Experimental autoimmune uveoretinitis: a model system for immunointervention: a review

Blocking the inflammasome: A novel approach to treat uveitis

Uveitis is a complex ocular inflammatory disease often accompanied by bacterial or viral infections (infectious uveitis) or underlying autoimmune diseases (non-infectious uveitis). Treatment of the underlying infection along with corticosteroid-mediated suppression of acute inflammation usually resolves infectious uveitis. However, to develop more effective therapies for non-infectious uveitis and to better address acute inflammation in infectious disease, an improved understanding of the underlying inflammatory pathways is needed. In this review, we discuss the disease aetiology, preclinical in vitro and in vivo uveitis models, the role of inflammatory pathways, as well as current and future therapies. In particular, we highlight the involvement of the inflammasome in the development of non-infectious uveitis and how it could be a future target for effective treatment of the disease.

Cytokine Signaling Protein 3 Deficiency in Myeloid Cells Promotes Retinal Degeneration and Angiogenesis through Arginase-1 Up-Regulation in Experimental Autoimmune Uveoretinitis

The suppressor of cytokine signaling protein 3 (SOCS3) critically controls immune cell activation, although its role in macrophage polarization and function remains controversial. Using experimental autoimmune uveoretinitis (EAU) as a model, we show that inflammation-mediated retinal degeneration is exaggerated and retinal angiogenesis is accelerated in mice with SOCS3 deficiency in myeloid cells (LysM^Cre/+SOCS3^fl/fl). At the acute stage of EAU, the population of infiltrating neutrophils was increased and the population of macrophages decreased in LysM^Cre/+SOCS3^fl/fl mice compared with that in wild-type (WT) mice. Real-time RT-PCR showed that the expression of tumor necrosis factor-α, IL-1β, interferon-γ, granulocyte-macrophage colony-stimulating factor, and arginase-1 was significantly higher in the LysM^Cre/+SOCS3^fl/fl EAU retina in contrast to the WT EAU retina. The percentage of arginase-1⁺ infiltrating cells was significantly higher in the LysM^Cre/+SOCS3^fl/fl EAU retina than that in the WT EAU retina. In addition, bone marrow-derived macrophages and neutrophils from the LysM^Cre/+SOCS3^fl/fl mice express significantly higher levels of chemokine (C-C motif) ligand 2 and arginase-1 compared with those from WT mice. Inhibition of arginase using an l-arginine analog amino-2-borono-6-hexanoic suppressed inflammation-induced retinal angiogenesis without affecting the severity of inflammation. Our results suggest that SOCS3 critically controls the phenotype and function of macrophages and neutrophils under inflammatory conditions and loss of SOCS3 promotes the angiogenic phenotype of the cells through up-regulation of arginase-1.

Novel everolimus-loaded nanocarriers for topical treatment of murine experimental autoimmune uveoretinitis (EAU)

In the present study, therapeutic effect of topically applied everolimus (EV)-loaded methoxy-poly(ethylene-glycol)-hexyl substituted poly (lactic acid) (mPEGhexPLA) nanocarriers on experimental autoimmune uveoretinitis (EAU) were investigated. EAU was induced in B10.RIII mice via immunization with human interphotoreceptor retinoid-binding protein peptide 161-180 (hIRBPp161-180) in complete Freund's adjuvant. Everolimus-loaded mPEGhexPLA (EV/mPEGhexPLA) nanocarriers were prepared by using a solvent evaporation method. On days 12-21 postimmunization (p.i.), the right eyes were treated five times daily either with 10 μl of 0.5% everolimus formulation or PBS (control). The EAU score of the eyes was determined histologically. On day 21 p.i., the peripheral immune responses were measured in serum, cervical lymph nodes (LN), and spleens via hIRBPp161-180-specific serum antibodies, cytokine secretion (ELISA), lymphocyte proliferation, and FoxP3+ regulatory T cells (Treg; flow cytometry). Compared to the PBS-treated mice, unilateral topical everolimus treatment significantly reduced EAU severity in both eyes (p < .05). The treatment reduced the antigen (Ag)-specific hIRBPp161-180-induced proliferation (p < .05), IL-2, IL-17, and IFN-γ secretion from cells isolated from the left and right cervical LN (p < .05). Under everolimus treatment, IL-10 secretion and CD4⁺CD25⁺FoxP3⁺ Treg frequency from cervical LN were enhanced. The proliferative response and cytokine secretion as well as the frequency of splenic Treg were almost unchanged. Topical administration of an everolimus formulation improved EAU in both eyes. The effect might also be related to systemic immunosuppressive effects, as several systemic cellular immune responses were influenced.

Experimental autoimmune uveitis and other animal models of uveitis: An update

Over the past several decades, animal models of autoimmune uveitis directed at eye-specific antigens (Ags) have been developed. These have allowed researchers to understand the basic mechanisms that lead to these diseases and also recently helped the researchers in translational research for therapeutic interventions. Experimental autoimmune uveitis (EAU) is an animal disease model of human endogenous uveitis and can be induced in susceptible animals by immunization with retinal Ags. Ever since the first description of EAU in mice in 1988, several animal models of uveitis has been described by researchers. Disease-specific model for cytomegalovirus retinitis and tubercular uveitis has evolved our understanding of these complex entities. Endotoxin induced uveitis is another useful model for anterior uveitis, which is not an autoimmune process and is triggered by injection of bacterial endotoxin (lipopolysaccharides) resulting in a rapid short lasting uveitis. The current article will give an insight into the various EAU animal models and their current implications in translational research. The article will also highlight the different grading systems for EAU in the animal model.

Targeting the complement system for the management of retinal inflammatory and degenerative diseases

The retina, an immune privileged tissue, has specialized immune defense mechanisms against noxious insults that may exist in diseases such as age-related macular degeneration (AMD), diabetic retinopathy (DR), uveoretinitis and glaucoma. The defense system consists of retinal innate immune cells (including microglia, perivascular macrophages, and a small population of dendritic cells) and the complement system. Under normal aging conditions, retinal innate immune cells and the complement system undergo a low-grade activation (parainflammation) which is important for retinal homeostasis. In disease states such as AMD and DR, the parainflammatory response is dysregulated and develops into detrimental chronic inflammation. Complement activation in the retina is an important part of chronic inflammation and may contribute to retinal pathology in these disease states. Here, we review the evidence that supports the role of uncontrolled or dysregulated complement activation in various retinal degenerative and angiogenic conditions. We also discuss current strategies that are used to develop complement-based therapies for retinal diseases such as AMD. The potential benefits of complement inhibition in DR, uveoretinitis and glaucoma are also discussed, as well as the need for further research to better understand the mechanisms of complement-mediated retinal damage in these disease states.

Evaluation of mouse experimental autoimmune uveoretinitis by spectral domain optical coherence tomography

AIMS

To evaluate the efficacy of spectral domain optical coherence tomography (SD-OCT) in monitoring the development of mouse experimental autoimmune uveoretinitis (EAU) as an animal model of endogenous uveitis, and to develop an OCT-based grading system for EAU severity.

METHODS

C57BL/6 mice were immunised with human interphotoreceptor retinoid-binding protein (amino acid sequence 1-20) peptide and complete Freund's adjuvant to induce EAU. The development of EAU was monitored by SD-OCT serially throughout the disease course, and the images were graded from 1 to 4 and compared with the clinical and histopathological grades.

RESULTS

SD-OCT images depicted retinal lamella structures including the inner segment/outer segment (IS/OS) line in normal mice. Retinal structural changes were observed on SD-OCT images in mice that developed EAU clinically scored as grade 1 or higher, which precisely corresponded to the pathological findings. The SD-OCT images of EAU were graded as follows: grade 1, a few infiltrating cells in the vitreous and retina; grade 2, increased vitreous cells, retinal vasculitis, and granulomatous lesion; grade 3, cell infiltration into the whole retina, disappearance of IS/OS line, and destruction of the retinal layer structure; and grade 4, disappearance of the outer retina. The SD-OCT grade of EAU based on these criteria correlated significantly with both the clinical grade (R(2)=0.282, p<0.005) and histopathological grade (R(2)=0.846, p<0.0001).

CONCLUSIONS

SD-OCT is useful for evaluating the development and severity of mouse EAU. The SD-OCT scoring system we developed accurately reflects clinical and histopathological changes.

Comparative analysis of induced vs. spontaneous models of autoimmune uveitis targeting the interphotoreceptor retinoid binding protein

Animal models of autoimmunity to the retina mimic specific features of human uveitis, but no model by itself reproduces the full spectrum of human disease. We compared three mouse models of uveitis that target the interphotoreceptor retinoid binding protein (IRBP): (i) the "classical" model of experimental autoimmune uveitis (EAU) induced by immunization with IRBP; (ii) spontaneous uveitis in IRBP T cell receptor transgenic mice (R161H) and (iii) spontaneous uveitis in Autoimmune Regulator (AIRE)(-/-) mice. Disease course and severity, pathology and changes in visual function were studied using fundus imaging and histological examinations, optical coherence tomography and electroretinography. All models were on the B10.RIII background. Unlike previously reported, IRBP-induced EAU in B10.RIII mice exhibited two distinct patterns of disease depending on clinical scores developed after onset: severe monophasic with extensive destruction of the retina and rapid loss of visual signal, or lower grade with a prolonged chronic phase culminating after several months in retinal degeneration and loss of vision. R161H and AIRE(-/-) mice spontaneously developed chronic progressive inflammation; visual function declined gradually as retinal degeneration developed. Spontaneous uveitis in R161H mice was characterized by persistent cellular infiltrates and lymphoid aggregation, whereas AIRE(-/-) mice characteristically developed multi-focal infiltrates and severe choroidal inflammation. These data demonstrate variability and unique distinguishing features in the different models of uveitis, suggesting that each one can represent distinct aspects of uveitis in humans.

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.

Use of optical coherence tomography and electroretinography to evaluate retinal pathology in a mouse model of autoimmune uveitis

Experimental autoimmune uveoretinitis (EAU) in mice is a model for human autoimmune uveitis. Longitudinal follow-up is only possible by non-invasive techniques, but the information obtained by visual fundus examination can be limited. We therefore evaluated the efficacy of optical coherence tomography (OCT) and electroretinography (ERG) to monitor pathological and functional changes of the retina in vivo. OCT imaging and ERG recording as a measure of visual function were compared with visual fundoscopic imaging and histology findings in the same mouse. Our results showed that OCT imaging of the retina was well correlated with clinical and histological observations in mice during EAU. However, OCT imaging was more sensitive than fundoscopic imaging in detecting the cell infiltrates at the early phase of disease onset. Furthermore, by allowing multi-layer cross- and horizontal-sectional visualizations of retinal lesions longitudinally in a noninvasive fashion, OCT added information that could not be obtained by fundoscopic and histological examinations. Lastly, retinal thickness obtained by OCT imaging provided a key indicator reflecting disease activity, which showed a close association with visual dysfunction as measured by ERG recordings in EAU mice. Thus, our findings demonstrate that OCT is a highly sensitive and reliable technique, and a valuable method for the semi-quantitative evaluation of retinal inflammation in vivo in the mouse.

Complement expression in retinal pigment epithelial cells is modulated by activated macrophages

Complement activation is involved in a variety of retinal diseases. We have shown previously that a number of complement components and regulators can be produced locally in the eye, and that retinal pigment epithelial (RPE) cells are the major source of complement expression at the retina-choroidal interface. The expression of complement components by RPE cells is regulated by inflammatory cytokines. Under aging or inflammatory conditions, microglia and macrophages accumulate in the subretinal space, where they are in close contact with RPE cells. In this study, we investigated the effect of activated macrophages on complement expression by RPE cells. Mouse RPE cells were treated with the supernatants from un-activated bone marrow-derived macrophages (BM-DMs), the classically activated BM-DMs (M1) and different types of the alternatively activated BM-DMs (M2a by IL-4, M2b by immune complex and lipopolysaccharide (LPS), M2c by IL-10). The expression of inflammatory cytokines and complement genes by RPE cells were determined by real-time RT-PCR. The protein expression of CFB, C3, C1INH, and C1r was examined by Western blot. Our results show that un-stimulated RPE cells express a variety of complement-related genes, and that the expression levels of complement regulators, including C1r, factor H (CFH), DAF1, CD59, C1INH, Crry, and C4BP genes are significantly higher than those of complement component genes (C2, C4, CFB, C3, and C5). Macrophage supernatants increased inflammatory cytokine (IL-1β, IL-6, iNOS), chemokine (CCL2) and complement expression in RPE cells. The supernatants from M0, M2a and M2c macrophages mildly up-regulated (2-3.5-fold) CFB, CFH and C3 gene expression in RPE cells, whereas the supernatants from M1 and M2b macrophages massively increased (10-30-fold) CFB and C3 gene expression in RPE cells. The expression of other genes, including C1r, C2, C4, CFH, Masp1, C1INH, and C4BP in RPE cells was also increased by the supernatants of M1 and M2b macrophages; however, the increment levels were significantly lower than CFB and C3 genes. M1 and M2b macrophage supernatants enhanced CFB (Bb fragment) protein expression and C3 secretion by RPE cells. M1 macrophages may affect complement expression in RPE cells through the STAT1 pathway. Our results suggest that under inflammatory conditions, activated macrophages could promote the alternative pathway of complement activation in the retina via induction of RPE cell CFB and C3 expression.

Therapeutic targeting of STAT3 (signal transducers and activators of transcription 3) pathway inhibits experimental autoimmune uveitis

Mice with targeted deletion of STAT3 in CD4⁺ T-cells do not develop experimental autoimmune uveitis (EAU) or experimental autoimmune encephalomyelitis (EAE), in part, because they cannot generate pathogenic Th17 cells. In this study, we have used ORLL-NIH001, a small synthetic compound that inhibits transcriptional activity of STAT3, to ameliorate EAU, an animal model of human posterior uveitis. We show that by attenuating inflammatory properties of uveitogenic lymphocytes, ORLL-NIH001 inhibited the recruitment of inflammatory cells into the retina during EAU and prevented the massive destruction of the neuroretina caused by pro-inflammatory cytokines produced by the autoreactive lymphocytes. Decrease in disease severity observed in ORLL-NIH001-treated mice, correlated with the down-regulation of α4β1 and α4β7 integrin activation and marked reduction of CCR6 and CXCR3 expression, providing a mechanism by which ORLL-NIH001 mitigated EAU. Furthermore, we show that ORLL-NIH001 inhibited the expansion of human Th17 cells, underscoring its potential as a drug for the treatment of human uveitis. Two synthetic molecules that target the Th17 lineage transcription factors, RORγt and RORα, have recently been suggested as potential drugs for inhibiting Th17 development and treating CNS inflammatory diseases. However, inhibiting STAT3 pathways completely blocks Th17 development, as well as, prevents trafficking of inflammatory cells into CNS tissues, making STAT3 a more attractive therapeutic target. Thus, use of ORLL-NIH001 to target the STAT3 transcription factor, thereby antagonizing Th17 expansion and expression of proteins that mediate T cell chemotaxis, provides an attractive new therapeutic approach for treatment of posterior uveitis and other CNS autoimmune diseases mediated by Th17 cells.

Persistent inflammation subverts thrombospondin-1-induced regulation of retinal angiogenesis and is driven by CCR2 ligation

Neovascular retinal disease is a leading cause of blindness orchestrated by inflammatory responses. Although noninfectious uveoretinitis is mediated by CD4(+) T cells, in the persistent phase of disease, angiogenic responses are observed, along with degeneration of the retina. Full clinical manifestation relies on myeloid-derived cells, which are phenotypically distinct from, but potentially sharing common effector responses to age-related macular degeneration. To interrogate inflammation-mediated angiogenesis, we investigated experimental autoimmune uveoretinitis, an animal model for human uveitis. After the initial acute phase of severe inflammation, the retina sustains a persistent low-grade inflammation with tissue-infiltrating leukocytes for over 4 months. During this persistent phase, angiogenesis is observed as retinal neovascular membranes that arise from inflamed venules and postcapillary venules, increase in size as the disease progresses, and are associated with infiltrating arginase-1(+) macrophages. In the absence of thrombospondin-1, retinal neovascular membranes are markedly increased and are associated with arginase-1(-) CD68(+) macrophages, whereas deletion of the chemokine receptor CCR2 resulted in reduced retinal neovascular membranes in association with a predominant neutrophil infiltrate. CCR2 is important for macrophage recruitment to the retina in experimental autoimmune uveoretinitis and promotes chronicity in the form of a persistent angiogenesis response, which in turn is regulated by constitutive expression of angiogenic inhibitors like thrombospondin-1. This model offers a new platform to dissect the molecular and cellular pathology of inflammation-induced ocular angiogenesis.

The multifactorial nature of retinal vascular disease

Retinal vascular disease is the most common cause of macular edema (ME). While there are several etiologies of vascular compromise and subsequent macular leakage, diabetic retinopathy is the most prevalent and continues to challenge ophthalmologists and frustrate patients due to its refractory nature. In response to this epidemic, diabetic ME (DME) along with cystoid ME (CME) have been areas of active investigation both in the clinic and the laboratory. Several decades of basic science research have revealed a growing and complex array of cytokine growth factors and proinflammatory mediators which are capable of inciting the cellular changes that result in accumulation of fluid within the retina. Much of this new molecular foundation provides the current and fundamental scaffold for understanding the pathologic process of ME while simultaneously identifying potential therapeutic targets. Whereas CME has classically been treated with corticosteroids and nonsteroidal antiinflammatory drugs, recent clinical studies have demonstrated improved visual outcomes for DME treatment with light focal/grid laser, corticosteroids and anti-vascular endothelial growth factor antibodies. Yet, each of these treatments has differential effects on the multifactorial mechanisms of ME. This article reviews the anatomical, cellular and molecular derangements associated with ME and highlights specific pathways targeted by current treatments.

Peripheral CD25 positive T lymphocytes with biased T cell receptor Vbeta gene usage in autoimmune endogenous posterior uveitis

Aims-To determine T cell receptor (TCR) Vbeta gene usage in peripheral blood T lymphocytes of patients with endogenous posterior uveitis (EPU). If biased TCR variable (V) gene usage occurs in this autoimmune disease, it should be detectable in immune activated peripheral blood T cells in vivo.Methods-Relative proportions of each Vbeta gene family expressed in total peripheral blood lymphocytes (PBL) and in vivo activated (CD25+) T cells from patients with EPU and controls were determined using the anchored polymerase chain reaction (anchored PCR) in conjunction with a novel hybridisation assay. The TCR Vbeta repertoires seen in these cell populations were then compared.Results-Vbeta1 usage within the CD25+ lymphocytes of patients with EPU was substantially elevated (mean +/- SD 15 +/-9%) compared with control CD25+ cells (3.3 +/-2.4%).Conclusions-By contrasting the repertoires of these cell populations, biased TCR Vbeta gene usage was detected in patients with EPU, namely increased usage of Vbeta1 in CD25+ T cells from peripheral blood of these patients. This approach of directly analysing the activated T cells in blood, using bulk PBL as an internal control, has wide applicability where specific T cell subpopulations are thought to play an important aetiopathological role.

TNFR1-dependent regulation of myeloid cell function in experimental autoimmune uveoretinitis

Experimental autoimmune uveoretinitis is an autoimmune disease induced in mice, which involves the infiltration of CD11b(+) macrophages and CD4(+) T cells into the normally immune-privileged retina. Damage is produced in the target organ following the activation of Th1 and Th17 T cells and by the release of cytotoxic mediators such as NO by activated macrophages. The majority of immune cells infiltrating into the retina are CD11b(+) myeloid cells, but, despite the presence of these APCs, relatively limited numbers of T cells are observed in the retina during the disease course. These T cells do not proliferate when leukocytes are isolated from the retina and restimulated in vitro, although they do produce both IFN-gamma and IL-17. T cell proliferation was restored by depleting the myeloid cells from the cultures and furthermore those isolated myeloid cells were able to regulate the proliferation of other T cells. The ability of macrophages to regulate proliferation depends on activation by T cell-produced IFN-gamma and autocrine TNF-alpha signaling in the myeloid cells via TNFR1. In the absence of TNFR1 signaling, relative T cell expansion in the retina is increased, indicating that regulatory myeloid cells may also act in vivo. However, TNFR1 signaling is also required for macrophages, but not T cells, to migrate into the target organ. Thus, in TNFR1 knock out mice, the amplification of autoimmunity is limited, leading to resistance to experimental autoimmune uveoretinitis induction.

A suppressive oligodeoxynucleotide inhibits ocular inflammation

Synthetic oligodeoxynucleotides (ODN) expressing 'suppressive' TTAGGG motifs down-regulate a variety of proinflammatory and T helper type 1 (Th1)-mediated pathological immune responses. The ability of the archetypal suppressive ODN A151 to inhibit ocular inflammation was examined in two murine models: experimental autoimmune uveitis, induced by immunization with a retinal antigen, interphotoreceptor retinoid-binding protein (IRBP) and adoptively transferred ocular inflammation, induced by transferring Th1 cells specific to hen egg lysozyme (HEL) into recipient mice that express HEL in their eyes. A151 treatment suppressed the inflammation in both models. In addition, A151 inhibited IRBP-specific cytokine production and lymphocyte proliferation in mice immunized with IRBP. These findings suggest that suppressive ODN affects both afferent and efferent limbs of the immunopathogenic process and may be of use in the treatment of autoimmune ocular inflammation.

A clinical grading system for retinal inflammation in the chronic model of experimental autoimmune uveoretinitis using digital fundus images

Experimental autoimmune uveoretinitis (EAU), a widely used animal model of human posterior/pan-uveitis, is extremely valuable in allowing understanding of the pathogenesis of uveitis as well as in developing new treatments. Depending on the animal strain and immunization protocol used, the clinical course of EAU can be acute, severe and involving the anterior and posterior part of the eye, or chronic, mild and involving only the posterior part of the eye. Clinical signs of EAU can be examined by bio-microscopy. Using appropriate criteria EAU can be quantitatively evaluated clinically in living animals. However, correlation of research within different laboratories is difficult since clinical grading systems are subjective and susceptible to considerable variability. In this study, we have developed a recordable, image-based clinical grading system for the chronic models of EAU. Fundus images were taken from EAU mice using an endoscopic imaging system. Fundus changes were classified as (1) inflammatory changes (including optic disc inflammation, vasculitis and retinal tissue inflammation) and (2) retinal structural damage. Each element was scored separately based on the severity of the lesions, and the average score of the three inflammatory elements was used as the overall EAU clinical inflammation grade of the eye. The validity and reproducibility of the grading system was tested using a set of images scored independently in a masked manner by 5 individuals. The grading system proved robust, easy to use and reliable. We offer this image-based EAU clinical grading system as a useful quantitative evaluation method for clinical grading of the severity of inflammation in the chronic EAU model, in which the inflammation can be mild and mainly involves posterior part of the eye.

In vivo imaging of the immune response in the eye

The immune system is governed by dynamic events involving in part direct intercellular interactions between an immune cell and other cells or the cell's environment. Owing to its unique optical characteristics, the eye offers remarkable opportunities for the analysis of the immune system by intravital microscopy. In this review, we present a brief overview of the current state of knowledge of leukocyte trafficking in each of three anatomically distinct and medically important regions of the eye (cornea, iris, retina) as determined by the application of intravital microscopy to animal models of disease. Additionally, we discuss the use of ocular imaging in patients and volunteers. Finally, we examine the future prospects for this field in terms of its potential for impacting our understanding of fundamental immunological phenomena.

Mechanisms of leukocyte migration across the blood-retina barrier

Immune-mediated inflammation in the retina is regulated by a combination of anatomical, physiological and immuno-regulatory mechanisms, referred to as the blood-retina barrier (BRB). The BRB is thought to be part of the specialised ocular microenvironment that confers protection or "immune privilege" by deviating or suppressing destructive inflammation. The barrier between the blood circulation and the retina is maintained at two separate anatomical sites. These are the endothelial cells of the inner retinal vasculature and the retinal pigment epithelial cells on Bruch's membrane between the fenestrated choroidal vessels and the outer retina. The structure and regulation of the tight junctions forming the physical barrier are described. For leukocyte migration across the BRB to occur, changes are needed in both the leukocytes themselves and the cells forming the barrier. We review how the blood-retina barrier is compromised in various inflammatory diseases and discuss the mechanisms controlling leukocyte subset migration into the retina in uveoretinitis in more detail. In particular, we examine the relative roles of selectins and integrins in leukocyte interactions with the vascular endothelium and the pivotal role of chemokines in selective recruitment of leukocyte subsets, triggering adhesion, diapedesis and migration of inflammatory cells into the retinal tissue.

Upregulation of neurotrophic factor-related gene expression in retina with experimental autoimmune uveoretinitis by intravitreal injection of tacrolimus (FK506)

AIM

The current study was designed to determine whether intravitreal injection of tacrolimus (FK506) modulates the gene expression of neurotrophic factor-related molecules in the retina from eyes with induced experimental autoimmune uveoretinitis (EAU) in rats.

METHODS

Rats were immunised with interphotoreceptor retinoid binding protein peptide (R14) and given intravitreal injection of tacrolimus on day 12 after immunisation. As control, immunised rats received intravitreal injection of vehicle. On day 15 after immunisation, changes in the genetic programme associated with neuroprotection and inflammatory responses in the retinas from both groups were determined by DNA microarray analyses and confirmed by real-time PCR analyses.

RESULTS

The gene expression of inflammatory responses was markedly reduced in tacrolimus-treated eyes. Genes for molecules associated with neuroprotection (oestrogen receptor, erythropoietin receptor, gamma-aminobutyric acid receptor, protein kinase C, glial cell line-derived neurotrophic factor receptor, fibroblast growth factor and neuropeptide Y receptor) were upregulated in the retinas from tacrolimus-treated eyes.

CONCLUSIONS

Intravitreal injection of tacrolimus modulated the genes related to neuroprotection in the retina during the ongoing process of EAU. This treatment may be useful for the neuroprotection of retina with severe uveitis as well as for immunosuppression in the uveitic eyes.

Anti-inflammatory property of the cannabinoid receptor-2-selective agonist JWH-133 in a rodent model of autoimmune uveoretinitis

Previous studies have shown that cannabinoids have anti-inflammatory and immune-modulating effects, but the precise mechanisms of action remain to be elucidated. In this study, we investigated the effect of JWH 133, a selective agonist for cannabinoid receptor 2, the main receptor expressed on immune cells, in a model of autoimmune disease, experimental autoimmune uveoretinitis (EAU). JWH 133 suppressed EAU in a dose-dependent manner (0.015-15 mg/kg), and the suppressive effect could be achieved in the disease-induction stage and the effector stage. Leukocytes from mice, which had been treated with JWH 133, had diminished responses to retinal peptide and mitogen Con A stimulation in vitro. In vivo JWH 133 treatment also abrogated leukocyte cytokine/chemokine production. Further in vitro studies indicated that JWH 133 down-regulated the TLR4 via Myd88 signal transduction, which may be responsible for its moderate, suppressive effect on antigen presentation. In vivo JWH 133 treatment (1 mg/kg) also suppressed leukocyte trafficking (rolling and infiltration) in inflamed retina as a result of an effect on reducing adhesion molecules CD162 (P-selectin glycoprotein ligand 1) and CD11a (LFA-1) expression on T cells. In conclusion, the cannabinoid agonist JWH 133 has a high in vivo, anti-inflammatory property and may exert its effect via inhibiting the activation and function of autoreactive T cells and preventing leukocyte trafficking into the inflamed tissue.

Intravitreal injection of Tacrolimus (FK506) suppresses ongoing experimental autoimmune uveoretinitis in Rats

AIM

To determine whether intravitreal injection of tacrolimus suppresses ongoing experimental autoimmune uveoretinitis (EAU) in rats.

METHODS

Rats were immunised with interphotoreceptor retinoid-binding protein peptide (R14) and given an intravitreal injection of tacrolimus on day 12 after immunisation. Intraocular inflammation was assessed by slit-lamp biomicroscopy and histopathological examination. Interferon gamma and tumour necrosis factor alpha protein levels in the ocular tissues were measured. Gene expression of chemokines was determined in ocular tissues by reverse transcription-polymerase chain reaction. To evaluate the systemic effect of intravitreal injection of tacrolimus, delayed-type hypersensitivity was measured by ear swelling.

RESULTS

Clinical and pathological scores showed that ocular inflammation of tacrolimus-treated eyes was markedly less than that of vehicle-treated eyes. The amount of interferon gamma and tumour necrosis factor alpha was considerably inhibited in tacrolimus-treated eyes. The gene expression of monocyte chemattractant protein-1 (MCP-1) and regulated upon activation, normal T cell expressed and secreted (RANTES) was markedly reduced in tacrolimus-treated eyes. Delayed-type hypersensitivity responses were not impaired in tacrolimus-treated rats.

CONCLUSIONS

Intravitreal injection of tacrolimus was highly effective in suppressing the ongoing process of EAU without any side effects on systemic cellular immunity. This treatment may be useful in the management of patients with severe uveitis.

Differentiation to the CCR2+ inflammatory phenotype in vivo is a constitutive, time-limited property of blood monocytes and is independent of local inflammatory mediators

It is proposed that CCR2+ monocytes are specifically recruited to inflammatory sites, whereas CCR2- monocytes are recruited to normal tissue to become resident macrophages. Whether these subsets represent separate lineages, how differential trafficking is regulated and whether monocytes undergo further differentiation is uncertain. Using a mouse model of autoimmune uveoretinitis we examined monocyte trafficking to the inflamed retina in vivo. We show that bone marrow-derived CD11b+ F4/80- monocytes require 24 to 48 h within the circulation and lymphoid system before acquiring the CCR2+ phenotype and trafficking to the inflamed retina is enabled. This phenotype, and the capacity to traffic were lost by 72 h. Monocyte CCR2 expression followed a similar time course in normal mice indicating that differentiation to an inflammatory phenotype is a constitutive, time-limited property, independent of local inflammatory mediators. Phenotypic analysis of adoptively transferred cells indicated that circulating inflammatory monocytes also differentiate into CD11c+ and B220+ dendritic cells and F4/80+ tissue macrophages in vivo. Our data supports the hypothesis of continuous extravasation and progressive differentiation over time of inflammatory monocytes in the circulation rather than replication within the actively inflamed tissue, and supports the concept of myeloid dendritic cell differentiation from trafficking monocytes under physiological conditions in vivo.

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.

Recruitment of IFN-gamma-producing (Th1-like) cells into the inflamed retina in vivo is preferentially regulated by P-selectin glycoprotein ligand 1:P/E-selectin interactions

Although there is evidence that altering the Th1/Th2 balance toward Th2 cells may be important in the resolution of Th1-type autoimmune disease, adoptive transfer of Th2 cells is not effective in protecting against Th1-type disease and may cause disease. Therefore, we examined the recruitment of Th1- and Th2-like cells into the retina in the murine autoimmune disease experimental autoimmune uveoretinitis. CD4 T cells were polarized in vitro to IFN-gamma-producing Th1-like cells and non-IFN-gamma-producing Th2-like cells, labeled, and adoptively transferred. Trafficking to the retina in vivo was evaluated by scanning laser ophthalmoscopy and infiltration by confocal microscopy. There were more rolling and adherent Th1-like cells and they rolled more slowly than did Th2-like cells. Th1-like cells were preferentially recruited into the retinal parenchyma at both initiation and resolution. Surface P-selectin glycoprotein ligand 1 (PSGL-1) and LFA-1 were up-regulated on both populations but were expressed at higher levels on Th1-like cells. Up-regulation of CD44 expression was higher on Th2-like cells. P-selectin, E-selectin, and ICAM-1 are up-regulated on postcapillary venules in the retina. Pretreatment of Th1-like cells with anti-PSGL-1 inhibited rolling and infiltration of Th1-like cells but not Th2-like cells, providing direct in vivo evidence for the inability of Th2 to respond to P/E-selectin despite increased expression of PSGL-1. Anti-LFA-1 pretreatment inhibited infiltration of both Th1- and Th2-like cells, but more so Th-1. We suggest that random trafficking of activated T cells (both Th1 and Th2) across the blood-retina barrier is mediated by CD44:CD44R and LFA-1:ICAM-1, whereas preferential recruitment of Th1 cells is mediated by PSGL-1:P/E-selectin.

Reduction in shear stress, activation of the endothelium, and leukocyte priming are all required for leukocyte passage across the blood--retina barrier

The passage of leukocytes across the blood-retina barrier at the early stages of an inflammatory reaction is influenced by a complex series of interactions about which little is known. In particular, the relationship between hydrodynamic factors, such as shear stress and leukocyte velocity, to the adherence and subsequent extravasation of leukocytes into the retina is unclear. We have used a physiological method, scanning laser ophthalmoscopy, to track labeled leukocytes circulating in the retina, followed by confocal microscopy of retinal flatmounts to detect infiltrating cells at the early stage of experimental autoimmune uveitis. This has shown that retinal vessels are subjected to high shear stress under normal circumstances. During the inflammatory reaction, shear stress in retinal veins is reduced 24 h before leukocyte infiltration. This reduction is negatively correlated with leukocyte rolling and sticking in veins and postcapillary venules, the sites of leukocyte extravasation. Activation of vascular endothelial cells is also a prerequisite for leukocyte rolling and infiltration. In addition, antigen priming of leukocytes is influential at the early stage of inflammation, and this is seen clearly in the reduction in rolling velocity and adherence of the primed leukocytes in activated retinal venules, 9 days postimmunization.

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.

Immunological effects of allopurinol in the treatment of experimental autoimmune uveitis (EAU) after onset of the disease

PURPOSE

Allopurinol reduces oxidative tissue damage and exerts immunomodulating effects in the treatment of experimental autoimmune uveitis (EAU). However, the mechanism of the immunologic pathway remains unclear. In previous studies, treatment was started at the time of immunization. Therefore, whether allopurinol prevents the onset of the disease (i.e., acts in a protective manner) is not known.

METHODS

Sixteen male Lewis rats were used: 6 EAU without therapy [control]; 4 EAU with allopurinol treatment starting 7 days after immunization [AL7]; and 6 EAU with allopurinol treatment starting 11 days after immunization [AL11]. Their sera were tested against Western blots of sodium dodecyl sulfate-polyacrylamide gel electrophoresis of retinal proteins. Based on digital image analysis, analysis of discriminance was done.

RESULTS

There were significant immunomodulating effects in both therapy groups (Wilks' lambda 0.001, P < 0.008) compared to controls. However, the effects were more pronounced in the AL7 group, where peak intensities and the number of peaks were markedly more reduced.

CONCLUSIONS

Immunomodulating effects of allopurinol can be detected even if the therapy starts after the onset of the disease. Thus allopurinol strongly influences the immunologic mechanism in this model of autoimmune disease. In view of its minimal side effects, the drug could be a promising alternative for the therapy and prophylaxis of uveitis and other autoimmune diseases.

Allopurinol has immunomodulating activity following topical and systemic application in experimental autoimmune uveitis

PURPOSE

Allopurinol has beneficial effects in the systemic treatment of lens-induced uveitis and experimental autoimmune uveitis (EAU). This is believed to be due to a reduction of oxidative tissue damage through its dose-dependent free radical scavenging ability, and to an immunomodulating effect. The purpose of this study was to demonstrate the immunological effects on the IgG-antibody repertoire in EAU after topical and systemic allopurinol and steroids.

METHODS

We assigned 43 male Lewis rats to 6 different groups: healthy rats (BASE, n=3)

Xenopus IRBP, a phylogenetically remote protein, is uveitogenic in Lewis rats

Mammalian interphotoreceptor retinoid-binding proteins (IRBPs) are highly uveitogenic in Lewis rats. Xenopus laevis IRBP resembles mammalian IRBP in its four-fold structure, and has approximately 70% amino acid sequence identity with the bovine protein. This study investigated the uveitogenicity of recombinant Xenopus IRBP and two of its derived peptides in Lewis rats. Rats immunized with Xenopus IRBP developed uveoretinitis as well as pineal inflammation. The Xenopus molecule was, however, less immunopathogenic than the bovine IRBP. Of the two Xenopus IRBP peptides tested, 1180-1191 was remarkably uveitogenic, whereas sequence 521-540 exhibited low activity. It is assumed, therefore, that as with bovine IRBP, peptide 1180-1191 is the major uveitogenic sequence in Xenopus IRBP. The role individual residues of these peptides play in the immunopathogenic process is discussed. Our data thus demonstrate that despite its being phylogenetically remote, Xenopus IRBP is uveitogenic in Lewis rats

Dendritic cells and macrophages in the uveal tract of the normal mouse eye

BACKGROUND/AIMS

Dendritic cells (DC) and macrophages are components of the immune cell populations in the uveal tract whose density, distribution, turnover, and function may play a role in the maintenance of immunological homeostasis in the eye. Little is known of these cells in the mouse eye despite this being the predominant experimental model in many studies of ocular immune responses and immunoinflammatory mediated eye diseases. The aim of the present study was to obtain further immunophenotypic data on resident tissue macrophages and DC populations in the mouse uveal tract.

METHODS

Pieces of iris, ciliary body, and choroid dissected from perfusion fixed BALB/c mice were incubated whole in a variety of anti-macrophage and DC monoclonal antibodies (mAbs). Labelled cells were visualised using either single or double immunoperoxidase techniques.

RESULTS

Quantitative analysis and double immunolabelling revealed that 80% of F4/80(+) cells (a mAb that recognises both DC and macrophages) in the iris are macrophages (SER4(+)). The iris contained a network of Ia+ cells (412 (SD 130) cells/mm2) of which two thirds appear to be DC. A similar pattern was observed in the ciliary body and choroid. Only a few DC in the uveal tract were very weakly reactive for mAbs which recognise B7-1 (CD80), B7-2 (CD86), beta2 integrin (mAb N418), and multivesicular bodies associated with antigen presentation (mAb M342).

CONCLUSIONS

The present study reveals that the mouse uveal tract, like the rat, contains rich networks of DC and resident tissue macrophages. The networks of resident tissue macrophages in the mouse uveal tract closely resemble similar networks in non-ocular tissues. The phenotype of uveal tract DC suggests they are in the "immature" phase of their life cycle, similar to Langerhans cells of the skin, thus implying their role in situ within the eye is antigen capture and not antigen presentation.

Increased vascular endothelial growth factor (VEGF) and transforming growth factor beta (TGFbeta) in experimental autoimmune uveoretinitis: upregulation of VEGF without neovascularization

Experimental autoimmune uveoretinitis (EAU) was induced in Lewis rats and B10.A mice by immunization with S-antigen (S-Ag) to study the potential roles of vascular endothelial growth factor (VEGF) and the beta1 and beta2 isoforms of transforming growth factor (TGFbeta1 and TGFbeta2) during the progression of the disease. VEGF has been implicated as an angiogenic factor in ischemic retinopathies; however, Lewis rats developing EAU have high levels of VEGF in the retina, but no neovascularization. In the present study, immunohistochemical staining for VEGF, TGFbeta1 and TGFbeta2 was performed on the retinas of Lewis rats developing EAU or with oxygen-induced ischemic retinopathy. In rats immunized with S-antigen, a marked upregulation of VEGF was immunohistochemically visualized from the inner nuclear layer to the inner limiting membrane prior to blood-retinal barrier (BRB) failure and lymphocytic infiltration. VEGF is normally induced by hypoxia and its induction leads to neovascularization. Coincident with the increase in VEGF, there was increased immunoreactivity for TGFbeta1 and TGFbeta2 within the same layers of the retina. In contrast, rats with ischemic retinopathy and retinal neovascularization showed only a modest increase in VEGF immunoreactivity, which is largely confined to retinal ganglion cells and inner retinal vessels, and little or no increase in TGFbeta1 or TGFbeta2. In addition, in mice developing EAU, which does not have an abrupt onset as it does in rats and may involve neovascularization, a comparable upregulation of VEGF in the inner retina to that seen in rats developing EAU occurs with no increase in TGFbeta1 or TGFbeta2. Since TGFbeta can inhibit endothelial cell proliferation, it is likely that an increase in TGFbeta may prevent VEGF from exerting its endothelial growth activity in the rat EAU model, but VEGF may be operative in inducing BRB failure. These data suggest that there is a complex interaction among growth factors in the retina and that retinal neovascularization may require an imbalance between stimulatory and inhibitory factors.

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.

Nasal administration of retinal antigens maintains immunosuppression of uveoretinitis in cyclosporin-A-treated Lewis rats: future treatment of endogenous posterior uveoretinitis?

PURPOSE

Current treatment of autoimmune endogenous posterior uveoretinitis (EPU) is limited by drug toxicity, unpredictable relapses on dose reduction and resistance to therapy. Administration of autoantigens via gastrointestinal or respiratory mucosa prior to antigen exposure induces immune hyporesponsiveness (mucosal tolerance) to further antigen sensitisation. In this study we assessed whether mucosal tolerance induction was possible after immunisation with retinal antigens in experimental autoimmune uveoretinitis (EAU) in animals that were short-term immunosuppressed with cyclosporin A (CsA) to determine whether mucosal administration of retinal antigens can maintain immunosuppression in sensitised and immunosuppressed individuals.

METHODS

Female Lewis rats were immunised with retinal extract (RE) and then treated as follows. Group 1 received no specific therapy and served as control; group 2 were fed CsA from day 7 to day 20 post-immunisation; group 3 received inhalational tolerance therapy with RE in addition to CsA; tolerance therapy was continued after day 20 when CsA was stopped. Experiments varying the timing and dosage of both tolerising and immunising antigen were also performed, the details of which are described. Incidence, day of onset and clinical activity were recorded and histopathological assessment of intraocular inflammation, in particular the extent of autoimmune target-organ damage, was graded semiquantitatively.

RESULTS

Compared with controls and group 2, group 3 showed both a marked delay in disease onset and a reduction in disease severity. This effect was both dose and dose-timing dependent. Tissue damage assessed in terms of preservation of rod outer segments was significantly less in group 3.

CONCLUSIONS

The success of combination therapy, clinically, remains unknown at present but these results support continuing present clinical trials of mucosal tolerance therapy and in particular have future implications for either maintaining or inducing immunosuppression in autoimmune diseases in combination with present immunosuppressive therapies.

Phenotypic analysis of resident lymphoid cells in the conjunctiva and adnexal tissues of rat

The conjunctival associated lymphoid tissue is considered to be an integral part of the mucosal immune system. Under normal circumstances immune mechanisms in mucosal associated lymphoid tissue of the gut and bronchus can selectively suppress, rather than enhance, immune responsiveness to encountered antigens, inducing a state of tolerance. It is possible that conjunctival associated lymphoid tissue can also induce a state of tolerance to encountered antigens. Such a response may be exploited to modulate immune mediated ocular disease. Enhanced tolerance may protect the host against foreign antigen. Alternatively, under certain circumstances when the normal immune system is altered or disrupted the mucosal tissue may act to induce sensitisation and trigger immune mediated disease. The rat is frequently used as an animal model of immune mediated eye disease, but the normal profile of immune cells in the rat conjunctiva has not been studied. This information is essential for meaningful interpretation in the experimental situation. In this study we examined the immunophenotype of lymphoid tissue associated with the conjunctiva, lacrimal gland and Harderian gland of the Lewis rat. CD4+, Ia+ and the monocyte/macrophage population of cells were found predominantly in the substantia propria of the conjuctiva and interstitial connective tissue of the glands. CD8+ cells were distributed mainly in relation to the conjunctival and glandular epithelium. Goblet cells stained strongly with the monoclonal antibody (MAb) MRC OX-39, which is a marker for IL-2 receptors. The overall pattern of distribution of immunocompetent cells in the rat was found to be similar to that reported in humans.

Immunocytochemical study of retinal diode laser photocoagulation in the rat

AIM

To determine the nature of the cellular infiltrate, alterations in cell adhesion molecules, and MHC II antigen expression in the rat retina following diode laser retinal photocoagulation.

METHOD

20 normal Lister rats underwent diode laser photocoagulation of the retina. Frozen sections from eyes enucleated at 0, 1, 5, 13, and 33 days post laser were examined for T cells (R7.3), CD4 T cells (W3/25), activated CD4 T cells (OX-40), CD8 T cells (OX-8), B cells (OX-33), and macrophages (OX-42), MHC II antigen (OX-6), and E-Selectin-1, VCAM-1, and ICAM-1.

RESULTS

Retinal diode laser photocoagulation stimulated a wound healing response in the outer retina and choroid. The cellular infiltrate included macrophages and activated CD4 T cells at 13 and 33 days post laser. Glial cells in the inner plexiform and inner nuclear layers expressed MHC II antigen at 24 hours only. ICAM-1 antigen was induced in RPE cells and in Muller cells in the inner retina at all time intervals post laser and intense staining for ICAM-1 was present around intraretinal migrated cells at 13 and 33 days post laser. VCAM-1 antigen expression was induced in the choroidal vascular endothelium and RPE at 13 and 33 days after laser as was E-Selectin-1 antigen expression which was also evident focally at the external limiting membrane in association with migrated cells adjacent to the burn.

CONCLUSIONS

These results suggest that alterations in cell adhesion molecules may regulate the migration and activation of retinal pigment epithelium, macrophages and CD4 T cells at the outer blood-retinal barrier and choroid following diode laser photocoagulation of the normal Lister rat retina.

The effect of topical cyclosporin on conjunctiva-associated lymphoid tissue (CALT)

Topical cyclosporin A is increasingly being used in the treatment of ocular surface immune-mediated disorders. The availability of the drug in oil-based vehicles or collagen shields has restricted its use because of ocular irritation or blurring of vision. Although topical cyclosporin is being used more frequently, its effect on the immunocompetent cells of the conjunctiva is not known. Our aim was to study the effect of cyclosporin instillation on the immunocomponent cells of conjunctiva-associated lymphoid tissue (CALT) of Lewis rat, using a novel method of topical drug delivery. A suspension of collagen bits impregnated with cyclosporin A was instilled into eyes of Lewis rats for 4 days (group 1) or 8 days (group 2). Control rats (group 3) received the suspension without cyclosporin. Frozen sections of eyelids and conjunctiva were immunostained with the following monoclonal antibody markers: W3/13 (CD3), W3/25 (CD4, macrophages), OX-8 (CD8), MARD-3 (B cells), ED1, ED2 (macro/monocytes), OX-6 (class II MHC, Ia) and OX-39 (CD25, IL-2 receptor). Intraepithelial (IE) and substantia propria cells for each subset were counted and expressed as numbers per section. By day 8, intraepithelial and substantia propria cells for all the above markers, except B cells, showed a significant reduction in numbers. The p values were < 0.02 for W3/13 (CD3), W3/25 (CD4), OX-8 (CD8), OX-39 (CD25) (IE only), ED1, ED2 and OX-6 positive cells. Goblet cells of control animals showed strong positive reaction with OX-39 (CD25) antibody. This was completely abolished following 8 days of topical cyclosporin. This study demonstrated that topical cyclosporin A induces a marked reduction in numbers of all subtypes of immunocompetent cells in the conjunctival epithelium and substantia propria.

The ocular surface as part of the mucosal immune system: conjunctival mucosa-specific lymphocytes in ocular surface pathology

The mucosal immune system includes mucus membranes of the gut, respiratory and urogenital tracts. Mucosa-specific, intraepithelial lymphocytes (IELs), that correspond to the suppressor/cytotoxic subset and also express the human mucosal lymphocyte antigen (HML-1), are a unique component of this system. We have recently demonstrated these cells in the human conjunctiva, establishing the ocular surface as an integral part of the mucosal immune system. In this study we examined the distribution of lymphocyte subsets, with particular attention to mucosa-specific lymphocytes, in two ocular surface disorders, namely conjunctival intraepithelial neoplasia (CIN) and ocular cicatricial pemphigoid (OCP). Cryosections of biopsy specimen were immunostained using a panel of monoclonal antibodies against different lymphocyte subsets. In CIN, the CD8/HML ratio was decreased (1 +/- 0) and CD8/CD4 ratio was reversed (0.54 +/- 0.21). HML-1+ cells were distributed throughout the epithelial layers of dysplastic tissue. Biopsy specimens of OCP showed normal ratios of CD8/HML (1.4 +/- 0.16) but the CD8/CD4 was low (1.29 +/- 0.88). Association of HML-1+ cells with the basal layer of normal epithelium and with all layers of dysplastic epithelium suggests that expression of HML-1 antigen may be induced by actively dividing cells. HML-1+ cells may have a role in immune mechanisms associated with ocular surface disorders.

Therapeutic advances in immunosuppression

Immunosuppressive therapy is appropriate for the prevention or reversal of allograft rejection, and for the treatment of autoimmune disorders and allergic disease. Recent advances in our understanding of the cellular and molecular mechanisms that regulate immune responses have paralleled elucidation of the modes of action of a variety of therapeutic immunosuppressive agents, both 'old' and new. These developments have identified potential targets for more refined and specific intervention strategies that are now being tested in the clinic.

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.