Recoverin: a potent uveitogen for the induction of photoreceptor degeneration in Lewis rats

Non-paraneoplastic related retinopathy: clinical challenges and review

Autoimmune retinopathy (AIR) is a rare inflammatory condition characterized by progressive visual loss, abnormalities in visual fields and electroretinographic exams, along with presence of circulating anti-retinal antibodies. There are two main forms of AIR: paraneoplastic AIR (pAIR) and presumed non-paraneoplastic AIR (npAIR). NpAIR is considered a diagnosis of exclusion, since it is typically made after other causes of retinopathy have been investigated and the absence of malignancy is confirmed. Work-up of a npAIR case is challenging since there are no standartizaded protocols for diagnosis and treatment. The treatment regimen may vary from case to case, and it can be best guided by a set of parameters including electrophysiological responses, visual outcomes, and presence of anti-retinal antibodies. The purpose of this review is to summarize the principal clinical features, investigation, and management of npAIR.

Immune Cell Infiltration into the Eye Is Controlled by IL-10 in Recoverin-Induced Autoimmune Retinopathy

Autoimmune retinopathy (AIR) is a treatable condition that manifests in acute and progressive vision loss in patients. It has recently been determined that AIR is associated with an imbalance of T_H1 versus regulatory T cell immunity toward the retinal protein, recoverin. This study describes a new murine model to understand the immunopathology of AIR and its association with T cell responses toward recoverin. Immunization of C57BL/6 mice with recoverin resulted in ocular inflammation including infiltration of CD4⁺ and CD8⁺ T lymphocytes, B cells, and CD11b⁺Ly6C⁺ inflammatory monocytes in the eyes. Production of IFN-γ and IL-17 from T cells was exacerbated in IL-10 knockout (KO) mice and kinetics of disease development was accelerated. Infiltration of T cells and inflammatory monocytes into the eyes dramatically increased in recoverin-immunized IL-10 KO mice. An immunodominant peptide of recoverin, AG-16, was capable of inducing disease in IL-10 KO mice and resulted in expansion of AG-16 tetramer-specific CD4⁺ T cells in lymphoid organs and eyes. Adoptive transfer of recoverin-stimulated cells into naive mice was sufficient to induce AIR, and immunization of B cell-deficient mice led to a milder form of the disease. This model supports the hypothesis that recoverin-specific T cell responses are major drivers of AIR pathogenesis and that IL-10 is an important factor in protection.

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

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

GCAP1, Rab6, and HSP27: Novel Autoantibody Targets in Cancer-Associated Retinopathy and Autoimmune Retinopathy

PURPOSE

Autoantibodies (AAbs) with different retinal specificities were reported in cancer-associated retinopathy (CAR) and autoimmune retinopathy (AR). The goal was to identify the small retinal proteins of apparent molecular mass of 23-kDa often recognized by patients' AAbs.

METHODS

Sera specific for a 23-kDa retinal protein of 173 patients were investigated retrospectively by Western blotting and double immunofluorescence confocal microscopy. A proteomic analysis revealed new 23-kDa protein candidates, including guanylyl cyclase-activating proteins (GCAPs), heat shock protein 27 (HSP27), and Rab6A GTPase (Rab6A).

RESULTS

Among the cohort of 173 patients, only 68 had anti-recoverin AAbs and the remaining 105 reacted with 4 unique proteins, which were identified as a Rab6A, HSP27, GCAP1, and GCAP2. Confocal images from a double labeling study confirmed the reactivity of AAbs with different types of cells in human retina, consistent with the target protein's respective cellular functions. Patients (62/173) had been diagnosed with various kinds of cancer, including 20% of patients who had anti-recoverin, 11% anti-Rab6A, and 5% anti-HSP27 AAbs. Only 50% of recoverin-seropositive patients had cancer and the individuals with anti-recoverin AAbs had a significantly higher likelihood to be diagnosed with cancer than patients with other anti-23-kDa AAbs.

CONCLUSIONS

The newly discovered retinal autoantigens may be involved in pathogenicity of CAR and AR. The recognition of AAbs against various retinal proteins associated with autoimmune retinal degeneration broadens the group of proteins related with these entities.

TRANSLATIONAL RELEVANCE

Patients with anti-recoverin, anti-GCAP1, anti-Rab6A, and anti-HSP27 AAbs represented diverse clinical phenotypes, so the presence of disease-associated AAbs provides important information for molecular diagnosis.

Pathophysiology of JIA-associated uveitis

Juvenile idiopathic arthritis (JIA)-associated uveitis is an intriguing manifestation of JIA and an important contributor of long-term damage. Its pathophysiology is still poorly understood. This review summarizes current concepts. JIA is both a multifactorial and polygenetic disease. In the past 2 decades, multiple studies have indicated that the genetic contribution to both JIA and JIA-associated uveitis is modest. From an ophthalmological point of view, much of the pathophysiological data is derived from studies in experimental uveitis animal models. The pathophysiology of the arthritic manifestations of JIA has been studied extensively in humans. These studies have focused on the principal cells of the adaptive immune system, in particular different subsets of regulatory and effector T cells, as well as on antigen presenting cells or dendritic cells. With advancing technology and advancing knowledge of the underlying mechanisms of JIA-associated uveitis, new targets for therapy might evolve in the coming years.

A case of paraneoplastic optic neuropathy and outer retinitis positive for autoantibodies against collapsin response mediator protein-5, recoverin, and α-enolase

Background

Specific cross-reacting autoimmunity against recoverin or collapsin response mediator protein (CRMP)-5 is known to cause cancer-associated retinopathy or paraneoplastic optic neuropathy, respectively. We report a rare case with small cell lung carcinoma developing bilateral neuroretinitis and unilateral focal outer retinitis positive for these antibodies.

Case presentation

A 67-year-old man developed bilateral neuroretinitis and foveal exudation in the right eye. Optical coherence tomography showed a dome-shaped hyperreflective lesion extending from inner nuclear layer to the photoreceptor layer at the fovea in the right eye. Single-flash electroretinography showed normal a-waves in both eyes and slightly reduced b-wave in the left eye. Results of serological screening tests for infection were within normal limits. The patient’s optic disc swelling and macular exudation rapidly improved after oral administration of prednisolone. Systemic screening detected lung small cell carcinoma and systemic chemotherapy was initiated. Immunoblot analyses using the patient’s serum detected autoantibodies against recoverin, CRMP-5, and α-enolase, but not carbonic anhydrase II. Neuroretinitis once resolved after almost remission of carcinoma on imaging but it recurred following the recurrence of carcinoma.

Conclusions

The development of neuroretinitis in this cancer patient with anti-retinal and anti-optic nerve antibodies depended largely on the cancer activity, suggesting the possible involvement of paraneoplastic mechanisms. Patients with paraneoplastic optic neuropathy and retinopathy are likely to develop autoimmune responses against several antigens, thus leading to various ophthalmic involvements.

Autoimmune retinopathy

PURPOSE OF REVIEW

Autoimmune retinopathy (AIR) is an immune-mediated disorder characterized by progressive visual loss, abnormal electroretinographic and visual field findings in the presence of circulating anti-retinal antibodies. This review highlights advances made toward understanding the pathophysiology, clinical manifestations, and trends in the management of AIR.

RECENT FINDINGS

The pathophysiology of AIR is likely antibody-mediated. AIR serum autoantibodies are variable in their size and retinal tissue they target and can also be present in healthy controls and multiple autoimmune diseases. Rarely, AIR may be associated with dysregulated self-tolerance mechanisms in the thymus. Despite progress in research, our understanding of AIR remains incomplete. Lack of standardized methods for anti-retinal antibody testing continues to challenge the interpretation of seropositivity. Conventional immunosuppressives have been further studied, and promising immunomodulatory therapies, such as targeted B-cell therapy, have been introduced. Newer imaging modalities such as fundus autofluorescence and spectral domain optical coherence tomography may be helpful in diagnosis, monitoring progression of disease and response to treatment.

SUMMARY

AIR is a rare but vision-threatening disease whose pathogenesis is poorly defined. Lack of standardized clinical or laboratory criteria further complicates the diagnosis and management. Despite recent progress, further basic science research into the autoimmune process is needed. Prospective controlled clinical trials with immunomodulatory therapy can help define future treatment paradigms.

Proliferative vitreoretinopathy may be a risk factor in combined macular hole retinal detachment cases

OBJECTIVE

To review the incidence and closure rate of full-thickness macular holes (MH) in cases associated with concomitant rhegmatogenous retinal detachment (RRD).

METHODS

A retrospective consecutive case series was performed from patients undergoing surgical repair of RRD and simultaneous closure of MH. The presence of proliferative vitreoretinopathy (PVR), rates of hole closure and reattachment, and visual acuity outcomes were evaluated.

RESULTS

There were a total of 607 RRDs during the study period. The incidence of concomitant MH in RRD cases was 2.3% (14 of 607), and the overall incidence of PVR was 15.8% (96 of 607). All eyes with a MH had a primary break that was distinct from the MH. Five patients did not meet the inclusion criteria for review of the postoperative outcomes. In the remaining 9 patients, the retinal reattachment rate was 100%, and MH closure was achieved in 8 of 9 (89%) eyes after a single surgery. At the time of primary repair, PVR was present in 6 of these 9 cases (66.7%). There was a significant association between the presence of PVR and a concomitant MH (P = 0.0027). The mean preoperative visual acuity was 2.59 ± 0.649 logarithm of the minimum angle of resolution units and significantly improved to 1.23 ± 1.01 logarithm of the minimum angle of resolution units (P = 0.00124). Overall, 88.8% of patients showed an improvement in visual acuity at the final postoperative visit, and a visual acuity of 20/125 or better was achieved in 66.7% of cases.

CONCLUSION

Macular holes combined with a RRD are infrequent, and good anatomical results can be achieved after a simultaneous repair. Also, PVR may be more frequently encountered in this particular subset of RRDs.

Cancer-Induced, Immune-Mediated Ocular Degenerations

The means whereby vision can be lost from a disease located distant from the eye include autoimmunity, with sensitization resulting from extraocular stimuli, a process illustrated here by the immunologic confusion caused by cancers. The uncontrolled proliferation of malignancies commonly involves the expression of components of the central nervous system, but a damaging loss of tolerance is rare. When autoimmunity does develop, organ-specific antigens are more often involved than the more generalized and widely disseminated common neuronal components. A focus upon a single antigen is typical of the immune-mediated paraneoplasia, a collection of syndromes identified by unusual antibody reactions. This review provides an outline of the immunologic trail that led to the recognition of autoimmunity in paraneoplastic ocular degenerations, how specific antibody reactions aid in diagnosis, and the possibility of including antibodies in modes for sight-saving intervention. 'Those who do not know history are destined to repeat it'.

Embryonic stem cells and retinal repair

In this review we examine the potential of embryonic stem cells (ESCs) for use in the treatment of retinal diseases involving photoreceptors and retinal pigment epithelium (RPE). We outline the ontogenesis of target retinal cell types (RPE, rods and cones) and discuss how an understanding of developmental processes can inform our manipulation of ESCs in vitro. Due to their potential for cellular therapy, special emphasis is placed upon the derivation and culture of human embryonic stem cells (HESCs) and their differentiation towards a retinal phenotype. In terms of achieving this goal, we suggest that much of the success to date reflects permissive in vitro environments provided by established protocols for HESC derivation, propagation and neural differentiation. In addition, we summarise key factors that may be important for enhancing efficiency of retinal cell-type derivation from HESCs. The retina is an amenable component of the central nervous system (CNS) and as such, diseases of this structure provide a realistic target for the application of HESC-derived cellular therapy to the CNS. In order to further this goal, the second component of our review focuses on the cellular and molecular cues within retinal environments that may influence the survival and behaviour of transplanted cells. Our analysis considers both the potential barriers to transplant integration in the retina itself together with the remodelling in host visual centres that is known to accompany retinal dystrophy.

Recoverin as a cancer-retina antigen

In photoreceptor cells the Ca(2+) -binding protein recoverin controls phosphorylation of the visual receptor rhodopsin by inhibiting rhodopsin kinase (GRK-1). It can also serve as a paraneoplastic antigen in the development of retinal degeneration in some patients with cancer. The aberrant expression of recoverin in cancer cells and the presence of autoantibodies against recoverin are essential for the occurrence of cancer-associated retinopathy, which finally results in the apoptosis of photoreceptor cells. Noteworthy in cancer patients, the aberrant recoverin expression and the appearance of autoantibodies against recoverin are more frequent than paraneoplastic syndromes. We suggest the term "cancer-retina antigens" for this kind of proteins like recoverin that are solely expressed in retina and tumor tissues and evoke antibodies and/or T cells in patients with cancer. The rare development of a paraneoplastic syndrome is possibly caused by this immune response and probably depends on further events allowing to overcome the blood-retina barrier and the immune privileged status of the retina. It is still unknown whether aberrantly expressed recoverin could have a specific function in cancer cells, though it is suggested that it can be functionally associated with G-protein-coupled receptor kinases. This paper reviews the present knowledge on paraneoplastic syndromes associated with the aberrant expression of recoverin. A possible application of recoverin as a potential target for immunotherapy of cancer is discussed.

Multiple, parallel cellular suicide mechanisms participate in photoreceptor cell death

Photoreceptor degeneration in human photoreceptor dystrophies and in the relevant animal models has been thought to be executed by one common mechanism -- caspase-mediated apoptosis. However, recent experiments have challenged this concept. In previous experiments, analyzing gene expression in the degenerating rd/rd mouse retina, we have suggested that the gene defect leads to oxidative stress and altered metabolism, which may induce caspase-dependent and caspase-independent cell death mechanisms such as the activation of cystein-proteases, lysosomal proteases, autophagy and complement-mediated lysis. In this study we asked two questions. First, whether a temporal analysis of these different mechanisms during the course of degeneration would enable us to establish a causal relationship between these events; and second, whether photoreceptor degeneration in different models of photoreceptor dystrophies occurs by activating the same mechanisms. Three models of photoreceptor degeneration were chosen in which photoreceptor degeneration is caused by different events: the rd/rd mouse (calcium overload); the rds/rds mouse (structural defect); and light-damage (LD; oxidative stress). Marker genes were selected for the identified processes. PCR-analysis on laser capture microdissection samples was used to verify the expression of these genes in the rod photoreceptor layer. A temporal relationship between the processes was established at the mRNA level, using quantitative RT-PCR. The time course of gene expression was compared to that of cell loss (loss of rows of photoreceptor nuclei) and apoptosis (TUNEL labeling). Apoptosis and autophagy was analyzed using enzymatic assays. The time course of apoptosis and TUNEL labeling coincide in all three models. Complement-activated lysis was found to either parallel (rd/rd and rds/rds) or precede (LD) the development of TUNEL-positive cells. Autophagy was determined to parallel (rd/rd and LD) or lag (rds/rds) behind the development of TUNEL-positive cells. In all three models, glucose metabolism was found to be increased significantly prior to the onset of cell death, but then dropped in parallel with the loss of cells. The presence of the marker genes was verified by laser capture microdissection, and apoptosis (caspase activity) and autophagy (lysozyme and cathepsin activity) were verified in retina extracts. These results provide evidence that irrespective of whether photoreceptor degeneration is triggered by gene defects (lack of beta-PDE or rds/peripherin) or environmental stress (light-damage), a number of pro-apoptotic mechanisms are triggered leading to the degeneration of the photoreceptor cells. The temporal pattern of the different pathways suggests that the non-caspase-dependent mechanisms may actively participate in the demise of the photoreceptors, rather than represent a passive response of the retina to the presence of dying cells. Thus, unless the common upstream initiator for a given photoreceptor dystrophy is found, multiple rescue paradigms need to be used to target all active pathways.

Anti-recoverin antibodies induce an increase in intracellular calcium, leading to apoptosis in retinal cells

Autoantibodies against recoverin, a Ca2+-binding protein found in patients with cancer-associated retinopathy (CAR syndrome), penetrate retinal cells and induce their apoptosis via a mitochondrial pathway. The goal of this study was to investigate whether the entry of anti-recoverin antibody into E1A.NR3 retinal cells causes a change in intracellular Ca2+. Intracellular Ca2+ was measured using the Ca2+-sensitive fluorescent dye Fura-2 AM in living E1A.NR3 retinal cells treated with anti-recoverin antibody Rec-1, patients' autoantibodies, and control rat and human IgG. The exposure of retinal cells to Rec-1 antibody and to the CAR patients' autoantibodies in vitro caused a significant increase in intracellular Ca2+, while non-specific antibodies did not induce such an effect. Co-treatment of the E1A.NR3 cells with Rec-1 in the presence of nifedipine, a L-type Ca2+ channel blocker, significantly suppressed the increase of Ca2+. Treatment with nifedipine also blocked changes in the anti-apoptotic protein bcl-xL and in expressions of the pro-apoptotic protein bax. Nifedipine-treated cells also showed a decrease in cytosolic cytochrome c release and a decrease in caspase 3 activation, compared to cells treated only with Rec-1 antibody. The increase in the antibody-induced Ca2+ is at least in part dependent on extracellular Ca2+. Nifedipine was found to inhibit the entry of Ca2+ into the cells and to protect them from Rec-1-induced apoptosis. Increased levels of intracellular Ca2+ may lead to retinal dysfunction and degeneration in the CAR syndrome. Our results provide a molecular basis for the use of Ca2+ blockers in the treatment of the CAR syndrome.

Cancer-related diseases of the eye: the role of calcium and calcium-binding proteins

The eye provides unique opportunities to study complex biochemical pathways and to describe how components of these pathways contribute to the molecular basis of disease. In this article, the role of calcium-binding proteins in cancer-related diseases of the eye is reviewed. First, paraneoplastic syndromes, or so-called remote effects of cancer, arise from damage to tissues distant from any tumor or its metastases. Many of these syndromes are believed to be immune-mediated. Cancer-associated retinopathy (CAR), a blinding disease due to the degeneration of retinal photoreceptor cells, is one of the best characterized of the paraneoplastic syndromes. The CAR autoantigen has been identified as recoverin, a calcium-binding protein of the EF-hand superfamily. Its features as a calcium-binding protein, along with its function in photoreceptor cells and its role as the CAR autoantigen, are discussed. Next, unlike visual symptoms instigated by a distant tumor, ocular melanoma is the primary malignancy originating in the eye. ALG-2 encodes a pro-apoptotic calcium-binding protein that is down-regulated in ocular melanoma, thus providing these tumor cells with a selective advantage. In addition to background discussion of ALG-2, data describing the expression, cellular localization, and dimerization characteristics of ALG-2 in melanoma cells are presented. Biochemical studies of ALG-2 and its interactions with its target Alix/AIP1 also are presented. Finally, the function of ALG-2 in calcium-induced cell death is discussed. Additional calcium-binding proteins in retina and in ocular tumors are described in relation to different disease entities. Such proteins and their expression in the eye provide valuable examples bridging studies of protein chemistry, cellular function, and human disease.

Retinal antigens are recognized by antibodies present in sera of patients with multiple sclerosis

Multiple sclerosis (MS) is frequently accompanied by visual symptoms including those related to retinal disorders. Since they may be a consequence of an autoimmune reaction, we examined whether sera of patients with diagnosed MS and changes in visual-evoked potentials contain antibodies against retinal antigens (retAgs). Immunoblot analysis revealed that MS sera recognized mainly a 46-kD antigen, a 41-kD antigen, retinal arrestin, to a smaller extent also 70-, 56-, 43-, and 36-kD proteins. Patients whose sera showed the highest reactivity with 41- and 46-kD antigens had deficiencies in visual acuity, visual fields, ophthalmoscopy, and electroretinograms. Our observation suggests that antibodies to these retAgs may play a role in the origin of ophthalmologic impairment in MS.

Autoantibody-induced apoptosis as a possible mechanism of autoimmune retinopathy

Circulating antibodies specific to retinal proteins have been associated with retinal dysfunction in patients with retinopathy. Anti-recoverin antibodies found in patients with cancer-associated retinopathy (CAR) represent a unique model to study the relationship between retinal degeneration and autoimmunity. A body of evidence from in vitro and in vivo studies indicates that anti-recoverin autoantibodies are cytotoxic to retinal cells and induce apoptotic death of retinal photoreceptor cells, which leads to the degeneration of the photoreceptor cell layer. Similar to anti-recoverin autoantibodies, antibodies with other retinal specificities induce their target retinal cell death by activating a caspase 3-dependent apoptotic pathway. Thus, autoantibody-induced apoptosis may be a common pathway that leads to retinal death and blindness.

Functional analysis of the human recoverin gene promoter

PURPOSE

Following photoactivation of rhodopsin, recoverin inhibits rhodopsin kinase activity in retinal photoreceptors by reducing the binding of arrestin to rhodopsin and therefore prolonging the termination of the phototransduction cascade. To identify potential cis-elements that may be involved in understanding the mechanisms that determine the cell-specific expression of recoverin in retinal and cancerous cells, the promoter region of the human recoverin gene was studied in cultured human Y79 retinoblastoma cells.

METHODS

A 2.5 kb EcoRI fragment of a 9.4 kb cosmid that contains the 5' non-coding region of the human recoverin gene was sequenced and cloned into an expression vector upstream of a luciferase gene. Cultured Y79 human retinoblastoma cells were transfected with DNA constructs using lipofection. Deletion mutants were generated by site-directed mutagenesis, cloned into the expression vector, and transfected into Y79 cells. Reporter gene activity was measured with a luciferase assay, and normalized to beta-beta-galactosidase activity resulting from a co-transfected SV-beta-galactosidase SV40 vector.

RESULTS

Reporter gene expression in the transfected Y79 cells demonstrated an increase in activity between 232 and 620 bp from the translational start site of the recoverin gene. There was a decrease in the reporter gene expression between 900 and 1200 bp from the start site, followed by an increase between 1200 and 1440 bp.

CONCLUSIONS

This analysis suggests that there are cis-acting elements in the 5' non-coding region of the recoverin gene that are involved in the activation and suppression of gene expression.

Oral tolerance for treating uveitis - new hope for an old immunological mechanism

Oral tolerance induction has evolved as an attractive approach for the treatment of autoimmune uveitis. This approach is effective and generally void of the side effects associated with conventional immunosuppression. Following uptake of soluble antigen via the gut mucosa a specific systemic tolerance is generated. Experimental autoimmune diseases such as uveitis can efficiently be treated when autoantigens are fed to animals. The immunological mechanisms of oral tolerance are not well understood but are thought to involve the recognition of tolerogenic epitopes, generation of suppressor T cells and altered regulation of selected cytokines. The dose, purity of the antigen (tissue extract vs. single peptide) and concomitant treatment with cytokines were evaluated with the aim to enhance oral tolerance. Immunomodulatory drugs can abrogate oral tolerance. This requires careful evaluation with respect to therapeutic approaches in patients. The first clinical trials for treatment of uveitis with oral retinal autoantigen or an HLA-peptide crossreactive with S-Antigen show a promising therapeutic effect and confirmed the safety of this approach.

Peripheral expression of ocular antigens in regulation and therapy of ocular autoimmunity

The retina is a well-known immune-privileged tissue in the eye. Gene therapy and transgenic strategies have been taken to explore the relationship between the immune system and retinal antigens. Retroviruses were used to express retina-specific antigens or fragments systemically, leading to an antigen-specific loss of susceptibility to autoimmune disease. Transgenic strategies used a neo self-antigen, beta-galactosidase, or a known retinal antigen, interphotoreceptor retinoid-binding protein, to show that immune recognition of antigen by mice, which express solely in the retina, is not detectably different than that of mice that don't express this antigen. Together, these studies show that antigens expressed solely in the retina do not appear to be seen by the immune system, demonstrating that sequestration contributes to the lack of antigen recognition and absence of tolerance. Provision of these antigens outside of the retina provides the opportunity for development of peripheral tolerance, protection from autoimmunity, and potential therapies.

Experimental autoimmune uveitides: multiple antigens, diverse diseases

Human autoimmune uveitides are diverse and complex. Animal models have been developed for studying the pathogenesis of uveitis because of the difficulties in obtaining tissues from a patient's inflamed eye for experiments. There are animal models for experimental uveitis that provoke inflammation of different tissues of the eye and represent different forms of uveitis. Since inflammatory cells can infiltrate any part of the uvea and spill over to nonuveal tissues, such as retina, various antigens have been used to induce uveitis. Most of those models that represent autoimmune forms of uveitis are induced with proteins specific for photoreceptor cells (S-antigen, IRBP, rhodopsin, recoverin, phosducin). Nonretinal antigens, including melanin-associated proteins and myelin basic protein, are also good inducers of uveitis in animals.

Paraneoplastic neurologic disease antigens: RNA-binding proteins and signaling proteins in neuronal degeneration

Studies of the disorders known as paraneoplastic neurologic degenerations exemplify the successful application of modern molecular biological techniques to diseases, yielding, even for these extremely rare disorders, wide-ranging insight into basic neurobiology, tumor immunity, and autoimmune neurologic disease. Immune responses to paraneoplastic neurologic degeneration antigens, also called onconeural antigens, have been exploited to clone and characterize a number of neuron-specific proteins, including several RNA-binding proteins and new kinds of signaling molecules. The biology and functions of these proteins are reviewed, and a model in which their functions are related to the pathogenesis of autoimmune neurologic disease is discussed.

Uveitopathogenic sites in recoverin

PURPOSE

This study was carried out in order to determine the most potent and novel uveitopathogenic sites of recoverin using synthetic peptides.

METHODS

Several synthetic peptides containing the recoverin sequence plus adjuvants were injected into Lewis rats, and the uveitopathogenic sequence was defined, clinically, histologically, and immunologically.

RESULTS

Peptides containing of amino acids 57-85 and 136-167 induced severe EAU, and the lowest doses to induce EAU were 20 microg and 10 microg, respectively. Lymphocyte proliferative reactions were also positive for peptides 57-85 and 136-167. The core sequences within the uveitopathogenic site were 65-79 and 153-164. Peptides of amino acids 65-79 within 57-85 and 149-167 within 136-167 were the smallest in the recoverin sequence, respectively, that could induce severe EAU.

CONCLUSION

We found recoverin has some novel potent uveitopathogenic sites, 149-167. These findings of the uveitopathogenic sites in recoverin may lead to improved understanding of the pathogenesis of uveitis and the means to design specific treatment.

Distant cancer effects on standardised testing of peripheral vision

BACKGROUND

Profound central-retinal visual losses have been a major presenting factor reported in cancer and melanoma associated retinopathies (CAR, MAR). However, it is well established that standardised tests of peripheral retinal function are often the most sensitive detectors of early eye disease. This is a preliminary investigation of the responsiveness of the peripheral retina to "distant" (non-eye or CNS) cancers using easily obtained standardised tests.

METHODS

The design is a single blind study where test results are compared with published norms and a small age matched control group. Of 120 ambulatory cancer outpatients who were interviewed at routine follow up examinations, 111 volunteered and admitted a range of mild visual changes. 25 cancer patients completed all tests of peripheral vision function and a clinical screening. There were seven control subjects of the same age range.

RESULTS

98% (49 of 50) of eyes from the patient cohort were judged clinically normal following examinations which emphasised the central retina, fundus appearance, and static fields. On testing which emphasised the visual periphery, 46 (92%) eyes showed one or more quantitative abnormalities >2 SD from the age adjusted norm means. These abnormalities clustered mainly about dark adaptation (rod cell) sensitivity (31, 62% of measured sites), the blue sensitive retinal cells (17, 34% of measured eyes), and the oscillatory component (OP) of the electroretinogram (23, 46% of measured eyes). One control eye (7%) showed a significant dark adaptation abnormality and ERG reduction. There was no identifiable interaction between chemotherapy mode and the cancer associated retinal deficits (CARD). Antiretinal antibodies were found in sera from most patients and controls.

CONCLUSION

CARD is common in the retinal periphery of many cancer patients, and is distinct from rare CAR, MAR central-retinal responses. CARD has numerous potential clinical uses which justify expanded research with more defined large samples.

Calcium-binding proteins and nitric oxide in retinal function and disease

Regulation of phototransduction in photoreceptor cells occurs via several feedback loops. Some of these circuits involve the neuron-specific Ca2+-binding proteins recoverin and guanylyl cyclase-activating protein. Recent findings suggest that these proteins are also involved in retinal diseases. Another Ca2+-regulated process in the retina is the synthesis of nitric oxide, a substance of potential neurotoxicity. This review discusses several Ca2+-mediated processes in the retina.

Recoverin-associated retinopathy: a clinically and immunologically distinctive disease

PURPOSE

To compare the immune response to retinal antigens in a patient with a clinical condition resembling cancer-associated retinopathy with the immune responses of patients with other retinal degenerations or uveitis.

METHODS

Cellular and humoral immune responses to retinal S-antigen and recoverin were determined in one patient with disease resembling cancer-associated retinopathy, three patients with other retinal degenerations, and eight patients with uveitis.

RESULTS

A cellular immune response against recoverin was found only in the patient with the condition resembling cancer-associated retinopathy. Elevated levels of antibody against recoverin were found in this patient and in one of the three patients with a retinal degeneration, but in none of the eight patients with uveitis. In contrast, moderate lymphocyte responses to retinal S-antigen were found in most of the patients studied, and this response did not distinguish among the patient groups. Levels of serum antibodies against retinal S-antigen were also similar in all patients tested. Serum from the patient with disease resembling cancer-associated retinopathy produced strong immunostaining of the rods, cones, outer plexiform layer, and some cone bipolar cells, but serum from the patients with uveitis or other retinal degenerations did not show specific reactivity with the retina.

CONCLUSIONS

We propose that this immunologically and clinically distinctive condition be termed recoverin-associated retinopathy, and we suggest that a cellular immune response against recoverin may be a distinguishing feature of the disorder.

Characterization of a potent uveitopathogenic site derived from rat phosducin

Phosducin is a retinal and pineal phosphoprotein assumed to play an important role in visual phototransduction. Phosducin is also a uveitopathogenic retinal antigen, but its potency has been reported to be mild. During the course of studies aimed at identifying uveitopathogenic sites in phosducin, we found that rat phosducin possessed a potent uveitopathogenic site. In this study, we characterize the potent uveitopathogenic site by using synthetic peptides. Several synthetic peptides from this region plus adjuvants were injected into Lewis rats, and the uveitopathogenic core sequence was defined. We also determined the pivotal amino acid residues by using synthetic peptides with single residue substitution. Immunization with PDC(R)65-96 (amino acid residues 65 through 96 derived from rat phosducin) at doses of 0.83 nmol or more induced severe experimental autoimmune uveitis (EAU) in all rats within 12 days. Experimental autoimmune pinealitis (EAP) was also observed in all rats after immunization with 0.83 nmol or higher doses of the peptide. The lowest dose of the peptide to induce EAU and EAP was 0.24 nmol. The smallest peptide that induced EAU as severe as PDC(R)65-96 was PDC(R)77-87, which consisted of 11 amino acid residues (YELIHQDKEDE). The core sequence within the uveitopathogenic site was a pentapeptide (LIHQD), amino acid residues from 79 to 83. To determine the role of individual residues within PDC(R)77-87, we tested the uveitopathogenicity of analogues of PDC(R)75-85 and PDC(R)77-89, respectively, in which each of the residues from 77 to 87 was replaced by alanine (A). Analogous peptides bearing a single residue substitution at 80 (I-->A) and 82 (Q-->A), respectively, were not uveitopathogenic. Our findings demonstrated the presence of a potent uveitopathogenic site in PDC(R)65-96 whose potency in Lewis rats was comparable to that of S-antigen. The pivotal amino acid residues for uveitopathogenicity were the residues at 80 (I) and 82 (Q). The clinical and histological features of this EAU closely resembled those of the EAU induced by S-antigen and recoverin.

Calcium binding to recoverin: implications for secondary structure and membrane association

Recoverin is an EF-hand calcium-binding protein reportedly involved in the transduction of light by vertebrate photoreceptor cells. It also is an autoantigen in a cancer-associated degenerative disease of the retina. Measurements by circular dichroism presented here demonstrate that the binding of calcium to recoverin causes large structural changes. increasing the alpha-helical content of the protein and decreasing its beta-turn, beta-sheet and 'other' structures. The maximum helical content (67%) was observed at 100 microM free calcium and, unlike calmodulin, decreased as the calcium concentration was modulated in either direction from this value. Fluorescence measurements indicated that recoverin may aggregate or undergo structural changes independent of calcium binding as the calcium concentration is increased above 100 microM. EGTA also appeared to affect the structure of recoverin independent of its chelation of calcium. While calcium-induced conformational changes have been proposed to alter the membrane binding of recoverin through association of its myristoylated amino terminus, in the experiments presented here the partitioning of recoverin between the cytoplasmic and membrane compartments of the rod photoreceptor outer segment was unaffected by the concentration of calcium, therefore it appears unlikely that a calcium-myristoyl switch acts alone to anchor recoverin directly to the membrane. These experiments were conducted with native recoverin which is heterogeneously acylated, but mass spectrometry confirmed that simple chromatographic methods could be devised to isolate the different forms of recoverin for further studies.

Autoimmune retinopathy in the absence of cancer

PURPOSE

To report the clinical and immunologic features of two patients with progressive retinal degeneration and circulating antiretinal antibodies without systemic malignancy.

METHODS

Two patients were followed up for 5 to 7 years. Comprehensive medical and ophthalmic examinations and visual function testing included manual perimetry and standardized electroretinography. Patient sera were tested for antiretinal antibodies by Western blot and immunoperoxidase indirect cytochemistry techniques.

RESULTS

Two patients had family history of autoimmune disease. Each had severe monocular visual loss with photopsia, a ring scotoma, and abnormal electroretinogram despite a normal-appearing ocular fundus. One had a flat electroretinogram; the other had inner retina dysfunction, with selective b wave loss and abnormal oscillatory potentials. Both patients' sera had antiretinal antibodies that specifically labeled the inner plexiform layer of donor retina by indirect immunoperoxidase testing. Neither had any sign of cancer.

CONCLUSIONS

In two patients without systemic malignancy, the symptoms, perimetric findings, and normal fundus appearance resembled cancer associated retinopathy. Electroretinography and antibody findings indicating dysfunction of the inner retina are distinct from those of cancer-associated retinopathy. These two cases raise the possibility of an autoimmune mechanism for retinal degeneration that is not cancer associated. Further study is necessary to determine the role of antiretinal antibodies in these patients.

Uveitogenic 28/30 kD and 43 kD polypeptides in pigment epithelial membranes of the retina

The purpose of this study was the search for new intrinsic polypeptides of the retinal pigment epithelium (RPE) capable of evoking experimental uveitis. A membrane fraction was prepared from purified bovine RPE cells. The Triton X-100 soluble protein fraction was separated into polypeptide fractions by preparative gel electrophoresis, and the pathogenicity of the main isolated polypeptides was investigated in Lewis rats. After immunization, two hitherto unknown pigment epithelial polypeptides with M(r) 28/30 kD (doublet) and 43 kD (PEP-28/30 and PEP-43, respectively) elicited progressive pigment epitheliitis and choroiditis accompanied by extending plaque-shaped macrophage accumulations along the RPE-Bruch's membrane layer. No inflammatory foci were found within the neural retina. Polypeptide fractions with M(r) 14-17, 25 and 32/34 kD (doublet) (PEP-14/17, PEP-25 and PEP-32/34, respectively) appeared to be non-uveitogenic at the tested dose. PEP-28/30 and PEP-43 exhibited a partial antigenic relationship to PEP-65. PEP-28/30 exhibited marked reactivity to a monoclonal antibody previously raised to a 32 kD RPE-specific protein.

IN CONCLUSION

in addition to the previously described main RPE-specific membrane polypeptide PEP-65, the RPE appears to contain two more uveitogenic components, the intrinsic pigment epithelial membrane polypeptides PEP-28/30 and PEP-43. Like PEP-65, these antigens are able to evoke experimental autoimmune pigment epithelial protein-induced uveitis (EAPU) in rats.

Turned on by Ca2+! The physiology and pathology of Ca(2+)-binding proteins in the retina

Vertebrate photoreceptor cells can signal the absorption of a single photon and then modulate their response as the intensity of the light and the intensity of the background illumination vary, and it has long been recognized that Ca2+ ions contribute to the underlying processes. Recently, several Ca(2+)-binding proteins of the EF-hand family were identified that mediate the actions of Ca2+ during the response to light. Molecular interactions between these Ca(2+)-binding proteins and their cellular targets are amenable to study owing in part to the unique features of phototransduction. In addition, two of the proteins, recoverin and guanylate cyclase activating protein (GCAP), appear to be involved in separate degenerative diseases of the retina that arise in humans and in animal models of human disease. Information obtained from these studies should also be relevant to the growing number of homologous proteins found in other neural tissues.