adhesion molecules in the retina. In systemic immune response, HCQ inhibited the activation of naïve CD4⁺T cells and frequencies of T effector cells, and promoted T regulatory cells. HCQ decreased IRBP_1-20–specific T cell responses and proliferation of CD4⁺T cells in vitro. Further studies established that TNF-α induced RVECs to express inflammatory cytokines, chemokines, and adhesion molecules, whereas HCQ alleviated the alterations via the LOX-1/NF-κB pathways.

Conclusions

HCQ alleviates EAU by regulating the Teff/Treg balance and ameliorating RVECs dysfunction via the LOX-1/NF-κB axis. HCQ may be a promising therapeutic candidate for uveitis.

Anti-inflammatory Effects of GTE in Eye Diseases

Ocular inflammation is a common complication of various eye diseases with wide consequences from irritations to potentially sight-threatening complications. Green tea is a popular beverage throughout the world. One of the proven health benefits of consuming green tea extract (GTE) is anti-inflammation. Catechins are the biologically active constituents of GTE. In in vitro and in vivo studies, GTE and catechins present inhibition of inflammatory responses in the development of ocular inflammation including infectious, non-infectious or autoimmune, and oxidative-induced complications. Research on the ocular inflammation in animal models has made significant progress in the past decades and several key disease mechanisms have been identified. Here we review the experimental investigations on the effects of GTE and catechins on various ocular inflammation related diseases including glaucoma, age-related macular degeneration, uveitis and ocular surface inflammation. We also review the pharmacokinetics of GTE constituents and safety of green tea consumption. We discuss the insights and perspectives of these experimental results, which would be useful for future development of novel therapeutics in human.

Immunological Insights in Equine Recurrent Uveitis

Horses worldwide suffer from equine recurrent uveitis (ERU), an organ-specific, immune-mediated disease with painful, remitting-relapsing inflammatory attacks alternating with periods of quiescence, which ultimately leads to blindness. In course of disease, both eyes can eventually be affected and since blind horses pose a threat to themselves and their surroundings, these animals have to be killed. Therefore, this disease is highly relevant for veterinary medicine. Additionally, ERU shows strong clinical and pathological resemblance to autoimmune uveitis in man. The exact cause for the onset of ERU is unclear to date. T cells are believed to be the main effector cells in this disease, as they overcome the blood retinal barrier to invade the eye, an organ physiologically devoid of peripheral immune cells. These cells cause severe intraocular inflammation, especially in their primary target, the retina. With every inflammatory episode, retinal degeneration increases until eyesight is completely lost. In ERU, T cells show an activated phenotype, with enhanced deformability and migration ability, which is reflected in the composition of their proteome and downstream interaction pathways even in quiescent stage of disease. Besides the dysregulation of adaptive immune cells, emerging evidence suggests that cells of the innate immune system may also directly contribute to ERU pathogenesis. As investigations in both the target organ and the periphery have rapidly evolved in recent years, giving new insights on pathogenesis-associated processes on cellular and molecular level, this review summarizes latest developments in ERU research.

Deviant proteome profile of equine granulocytes associates to latent activation status in organ specific autoimmune disease

Equine recurrent uveitis (ERU) is a spontaneous, remitting-relapsing autoimmune disease driven by the adaptive immune system. Although T cells are described as the main effector cells in pathogenesis, granulocytes have also emerged as possible disease mediators. To explore the role of these innate immune cells, we investigated the whole cell proteome of granulocytes from equine recurrent uveitis cases and healthy controls. Among the 2362 proteins identified by mass spectrometry, we found 96 proteins with significantly changed abundance between groups (p < 0.05, fold change >1.2), representing 4.1% of total granulocyte proteome. Within these differential identifications, calgranulin B, a protein associated with pathogenesis in other autoimmune diseases, showed highest abundance in equine recurrent uveitis (18 fold). For a better interpretation of the results from our hypothesis-generating approach, we added a threshold for biological significance (ratio ERU/controls >2: 36 proteins) to the proteins with increased abundance in equine recurrent uveitis and analyzed their allocation to the subsets within the Immune System superpathway. The 36 differentially abundant proteins predominantly associated to RAF/MAP kinase cascade, MHC-I-mediated antigen presentation and neutrophil degranulation, suggesting a latently activated phenotype of these innate immune cells in disease. Raw data are available via ProteomeXchange with identifier PXD013648. SIGNIFICANCE: Our study provides new insights into the protein repertoire of primary equine granulocytes and identifies protein abundance changes associated to equine recurrent uveitis (ERU), an organ specific, spontaneously occurring autoimmune disease. We show that granulocyte proteins with increased abundance in ERU strongly associate to RAF/MAP kinase signaling, MHC-I antigen presentation and neutrophil degranulation, pointing to a more activated state of these cells in ERU cases. Since cells were obtained in quiescent stage of disease, latent activation of granulocytes underlines the role of these innate immune cells in ERU. These findings are highly relevant for veterinary medicine, further establishing the importance of granulocytes in this T cell-driven autoimmune disease. Moreover, they have translational quality for autoimmune uveitis in man, due to strong similarity in disease occurrence, progression and pathogenesis.

Green tea catechins alleviate autoimmune symptoms and visual impairment in a murine model for human chronic intraocular inflammation by inhibiting Th17-associated pro-inflammatory gene expression

Autoimmune uveitis is a sight-threatening disease mainly caused by dysregulation of immunity. We investigated the therapeutic effects of green tea extract (GTE) and its major component, epigallocatechin-3-gallate (EGCG), on a murine model of experimental autoimmune uveoretinitis (EAU). Oral administration of GTE, EGCG, dexamethasone, or water, which started 5 days before the induction, was fed every two days to each group. On day 21 post induction, the eyes were examined by confocal scanning laser ophthalmoscopy, optical coherence tomography (OCT), fundus fluorescein angiography (FFA) and electroretinography (ERG) prior to sacrificing the animals for histological assessments and gene expression studies. Retinal-choroidal thicknesses (RCT) and major retinal vessel diameter were measured on OCT sections and FFA images, respectively. Comparing to water-treated EAU animals, GTE attenuated uveitis clinical manifestations, RCT increase (1.100 ± 0.013 times vs 1.005 ± 0.012 times, P < 0.001), retinal vessel dilation (308.9 ± 6.189 units vs 240.8 units, P < 0.001), ERG amplitudes attenuation, histopathological ocular damages, and splenomegaly in EAU mice. The therapeutic effects of GTE were dose dependent and were comparable to dexamethasone. EGCG, a major active constituent of GTE, partially alleviated uveitic phenotypes including recovering visual function. Th-17 associated pro-inflammatory gene [interleukin 1 beta (IL-1β), IL-6, IL-17A, and tumor necrosis factor alpha (TNF-α)] expressions were down regulated by GTE and EGCG treatments, which showed no detectable morphological defects in liver and kidney in non-induced and EAU mice. Our findings suggest that GTE consumption can serve as a potent therapeutic agent as well as a food supplement for developing alternative treatments against autoimmune uveitis.

Doyne lecture 2016: intraocular health and the many faces of inflammation

Dogma for reasons of immune privilege including sequestration (sic) of ocular antigen, lack of lymphatic and immune competent cells in the vital tissues of the eye has long evaporated. Maintaining tissue and cellular health to preserve vision requires active immune responses to prevent damage and respond to danger. A priori the eye must contain immune competent cells, undergo immune surveillance to ensure homoeostasis as well as an ability to promote inflammation. By interrogating immune responses in non-infectious uveitis and compare with age-related macular degeneration (AMD), new concepts of intraocular immune health emerge. The role of macrophage polarisation in the two disorders is a tractable start. TNF-alpha regulation of macrophage responses in uveitis has a pivotal role, supported via experimental evidence and validated by recent trial data. Contrast this with the slow, insidious degeneration in atrophic AMD or in neovasular AMD, with the compelling genetic association with innate immunity and complement, highlights an ability to attenuate pathogenic immune responses and despite known inflammasome activation. Yolk sac-derived microglia maintains tissue immune health. The result of immune cell activation is environmentally dependent, for example, on retinal cell bioenergetics status, autophagy and oxidative stress, and alterations that skew interaction between macrophages and retinal pigment epithelium (RPE). For example, dead RPE eliciting macrophage VEGF secretion but exogenous IL-4 liberates an anti-angiogenic macrophage sFLT-1 response. Impaired autophagy or oxidative stress drives inflammasome activation, increases cytotoxicity, and accentuation of neovascular responses, yet exogenous inflammasome-derived cytokines, such as IL-18 and IL-33, attenuate responses.

The Role of Interleukin-22 and Its Receptor in the Development and Pathogenesis of Experimental Autoimmune Uveitis

IL-22 is a pro- and anti-inflammatory cytokine that is mainly produced by T cells and NK cells. Recent studies have reported the increased number of IL-22 producing T cells in patients with autoimmune noninfectious uveitis; however, the correlation between IL-22 and uveitis remains unclear. In this study, we aimed to determine the specific role of IL-22 and its receptor in the pathogenesis of uveitis. Serum concentration of IL-22 was significantly increased in uveitis patients. IL-22Rα was expressed in the retinal pigment epithelial cell line, ARPE-19. To examine the effect of IL-22, ARPE-19 was treated with recombinant IL-22. The proliferation of ARPE-19 and the production of monocyte chemoattractant protein (MCP)-1 from ARPE-19 were clearly elevated. IL-22 induced MCP-1 which facilitated the migration of inflammatory cells. Moreover, IL-22 increased the IL-22Rα expression in ARPE-19 through the activation of PI3K/Akt. Experimental animal models of uveitis induced by interphotoreceptor retinoid binding protein 1-20 (IRBP1-20) exhibited elevation of hyperplasia RPE and IL-22 production. When CD4+ T cells from the uveitis patients were stimulated with IRBP1-20, the production of IL-22 definitely increased. In addition, we examine the regulatory role of cysteamine, which has an anti-inflammatory role in the cornea, in uveitis through the down-regulation of IL-22Rα expression. Cysteamine effectively suppressed the IRBP1-20-induced IL-22Rα expression and prevented the development of IRBP1-20-induced uveitis in the experimental animal model. These finding suggest that IL-22 and its receptor have a crucial role in the development and pathogenesis of uveitis by facilitating inflammatory cell infiltration, and that cysteamine may be a useful therapeutic drug in treating uveitis by down-regulating IL-22Rα expression in RPE.

Uveitis and glaucoma: new insights in the pathogenesis and treatment

Glaucoma is a potentially blinding complication of uveitis, where intraocular inflammation, secondary corticosteroid response, and varying types and degrees of angle abnormalities contribute to its pathogenesis. Management of uveitic glaucoma remains challenging. Treatment is targeted at reducing the inflammation and lowering the intraocular pressure. Recent studies have highlighted the role of viruses, such as cytomegalovirus, herpes simplex virus, and more recently Ebola virus, in the pathogenesis of uveitic glaucoma. Antiviral therapy may be beneficial in eyes with detectable viral DNA. The success of glaucoma surgery is decreased in eyes with uveitic glaucoma, and surgical interventions are associated with a higher incidence of postoperative complications. Novel glaucoma surgical and laser treatments may improve the predictability of surgery for uveitic glaucoma, but these require further evaluation.

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.

CD73 expression in RPE cells is associated with the suppression of conventional CD4 cell proliferation

CD73 is intensively involved in the regulation of immune responses through the conversion of pro-inflammatory ATP to immunosuppressive adenosine. Herein, we clarified whether cells in the retina express CD73 and participate in the regulation of inflammatory eye diseases such as experimental autoimmune uveitis (EAU). First, immunofluorescence staining was performed to compare the distribution of CD73(+) cells in the retinas of EAU-induced and normal B10RIII mice. The results revealed that a layer of cells in the normal retina that was consistent with the location of retinal pigment epithelial (RPE) cells strongly expressing CD73, and the expression was markedly reduced in the presence of EAU. Thereafter, EAU was also induced in C57BL/6 mice by active immunization or adoptive transfer. CD73 expression in isolated RPE cells was assessed by real-time RT-PCR and western blotting, and the catalytic abilities of the cells to convert AMP to adenosine were determined using HPLC analyses. Compared to the normal control, significantly decreased CD73 expression and AMP catalytic ability were found in the RPE cells isolated from inflamed eyes. CD73 expression and activity were also studied in cultured RPE cells treated with different stimuli, such as Toll-like receptor ligands and cytokines. Highly varied functional CD73 expression was observed in RPE cells through cytokines or Toll-like receptor agonist treatments. Finally, whether RPE cells could regulate the immune response, particularly the proliferation of CD4 cells, through surface-expressed CD73 was determined using a two-chamber assay. The robust inhibition of conventional T-cell proliferation was uniquely observed when CD73(+) RPE cells in the upper chamber were in the presence of AMP. To further confirm the function of CD73 in RPE cells, Cd73(-/-) RPE cells were isolated, and CD73-rescued control cells were constructed. CD73(+)Cd73(-/-) RPE, not Cd73(-/-) RPE, significantly suppressed interacted CD4 cells proliferation and cytokine production. Taken together, these data suggest that naive RPE cells suppressed the immune response through their high expression of CD73. The expression of CD73 in RPE cells could be regulated through many factors, and down-regulated CD73 expression attenuated the suppressive effect of RPE on the proliferation of conventional CD4 cells.

Autoimmune and autoinflammatory mechanisms in uveitis

The eye, as currently viewed, is neither immunologically ignorant nor sequestered from the systemic environment. The eye utilises distinct immunoregulatory mechanisms to preserve tissue and cellular function in the face of immune-mediated insult; clinically, inflammation following such an insult is termed uveitis. The intra-ocular inflammation in uveitis may be clinically obvious as a result of infection (e.g. toxoplasma, herpes), but in the main infection, if any, remains covert. We now recognise that healthy tissues including the retina have regulatory mechanisms imparted by control of myeloid cells through receptors (e.g. CD200R) and soluble inhibitory factors (e.g. alpha-MSH), regulation of the blood retinal barrier, and active immune surveillance. Once homoeostasis has been disrupted and inflammation ensues, the mechanisms to regulate inflammation, including T cell apoptosis, generation of T_reg cells, and myeloid cell suppression in situ, are less successful. Why inflammation becomes persistent remains unknown, but extrapolating from animal models, possibilities include differential trafficking of T cells from the retina, residency of CD8⁺ T cells, and alterations of myeloid cell phenotype and function. Translating lessons learned from animal models to humans has been helped by system biology approaches and informatics, which suggest that diseased animals and people share similar changes in T cell phenotypes and monocyte function to date. Together the data infer a possible cryptic infectious drive in uveitis that unlocks and drives persistent autoimmune responses, or promotes further innate immune responses. Thus there may be many mechanisms in common with those observed in autoinflammatory disorders.

Vascular adhesion protein 1 in the eye

Semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1), a dual-function molecule with adhesive and enzymatic properties, is expressed on the surface of vascular endothelial cells of mammals. It also exists as a soluble form (sVAP-1), which is implicated in oxidative stress via its enzymatic activity and can be a prognostic biomarker. Recent evidence suggests that VAP-1 is an important therapeutic target for several inflammation-related ocular diseases, such as uveitis, age-related macular degeneration (AMD), and diabetic retinopathy (DR), by involving in the recruitment of leukocytes at sites of inflammation. Furthermore, VAP-1 plays an important role in the pathogenesis of conjunctival inflammatory diseases such as pyogenic granulomas and the progression of conjunctival lymphoma. VAP-1 may be an alternative therapeutic target in ocular diseases. The in vivo imaging of inflammation using VAP-1 as a target molecule is a novel approach with a potential for early detection and characterization of inflammatory diseases. This paper reviews the critical roles of VAP-1 in ophthalmological diseases which may provide a novel research direction or a potent therapeutic strategy.

Characterization of retinal expression of vascular cell adhesion molecule (VCAM-1) during experimental autoimmune uveitis

Leukocyte adhesion to the blood retinal barrier is a critical step in the pathogenesis of non-infectious uveitis and is mediated in part through the induction of adhesion molecules on retinal cells. Here, we have investigated the retinal expression of Vascular Cell Adhesion Molecule 1 (VCAM-1) in mouse experimental models of non-infectious uveitis. For each eyes, a histological score was given, and the expression of VCAM-1 analyzed by immunohistology. Co-labellings for GFAP, endoglin, aquaporin 4 and recoverin were also performed in order to determine which cell type expressed VCAM-1. In low grade uveitis, obtained after adoptive transfer of semi-purified autoreactive lymphocytes, VCAM-1 was only punctually expressed in the internal limiting membrane and epithelial cells of the ciliary body. Using the same adoptive transfer protocol, we found that, in correlation with disease severity, the staining extended to all internal limiting membranes, vasculitis lesions, Müller cell extensions, outer limiting membranes and RPE cells. VCAM-1 expression in the inner limiting membrane and Müller cell extensions co-stained with GFAP expression. In vasculitis lesions, VCAM-1 co-localized with either GFAP and endoglin expression. The labeling in the outer limiting membrane, did not exactly co-stained with AQ4 (Müller cells marker) or recoverin (photoreceptor marker) and the nature of this expression remained unexplained. Finally, VCAM-1 expression was also analyzed in classical experimental autoimmune uveitis eyes, and a similar pattern of expression was found. In conclusion VCAM-1 is expressed on all blood retinal barrier cells during experimental non-infectious uveitis and might thus play an important role in inflammatory cell recruitment during disease development.

Therapeutic dosing of fingolimod (FTY720) prevents cell infiltration, rapidly suppresses ocular inflammation, and maintains the blood-ocular barrier

Fingolimod (FTY720) is an FDA-approved therapeutic drug with efficacy demonstrated in experimental models of multiple sclerosis and in phase III human multiple sclerosis trials. Fingolimod prevents T-cell migration to inflammatory sites by decreasing expression of the sphingosine-1 phosphate receptor normally required for egress from secondary lymphoid tissue. As a preclinical model of human uveitis, experimental autoimmune uveoretinitis permits assessment of immunotherapeutic efficacy. Murine experimental autoimmune uveoretinitis is induced by activation of retinal antigen-specific CD4(+) T cells that infiltrate the eye. High-dose fingolimod treatment administered before disease onset reduces ocular infiltration within hours of administration and suppresses clinicopathologic expression of experimental autoimmune uveoretinitis. In the present investigation of the efficacy of fingolimod treatment for established disease, single-dose treatment was effective and immunosuppressive ability was maintained through a dose range, demonstrating significant and rapid reduction in CD4(+) cell infiltration at clinically relevant therapeutic doses of fingolimod. A repeated-treatment regimen using a dose similar to that in current multiple sclerosis patient protocols significantly reduced infiltration within 24 hours of administration; importantly, repeated doses did not compromise the vascular integrity of the blood-ocular barrier. On withdrawal of fingolimod, drug-induced remission was lost and recrudescence of clinical disease was observed. These results support a strong therapeutic potential for fingolimod as an acute rescue therapy for the treatment of ocular immune-mediated inflammation.

Protective effect of pristane on experimental autoimmune uveitis

This study evaluates the effects of pristane and phytol, two mineral oils with pro-oxidative effects, on the course of experimental autoimmune uveitis. C57BL6 mice were immunized with IRBP1-20 peptide emulsified in CFA and treated five days prior to immunization with phytol or with pristane or with PBS as control. Administration of pristane reduces the incidence and severity of IRBP-induced uveitis as demonstrated by the decrease in vasculitis and inflammatory foci in fundus and by a reduction in histological damages and leukocyte infiltration compared to untreated or phytol-treated mice. The protective effect observed is associated with a decreased activation of peripheral CD4+ and CD8+ T lymphocytes and a decrease in the intensity of the Th1 and Th17 autoimmune response to IRBP in pristane-treated mice compared to control mice, as evidenced by the decreased production of IFNγ and IL17 by IRBP-specific lymphocytes from lymph nodes draining the site of immunization and by the increased production of anti-IRBP IgG1 over IgG2a. In addition, HUVEC and ARPE-19 cells incubated with the sera of mice treated with pristane presented a reduced production of H(2)O(2). The benefit of lowering the systemic oxidative stress by pristane in the course of EAU was confirmed by injecting the antioxidant NAC in IRBP-immunized mice. As pristane, NAC decreased clinical and histological inflammation of the retina and preserved the integrity of the hemato-retinal barrier. Finally, the protective effect of pristane on the development of EAU suggests that some mineral oils may represent a new therapeutic strategy in human uveitis.

A look at autoimmunity and inflammation in the eye

Autoimmune and inflammatory uveitis are a group of potentially blinding intraocular inflammatory diseases that arise without a known infectious trigger and are often associated with immunological responses to unique retinal proteins. In the United States, about 10% of the cases of severe visual handicap are attributed to this group of disorders. As I discuss here, experimental models of ocular autoimmunity targeting retinal proteins have brought about a better understanding of the basic immunological mechanisms involved in the pathogenesis of uveitis and are serving as templates for the development of novel therapies.

Anti-inflammatory treatment of uveitis with biologicals: new treatment options that reflect pathogenetic knowledge of the disease

BACKGROUND

Endogenous uveitis is a sight-threatening disease. In addition to corticosteroids, immunosuppressive agents are commonly used to treat patients with severe course. Immunosuppressive drugs act nonspecifically, rather than providing a specific interaction with the critical pathogenetic pathways of uveitis. Better knowledge of the basic mechanisms underlying uveitis and of the molecules that are important for regulating inflammation has helped to create new and more specific treatment approaches. Biological therapy for inflammatory diseases employs substances that interfere with specific molecules or pathways induced in the body during the inflammatory process.

METHODS

This review gives an overview on molecules that play a critical role in the pathogenetic process of uveitis, as has been observed in patients or the respective animal models, and summarizes the current experience with biologicals for the treatment of uveitis refractive to conventional immunosuppressives.

Unlike Th1, Th17 cells mediate sustained autoimmune inflammation and are highly resistant to restimulation-induced cell death

Both Th1 and Th17 T cell subsets can mediate inflammation, but the kinetics of the pathogenic processes mediated by these two subsets have not been investigated. Using an experimental system in which TCR-transgenic Th1 or Th17 cells specific for hen egg lysozyme induce ocular inflammation in recipient mice expressing eye-restricted hen egg lysozyme, we found important differences in the in vivo behavior of these two subsets. Th1 cells initially proliferated considerably faster and invaded the eye more quickly than their Th17 counterparts, but then disappeared rapidly. By contrast, Th17 cells accumulated and remained the majority of the infiltrating CD4(+) cells in the eye for as long as 25 days after transfer, mediating more long-lasting pathological changes. Unlike Th1, Th17 cells were highly resistant to restimulation-induced apoptosis, a major pathway by which autoimmune and chronically restimulated Th1 cells are eliminated. Th17 cells had reduced Fas ligand production and resistance to Fas-induced apoptosis, relative to Th1 cells, despite similar surface expression of Fas. Th17-induced ocular inflammation also differed from Th1-induced inflammation by consisting of more neutrophils, whereas Th1-induced disease had higher proportions of CD8 cells. Taken together, our data show that pathogenic processes triggered by Th17 lag behind those induced by Th1, but then persist remarkably longer, apparently due to the relative resistance of Th17 cells to restimulation-induced cell death. The long-lasting inflammation induced by Th17 cells is in accord with these cells being involved in chronic conditions in humans.

Phenotype switching by inflammation-inducing polarized Th17 cells, but not by Th1 cells

Th1 and Th17 cells are characterized by their expression of IFN-gamma or IL-17, respectively. The finding of Th cells producing both IL-17 and IFN-gamma suggested, however, that certain Th cells may modify their selective cytokine expression. In this study, we examined changes in cytokine expression in an experimental system in which polarized Th1 or Th17 cells specific against hen egg lysozyme induce ocular inflammation in recipient mice expressing hen egg lysozyme in their eyes. Whereas only IFN-gamma was expressed in eyes of Th1 recipient mice, substantial proportions of donor cells expressed IFN-gamma or both IFN-gamma and IL-17 in Th17 recipient eyes. The possibility that nonpolarized cells in Th17 preparations were responsible for expression of IFN-gamma or IFN-gamma/IL-17 in Th17 recipient eyes was contradicted by the finding that the proportions of such cells were larger in recipients of Th17 preparations with 20-25% nonpolarized cells than in recipients of 35-40% preparations. Moreover, whereas incubation in vitro of Th1 cells with Th17-polarizing mixture had no effect on their phenotype, incubation of Th17 with Th1-polarizing mixture, or in the absence of cytokines, converted most of these cells into IFN-gamma or IFN-gamma/IL-17-expressing cells. In addition, Th17 incubated with the Th1 mixture expressed T-bet, whereas no ROR-gamma t was detected in Th1 incubated with Th17 mixture. Thus, polarized Th1 cells retain their phenotype in the tested systems, whereas Th17 may switch to express IFN-gamma or IFN-gamma/IL-17 following activation in the absence of cytokines, or exposure to certain cytokine milieus at the inflammation site or in culture.

Both Th1 and Th17 are immunopathogenic but differ in other key biological activities

The role of Th17 lymphocytes in immunopathogenic processes has been well established, but little is known about their basic cell features. In this study, we compared polarized Th1 and Th17 for key biological activities related to pathogenicity and trafficking. Th1 and Th17 lineages were derived from TCR-transgenic CD4 murine cells specific against hen egg lysozyme. When adoptively transferred into mice expressing hen egg lysozyme in their eyes, both Th1 and Th17 induced ocular inflammation but with slight differences in histological pathology. PCR analysis revealed selective expression of IFN-gamma or IL-17 in eyes of Th1 or Th17 recipients, respectively. Additionally, Th1 and Th17 were found to differ in three other key activities: 1) Th17 cells were inferior to Th1 cells in their capacity to trigger massive lymphoid expansion and splenomegaly; 2) the proportion of Th1 cells among infiltrating cells in inflamed recipient eyes declined rapidly, becoming a minority by day 7, whereas Th17 cells remained in the majority throughout this period; and 3) remarkable differences were noted between Th1 and Th17 cells in their expression of certain surface markers. In particular, reactivated Th1 expressed higher levels of CD49d and alpha(4)beta(7) (mucosal homing) in vitro and higher levels of CXCR3 (Th1 trafficking) in vivo. Reactivated Th17, however, expressed higher levels of alpha(E)beta(7) (epithelial tissue homing) and CD38 (activation, maturation and trafficking) in vitro, but in vivo Th17 expressed higher levels of alpha(4)beta(7) and CCR6 (lymphocyte trafficking). These data reveal that Th1 and Th17 cells differ in several key biological activities influencing migration and pathogenic behavior during inflammatory disease.

New perspectives on effector mechanisms in uveitis

Experimental autoimmune uveitis (EAU) in its several variants represents human autoimmune uveitis and has been instrumental in obtaining insights into the basic mechanisms of disease. Studies have uncovered that in addition to CD4+ Th1 cells, uveitis can be induced also by CD8+ T cells. Antibodies may have a secondary role after the blood-retinal barrier has been broken. The role in uveitis of a recently discovered IL-17-producing effector T cell type, Th17, is being intensively studied. Th17 cells elicit EAU, can be found in uveitic eyes along with Th1 cells, and are dominant in some types of EAU. In other types of EAU, Th1 cells have a dominant role. The dominant effector type is at least in part determined by conditions under which initial exposure to self-antigen occurs. These findings shed light on the heterogeneity of human disease and may ultimately help to develop better and more rational treatment strategies for human uveitis.

Retinal Mueller Glial Cells Trigger the Hallmark Inflammatory Process in Autoimmune Uveitis

Spontaneous equine recurrent uveitis (ERU) is an incurable autoimmune disease affecting the eye. Although retinal-autoantigen specific T-helper 1 cells have been demonstrated to trigger disease progression and relapses, the molecular processes leading to retinal degeneration and consequent blindness remain unknown. To elucidate such processes, we studied changes in the total retinal proteome of ERU-diseased horses compared to healthy controls. Severe changes in the retinal proteome were found for several markers for blood-retinal barrier breakdown and whose emergence depended upon disease severity. Additionally, uveitic changes in the retina were accompanied by upregulation of aldose 1-epimerase, selenium-binding protein 1, alpha crystallin A chain, phosphatase 2A inhibitor (SET), and glial fibrillary acidic protein (GFAP), the latter indicating an involvement of retinal Mueller glial cells (RMG) in disease process. To confirm this, we screened for additional RMG-specific markers and could demonstrate that, in uveitic retinas, RMG concomitantly upregulate vimentin and GFAP and downregulate glutamine synthetase. These expression patterns suggest for an activated state of RMG, which further downregulate the expression of pigment epithelium-derived factor (PEDF) and begin expressing interferon-gamma, a pro-inflammatory cytokine typical for T-helper 1 cells. We thus propose that RMG may play a fatal role in uveitic disease progression by directly triggering inflammatory processes through the expression and secretion of interferon-gamma.

Active participation of antigen-nonspecific lymphoid cells in immune-mediated inflammation

The pathogenic process of tissue-specific autoimmune disease depends to a large extent on recruitment of Ag-nonspecific cells into the target tissue. Little is known, however, about the recruitment process and the features that characterize the recruited cells. In this study, we analyzed the recruitment of Ag-nonspecific lymphoid cells into an inflammatory site by using an experimental system in which TCR-transgenic Th1 cells are adoptively transferred to induce ocular inflammation in recipient mice that express the target Ag in their eyes. A sharp increase in number of all host cell populations was observed in the recipient spleen, reaching a peak on day 4 postcell transfer and declining thereafter. A large portion of the host's spleen CD4 cells underwent phenotypic changes that facilitate their migration into the target organ, the eye. These changes included increased expression of the chemokine receptor CXCR3, and the adhesion molecule CD49d, as well as a decline in expression of CD62L. The host lymphocytes migrated into the recipient mouse eye more slowly than the donor cells, but became the great majority of the infiltrating cells at the peak of inflammation on day 7 postcell injection. Interestingly, the mass migration of host T cells was preceded by an influx of host dendritic cells, that reached their peak on day 4 postcell injection. The eye-infiltrating host CD4 lymphocytes underwent additional changes, acquiring a profile of activated lymphocytes, i.e., up-regulation of CD25 and CD69. Our results thus provide new information about the active participation of Ag-nonspecific lymphoid cells in immune-mediated inflammation.

Sialoadhesin promotes the inflammatory response in experimental autoimmune uveoretinitis

Macrophages are a prominent component of the effector cell compartment in a number of CD4+ T cell-mediated organ-specific autoimmune diseases. In this study, we investigated the role of the sialic acid binding Ig-like lectin sialoadhesin (Sn, Siglec-1) in a model of interphotoreceptor retinal binding protein peptide-induced experimental autoimmune uveoretinitis in mice with targeted deletion of Sn. Our data show that compared with wild-type mice, experimental autoimmune uveoretinitis is reduced in severity in the initial stages in the Sn knockout (KO) mice. In addition, there is a reduction in the proliferative capacity of T cells from the KO mice draining lymph nodes after immunization with interphotoreceptor retinal binding protein peptides, which is manifest some days before disease onset and persists for the duration of disease. Furthermore, activated T cells from the draining lymph nodes of Sn KO mice secrete lower levels of IFN-gamma. The data suggest a role for Sn in "fine tuning" the immune response to autoantigens by modulating T cell priming.

A selective role for the TNF p55 receptor in autocrine signaling following IFN-gamma stimulation in experimental autoimmune uveoretinitis

IFN-gamma stimulates macrophage activation and NO production, which leads to destruction of the retina in experimental autoimmune uveoretinitis. In this study, we investigate the mechanism of disease resistance in TNF p55 receptor-deficient animals. We show that although T cell priming is relatively unaffected, macrophages lacking the TNF p55 receptor fail to produce NO following IFN-gamma stimulation because of a requirement for autocrine TNF-alpha signaling through the TNF p55 receptor. In contrast to the impaired activation of NO synthesis, MHC class II up-regulation was indistinguishable in wild-type and TNFRp55-/- mice stimulated with IFN-gamma. These defects could be overcome by stimulating macrophages with LPS. Together, these results show that selected aspects of IFN-gamma activation are controlled by autocrine secretion of TNF-alpha, but that this control is lost in the presence of signals generated by pathogen-associated molecular patterns recognizing receptors.

The effect of the CC chemokine receptor antagonist Met-RANTES on experimental autoimmune uveitis and oral tolerance

Lymphocyte trafficking is controlled in part by the actions of chemokines. In rat experimental autoimmune uveitis (EAU) we observed differential therapeutic effects of Met-RANTES, a CCR1/CCR5 receptor antagonist, depending on the retinal antigen peptides inducing the disease and the time of application during the afferent or efferent immune response. CCR1 and/or CCR5 blockade may have inhibitory effects on different phases of the autoimmune response, depending on the antigen specificity of T cells in EAU. In contrast, Met-RANTES enhanced therapeutic oral tolerance independently of orally applied antigen.

Effects of intravitreal injection of tacrolimus (FK506) in experimental uveitis

PURPOSE

To examine the immunosuppressive and neuroprotective effects of intravitreal injection of tacrolimus in experimental uveitis.

METHODS

Tacrolimus (40 microg) was injected intravitreally in rabbits to examine safety. Experimental uveitis was induced in rabbits by systemic immunization with bovine serum albumin (BSA) followed by intravitreal challenge with BSA. On day 1 after BSA challenge, tacrolimus (20 or 40 microg) or betamethasone (400 microg) was injected intravitreally in one eye and balanced salt solution in the contralateral eye. The eyes were evaluated by slit-lamp biomicroscopy, electroretinography, and histopathology.

RESULTS

No local or systemic adverse reaction was observed in normal rabbits. In experimental uveitis, intravitreal injection of tacrolimus significantly reduced intraocular inflammation in histopathological analysis (p < 0.03). Amplitudes on the electroretinogram were restored (p < 0.01), and retinal thickness was preserved in tacrolimus-treated eyes (p < 0.03).

CONCLUSIONS

In experimental uveitis, intravitreal injection of tacrolimus effectively suppresses ocular inflammation and preserves retinal architecture.

The role of tumour necrosis factor (TNF-alpha) in experimental autoimmune uveoretinitis (EAU)

The pleiotropic cytokine tumour necrosis factor-alpha (TNF-alpha) is released from cells that include macrophages and T-cells during inflammatory responses, orchestrating the initiation of further leucocytic infiltration via adhesion molecule upregulation, dendritic cell maturation and survival, macrophage activation and driving Th1 T-cells responses within tissues. Exposure to TNF also plays a role in maintaining tissue homeostasis, particularly relating to resident cell responses of both microglia and retinal pigment epithelium. Depending on the balance between duration and dose of TNF exposure, an environment where full expression of inflammatory and autoimmune responses within tissues may occur. In experimental autoimmune uveoretinitis (EAU), increased tissue concentrations of TNF facilitate the on-going T-cell effector responses and macrophage activation. These are responsible for targeted and bystander tissue damage and can be suppressed by anti-TNF therapies, in particular, those directed at the p55 TNF receptor. The ability to suppress disease experimentally has led to the successful translation of anti-TNF therapy for treatment of uveitis in cohort studies and phase I/II trials where, additionally, altered peripheral blood CD4(+) T-cell profiles can be demonstrated following each treatment.

Regulation, counter-regulation, and immunotherapy of autoimmune responses to immunologically privileged retinal antigens

Our interests revolve around the study of biological mechanisms regulating self-tolerance to immunologically privileged retinal proteins that serve as targets in sight-threatening autoimmune uveitic disease. These studies are aimed at understanding how selftolerance to these antigens develops during ontogeny and is maintained during adulthood, the processes involved in its pathological breakdown, the regulatory mechanisms that bring about remission and recovery, and, finally, how we can utilize knowledge of these processes for therapeutic restoration of tolerance. To answer these questions, we use the experimental autoimmune uveitis (EAU) model in rats and mice. Because of the commonality of underlying immunological mechanisms, lessons and concepts learned in experimental ocular models are applicable to other disease entities, and, conversely, data gleaned from other autoimmune diseases are applicable to the study of uveitis.

Control of myeloid activity during retinal inflammation

Combating myeloid cell-mediated destruction of the retina during inflammation or neurodegeneration is dependent on the integrity of homeostatic mechanisms within the tissue that may suppress T cell activation and their subsequent cytokine responses, modulate infiltrating macrophage activation, and facilitate healthy tissue repair. Success is dependent on response of the resident myeloid-cell populations [microglia (MG)] to activation signals, commonly cytokines, and the control of infiltrating macrophage activation during inflammation, both of which appear highly programmed in normal and inflamed retina. The evidence that tissue CD200 constitutively provides down-regulatory signals to myeloid-derived cells via cognate CD200-CD200 receptor (R) interaction supports inherent tissue control of myeloid cell activation. In the retina, there is extensive neuronal and endothelial expression of CD200. Retinal MG in CD200 knockout mice display normal morphology but unlike the wild-type mice, are present in increased numbers and express nitric oxide synthase 2, a macrophage activation marker, inferring that loss of CD200 or absent CD200R ligation results in "classical" activation of myeloid cells. Thus, when mice lack CD200, they show increased susceptibility to and accelerated onset of tissue-specific autoimmunity.

Imaging ocular immune responses by intravital microscopy

The eye offers excellent opportunities to observe cellular interactions in vivo. This applies especially to the immune response in which discrete events can be studied, including cell trafficking, transendothelial migration, adhesion, antigen presentation, and T cell activation. Intravital microscopy has allowed study of immune cell interactions in tissues such as the conjunctiva, the inflamed cornea, and the iris. Thus the realtime observation of presentation of antigen injected into the anterior chamber of the eye can be imaged using fluorescently labelled antigen and cells. Application of the scanning laser ophthalmoscope to the rat and mouse eye allows analysis of leukocyte-endothelial interactions in the retinal and choroidal circulations. These studies have provided important information on rolling and adhesion of leukocytes in real time in different microvascular beds that have not been manipulated in any way and has, for instance, provided quantitation to the effects of shear stress on leukocyte-endothelial adhesion. In addition, the model permits an accurate analysis of the timing of trafficking of T cells into the eye and the possibility of determining which cells, if any, may be responsible for antigen presentation in the tissues as opposed to the secondary lymphoid organs. Finally, these experimental methods are now being applied to the human eye and should prove valuable in determining the nature of tissue damage events in the eye as well as evaluating the response to treatments.

Pertussis toxin inhibits induction of tissue-specific autoimmune disease by disrupting G protein-coupled signals

Pertussis toxin (PTX) has been used for many years as an adjuvant that promotes development of tissue-specific experimental autoimmune diseases such as experimental autoimmune encephalomyelitis, experimental autoimmune uveitis (EAU), and others. Enhancement of vascular permeability and of Th1 responses have been implicated in this effect. Here we report a surprising observation that, in a primed system, PTX can completely block the development of EAU. Disease was induced in B10.RIII mice by adoptive transfer of uveitogenic T cells, or by immunization with a uveitogenic peptide. A single injection of PTX concurrently with infusion of the uveitogenic T cells, or two injections 7 and 10 days after active immunization, completely blocked development of EAU. EAU also was prevented by a 1-h incubation in vitro of the uveitogenic T cells with PTX before infusing them into recipients. Uveitogenic T cells treated with PTX in vitro and lymphoid cells from mice treated with PTX in vivo failed to migrate to chemokines in a standard chemotaxis assay. Neither the isolated B-oligomer subunit of PTX that lacks ADP ribosyltransferase activity nor the related cholera toxin that ADP-ribosylates G(s) (but not G(i)) proteins blocked EAU induction or migration to chemokines. We conclude that PTX present at the time of cell migration to the target organ prevents EAU, and propose that it does so at least in part by disrupting signaling through G(i) protein-coupled receptors. Thus, the net effect of PTX on autoimmune disease would represent an integration of enhancing and inhibitory effects.

Identification of Th2-type suppressor T cells among in vivo expanded ocular T cells in mice with experimental autoimmune uveoretinitis

Experimental autoimmune uveoretinitis (EAU), which is a T cell mediated organ specific autoimmune disease, is induced by immunization with interphotoreceptor retinoid binding protein (IRBP) in susceptible strains of mice. It has been found that IRBP-derived peptide 518-529 (p518-529) generates Th2-type responses and inhibits IRBP-induced EAU, indicating that the p518-529 might be an epitope for suppressor T cells in IRBP-induced EAU. First, we observed that there were T cells producing the Th2 type cytokines such as IL-4 and IL-10 in late phase of EAU. Furthermore, to examine whether p518-529-reactive T cells expand in the eye during EAU, T cell receptor (TCR) of ocular T cells was compared with that of p518-529 reactive T cells in spleen from mice with EAU by PCR-single strand conformation polymorphism (PCR-SSCP) and nucleotide sequence analysis. SSCP and sequence analyses indicated that p518-529 reactive TCR BV10+ T cells bearing amino acid motif(PWG) and TCR BV13+ T cells bearing amino acid motif(PGLGGY) in their complementary-determining region 3 (CDR3) region were clonally expanding in ocular tissues on day 28 after immunization, although these T cells were not detected on day 14. These findings demonstrate that p518-529 reactive Th2-type T cells expand oligoclonally in the uveitic eyes in the late stage of EAU and may function as Th2-type suppressor T cells for improvement of the disease.

Restricted and shared patterns of TCR beta-chain gene expression in silicone breast implant capsules and remote sites of tissue inflammation

Silicone breast implants (SBI) induce formation of a periprosthetic, often inflammatory, fibrovascular neo-tissue called a capsule. Histopathology of explanted capsules varies from densely fibrotic, acellular specimens to those showing intense inflammation with activated macrophages, multinucleated giant cells, and lymphocytic infiltrates. It has been proposed that capsule-infiltrating lymphocytes comprise a secondary, bystander component of an otherwise benign foreign body response in women with SBIs. In symptomatic women with SBIs, however, the relationship of capsular inflammation to inflammation in other remote tissues remains unclear. In the present study, we utilized a combination of TCR beta-chain CDR3 spectratyping and DNA sequence analysis to assess the clonal heterogeneity of T cells infiltrating SBI capsules and remote, inflammatory tissues. TCR CDR3 fragment analysis of 22 distinct beta variable (BV) gene families revealed heterogeneous patterns of T cell infiltration in patients' capsules. In some cases, however, TCR BV transcripts exhibiting restricted clonality with shared CDR3 lengths were detected in left and right SBI capsules and other inflammatory tissues. DNA sequence analysis of shared, size-restricted CDR3 fragments confirmed that certain TCR BV transcripts isolated from left and right SBI capsules and multiple, extracapsular tissues had identical amino acid sequences within the CDR3 antigen binding domain. These data suggest that shared, antigen-driven T cell responses may contribute to chronic inflammation in SBI capsules as well as systemic sites of tissue injury.

Modulating phenotype and cytokine production of leucocytic retinal infiltrate in experimental autoimmune uveoretinitis following intranasal tolerance induction with retinal antigens

BACKGROUND/AIM

Nasal administration of retinal antigens induces systemic tolerance which results in suppression of experimental autoimmune uveoretinitis (EAU) when subsequently exposed to antigen. The aim was to establish if tolerance induction alters retinal infiltrating leucocyte phenotype and cytokine profile in tolerised animals when there is significantly reduced tissue destruction despite immunisation with retinal antigen.

METHODS

Female Lewis rats were tolerised by intranasal administration with retinal extract (RE) before immunisation with RE to induce EAU. Control animals were administered phosphate buffered saline (PBS) intranasally. Post immunisation, daily clinical responses were recorded and at the height of disease, retinas were removed and either infiltrating leucocytes isolated for flow cytometric phenotype assessment and intracellular cytokine production, or chorioretina processed for immunohistochemistry. Fellow eyes were assessed for cytokine mRNA by semiquantitative RT-PCR.

RESULTS

Flow cytometric analysis showed that before clinical onset of EAU there is no evidence of macrophage infiltration and no significant difference in circulating T cell populations within the retina. By day 14 a reduced retinal infiltrate in tolerised animals was observed and in particular a reduction in numbers of "activated" (with respect to CD4 and MHC class II expression) macrophages. Immunohistochemistry confirmed these findings and additionally minimal rod outer segment destruction was observed histologically. Cytokine analysis revealed that both IL-10 mRNA and intracellular IL-10 production was increased in tolerised eyes 7 days post immunisation. Although by day 14 post immunisation, IL-10 production was equivalent in both groups, a reduced percentage of IFN-gamma + macrophages and IFN-gamma + CD4+ T cells with increased percentage of IL-4+ CD4+ T cells were observed in tolerised animals.

CONCLUSIONS

Leucocytic infiltrate is not only reduced in number but its distinct phenotype compared with controls implies a reduced activation status of infiltrating monocyts to accompany increased IL-10 and reduced IFN-gamma production in tolerised animals. This modulation may in turn contribute towards protection against target organ destruction in EAU.

Acute immunosuppression and syngeneic bone marrow transplantation in ocular autoimmunity abort disease, but do not result in induction of long-term protection

Acute immunosuppression induced by total body irradiation (TBI) or cyclophosphamide (Cy) treatment, followed by syngeneic bone marrow transplantation (SBMT), was reported to be effective in inducing long-term tolerance in some autoimmune disease models. We examined the efficacy of this approach in the mouse model of experimental autoimmune uveoretinitis (EAU). Development of EAU induced by the interphotoreceptor retinoid binding protein (IRBP) was abolished almost completely by either TBI or Cy treatment, followed by SBMT, instituted one week after priming. In parallel, IRBP-specific delayed-type hypersensitivity (DTH) responses and lymph node cell proliferation were strongly suppressed or abolished. However, when these IRBP-immunized, lymphoablated and BM reconstituted mice were rechallenged with the immunizing antigen seven weeks after the primary immunization, they were not protected from developing disease, despite the fact that DTH and lymph node cell proliferation to the antigen were suppressed relative to controls. TBI treatment appeared somewhat more effective than Cy treatment as judged by its more profound effect on immunological responses. These results demonstrate the ability of acute immunosuppression followed by reconstitution of the immune system to inhibit the development of EAU, although long-term protection from disease was not achieved.

Experimental mucosal induction of uveitis with the 60-kDa heat shock protein-derived peptide 336-351

Subcutaneous (s.c.) immunization of rats with the human 60-kDa heat shock protein (HSP)-derived peptide 336-351 induced clinical and/or histological uveitis in 80 % of rats. Subsequent experiments to prevent the development of uveitis by oral or nasal administration of the peptide have failed. Instead, uveitis was induced in 74.6 % of rats given the peptide orally (5 times), in 75 % given the peptide nasally (5 times) or 91.7 % of those administered the peptide by both routes (10 times). Histological examination showed that any one route of administration of the peptide elicited iridocyclitis in 42.2 % but loss of photoreceptors only in 4.9 % of rats. In contrast, sequential administrations of the peptide by a combined mucosal-s.c. route resulted in iridocyclitis in only 25 % but loss of photoreceptors in 40 % of animals. Examination of mRNA from CD4-enriched splenic cells by reverse transcription-PCR failed to yield significant differences in Th1 or Th2 cytokines. Treatment with monoclonal antibody (mAb) to CD4 yielded a dose-dependent decrease in uveitis from 82 % to 25 %. Similarly, treatment with IL-4 significantly decreased the development of uveitis from 68 % to 30.4 %. Conversely, treatment of the rats with mAb to CD8 greatly enhanced the onset of uveitis (from about 22 days in the controls to 11 days) and all the rats developed uveitis by day 24. Thus, CD4+ cells mediate, whereas CD8+ cells suppress the development of uveitis. We suggest that this novel experimental mucosal model of induction of uveitis by the human 60-kDa HSP-derived peptide 336-351, which is specific in stimulating T cell responses in Behcet's disease, is consistent with the oro-genital onset of this disease and the development of uveitis.

Phenotypic analysis of retinal leukocyte infiltration during combined cyclosporin A and nasal antigen administration of retinal antigens: delay and inhibition of macrophage and granulocyte infiltration

Nasal antigen administration successfully suppresses a model of organ-specific autoimmune disease, experimental autoimmune uveoretinitis (EAU), when administered prior to immunisation. We have previously shown that nasal antigen therapy for active disease or in primed, sensitised animals does not reliably or consistently suppress histological disease. However, when nasal antigen administration is combined with cyclosporin A (CsA) therapy, rod outer segment destruction (target organ) is reduced despite the presence of clinical and histological leukocytic infiltration of the eye. In this study, two colour flow cytometric phenotypic analysis of retinal and choroidal leukocytic infiltration of animals treated with either CsA alone, combined therapy with CsA and inhalational tolerance therapy with retinal antigens or sham treated controls was performed. There was no clinical difference between the two treated groups. Flow cytometric phenotypic analysis was performed in all groups at both maximal clinical disease and during resolution of clinical signs. Although the cell number within the infiltrate was reduced in combined treated group, CD4+ IL-2R+ T cells were still present in large numbers, in contrast to the markedly reduced numbers of ED7+ (macrophages/granulocytes) cells infiltrating during height of disease. In the CsA-nasal antigen treated group, when clinical inflammation had subsided, an increase in both macrophages and granulocyte numbers in the chorioretina was observed. The cell numbers were always less than CsA-only treated animals. Despite the late cellular influx of monocytes/macrophages, rod outer segment (ROS) integrity as determined histologically, was maintained. Nasal antigen administration of retinal antigens in CsA-only treated animals (combined therapy group) protects against target organ damage without inhibiting activated T cell traffic to the eye. These results suggest that recruitment of macrophages to the target tissue is central to autoimmune target organ damage, the mechanisms of which are discussed.

Inhibition of tumor necrosis factor activity minimizes target organ damage in experimental autoimmune uveoretinitis despite quantitatively normal activated T cell traffic to the retina

Recent studies demonstrated that administration of a p55-tumor necrosis factor (TNF) receptor IgG-fusion protein (TNFR-IgG) prevented the clinical onset of experimental autoimmune encephalomyelitis but did not alter the number or tissue distribution of autoantigen-specific CD4+ effector T cells which trafficked into the central nervous system. To determine whether specific target tissues of autoimmune damage remain intact after TNFR-IgG treatment despite the presence of inflammatory cells within the tissues, we examined rats with experimental autoimmune uveoretinitis (EAU), as in this model, the main target of autoreactive CD4+ T cells, the retinal rod outer segments (ROS), can be examined readily by light microscopy. As judged by direct ophthalmoscopy, the onset of inflammation in the anterior chamber of the eye in EAU following administration of TNFR-IgG was delayed by 6 days compared to untreated controls, but the magnitude of the response was only slightly less than controls. Histological examination of the retinae and direct assessment of retinal inflammation revealed a disproportionate sparing of ROS in the TNFR-IgG-treated animals despite a level of retinal inflammation not substantially less than controls in which ROS damage was marked. Analysis of retinal leukocytes by immunofluorescence microscopy and flow cytometry indicated that approximately equal numbers of CD4+ alpha beta TCR+ lymphocytes were present in treated and control retinae, more than 30% of CD4+ cells in both experimental groups expressed the CD25 or MRC OX40 activation markers and most cells, which would include the CD4+ T lymphocytes, were activated as evidenced by MHC class II expression. Fewer activated macrophages and granulocytes were present in the treated retinae, possibly reflecting the lower level of tissue damage and subsequent accumulation of these inflammatory cells. The results demonstrate directly that a tissue specifically targeted for autoimmune destruction can be protected despite the influx of fully activated CD4+ T cells.