Expression of HLA-DR antigen on retinal pigment epithelial cells in retinitis pigmentosa

Microbiome and Inherited Retinal Degenerations

Inherited retinal degenerations (IRDs) represent a genetically and clinically heterogeneous group of progressive and visually debilitating disorders that can lead to irreversible visual loss. Our understanding of IRD pathogenesis at both the genetic and cellular levels has increased tremendously over the past two decades, but the exact pathogenic mechanisms remain incompletely understood. Enhanced understanding of the pathophysiology of these diseases can result in new treatment targets. Alterations in the human gut microbiome play a key role in the pathogenesis of many ocular and nonocular diseases, such as age-related macular degeneration, neurologic and metabolic disorders, and autoimmune conditions. The gut microbiome regulates the susceptibility of mice to develop experimental autoimmune uveitis, a model for autoimmune disease of the posterior portion of the eye elicited by the systemic response to retinal antigens. Because of the mounting evidence in favor of a role for local and systemic inflammatory and autoimmune-mediated components to IRD pathogenesis, this review presents the current knowledge of gut microbiome in IRDs and discusses the association between possible changes in gut microbiome and pathogenesis of these diseases, with special attention to their possible contribution to the inflammatory underpinnings of IRDs.

Soluble Collectin 11 (CL-11) Acts as an Immunosuppressive Molecule Potentially Used by Stem Cell-Derived Retinal Epithelial Cells to Modulate T Cell Response

Retinal pigment epithelium (RPE) cell allotransplantation is seen as a possible solution to retinal diseases. However, the RPE-complement system triggered by the binding of collectin-11 (CL-11) is a potential barrier for RPE transplantation as the complement-mediated inflammatory response may promote T cell recognition. To address this, we investigated the role of CL-11 on T cell immuno-response. We confirmed that RPE cells up-regulated MHC class I and expressed MHC class II molecules in an inflammatory setting. Co-cultures of RPE cells with T cells led to the inhibition of T cell proliferation. We found that CL-11 was partially responsible for this effect as T cell binding of CL-11 inhibited T cell proliferation in association with the downregulation of CD28. We also found that the suppressive action of CL-11 was abrogated in the presence of the RGD peptide given to block the T cell binding of CL-11 by its collagen-like domain. Because RPE cells can bind and secrete CL-11 under stress conditions, we postulate that soluble CL-11 contributes to the immunosuppressive properties of RPE cells. The investigation of this dual biological activity of CL-11, namely as a trigger of the complement cascade and a modulator of T cell responses, may provide additional clues about the mechanisms that orchestrate the immunogenic properties of RPE cells.

Ocular immune privilege and retinal pigment epithelial cells

The ocular tissue microenvironment is immune-privileged and uses multiple immunosuppressive mechanisms to prevent the induction of inflammation. The retinal pigment epithelium plays an essential role in ocular immune privilege. In addition to serving as a blood barrier separating the fenestrated choriocapillaris from the retina, the retinal pigment epithelium is a source of immunosuppressive cytokines and membrane-bound negative regulators that modulate the activity of immune cells within the retina. This article reviews the current understanding of how retinal pigment epithelium cells mediate immune regulation, focusing on the changes under pathologic conditions.

The double-edged sword of inflammation in inherited retinal degenerations: Clinical and preclinical evidence for mechanistically and prognostically impactful but treatable complications

We present retrospective data from our clinical research efforts of the past several years alongside a review of past and current clinical and preclinical data independently by several investigators supporting our clinical evidence for the importance of inflammation in inherited retinal degenerations (IRDs). We show how inflammation is a complicating factor in IRDs but, if recognized and managed, also a great opportunity to mitigate disease severity immediately, improve patient prognosis and quality of life, extend the treatment windows for gene-specific and agnostic therapeutic approaches, mitigate the impact of inflammatory complications on the accurate estimate of vision changes in IRD natural history studies, improve the chances of safer outcomes following cataract surgery, and potentially reduce the likelihood of inflammatory adverse events and augment the efficacy of viral vector-based treatment approaches to IRDs. Manuscript contribution to the field. Inflammation has been suspected to be at play in IRDs since the beginning of the 1900s and became a research focus through the early 1990s but was then largely abandoned in favor of genetic-focused research. Thanks to regained cognizance, better research tools, and a more holistic approach to IRDs, the recent reappraisal of the role of inflammation in IRDs has brought back to the surface its importance. A potential confounder in natural history studies and a limiting factor in clinical trials if not accounted for, inflammation can be managed and often offers an opportunity for immediately improved prognosis and outcomes for IRD patients. We present our retrospective clinical evidence for connections with a measurable secondary autoimmune component that can develop in IRDs and contribute to vision loss but is at least in part treatable. We also present ample lines of evidence from the literature corroborating our clinical observations at the preclinical level.

Inhibiting TLR7 Expression in the Retinal Pigment Epithelium Suppresses Experimental Autoimmune Uveitis

Experimental autoimmune uveitis (EAU), a model of human uveitis, is an organ-specific, T cell-mediated autoimmune disease. Autoreactive T cells can penetrate the blood-retinal barrier, which is a physical defense composed of tight junction-linked retinal pigment epithelial (RPE) cells. RPE cells serve as antigen-presenting cells (APCs) in the eye since they express MHC class I and II and Toll-like receptors (TLRs). Although previous studies have shown that supplementation with TLR agonists exacerbates uveitis, little is known about how TLR signaling in the RPE contributes to the development of uveitis. In this study, we isolated the RPE from EAU mice, which were induced by active immunization (aEAU) or adoptive transfer of antigen-specific T cells (tEAU). The expression of TLRs on RPE was determined, and both aEAU and tEAU mice exhibited induced tlr7 expression. The TLR7 agonist R848 was shown to induce aggressive disease progression, along with significantly elevated levels of the uveopathogenic cytokine IL-17. Furthermore, not only IL-17 but also R848 appeared to enhance the inflammatory response and to impair the barrier function of the RPE, indicating that TLR7 signaling is involved in the pathogenesis of EAU by affecting the behaviors of the RPE and consequently allowing the infiltration of autoreactive T cells intraocularly. Finally, local application of shRNA against TLR7 delivered by recombinant AAV effectively inhibited disease severity and reduced IFN-γ and IL-17. Our findings highlight an immunomodulatory role of RPE TLR7 in EAU development and provide a potential therapeutic strategy for autoimmune uveitis.

Immune responses to retinal gene therapy using adeno-associated viral vectors - Implications for treatment success and safety

Recombinant adeno-associated virus (AAV) is the leading vector for gene therapy in the retina. As non-pathogenic, non-integrating, replication deficient vector, the recombinant virus efficiently transduces all key retinal cell populations. Successful testing of AAV vectors in clinical trials of inherited retinal diseases led to the recent approval of voretigene neparvovec (Luxturna) for the treatment of RPE65 mutation-associated retinal dystrophies. However, studies applying AAV-mediated retinal gene therapy independently reported intraocular inflammation and/or loss of efficacy after initial functional improvements. Both observations might be explained by targeted removal of transduced cells via anti-viral defence mechanisms. AAV has been shown to activate innate pattern recognition receptors (PRRs) such as toll-like receptor (TLR)-2 and TLR-9 resulting in the release of inflammatory cytokines and type I interferons. The vector can also induce capsid-specific and transgene-specific T cell responses and neutralizing anti-AAV antibodies which both limit the therapeutic effect. However, the target organ of retinal gene therapy, the eye, is known as an immune-privileged site. It is characterized by suppression of inflammation and promotion of immune tolerance which might prevent AAV-induced immune responses. This review evaluates AAV-related immune responses, toxicity and inflammation in studies of retinal gene therapy, identifies influencing variables of these responses and discusses potential strategies to modulate immune reactions to AAV vectors to increase the safety and efficacy of ocular gene therapy.

The RPE Cell and the Immune System

The RPE cell plays a pivotal role in retinal immunity. In fact, the RPE cell orchestrates both innate and adaptive immunity and contains a plethora of factors to regulate the immune response. Many immunoregulatory activities of the RPE cell are accomplished through cytokine production, toll-like receptor (TLR) activation, complement regulation and antigen presentation. The RPE cells immune regulatory network plays an essential role in retinal immunity and autoimmunity, retinal infections and in a variety of retinal degenerative disorders. Understanding the immune regulatory properties of this cell may provide additional clues to disease mechanisms that may lead to future treatments for many human retinal diseases.

A review of the immunologic findings observed in retinitis pigmentosa

Most patients suffering from retinitis pigmentosa (RP) inherit the disorder; however, the immune-pathologic features associated with this disease have yet to be extensively studied. Six reports correlate antiretinal immune activity with vision deterioration in RP patients. Some of these patients have sporadic RP that occurs in excess of expected gene segregation during inheritance. The hypothesis that a primary immune-mediated disease process occurs in this sporadic group is supported by significant associations of RP with autoimmune endocrinopathies and other immune-related conditions or factors; however, no immunologic difference regarding RP family history is reported in the peripheral blood studies of RP patients. Twenty-one percent to 51% of RP patients display antiretinal antibodies, whereas 19-58% have antiretinal lymphocyte reactivity to retinal extract, and 60-85% have activated T cells. Mutations in animal models of RP have been shown to cause endoplasmic reticulum stress that may initiate immunopathology for genetic RP, but oxidative stress also encourages immune cytotoxicity. In addition, necrotic cell death is evident, which promotes inflammatory conditions. We review mechanisms and evidence for an occult inflammation in genetic RP and examine reports of efficacy in retarding RP progression with anti-inflammatory agents in clinical trials.

Ocular Stem Cell Research from Basic Science to Clinical Application: A Report from Zhongshan Ophthalmic Center Ocular Stem Cell Symposium

Stem cells hold promise for treating a wide variety of diseases, including degenerative disorders of the eye. The eye is an ideal organ for stem cell therapy because of its relative immunological privilege, surgical accessibility, and its being a self-contained system. The eye also has many potential target diseases amenable to stem cell-based treatment, such as corneal limbal stem cell deficiency, glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa (RP). Among them, AMD and glaucoma are the two most common diseases, affecting over 200 million people worldwide. Recent results on the clinical trial of retinal pigment epithelial (RPE) cells from human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) in treating dry AMD and Stargardt’s disease in the US, Japan, England, and China have generated great excitement and hope. This marks the beginning of the ocular stem cell therapy era. The recent Zhongshan Ophthalmic Center Ocular Stem Cell Symposium discussed the potential applications of various stem cell types in stem cell-based therapies, drug discoveries and tissue engineering for treating ocular diseases.

Targeting inflammation in emerging therapies for genetic retinal disease

Genetic retinal diseases such as age-related macular degeneration and monogenic diseases such as retinitis pigmentosa account for some of the commonest causes of blindness in the developed world. Diverse genetic abnormalities and environmental causes have been implicated in triggering multiple pathological mechanisms such as oxidative stress, lipofuscin deposits, neovascularisation, and programmed cell death. In recent years, inflammation has also been highlighted although whether inflammatory mediators play a central role in pathogenesis or a more minor secondary role has yet to be established. Despite this, numerous interventional studies, particularly targeting the complement system, are underway with the promise of novel therapeutic strategies for these important blinding conditions.

Autosomal recessive retinitis pigmentosa due to ABCA4 mutations: clinical, pathologic, and molecular characterization

PURPOSE

Autosomal recessive retinitis pigmentosa (ARRP) is a genetically heterogeneous condition characterized by progressive loss of retinal photoreceptor cells. In order to gain new insights into the pathogenesis of ARRP, we evaluated the morphological, biochemical, and gene expression changes in eyes from a human donor with ARRP due to mutations in the ABCA4 gene.

METHODS

Eyes were obtained postmortem from a donor with end-stage retinitis pigmentosa. The coding sequences of the RDS, RHO, and ABCA4 genes were screened for disease-causing mutations. Morphological changes in different regions of the retina were examined histologically, and levels of lipofuscin-associated bisretinoids were measured. Gene expression was examined in retinal/choroidal tissue using microarray analysis, and all parameters were compared to those in unaffected control donors.

RESULTS

Genetic analysis of the donor's DNA identified two mutations in the ABCA4 gene, IVS14+1G > C and Phe1440del1 cT, each on a separate allele. Morphological evaluation revealed complete loss of the outer nuclear layer, remodeling of the inner retina, loss of retinal vasculature, and regional neovascularization. The retinal pigment epithelium and choriocapillaris exhibited regional preservation. Microarray analysis revealed loss of photoreceptor cell-associated transcripts, with preservation of multiple genes expressed specifically in inner retinal neurons.

CONCLUSIONS

The persistence of transcripts expressed by inner retinal neurons suggests that despite significant plasticity that occurs during retinal degeneration, bipolar cells and ganglion cells remain at least partially differentiated. Findings from this study suggest that some forms of therapy currently under investigation may have benefit even in advanced retinal degeneration.

Immune regulation in the retina

Immune reactivity in the retina can be critically important in inflammation and infections, but regulation of this response is essential. The retinal pigment epithelial (RPE), a unique retinal cell, displays a number of essential functions to support the health of the retina. In this review, we highlight how the RPE cell plays a pivotal role in immune defense. The RPE cell orchestrates both innate and adaptive immunity since it expresses TLRs, complement components, MHC class I and II molecules, and serves as an antigen presenting cell. Moreover, both of these immune responses result in the production of a plethora of cytokines, mainly proinflammatory. In order to counteract these inflammatory factors and silence unwanted immune reactivity, the RPE cell also generates suppressive molecules. Recently, chronic immune reactivity has been implicated in a number of retinal diseases, such as age-related macular degeneration (AMD). Current evidence suggests that the generation of excessive retinal inflammation may be the consequence of a loss of RPE immunosuppressive factors. Herein, we summarize the varied interactions of the RPE cell with the immune response and highlight how the RPE cell survives and participates in this dynamic environment.

Acute anterior uveitis and HLA-B27

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

A role for local inflammation in the formation of drusen in the aging eye

PURPOSE

The accumulation of numerous or confluent drusen, especially in the macula, is a significant risk factor for the development of age-related macular degeneration (AMD). Identifying the origin and molecular composition of these deposits, therefore, has been an important, yet elusive, objective for many decades. Recently, a more complete profile of the molecular composition of drusen has emerged.

DESIGN

In this focused review, we discuss these new findings and their implications for the pathogenic events that give rise to drusen and AMD.

METHODS

Tissue specimens from one or both eyes of more than 400 human donors were examined by light, confocal or electron microscopy, in conjunction with antibodies to specific drusen-associated proteins, to help characterize the transitional events in drusen biogenesis. Quantification of messenger RNA from the retinal pigment epithelium (RPE)/choroid of donor eyes was used to determine if local ocular sources for drusen-associated molecules exist.

RESULTS

The results indicate that cellular remnants and debris derived from degenerate RPE cells become sequestered between the RPE basal lamina and Bruch's membrane. We propose that this cellular debris constitutes a chronic inflammatory stimulus, and a potential "nucleation" site for drusen formation. The entrapped cellular debris then becomes the target of encapsulation by a variety of inflammatory mediators, some of which are contributed by the RPE and, perhaps, other local cell types; and some of which are extravasated from the choroidal circulation.

CONCLUSIONS

The results support a role for local inflammation in drusen biogenesis, and suggest that it is analogous to the process that occurs in other age-related diseases, such as Alzheimer's disease and atherosclerosis, where accumulation of extracellular plaques and deposits elicits a local chronic inflammatory response that exacerbates the effects of primary pathogenic stimuli.

Retinal pigment epithelium-immune system interactions: cytokine production and cytokine-induced changes

Vision is dependent on proper function of several intraocular structures. Immune responses to eliminate invading pathogens from the eye may threat vision by causing damage to these structures. Therefore, immunological defence of the eye should be carefully balanced between efficacy and maintenance of functional integrity. The eye is equipped with several regulatory mechanisms to prevent certain immune and inflammatory responses and is, therefore, regarded as an immune privileged site. The retinal pigment epithelium (RPE) contributes to the immune privileged status of the eye as part of the blood-eye barrier and by the secretion of immunosuppressive factors inside the eye. RPE cells, however, may also play an important role in the development of immune and inflammatory responses in the posterior part of the eye. During the last decade it has become clear that RPE cells are highly sensitive to a variety of inflammatory cytokines. Under inflammatory conditions, RPE cells produce a myriad of cytokines that may activate the resident ocular cells or attract and activate leukocytes. Cytokine stimulation of RPE cells causes profound effects, including nitric oxide secretion, cell surface expression of MHC class II and adhesion molecules and abrogation of barrier function. This article provides a comprehensive review of the literature concerning RPE cells and cytokines.

Human immunodeficiency virus type 1 can infect human retinal pigment epithelial cells in culture and alter the ability of the cells to phagocytose rod outer segment membranes

Human immunodeficiency virus type 1 (HIV-1) has been found in the vitreous of persons with AIDS. Here we investigated the susceptibility of human retinal pigment epithelial (RPE) cells to HIV-1 infection in culture and the effects of HIV-1 on the phagocytic function of the RPE. We found that 10 of 11 populations of RPE cells isolated from different fetal or adult eyes were susceptible to low-level replication of HIV-1/NL4-3 as determined by the detection of viral DNA and spliced viral RNA encoding envelope. HIV-1 infection was not inhibited by recombinant soluble CD4, suggesting that CD4 is not required for virus entry into RPE cells. RPE cells fused with target cells constitutively expressing HIV-1 envelope glycoproteins, indicating that HIV-1 enters cells by receptor-mediated fusion. Exposure to HIV-1 or recombinant gp120 caused a two- to four-fold increase in the binding and uptake of isolated rod outer segments by RPE cells. These findings introduce a new cell target of HIV-1 replication in the eye and indicate that RPE cells function aberrantly when exposed to HIV-1 or its envelope glycoprotein.

Expression of interferon-gamma in the lens exacerbates anterior uveitis and induces retinal degenerative changes in transgenic Lewis rats

Interferon-gamma (IFN-gamma) is a pleiotropic cytokine that has been implicated in immunopathogenic mechanisms of a number of inflammatory diseases of autoimmune or infectious disease etiology. However, its exact role is still a matter of debate. In experimental mouse models, IFN-gamma has been shown to exacerbate autoimmune thyroiditis, insulin-dependent diabetes mellitus, and autoimmune neuritis while it confers protection against experimental allergic encephalomyelitis and experimental uveitis. In this study, we generated transgenic rats with constitutive expression of IFN-gamma in the eye to study its paracrine effects and to investigate whether local production of IFN-gamma also confers protection against uveitis in the rat species. We show here that chronic exposure of ocular cells to IFN-gamma results in apoptotic death of retinal ganglion cells, development of chronic choroiditis, formation of retinal in-foldings, and activation of proinflammatory genes. In contrast to its protective systemic effect in the mouse, constitutive secretion of IFN-gamma in the rat eye was found to predispose the development of severe anterior uveitis and induction of retinal degenerative processes that impair visual acuity. Our data underscore the danger in extrapolation of cytokine effects in the mouse to humans without corroborating evidence in other species.

High expression of immunotherapy candidate proteins gp100, MART-1, tyrosinase and TRP-1 in uveal melanoma

In the treatment of cutaneous melanoma, provisional therapeutic strategies have been designed to combat tumour load using T cells that are sensitized with peptides derived from melanoma autoantigens, such as glycoprotein 100 (gp100), melanoma antigen recognized by T cells 1 (MART-1 or MelanA), tyrosinase and tyrosinase-related protein 1 (TRP-1). We recently found that gp100, MART-1 and tyrosinase are heterogeneously expressed in human cutaneous melanoma (De Vries et al (1997) Cancer Res 57: 3223-3229). Here, we extended our investigations on expression of these immunotherapy candidate proteins to uveal melanoma lesions. Cryostat sections from 11 spindle-type, 21 mixed and epithelioid tumours and four metastasis lesions were stained with antibodies specifically recognizing gp100, MART-1, tyrosinase and TRP-1. In addition, we used the DOPA reaction to detect tyrosinase enzyme activity as a confirmation of the tyrosinase immunohistochemical results. High expression of gp100, MART-1 and tyrosinase was found in the uveal melanoma lesions: 80% of the lesions displayed 75-100% positive tumour cells. TRP-1 positivity was slightly less: approximately 65% of the lesions stained in the 75-100% positive tumour cell category. All uveal melanoma lesions were positive for the four markers studied, this being in contrast to cutaneous melanoma where 17% of the advanced primary lesions and metastases were negative. The presence of these antigens was a little lower in metastases. We conclude that uveal melanomas and their metastases express melanocyte-lineage immunotherapy candidate proteins very abundantly. Uveal melanomas differ in this respect from cutaneous melanoma, in which the expression of these immunotherapy antigens was much more heterogeneous. This makes uveal melanoma a suitable candidate tumour for immunotherapeutic approaches.

Immunohistochemical studies in equine recurrent uveitis (ERU)

Despite extensive clinical research, the etiology of equine recurrent uveitis (ERU) is still unknown. After an immunologic pathogenesis was established in recurrent uveitis in humans, a similar pathogenic mechanism was assumed to exist in ERU. To investigate whether immunopathologic mechanisms are involved in ERU, 20 eyes of 15 horses with ERU were examined immunohistochemically with a T cell marker, B cell marker, and anti-major histocompatibility complex (MHC) class II antibodies. Twenty-six eyes of 20 horses were used for investigation of MHC class II antigen expression in normal equine eyes. In 18 eyes of 14 horses, the number of T cells in the inflammatory cell population within the uvea was assessed. In 16/18 eyes (89%), the T lymphocyte fraction was > 70%. This cell population was distributed mostly in a diffuse manner throughout the uvea and also within the mantle zone of follicular lymphocytic aggregates. Foci of B lymphocytes could be found within the center of follicular aggregates in three eyes. The expression of MHC class II antigen on resident ocular cells was evaluated in 10 eyes of six horses with ERU. An increase of MHC class II antigen expression in the trabecular meshwork and on the nonpigmented ciliary epithelium was noted as was a deviant expression on proliferating Müller cells and retinal pigment epithelial cells. The predominance of T cells in the inflammatory infiltrates supports the central role of a cell-mediated immune response. Furthermore, the observation of a deviant MHC class II expression on resident ocular cells suggests that aberrant immune regulation may play a role in the pathogenesis of ERU.

MHC class II positive retinal pigment epithelial (RPE) cells can function as antigen-presenting cells for microbial superantigen

Retinal pigment epithelial (RPE) cells induced to express MHC class II (HLA-DR) by incubation with interferon gamma (IFN-gamma) were investigated for their ability to present a microbial superantigen to T lymphocytes. Superantigens bind to MHC class II antigens and appear to play a role in a number of infectious and autoimmune diseases through stimulation of large numbers of T cells. Primary cultures of human RPE cells treated with IFN-gamma for three days to induce HLA-DR expression bound staphylococcal enterotoxin E (SEE) via HLA-DR and presented SEE to T cells as measured by proliferation of purified peripheral blood T cells and IL-2 synthesis by the Jurkat T cell line. Untreated RPE cells were essentially ineffective as superantigen presenting cells. These results suggest that MHC class II expressing RPE cells could contribute to immune and inflammatory activity in the eye by presenting superantigens to T lymphocytes.

Increased risk of autoimmune hypothyroidism in patients affected by retinitis pigmentosa

Patients with Retinitis Pigmentosa (RP) show hemeralopia, restricted field of vision and reduced visual acuity, owing to the degeneration and proliferation of photoreceptors and a retinal pigment epithelium. The prevalence in Italy is 1:4,000. A certain number of "syndromic" associations have been described, and, in particular, also that with hypothyroidism, but very few cases have been studied. We describe a family of 40 people, spanning four generations, in which we have recorded the presence of autosomic dominant RP, associated with autoimmune hypothyroidism or with circulating antithyroid autoantibodies (ATA), currently considered as the expression of active autoimmune thyroiditis or a risk factor for this complaint. We measured, in all members, TSH, FT3, FT4, antithyroglobulin and antithyroperoxidase autoantibodies. A fundus oculi examination was performed in every subject, as well as a careful examine of the anterior region on the neck. A control population of 100 healthy people was also studied. Our data show a higher prevalence of ATA, statistically significant, in the patients with RP and in their relatives, compared with the control population and the data from the literature (13 cases over 40 = 32.5%; p < 0.01). 3 patients with RP and ATA were affected by clinically evident hypothyroidism. 10 patients with ATA were clinically euthyroid; 8 patients affected by RP did not show circulating ATA at the time of the study. The interest for the physician in this "syndromic" retinal distrophy reflects the need, emerging from our data, to test the thyroid function in the subjects with RP and in members of their families, since circulating ATA are considered a risk factor for the development of autoimmune hypothyroidism.

The influence of penetrating keratoplasty and cyclosporin A therapy on MHC class II (Ia)-positive cells in the rat iris and choroid

BACKGROUND

The presence of Ia-positive cells (MHC class II equivalent) has been previously reported in the iris and choroid of various species. They have been reported to have both round and dendritic morphologies; the latter may represent classic dendritic cells, potent antigen-presenting cells (APCs). It is possible that the dendritic-like cells play a important role in (auto)immune processes of uveal and other ocular tissues. Using the flat or whole mount technique, the distribution of Ia-positive cells in the rat iris and choroid was investigated following penetrating keratoplasty (PKP) and following treatment with cyclosporin A (CsA).

METHODS

Lewis (LW) rats received corneal buttons from Lewis-Brown Norway (LW-BN) donors and were randomly assigned to the following groups: (i) operated, untreated (n = 24); (ii) operated, CsA-treated (10 mg/kg i.m.; n = 22). Controls were groups (iii) normal LW rats (n = 13); (iv) unoperated, CsA-treated (16 days' treatment; n = 8); (v) anterior perforation of the anterior chamber (n = 3); (vi) eight corneal sutures only (n = 4); (vii) syngeneic operated (LW to LW; n = 4). Animals of groups (i) and (ii) were killed on the 5th, 9th and 13th postoperative days and on appearance of the corneal rejection (group i, day 13; group ii, day 16). Both eyes were enucleated, immediately fixed, and iris-choroid flat mounts were examined for Ia-positive cells using APAAP immunohistochemistry.

RESULTS

In the normal Lewis rat iris, scattered Ia-positive cells of both nondendritic and dendritic morphology were observed. CsA treatment in the unoperated rat did not result in a significant decrease in the percentage of dendritic cells in the iris or choroid. Anterior chamber perforation, the placement of sutures in the cornea and syngeneic PKP resulted in a moderate increase in iris Ia-positive cells. Allogeneic transplantation resulted in a large increase in both types of Ia-positive cells, particularly on day 13 with corneal rejection. In group ii, an initial decrease in Ia-positive cells until day 13 was observed; upon rejection (day 16), the histological picture was similar to that of untreated animals. Alterations in the operated choroid were also apparent following CsA treatment.

CONCLUSION

Corneal transplantation in the Lewis rat results in an increase in Ia-positive cells in the iris; CsA therapy can delay but not prevent this reaction. Changes in choroidal Ia-positive cells following PKP were not apparent, their numbers being affected only by CsA treatment following grafting.

MHC class II antigen expression by ocular cells in proliferative diabetic retinopathy

An immunohistological study was performed on ciliary biopsies of the pars plana obtained surgically in 10 patients suffering from diabetic retinopathy and on 15 surgical specimens of pre-retinal neovascularized membranes. Using immunofluorescence and immunoperoxidase procedures, linear deposits of IgG, IgA and complement components were found in the 8 pars plana from patients with proliferative diabetic retinopathy, at the basal pole of the pigment epithelial cells and within the stroma. In contrast, these deposits were absent from normal pars plana and from the cases of background retinopathy. Moreover, pigment and non-pigment epithelial cells were found to express HLA DR and DQ determinants, in six of the eight patients with proliferative retinopathy. Immunohistological examination of pre-retinal membranes showed deposition of immunoglobulins and complement components within the connective stroma and along the new blood vessels. Endothelial cells of the newly formed vascular walls strongly expressed class II antigens on their membrane, as well as scattered stromal cells. As neither pigment epithelial cells nor retinal vascular endothelial cells normally express class II determinants, our results suggest the involvement of immunological phenomena in intraocular proliferative diseases and eventual interactions between the immune system and peptide growth factors. However, whether or not this immune reaction plays a role in the initiation or extension of intra-ocular proliferation remains to be determined.

Clinical and immunohistochemical correlation of herpetic keratitis with the expression of HLA-DR antigen

The corneal buttons after corneal graft of 22 patients with herpetic keratitis were studied (16 male, 6 female; 7-87 years of age). Ten still had active inflammation, while 12 had stabilized by the time of the study. Different degrees of neovascularization were observed in 19 cases. HLA-DR antigen was detected in the corneal epithelium in 7 of 22 cases (32%), in the corneal stroma in 17 of 22 cases (77%), and in the endothelium in 9 cases (41%) by using the immunohistochemical technique. The expression of HLA-DR antigen was more common and more marked in active herpetic keratitis (90%) and in neovascularized corneas (84%). The frequency and density of HLA-DR expression in perforating corneal ulcers were no higher than in other cases, but anterior synechia was accompanied by strong expression of HLA-DR antigen in the corneas. The expression of HLA-DR antigen was not only detected in the peripheral, but also in the central area of the specimens. The cells expressing HLA-DR antigen in corneas were mainly corneal cells. The results showed a close relationship between HSV-keratitis and the expression of HLA-DR antigen, which may be induced during the clinical course of the disease. The expression of HLA-DR might be one of the factors in the recurrent onset of the disease and a significant sign of the prognosis of corneal transplantation for these patients.

Experimental autoimmune uveoretinitis in the RCS rat: the influence of photoreceptor degeneration on disease expression

S-antigen induced experimental autoimmune uveoretinitis (EAU) was produced in the Royal College of Surgeons (RCS) strain of rat which develops a photoreceptor dystrophy within 2 weeks of birth. Animals were sensitised at 60, 90, and 105 days of age: all animals developed disease, but onset was significantly delayed in older (105 day) animals compared with those aged 60 days at sensitisation (p 0.003). Disease was characterised by the early development of complete serous retinal detachment which resolved in a few days: the prevalence of retinal detachment was increased to 80% in dystrophic animals compared with 10% in the congenic, non-dystrophic controls (p < 0.001). Anterior uveitis was seen in 17/30 control strain eyes, but in none of 30 dystrophic eyes (p < 0.001). Genetically determined photoreceptor and retinal pigment epithelium dysfunction in the RCS rat, which may involve the local accumulation of altered S-antigen, predisposes the dystrophic strain to display an acute retinal detachment in the early stages of EAU. This phenomenon illustrates how biochemical dysfunction of a target organ may influence susceptibility, form, and severity of an experimental autoimmune disease.

Lipopolysaccharide and cytokines induce a macrophage-type of nitric oxide synthase in bovine retinal pigmented epithelial cells

The present study demonstrates that bovine retinal pigmented epithelial cells, which are neuroectodermal in origin, produce nitric oxide (NO) upon treatment with interferon-gamma in the presence of lipopolysaccharide or tumor necrosis factor-alpha. NO production was measured by the accumulation of the stable endproduct NO2-. The biosynthesis of NO requires an induction period of approximately 12 hours and continues for at least 96 hours. The synthesis was abolished by the stereoselective inhibitors of NO synthase, NG-monomethyl-L-arginine and NG-nitro-L-arginine-benzylester. Cycloheximide and dexamethasone blocked cytokine-induced NO production. The results indicate that endotoxin and cytokines are capable of inducing NO synthase of the macrophage type, in retinal pigmented epithelial cells.

CD68 antigen expression by human retinal pigment epithelial cells

Although a primary role of the retinal pigment epithelium (RPE) is the phagocytosis of aged outer segment membranes, the RPE may also phagocytize particulates via several specific receptors that are characteristically present on mononuclear phagocytes of bone marrow origin. In recent immunophenotypic studies, CD68 monoclonal antibodies (mAb) have been shown to react selectively with a specific 110 kDa cytoplasmic glycoprotein present in mononuclear phagocytes from various sources. Designated as anti-macrophage antibodies that react with this macrophage-associated antigen, CD68 antibodies are now widely used for immunohistochemical identification of mononuclear phagocytes. Using a panel of CD68 mAb (KP1, EMB11, Ki-M6, Y1/82A, and Y2/131) we performed immunohistochemistry on three cytospin preparations of freshly isolated human RPE cells, three primary human RPE cultures, and 12 human RPE cell lines maintained in culture for up to 40 passages. Cytospin preparations of freshly isolated RPE cells demonstrated heavy reactivity in 5% of cells. Five- to 7-day-old primary RPE cultures exhibited uniform, heavy staining of all cells. Strong immunohistochemical reactivity persisted in all 12 cell lines at various passages up to and including passage 40. Stimulation of cultured RPE cells with interferon-gamma (100 U ml-1) for 24 and 48 hr did not produce observable differences in CD68 staining. RPE cells failed to stain when control mAb or mouse serum were substituted for the primary antibody. The constitutive expression of CD68 by neuroectodermally-derived RPE cells extends their immunophenotypic similarities with mesenchymally-derived mononuclear phagocytes and provides an additional antigenic marker to identify RPE cells in vitro.

Systemic immunostimulation after retinal laser treatment in retinitis pigmentosa

Systemic immunostimulation followed an experimental treatment trial of scatter argon laser photocoagulation directed to the retina of one eye of 10 patients with heredo-degenerative retinitis pigmentosa (RP). Significantly increased RP lymphocyte CD25, CD26, and CD4/CD26 activation epitope expressions over prelaser values and controls were found with a normalization of soluble interleukin-2 receptor secretion after laser treatment. Serum interferon-gamma was low both pre- and postlaser. Interestingly, when a panel of viral antibodies was tested, only those to rubella virus were elevated in the early postlaser period. The character of RP immunostimulation after laser-induced inflammation could be consistent with an antigenic stimulus from laser-released retinal proteins which might be of autoimmune or latent infectious origin. Enhanced immune responses may be a common but unrecognized sequellae of retinal laser.

Interleukin-6 (IL-6) gene expression and secretion by cytokine-stimulated human retinal pigment epithelial cells

Retinal and choroidal inflammatory lesions are important causes of visual loss, but the mechanisms regulating intraocular inflammation remain poorly understood. By virtue of its position at the blood-retina barrier, the retinal pigment epithelium (RPE) cells may be critical to the initiation and propagation of ocular inflammation. Previously we showed that cytokine-stimulated RPE cells produce interleukin-8, a well-defined chemotactic factor for neutrophils and lymphocytes. In this study, we found that human RPE cells stimulated by human recombinant interleukin-1-beta (rIL-1 beta) or tumor necrosis factor-alpha (rTNF-alpha) produce interleukin-6 (IL-6). Using a plasmacytoma proliferation assay, significant levels of IL-6 were found in media of RPE cells stimulated with either rIL-1 beta or rTNF-alpha for 4 hr. Progressive accumulation of IL-6 in media overlying stimulated RPE cells occurred over the subsequent 20 hr. IL-1 beta was a significantly more potent stimulator of RPE IL-6 production than TNF-alpha, RPE IL-6 production in response to each of these cytokines was also dose-dependent over a range of 20 pg to 20 ng ml-1. Specific anti IL-6 antibody, but not control immunoglobulin, neutralized RPE-derived IL-6 activity in the plasmacytoma proliferation assays. RPE IL-6 mRNA levels were detectable 1 hr after cytokine stimulation, plateaued within 8 hr in 24-hr assays, and demonstrated dose-dependent kinetics in 6 hr assays. Lipopolysaccharide failed to induce RPE IL-6 mRNA expression or RPE IL-6 production.(ABSTRACT TRUNCATED AT 250 WORDS)

Interferon-gamma induces the expression of major histocompatibility antigens by human retinal glial cells

Retinal glial cells normally do not express major histocompatibility (MHC) molecules. However, the expression of MHC antigens by retinal glial cells under certain pathological conditions suggests that these cells may play a role in immune responses of the retina. At present, the identity of molecules that may regulate the expression of class I and class II MHC antigens by retinal glial cells has not been established. Since interferon-gamma (IFN-gamma) induces MHC antigens in a variety of cell types, we examined the effect of this lymphocyte product on class I and class II antigen expression by human retinal glial cells in culture. Glial cells derived from post-mortem donor eyes were exposed to recombinant human IFN-gamma. Cells with MHC class I or class II antigens were detected with the use of specific monoclonal antibodies that were labeled directly or indirectly with fluorescent probes. Fluorescence of labeled cells was assayed by flow cytometry. Exposure to IFN-gamma increased the expression of class I and class II antigens by the retinal glial cells. Double labeling studies showed that 90% of the glial cells induced to express class II antigens also had class I antigens. Overall, the results show that IFN-gamma can regulate the expression of MHC molecules by human retina glial cells in culture. These findings are consistent with the concept that glia may play a role in immunological disorders affecting the retina.

Antiretinal antibodies in serum of patients with age-related macular degeneration

Antibodies, immunoreactive with normal human retinal proteins, were detected by Western immunoblot analysis in the sera of 30 patients with age-related macular degeneration (AMD). Sera from 14 of these patients demonstrated positive binding predominantly to a doublet protein of molecular weight between 58 and 62 kD. The sera from the remaining 16 patients and from 12 control subjects reacted either weakly or not at all with the doublet protein. No correlation was found with any specific type of AMD. The serum antibodies also immunocrossreacted with the same proteins from isolated photoreceptor outer segments; this was confirmed by indirect immunofluorescence on intact retinas. The crossreactivity of the serum antibodies with a protein of Mr 58 to 62 kD, the lower band present in the bovine purified neurofilament-68 kD preparation, suggests strongly that this protein may be a component of the neuronal cytoskeleton. However, it is not clear whether these autoantibodies play a direct role in the etiology of AMD or represent a nonspecific response to retinal damage.

Immunohistologic study of epiretinal membranes in proliferative vitreoretinopathy

We performed an immunohistologic study on 11 specimens of epiretinal membranes surgically obtained from patients who had rhegmatogenous retinal detachment with proliferative vitreoretinopathy. Immunostaining procedures were used to identify immunoglobulin and complement deposits, to visualize class II antigen expression by proliferating cells, and to determine eventual infiltration by cells of the immune system. Diffuse deposits of IgG, IgA, IgE, C1q, C3c, and C3d were found in epiretinal membranes, whereas numerous cells, including glial or pigmented epithelial cells, expressed HLA-DR and HLA-DQ antigens. Some macrophages and B or T8 lymphocytes were identified. These results suggest activation of the immune system during the course of proliferative vitreoretinopathy. Class II antigen expression could be dependent upon growth-promoting factors and interferon gamma and could play a crucial role in this immune reaction, which resulted in immunoglobulin deposition and activation of complement. However, the eventual role of immune phenomena in the extension of proliferative processes remains to be determined.

Evaluation of Ia expression in rat ocular tissues following inoculation with interferon-gamma

It is becoming increasingly clear that IFN-gamma is a potent immunoregulatory protein which influences MHC class II (Ia) antigen expression and cellular functions of B cells, T cells, NK cells and macrophages. During the past 5 yr our laboratory has provided evidence that IFN-gamma modulates class II antigens on retinal cells (retinal pigment epithelial cells, endothelial cells) and is localized within the eye during human inflammatory conditions. In this study we evaluate the direct effect of IFN-gamma on ocular tissue. Lewis rats were inoculated intravitreally or under the retina with either recombinant IFN-gamma (20,000 U) or saline. At 2 hr, 1, 2 and 6 days postinoculation, the eyes were removed and frozen sections were evaluated by immunocytochemical staining with monoclonal anti-Ia antibodies and an irrelevant monoclonal anti-T cell antibody. Saline treated tissue and tissue removed 2 hr after IFN-gamma inoculation showed no significant staining for Ia antigens. However, eyes evaluated 24 hr after IFN-gamma inoculation revealed Ia expression on a variety of ocular cells localized in the conjunctiva and anterior segment, such as conjunctival epithelium, keratocytes, iris epithelium, ciliary epithelium and choroidal cells. In the retina, retinal pigment epithelial (RPE) cells were Ia positive only when IFN-gamma was injected directly under the retina. In conjunction with Ia expression, two striking changes were noted. An iritis was seen and infiltrating cells were detected in the inner retinal layers. Both of these phenomena have been observed in certain inflammatory eye diseases. These studies clearly substantiate the concept that IFN-gamma can regulate class II antigens in the eye and thus may perpetuate immune reactivity in this site.

HLA DR and DQ expression on human retinal pigment epithelial cells in vitro

In a previous immunohistopathological study, we demonstrated a deviant expression of class II antigens on the uveal pigment epithelial cells of patients with proliferative diabetic retinopathy. The mechanisms triggering this abnormal expression by epithelial cells are not well known, and we tried to induce this phenomenon on primary cultures of human retinal pigment epithelial (RPE) cells. Confluent RPE-cell monolayers were supplemented with several biological or chemical reagents [recombinant interferon gamma, phytohemagglutinin A-P (PHA-P), phorbol-myristate acetate (PMA), recombinant interleukin-2, fibroblast growth factor (FGF), Insulin], to investigate their ability to induce HLA DR and DQ expression. On days 1, 3 and 5 after stimulation, the cells were incubated with monoclonal antibodies directed against human class II antigens: all reagents used failed to induce class II antigen: all reagents used failed to induce class II antigen expression. However, on day 7, we demonstrated the presence of numerous positive HLA DR and HLA DQ cells stimulated by gamma interferon, the percentages being closely related to the dose of this lymphokine. These findings, together with those of other investigators and our previous work on uveal pigmented epithelial cells in diabetic patients, may shed light on the exact implication of RPE in many poorly documented ocular diseases.

Sympathetic ophthalmia, a genuine autoimmune disease

Intraocular inflammation of exogenous origin, which may lead to the loss of visual function in both eyes, i.e. SO confronts ophthalmologists much less rarely than might be expected. Epidemiological studies comprising ergophthalmological aspects underscore this. Questions with regard to therapy should consider the fact that the T cell-mediated cytotoxic disease which causes the transition from the initially unilateral subthreshold exogenous uveitis into the bilateral progressive phase is by no means a rare disorder, especially in secondary surgical operations on predamaged eyes with fresh intraocular hemorrhages, vascular neoplasia and secondary glaucoma. This should be recalled again by practicing ophthalmologists, thus enabling the prevention of SO. If SO is a "forme fruste" of retinitis pigmentosa, as is very likely to be the case, further clarification requires clinicopathologic studies in close collaboration with immunologists.

Immunohistologic study of proliferative vitreoretinopathy

An immunohistologic study was performed on pars plana specimens obtained by biopsy in ten patients with rhegmatogenous retinal detachment, with or without proliferative vitreoretinopathy. Using immunofluorescence or immunoperoxidase procedures, linear deposits of IgG, IgA, and complement components were found in the eight cases of retinal detachment with proliferative vitreoretinopathy at the basal pole of the pigment epithelial cells and within the stroma. In contrast, these deposits were absent from the normal pars plana and from the retinal detachment without proliferative vitreoretinopathy. Moreover, pigment and nonpigment epithelial cells were found to express HLA-DR and HLA-DQ determinants in six of the eight patients with proliferative vitreoretinopathy. Our results are similar to those obtained in a previous study on proliferative diabetic retinopathy, which suggests the involvement of autoimmune phenomena in proliferative diseases and eventual interactions between the immune system and peptide growth factors. However, whether or not this immune reaction functions in the initiation or extension of intraocular proliferative syndromes remains to be determined.

Proliferative vitreoretinopathy membranes. An immunohistochemical study

Proliferative vitreoretinopathy (PVR) is the leading cause of failure after retinal detachment surgery. Therefore, both the extracellular matrix and cellular components of preretinal membranes from 23 eyes with PVR were characterized immunohistochemically. The membrane stroma was composed primarily of types I, II, and III collagen. Laminin and both heparan sulfate proteoglycans and collagens types IV and V were co-distributed in discrete regions within the stroma. Glial and retinal pigment epithelial (RPE) cell populations were identified in these membranes using specific immunohistochemical markers as was a small but significant macrophage population. Double-labeling experiments indicated that RPE cells in these membranes expressed the class II histocompatibility antigen HLA-DR, although neither the RPE monolayer in situ nor cultured RPE cells was HLA-DR positive unless induced by gamma interferon. Only rare isolated vascular endothelial cells were detected in 5 of the 23 membranes.

Immune alterations associated with T lymphocyte activation and regulation in retinitis pigmentosa patients

Altered immunoregulation, suggested previously in the heredo-familial retinal degeneration, retinitis pigmentosa (RP), led us to examine cell-mediated immune responses in 58 RP patients who expressed either recessive or dominant inheritance. Increased absolute numbers of activated T-cells, quantitated by flow cytometry using the Ta1 epitope, were found in the peripheral blood of 60% of these RP patients. The unusual finding was equally distributed between dominant (16 of 25) and recessive (19 of 33) types of RP, suggesting an immune process present in both patterns of heredity. Additional altered lymphocyte immunoregulation was suggested in all RP by lymphocyte responses to stimulants modified by indomethacin or histamine in vitro. Although no clear association could be found between Tal expression and demographic factors including age, sex, years with RP symptoms, or percentage of life with RP disease, the significantly altered immunoregulatory responses in RP may be related to the pathogenesis of RP.

HLA DR and DQ distribution in normal human ocular structures

HLA DR and DQ distribution was investigated in normal human ocular tissues, together with class I antigens and immunocompetent cell subsets, by immunofluorescence and immunoperoxidase procedures. In the anterior segment, our findings, consistent with those of previous reports, showed the wide distribution of class I antigens, specially in the corneal epithelium, while class II antigens were restricted to very rare cells scattered in the conjunctiva, the peripheral cornea and the stroma of the ciliary processes. Some non pigmented epithelial cells of the ciliary processes were HLA DR and DQ positive. In the posterior segment, class I antigens were abundantly represented in the choroid and the retinal layers. Few HLA DR and DQ positive cells were seen in the choroid, similar to those found in the anterior segment. Normal RPE did not react with any monoclonal antibody, but numerous cells located in the retina were strongly HLA DR and DQ positive, all around the blood vessels, and not at the sites of endothelial cells. The characterization of those cells, which could be hypothetized as pericytes needs further studies but suggests close relationships between neuroretina and the immune system. This study may provide insight in the implication of the immune system in many poorly understood ocular diseases.

Anti-Ia antibody diminishes ocular inflammation in experimental autoimmune uveitis

An experimental model of inflammatory eye disease, experimental autoimmune uveitis (EAU), was established by injecting rats in the footpad with S-antigen in complete Freund's adjuvant. This model system was used to evaluate the role of major histocompatibility complex (MHC) class II antigens (Ia) in the pathogenesis of this T cell mediated disease. One day prior to S-antigen priming, rats were injected with either anti-Ia antibodies or with mouse ascites. Clinical and histopathological analysis of eyes from rats treated with anti-Ia antibody showed less ocular inflammation as well as a delay in onset of EAU when compared to controls (p = 0.01). Furthermore, immunocytochemical evaluation demonstrated that tissue obtained from animals receiving anti-Ia therapy also expressed less Ia antigen, as well as a diminution in the number of infiltrating macrophages and lymphocytes. These data show that anti-Ia treatment significantly modifies the course of EAU in the rat. In addition, this study suggests that MHC class II antigen expression may be involved in the initiation and continuation of immune responses that results in ocular inflammatory diseases.

Clinical investigation of retinitis pigmentosa

The diagnostic features and future research directions of retinitis pigmentosa were documented in this update and review of the subject. An extensive and current bibliography is provided.

Immune responsiveness to retinal S-antigen and opsin in serpiginous choroiditis and other retinal diseases

The immune responsiveness to bovine retinal S-antigen and opsin has been investigated in some retinal disorders by means of in vitro lymphocyte proliferation, leukocyte migration inhibition and enzyme linked immune sorbent assays (ELISA). Sensitisation to S-antigen was observed in serpiginous choroiditis, but not in acute posterior multifocal placoid pigment epitheliopathy (APMPPE) or retinitis pigmentosa. No significant immune responsiveness was detected to opsin in any of the three diseases. Elevated antibody titers to S-antigen were observed in some individual patients and healthy subjects. However, none of the patient groups exhibited an elevated antibody titer as compared to the control group. Although serpiginous choroiditis and APMPPE share some prominent clinical characteristics, the sensitisation in the former disease may perhaps be attributed to more severe and prolonged damage of the photoreceptor cells and blood-retina barrier. A combination of previous and present results suggests that in immunological investigations of retinitis pigmentosa patients it is more effective to use human than bovine S-antigen as test antigen because a species specific epitope seems to be involved.

Immune mechanisms in autoimmune ocular disease

Aberrant expression of Class II MHC antigens (Ia) by non-immune cells is considered to be an important mechanism in the pathogenesis of autoimmune disease processes including those affecting the eye. It is suggested that circulating autoreactive T-cells are directed to their target organ as a result of aberrant expression of Ia antigens by the vascular endothelium of that organ. This hypothesis was tested in this study using two different models of severe ocular inflammation, induced by either S-antigen or bovine serum albumin (BSA). The retinal vascular endothelium becomes Ia + in S-antigen induced inflammation but not in inflammation induced by BSA. The accumulation in the eye of a T-cell line, ThS, specific for an ocular antigen (S-antigen), was compared in the two types of ocular inflammation and compared to that of another T-cell line, ThP, specific for a non-ocular antigen (PPD). In S-antigen induced inflammation, there was much greater accumulation of ThS than ThP whereas in BSA induced inflammation, both T-cell lines accumulated to the same extent but more than in uninflamed eyes. These results suggest that when the retinal vascular endothelium expresses Ia antigens during an inflammatory process, autoreactive T-cells will be specifically retained in the eye as a result of this and perpetuate the autoimmune destructive process.

Immunohistopathologic findings in proliferative diabetic retinopathy

We performed immunopathologic studies on pars plana specimens obtained by biopsy in patients with diabetes mellitus type I or II and by autopsy in diabetic patients and normal subjects. Frozen sections were treated with several antisera, including anti-IgG, complement components, and major histocompatibility complex antigens, as well as anti-factor VIII to detect vascular structures. The results showed IgG in a linear pattern at the basal pole of pigment epithelial cells and complement deposits of C3c, C3d, and C4 at the same location and in the stroma. HLA-DR expression was found at the level of the pigmented cells. These data suggest that some autoimmune processes may be involved in proliferative diabetic retinopathy at the level of the pigment epithelium, but it is unknown whether they are an epiphenomenon of neovascularization or if they play a role in its initiation.