Interphotoreceptor retinoid binding protein induced experimental autoimmune uveitis: an immunophenotypic analysis using alkaline phosphatase anti-alkaline phosphatase staining, dual immunofluorescence and confocal microscopy

Effect of Esculetin on Tert-Butyl Hydroperoxide-Induced Oxidative Injury in Retinal Pigment Epithelial Cells In Vitro

Esculetin is a coumarin-derived compound with antioxidant and anti-inflammatory properties. The current study aims to evaluate the therapeutic implications of esculetin on retinal dysfunction and uncover the underlying mechanisms. Tert-butyl hydroperoxide (t-BHP) at a concentration of 300 μM was used to induce oxidative stress in human retinal pigment epithelial cell line (ARPE-19) cells. Esculetin at concentrations below 250 μM did not cause cytotoxicity to ARPE-19 cells. Cell viability analysis confirmed that t-BHP induced oxidative injury of ARPE-19 cells. However, ARPE-19 cells were protected from t-BHP-induced oxidative injury by esculetin in a concentration-dependent manner. As a result of the TUNEL assay to confirm apoptosis, esculetin treatment reduced the number of TUNEL-positive cells. Esculetin down-regulated the expression levels of Bax, Caspase-3, and PARP and up-regulated the expression level of Bcl2. Collectively, this study demonstrates that esculetin exerts potent antioxidant properties in ARPE-19 cells, inhibiting t-BHP-induced apoptosis under the regulation of apoptotic factors.

Intravitreal combination of dexamethasone sodium phosphate and bevacizumab in the treatment of exudative AMD

The purpose of this study is to investigate the efficacy and safety of intravitreal dexamethasone sodium phosphate (DSP) combined with bevacizumab for the treatment of neovascular age-related macular degeneration (AMD). In this non comparative case study, 30 eyes of 27 patients with CNV due to AMD received intravitreal DSP (0.2 mg) and bevacizumab (1.25 mg) during a 6-month PRN (pro re nata) dosing regimen. Visual acuity, macular thickness and intraocular pressure (IOP) were monitored and recorded. After 6 months, mean retinal thickness decreased from 423.5 ± 75.3 to 228.2 ± 34.5 and mean visual acuity improved from 0.9 ± 0.39 logMAR to 0.53 ± 0.34 (p = 0.001) logMAR. During the trial period, 81 intravitreal injections were performed in 30 eyes, thus the mean number of injections per eye was 2.7 ± 1.1. 86.7% of the eyes required 3 or less injections while only 13.3% needed 4 or more injections. None of the patients, phakic or pseudophakic, manifested an elevation of IOP during the treatment, ranging between 12 and 22 mmHg. Combined DSP and bevacizumab offers encouraging results in the challenge of AMD treatment, providing immediate response of macular edema, reduced number of intravitreal injections and stabilization or improvement of visual acuity.

Bowman lecture on the role of inflammation in degenerative disease of the eye

Inflammation, in the pathogenesis of many diseases previously thought to be strictly genetic, degenerative, metabolic, or endocrinologic in aetiology, has gradually entered the framework of a general mechanism of disease. This is exemplified by conditions such as Parkinson's disease, Alzheimer's disease, atherosclerosis, diabetes, and the more recently described Metabolic Syndrome. Chronic inflammatory processes have a significant, if not primary role, in ophthalmic diseases, particularly in retinal degenerative diseases. However, inflammation itself is not easy to define, and some aspects of inflammation may be beneficial, in a process described as 'para-inflammation' by Medhzitov. In contrast, the damaging effects of inflammation, mediated by pro-inflammatory macrophages through activation of the intracellular protein-signalling complexes, termed inflammasomes, are well recognised and are important therapeutic targets. In this review, the range of inflammatory processes in the eye is evaluated in the context of how these processes impact upon retinal degenerative disease, particularly diabetic retinopathy and age-related macular degeneration.

MCP-1-activated monocytes induce apoptosis in human retinal pigment epithelium

PURPOSE

The inflammatory response in age-related macular degeneration (AMD) is characterized by mononuclear leukocyte infiltration of the outer blood-retina barrier formed by the retinal pigment epithelium (RPE). A key mechanistic element in AMD progression is RPE dysfunction and apoptotic cell loss. The purpose of this study was to evaluate whether monocyte chemoattractant protein (MCP)-1-activated monocytes induce human RPE apoptosis and whether Ca(2+) and reactive oxygen species (ROS) are involved in this process.

METHODS

A cell-based fluorometric assay was used to measure intracellular Ca(2+) concentrations ([Ca(2+)](i)) in RPE cells loaded with fluorescent Ca(2+) indicator. Intracellular RPE ROS levels were measured by using the 5- and 6-chloromethyl-2',7'-dichlorodihydrofluorescence diacetate acetyl ester (CM-H(2)DCFDA) assay. RPE apoptosis was evaluated by activated caspase-3, Hoechst staining, and apoptosis ELISA.

RESULTS

MCP-1-activated human monocytes increased [Ca(2+)](i), ROS levels, and apoptosis in RPE cells, all of which were inhibited by 8-bromo-cyclic adenosine diphosphoribosyl ribose (8-Br-cADPR), an antagonist of cADPR. Although the ROS scavengers pyrrolidinedithiocarbamate (PDTC) and N-acetylcysteine (NAC) significantly inhibited ROS production and apoptosis induced by activated monocytes, they did not affect induced Ca(2+) levels. The induced Ca(2+) levels and apoptosis in RPE cells were inhibited by an antibody against cluster of differentiation antigen 14 (CD14), an adhesion molecule expressed by these cells.

CONCLUSIONS

These results indicate that CD14, Ca(2+), and ROS are involved in activated monocyte-induced RPE apoptosis and that cADPR contributes to these changes. Understanding the complex interactions among CD14, cADPR, Ca(2+), and ROS may provide new insights and treatments of retinal diseases, including AMD.

Proliferation of retinal pigment epithelial cells induced by (R,R)-XY-10 and (S,S)-XY-10 and their action mechanisms

AIM

To investigate the mechanism of proliferation effect induced by (R,R)-XY-10 and (S,S)-XY-10 on retinal pigmented epithelial cells (ARPE-19).

METHODS

Human retinal pigmented epithelial cells (ARPE-19) and human umbilical vein endothelial cells (HUVECs) were used to investigate the effect of (R,R)-XY-10 and (S,S)-XY-10 on cell growth, and their mechanisms of proliferative action by using ERK, AKT, PI3K, Protein kinase C (PKC) and Nitric oxide synthase (NOS) inhibitors.

RESULTS

(R,R)-XY-10 and (S,S)-XY-10 dose-dependently increased ARPE-19 cell proliferation, but not on HUVECs. When treated with proliferative inhibitors, H-7 (5µmol/L), hypericin (20µmol/L), PD98059 (2µmol/L), LY294002 (50µmol/L), SH-5 (10µmol/L) and L-NAME (100µmol/L), the proliferative effect was reduced by H-7, hypericin, PD98059 and LY294002, but not by SH-5 and L-NAME.

CONCLUSION

(R,R)-XY-10 and (S,S)-XY-10 can induce cell proliferation through MAPK and PI3K dependent pathway.

Activated monocytes induce human retinal pigment epithelial cell apoptosis through caspase-3 activation

Dysfunction and loss of human retinal pigment epithelial (HRPE) cells is a significant component of many ocular diseases, in which mononuclear phagocyte infiltration at the HRPE-related interface is also observed. In this study, we investigated whether HRPE cell apoptosis may be induced by overlay of IFN-gamma-activated monocytes. Human monocytes primed with IFN-gamma overlaid directly onto HRPE cells elicited significant increases in terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive HRPE cells (p < 0.0001) and decreases of proliferating cell nuclear antigen-positive (p < 0.0001) HRPE cells. The activated monocytes also induced HRPE cell caspase-3 activation, which was inhibited by the caspase-3 inhibitor, Z-DEVD-fmk. However, co-incubations in which activated monocytes were prevented from direct contact with HRPE cells or in which the monocytes were separated from the HRPE cells after 30 minutes of direct contact, did not induce significant HRPE cell apoptosis. Function-blocking anti-CD18 and anti-intercellular adhesion molecule-1 (ICAM-1) antibodies significantly reduced activated monocyte-induced TUNEL-positive HRPE cells by 48% (p = 0.0051) and 38% (p = 0.046), respectively. Anti-CD18 and anti-ICAM-1 antibodies significantly inhibited caspase-3 activity by 56% (p < 0.0001) and 45% (p < 0.0001), respectively. However, antibodies to vascular cell adhesion molecule-1, TNF-alpha, IL-1beta, or TNF-related apoptosis-inducing ligand did not inhibit apoptosis or caspase-3 activation. Direct overlay of monocytes also induced reactive oxygen metabolites (ROM) within HRPE cells. The intracellular HRPE cell ROM production was inhibited by the anti-CD18 and anti-ICAM-1 antibodies, but not by superoxide dismutase, presumably due to its failure to penetrate into HRPE cells. Accordingly, neither superoxide dismutase nor N(G)-monomethyl-L-arginine had significant effects on HRPE cell apoptosis or caspase-3 activation. Our results suggest that activated monocytes may induce ROM in HRPE cells through cell-to-cell contact, in part via CD18 and ICAM-1, and promote HRPE cell apoptosis. These mechanisms may compromise HRPE cell function and survival in a variety of retinal diseases.

Total dose and frequency of administration critically affect success of nasal mucosal tolerance induction

AIMS

Nasal tolerance induction with autoantigens can effectively protect against a variety of experimental models of autoimmune disease. The aims of this study were to characterise the dosage and kinetics of inhibition of experimental autoimmune uveoretinitis (EAU) via intranasal administration of the uveitogenic antigen interphotoreceptor retinal binding protein (IRBP) in the murine model of IRBP induced EAU.

METHODS

B10RIII mice were tolerised by intranasal administration of IRBP either with a long term multiple low dose or a short term/high dosing regimen before subcutaneous immunisation with IRBP in complete Freund's adjuvant (CFA). On day 15 post-immunisation, mice were killed and eyes were removed for histological examination and quantification of inflammatory cell infiltration and degree of target organ (rod outer segment, ROS) destruction.

RESULTS

Nasal administration of multiple low doses of IRBP (1 microg or 3 microg IRBP per mouse per day for 10 days) significantly protected mice from IRBP induced EAU. Short term/high dose regimens were only effective when given either as a single or, at most, as two consecutive doses (40 microg per dose). Multiple doses in the range of 45-120 microg over 3 days afforded no protection.

CONCLUSIONS

These results indicate that both dose and frequency of intranasal antigen administration are pivotal to tolerance induction and subsequent suppression of T cell mediated autoimmune disease.

Uveitogenic epitopes of retinal S-antigen are generated in vivo via an alternative antigen-presentation pathway

We have found that different antigen-processing pathways are involved in the induction of experimental autoimmune uveoretinitis (EAU) by the retinal autoantigens S-antigen and interphotoreceptor retinoid-binding protein (IRBP). Although in vitro T-cell proliferative responses to IRBP were completely inhibited in the presence of irreversible cysteine protease inhibitors, no significant reduction of S-antigen proliferative responses was found. Furthermore, acidic proteolysis of S-antigen by the cysteine protease cathepsin B prior to immunization radically reduced pathogenicity (disease severity). In addition, in vitro processing of S-antigen, but not IRBP, was also found to be resistant to the action of cycloheximide and lysosomotropic agents, inhibition of proliferation only occurring after extended exposure of antigen-presenting cells to methyl amine or high concentrations of chloroquine. These data indicate that an alternative pathway of antigen processing exists for S-antigen, which is independent of processing within the normal endolysosomal pathway and that uveitogenic peptides of naturally processed S-antigen bind to major histocompatibility complex class II antigens either at the cell surface or within very early endosomes where cathepsin B is inactive.

Marrow-derived activated macrophages are required during the effector phase of experimental autoimmune uveoretinitis in rats

PURPOSE

Experimental autoimmune uveoretinitis (EAU), an established model for human endogenous (autoimmune) posterior uveitis, is a CD4+ T cell-mediated disease inducible in Lewis rats by intradermal inoculation with retinal antigens. Immunohistochemical studies have previously documented the lymphocyte profiles during various stages of the disease process. The purpose of the present study was to investigate the role of macrophages in EAU.

METHODS

EAU was induced in Lewis rats, and the effect of macrophage depletion, using the drug dichlorodimethylene diphosphonate (Cl2MDP) encapsulated in liposomes and administered intravenously, was assessed based on the clinical and histological profile of the disease.

RESULTS

The results have shown that in control animals macrophages occur early, feature prominently throughout the course of the disease and display considerable heterogeneity: marrow-derived ED1+ cells and ED3+ cells are the major infiltrating cells, with many cells also expressing ED7 and ED8. In contrast, few cells expressed the ED2 antigen during EAU, even though ED2+ "resident" macrophages occur in the normal choroid. Macrophage depletion, using intravenously injected dichloromethylene diphosphonate (Cl2MDP) enclosed in liposomes, caused a delay in the onset and a reduction in the severity of EAU when administered during the "effector" stage of the disease, i.e. 9-11 days after inoculation with retinal antigen. The delay in disease onset was greater when liposomes were mannosylated and was accompanied by a reduction in the overall inflammatory cell infiltrate into the eye and reduced tissue damage. In addition, there was a reduction in the level of expression of MHC Class II antigen and CR3 (ED7) antigen, a marker of macrophage activation, in Cl2MDP-treated animals compared to controls.

CONCLUSION

These results suggest that blood-borne, activated macrophages are major effectors of tissue damage during EAU.

The distribution of immune cells in the uveal tract of the normal eye

Inflammatory and immune-mediated diseases of the eye are not purely the consequence of infiltrating inflammatory cells but may be initiated or propagated by immune cells which are resident or trafficking through the normal eye. The uveal tract in particular is the major site of many such cells, including resident tissue macrophages, dendritic cells and mast cells. This review considers the distribution and location of these and other cells in the iris, ciliary body and choroid in the normal eye. The uveal tract contains rich networks of both resident macrophages and MHC class II+ dendritic cells. The latter appear strategically located to act as sentinels for capturing and sampling blood-borne and intraocular antigens. Large numbers of mast cells are present in the choroid of most species but are virtually absent from the anterior uvea in many laboratory animals; however, the human iris does contain mast cells. Small numbers of what are presumed to be trafficking lymphocytes are present in the uveal tract of normal eyes. There is little data available on the presence or absence of eosinophils. The role of these various cell types in immune homeostasis and ocular inflammation is briefly considered.

Monocyte-induced cytokine expression in cultured human retinal pigment epithelial cells

Monocytes and retinal pigment epithelial cells are intimately associated in membranes of eyes with proliferative vitreoretinopathy and in certain types of uveitis. The goal of this study was to determine whether monocytes modulate cytokine expression in retinal pigment epithelial cells, and if so, to identify the monocyte products responsible for this effect. Cultured human retinal pigment epithelial cells were exposed to varying concentrations of monocyte-conditioned medium from unstimulated human monocytes for 1-48 hr, or from monocytes prestimulated with lipopolysaccharide. mRNA expression of interleukin-1 beta, interleukin-6, interleukin-8, melanoma growth stimulating activity/gro alpha and gamma, macrophage colony stimulating factor, transforming growth factor-beta 2, basic fibroblast growth factor and activin beta A chain was determined by reverse transcription polymerase chain reaction. Protein secretion of selected cytokines, interleukin-1 beta, interleukin-6, interleukin-8, macrophage colony stimulating factor and transforming growth factor-beta 2 was measured in RPE-conditioned medium by ELISA. Retinal pigment epithelial cells constitutively expressed mRNA for interleukin-6, macrophage colony stimulating factor, transforming growth factor-beta 2, basic fibroblast growth factor and activin beta A chain. Interleukin-1 beta, melanoma growth stimulating activity/gro alpha and gamma and interleukin-8 were not expressed under basal conditions. Stimulated monocyte-conditioned medium markedly induced mRNA of all cytokines except basic fibroblast growth factor and transforming growth factor-beta 2 in a dose- and time-dependent manner. Unstimulated monocyte-conditioned medium was a less potent inducing agent, but still enhanced mRNA expression of interleukin-6, interleukin-8 and melanoma growth stimulating activity/gro alpha. Stimulated monocyte-conditioned medium also induced a time-dependent increase in interleukin-6, Interleukin-8, macrophage colony stimulation factor and transforming growth factor-beta 2, but not interleukin-1 beta protein secretion (p < 0.05 for all time points). Neutralizing antibodies to interleukin-1 beta, or tumour necrosis factor alpha, but not interleukin-1 alpha, significantly reduced cytokine mRNA expression induced by stimulated monocyte-conditioned medium. The combination of all three neutralizing antibodies almost entirely eliminated monocyte-induced mRNA expression and protein production of all cytokines studied. Activated monocytes secrete a heterogeneous mixture of products that together strongly induce expression of multiple cytokines in human retinal pigment epithelial cells. Most if not all of the inducing effect can be accounted for by interleukin-1 beta and tumour necrosis factor alpha. Because cytokines have been implicated in proliferative vitreoretinopathy and uveitis, monocyte-mediated cytokine expression by RPE cells may serve to initiate and perpetuate these diseases.

Immunomodulation of experimental autoimmune uveoretinitis: a model of tolerance induction with retinal antigens

Experimental autoimmune uveoretinitis (EAU) is a CD4+ T-lymphocyte mediated inflammation of the uveal tract and retina. As a model of human posterior uveitis it permits further understanding of the underlying immunopathogenesis of uveitis. It also allows for preclinical trials of immunosuppressive therapies and in vivo assessment of alternative strategies for immunointervention. This review highlights possible immunostrategic modalities which prevent the initiation or perpetuation of the immune response, and in particular reports on the novel effect of intranasal induction of tolerance with retinal antigens, prior to immunisation with retinal antigens. The mechanisms and potential application of this 'natural' method of immunosuppression in the treatment of autoimmune disease are discussed.

Retinal antigen specific lymphocytes, TCR-gamma delta T cells and CD5+ B cells cultured from the vitreous in acute sympathetic ophthalmitis

CD5+ B lymphocytes and TCR gamma-delta T lymphocytes, phenotypes implicated in the pathogenesis of autoimmune disease, were isolated from the vitreous in a case of acute sympathetic ophthalmitis. These cells were obtained using a method which allows the selective maintainance in vitro of in vivo activated T lymphocytes. Dual colour flow cytometry showed that after 3 days culture in IL-2 containing medium 61% of cells were CD5/CD19 + ve and 41% CD3/TCR gamma delta + ve. Of the total CD3 + ve population, 15% were gamma/delta negative. These cells formed a population which also responded in a proliferation assay to retinal antigens. Histologically the eye showed a marked mononuclear cell infiltration of the retina, ciliary body and choroid. Granulomatous lesions within the choroid contained lymphocytes, plasma cells and multinucleate giant cells. Immunocytochemistry showed lymphocyte populations to be predominantly CD2 + ve CD3 + ve T lymphocytes of the CD4 sub-set. Distribution of monocytes/macrophages throughout the lesions and restriction of B-lymphocytes to granulomata were all consistent with a DTH type reaction. Despite immunosuppressive therapy, the expression of activation antigens HLA-DR and ICAM-1 on infiltrating and resident ocular tissue cells was high, although IL-2 receptor (CD25) expression was virtually absent. Flow cytometric analysis of peripheral blood cells prior to treatment with Cyclosporin-A showed systemic activation of lymphocytes, with high levels of HLA-DR and CD25 expression and a raised CD4/CD8 ratio.

Antigen processing and presentation in the eye: a review

The recognition event between self-antigen, the MHC and the T cell receptor has become the target for potential immunotherapy of T cell mediated autoimmune disease. For this approach to succeed in uveoretinitis, uniformity in T cell receptor usage, restricted MHC usage and limited epitope recognition by individuals would be required. In this study we have shown that despite clonal heterogeneity of response to multideterminate retinal extract antigens, proliferation to the antigens tested was restricted by the IA MHC class II molecule. Different patterns of reactivity to retinal antigens in the presence of various protease inhibitors was observed. Natural processing of IRBP appears to be complex, requiring a number of enzymes to generate immunogenic fragments, in contrast, for S-antigen, plasmin alone may suffice. The RPE cells which are potential processors and presenters of retinal antigens produce PGE2 and may act as suppressors of ocular inflammation.