Major retinal autoantigens remain stably expressed during all stages of spontaneous uveitis

Differential Expression of ARG1 and MRC2 in Retinal Müller Glial Cells During Autoimmune Uveitis

Retinal Müller glial cells (RMG) play a crucial role in retinal neuroinflammation, including autoimmune uveitis. Increasing evidence supports their function as active modulators of immune responses and potential atypical antigen-presenting cells (APCs). To further investigate this hypothesis, we conducted a differential proteome analysis of primary equine RMG from healthy controls and horses with equine recurrent uveitis (ERU), a spontaneous model of autoimmune uveitis. This analysis identified 310 proteins with differential abundance. Among these, the Major Histocompatibility Complex (MHC) class II and the enzyme Arginase 1 (ARG1) were significantly enriched in RMG from uveitis-affected horses, whereas Mannose Receptor C-type 2 (MRC2) and its interactor Thrombospondin 1 (THBS1) were more abundant in healthy RMG. The detection of MHC class II in equine RMG, consistent with previous studies, validates the robustness of our approach. Furthermore, the identification of ARG1 and MRC2, together with THBS1, provides new insights into the immunomodulatory and antigen-presenting properties of RMG. Immunohistochemical analyses confirmed the proteomic findings and revealed the spatial distribution of ARG1 and MRC2. ARG1 and MRC2 are thus markers for RMG in the neuroinflammatory or physiological milieu and highlight potential differences in the immune function of RMG, particularly in antigen presentation.

Effect of gentamicin on CD3+ T-lymphocyte proliferation for treatment of equine recurrent uveitis: An in vitro study

OBJECTIVE

The objective of the study was to determine the effect of gentamicin on CD3+ T-lymphocyte proliferation and cell viability using an in vitro cell culture model as a means of investigating the mechanism of action of low-dose intravitreal gentamicin injection.

ANIMALS STUDIED

Three adult horses with no evidence of ophthalmic or systemic disease.

PROCEDURE

Peripheral blood lymphocytes were treated with gentamicin at concentrations 37.5 μg/mL, 112.5 μg/mL, 187 μg/mL, 375 μg/mL, or 750 μg/mL then stimulated to proliferate with concanavalin A (ConA). 4',6-diamidino-2-phenylindole (DAPI) and carboxyfluoroscein succinimidyl ester (CSFE) were used as markers of cell viability and cell proliferation, respectively. Following 5-day culture, live cell counts and CSFE fluorescent intensity data were collected via automated cell count and flow cytometry. The experimental design was duplicated using preservative-free gentamicin and a proprietary brand formulation. Statistical analysis was performed using two-way ANOVA with Tukey's multiple comparison test.

RESULTS

No statistically significant comparisons in CD3+ T-lymphocyte live cell counts and geometric mean fluorescent intensity of CSFE were identified between gentamicin concentrations or formulations.

CONCLUSIONS

Gentamicin had no effect on equine peripheral blood CD3+ T-lymphocyte cell viability and proliferation in concentrations ranging from "safe" to "retinotoxic" in relation to intravitreal injection volumes. Low-dose intravitreal gentamicin may not suppress the Th1- and Th17-mediated immune response.

Developing advanced therapeutics through the study of naturally occurring immune-mediated ocular disease in domestic animals

This review, which is part of the "Currents in One Health" series, describes the importance of the study of immune-mediated ocular disease in the development of innovative therapeutics, such as cell and gene therapy for the eye. Recent examples of cell and gene therapy studies from the author's laboratory are reviewed to emphasize the importance of One Health initiatives in developing innovative therapies for ocular diseases. Spontaneous immune-mediated corneal disease is common in horses, cats, dogs, and humans. Autologous bone marrow-derived mesenchymal stem cells (BM-MSCs) injected subconjunctivally resulted in the resolution of naturally occurring immune-mediated keratitis (IMMK) without adverse effects. These results support that autologous subconjunctival BM-MSC therapy may be a viable treatment alternative for IMMK. Furthermore, the use of subconjunctival MSCs may be an effective method to treat ocular surface immune-mediated diseases in humans and other species, including herpetic stromal keratitis and immunologic dry eye disease. Furthermore, the use of adeno-associated viral (AAV) vectors to deliver the immunosuppressive transgene cDNA of equine interleukin 10 (eqIL-10) or human leukocyte antigen G injected intravitreally was shown to be safe and inhibited the development of uveitis in the experimental autoimmune uveitis rat model. Efficacy and safety studies of ocular gene therapy in models will pave the way for clinical trials in animals with naturally occurring immune-mediated diseases, such as a therapeutic clinical trial for AAV-eqIL-10 in horses with equine recurrent uveitis.

A review of investigated risk factors for developing equine recurrent uveitis

Equine recurrent uveitis (ERU) is an ocular inflammatory disease that can be difficult to manage clinically. As such, it is the leading cause of bilateral blindness for horses. ERU is suspected to have a complex autoimmune etiology with both environmental and genetic risk factors contributing to onset and disease progression in some or all cases. Work in recent years has aimed at unraveling the primary triggers, such as infectious agents and inherited breed-specific risk factors, for disease onset, persistence, and progression. This review has aimed at encompassing those factors that have been associated, implicated, or substantiated as contributors to ERU, as well as identifying areas for which additional knowledge is needed to better understand risk for disease onset and progression. A greater understanding of the risk factors for ERU will enable earlier detection and better prognosis through prevention and new therapeutics.

Infectious Uveitis in Horses and New Insights in Its Leptospiral Biofilm-Related Pathogenesis

Uveitis is a sight-threatening eye disease in equids known worldwide that leads to considerable pain and suffering. By far the most common type of uveitis in Germany and neighboring countries is classical equine recurrent uveitis (ERU), which is caused by chronic intraocular leptospiral infection and is the main cause of infectious uveitis in horses. Other infectious causes are extremely rare and are usually clinically distinguishable from ERU. ERU can be treated very effectively by vitreous cavity lavage (vitrectomy). For proper indications of this demanding surgery, it is necessary to differentiate ERU from other types of uveitis in which vitrectomy is not helpful. This can be conducted on the basis of anamnesis in combination with ophthalmologic findings and by aqueous humor examination. During vitrectomy, vitreous material is obtained. These vitreous samples have historically been used for numerous etiologic studies. In this way, a chronic intraocular leptospiral infection has been shown to be the cause of typical ERU and, among other findings, ERU has also been recognized as a biofilm infection, providing new insights into the pathogenesis of ERU and explaining some thus far unexplainable phenomena of ERU. ERU may not only have transmissible aspects to some types of uveitis in humans but may also serve as a model for a spontaneously occurring biofilm infection. Vitreous material obtained during therapeutically indicated vitrectomy can be used for further studies on in vivo biofilm formation, biofilm composition and possible therapeutic approaches.

Immunological Insights in Equine Recurrent Uveitis

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

Leptospiral antibody prevalence and surgical treatment outcome in horses with Equine Recurrent Uveitis (ERU) in Switzerland

OBJECTIVE

To evaluate leptospiral antibody prevalence in 65 horses with ERU and compare outcome in 36 surgically treated eyes (2010-2015).

PROCEDURES

Retrospective data analysis of horses with ERU (n = 65). C-value calculation with microagglutination assay titer (MAT) results for Leptospira spp. Evaluation of follow-up data after pars plana vitrectomy (PPV, n = 21 eyes) and suprachoroidal cyclosporine device implantation (SCDI, n = 15 eyes). Differences between groups were statistically analyzed using Fishers exact test, significance set at P < .05.

RESULTS

Positive leptospiral titers were found in 28/65 blood, 31/65 aqueous humor (AH), and 19/20 vitreal (post-PPV) samples. The most common intraocular serovars were Leptospira interrogans grippotyphosa, pomona, and bratislava. Intraocular antibody production was suspected in samples of 22 horses (c-values > 1). Mean follow-up of surgical cases was 3.8 years (PPV) and 3.4 years (SCDI). PPV was performed in 21 eyes with positive, SCDI in 15 eyes with negative leptospiral test results. Uveitis recurred less often after PPV (2/21) compared to SCDI (6/15, P = .04). Retinal detachment occurred after PPV only (5/21, SCDI 0/15, P = .06), whereas only SCDI-treated eyes were enucleated (PPV 0/21, SCDI 3/15, P = .06). Blindness or visual impairment was equally likely to occur in both treatment groups after surgery (PPV 7/21, SCDI 7/15, P = .5).

CONCLUSIONS

Leptospiral antibody prevalence is high in horses with ERU in Switzerland. Recurrence of uveitis is uncommon following PPV in the present study; an increased risk of retinal detachment exists. Enucleation is more often warranted in horses after SCDI in this study due to a higher uveitis recurrence.

Genetic investigation of equine recurrent uveitis in Appaloosa horses

Equine recurrent uveitis (ERU) is characterized by intraocular inflammation that often leads to blindness in horses. Appaloosas are more likely than any other breed to develop insidious ERU, distinguished by low-grade chronic intraocular inflammation, suggesting a genetic predisposition. Appaloosas are known for their white coat spotting patterns caused by the leopard complex spotting allele (LP) and the modifier PATN1. A marker linked to LP on ECA1 and markers near MHC on ECA20 were previously associated with increased ERU risk. This study aims to further investigate these loci and identify additional genetic risk factors. A GWAS was performed using the Illumina Equine SNP70 BeadChip in 91 horses. Additive mixed model approaches were used to correct for relatedness. Although they do not reach a strict Bonferroni genome-wide significance threshold, two SNPs on ECA1 and one SNP each on ECA12 and ECA29 were among the highest ranking SNPs and thus warranted further analysis (P = 1.20 × 10^-5 , P = 5.91 × 10^-6 , P = 4.91 × 10^-5 , P = 6.46 × 10^-5 ). In a second cohort (n = 98), only an association with the LP allele on ECA1 was replicated (P = 5.33 × 10^-5 ). Modeling disease risk with LP, age and additional depigmentation factors (PATN1 genotype and extent of roaning) supports an additive role for LP and suggests an additive role for PATN1. Genotyping for LP and PATN1 may help predict ERU risk (AUC = 0.83). The functional role of LP and PATN1 in ERU development requires further investigation. Testing samples across breeds with leopard complex spotting patterns and a denser set of markers is warranted to further refine the genetic components of ERU.

Prognosis and impact of equine recurrent uveitis

REASONS FOR PERFORMING STUDY

Equine recurrent uveitis (ERU) is a leading cause of vision loss in horses.

OBJECTIVES

To assess the prognosis and impact of ERU on affected horses and their owners by evaluating the signalment, treatment and outcome (including the loss of use, vision assessment and economic loss).

STUDY DESIGN

Retrospective impact study.

METHODS

Medical records of horses presenting to the North Carolina State University Veterinary Health Complex (NCSU-VHC) with ERU between 1999 and 2014 were reviewed. Signalment, clinical signs, ophthalmic examination findings, treatments and outcomes were evaluated. Owner questionnaires were completed regarding vision, job/role, monetary value, diagnostic and treatment costs, concurrent illness and outcomes.

RESULTS

Records of 224 horses (338 eyes) with ERU were reviewed. There was an overrepresentation of Appaloosas (54; 24.1%), Hanoverians (11; 4.9%) and other Warmbloods (13; 5.8%). Ninety-six eyes (28.4%) were diagnosed as blind and 38 eyes (11.2%) with glaucoma on initial evaluation. Leptospirosis titres of serum and/or aqueous humour were obtained in 88 horses and were positive in 40 horses (45.5%), with L. pomona being the most frequently isolated serovar. Globe loss at the NCSU-VHC occurred in 41 ERU eyes (12.1% of total). Owner questionnaires were evaluated in 194 horses (86.6%) and 91 horses (46.9%) were reported blind in the affected eye(s). Fifty-seven horses (29.4%) did not return to their previous role, while 61 (31.4%) performed at a reduced level. Equine recurrent uveitis decreased the monetary value of 164 horses. Twenty-nine horses (14.9%) were euthanised and 37 (19.1%) underwent change in ownership as a direct result of ERU.

CONCLUSIONS

The impact of ERU is attributed to the high frequency of blindness, globe loss and loss of function. Euthanasia and change of ownership are common sequelae to the progressive nature of ERU. These factors, along with financial costs of the disease, have a significant impact on affected horses and their owners.

Equine recurrent uveitis: Human and equine perspectives

Equine recurrent uveitis (ERU) is a spontaneous disease characterised by repeated episodes of intraocular inflammation. The epidemiology of ERU has not been fully elucidated, but the condition appears to be much more common in horses than is recurrent uveitis in humans, especially in certain breeds and geographical regions. Both humans and horses show a similarly altered immune response and a marked autoimmune response as the primary disease pathophysiology. However, an inciting cause is not always clear. Potential inciting factors in horses include microbial agents such as Leptospira spp. Microbial factors and genetic predisposition to the disease may provide clues as to why the horse appears so susceptible to this disease. The aim of this review is to discuss the immunology and genetics of ERU, compare the disease in horses with autoimmune anterior uveitis in humans, and discuss potential reasons for the increased prevalence in the horse.

Novel localization of peripherin 2, the photoreceptor-specific retinal degeneration slow protein, in retinal pigment epithelium

Retinal pigment epithelium (RPE) builds the outer blood-retinal barrier of the eye. Since one typical feature of the autoimmune disease, equine recurrent uveitis (ERU), is the breakdown of this barrier, we recently performed comparative analysis of healthy and uveitic RPE. We identified for the first time peripherin 2, which is responsible for visual perception and retina development, to be localized in RPE. The purpose of this study was therefore to validate our findings by characterizing the expression patterns of peripherin 2 in RPE and retina. We also investigated whether peripherin 2 expression changes in ERU and if it is expressed by the RPE itself. Via immunohistochemistry, significant downregulation of peripherin 2 in uveitic RPE compared to the control was detectable, but there was no difference in healthy and uveitic retina. A further interesting finding was the clear distinction between peripherin 2 and the phagocytosis marker, rhodopsin, in healthy RPE. In conclusion, changes in the expression pattern of peripherin 2 selectively affect RPE, but not retina, in ERU. Moreover, peripherin 2 is clearly detectable in healthy RPE due to both phagocytosis and the expression by the RPE cells themselves. Our novel findings are very promising for better understanding the molecular mechanisms taking place on RPE in uveitis.

Spontaneous development of autoimmune uveitis Is CCR2 dependent

Development of novel strategies to treat noninfectious posterior uveitis is an ongoing challenge, in part because of limited availability of animal models that mimic the naturally occurring disease in humans. Mice deficient in the autoimmune regulatory gene Aire develop a spontaneous T-cell and macrophage-mediated autoimmune uveitis that closely recapitulates human endogenous uveitis and thus provide a useful model for mechanistic and therapeutic investigations. Lymphocytic and mononuclear infiltration of the retina in Aire knockout (KO) mice triggers the onset of uveitis from initial retinal inflammation to eventual destruction of the neuroretina with loss of photoreceptors. The C-C chemokine receptor type 2 protein (CCR2) functions in directing monocyte and macrophage migration to inflamed tissues via interaction with monocyte chemotactic proteins. Using the Aire KO mouse model, we demonstrated an essential role for CCR2 in the pathogenesis of autoimmune-mediated uveitis. Loss of functional CCR2 effectively reduced immune cell infiltration and rescued the retina from destruction. CCR2-dependent migration of bone marrow-derived cells provided the driving force for retinal inflammation, with CCR2-expressing mononuclear cells contributing to retinal damage via recruitment of CD4(+) T cells. These studies identify the CCR2 pathway as a promising therapeutic target that may prove an effective approach to treat uveitis associated with autoimmunity.

Genetic risk factors for insidious equine recurrent uveitis in Appaloosa horses

Appaloosa horses are predisposed to equine recurrent uveitis (ERU), an immune-mediated disease characterized by recurring inflammation of the uveal tract in the eye, which is the leading cause of blindness in horses. Nine genetic markers from the ECA1 region responsible for the spotted coat color of Appaloosa horses, and 13 microsatellites spanning the equine major histocompatibility complex (ELA) on ECA20, were evaluated for association with ERU in a group of 53 Appaloosa ERU cases and 43 healthy Appaloosa controls. Three markers were significantly associated (corrected P-value <0.05): a SNP within intron 11 of the TRPM1 gene on ECA1, an ELA class I microsatellite located near the boundary of the ELA class III and class II regions and an ELA class II microsatellite located in intron 1 of the DRA gene. Association between these three genetic markers and the ERU phenotype was confirmed in a second population of 24 insidious ERU Appaloosa cases and 16 Appaloosa controls. The relative odds of being an ERU case for each allele of these three markers were estimated by fitting a logistic mixed model with each of the associated markers independently and with all three markers simultaneously. The risk model using these markers classified ~80% of ERU cases and 75% of controls in the second population as moderate or high risk, and low risk respectively. Future studies to refine the associations at ECA1 and ELA loci and identify functional variants could uncover alleles conferring susceptibility to ERU in Appaloosa horses.

Retinal glycoprotein enrichment by concanavalin a enabled identification of novel membrane autoantigen synaptotagmin-1 in equine recurrent uveitis

Complete knowledge of autoantigen spectra is crucial for understanding pathomechanisms of autoimmune diseases like equine recurrent uveitis (ERU), a spontaneous model for human autoimmune uveitis. While several ERU autoantigens were identified previously, no membrane protein was found so far. As there is a great overlap between glycoproteins and membrane proteins, the aim of this study was to test whether pre-enrichment of retinal glycoproteins by ConA affinity is an effective tool to detect autoantigen candidates among membrane proteins. In 1D Western blots, the glycoprotein preparation allowed detection of IgG reactions to low abundant proteins in sera of ERU patients. Synaptotagmin-1, a Ca2+-sensing protein in synaptic vesicles, was identified as autoantigen candidate from the pre-enriched glycoprotein fraction by mass spectrometry and was validated as a highly prevalent autoantigen by enzyme-linked immunosorbent assay. Analysis of Syt1 expression in retinas of ERU cases showed a downregulation in the majority of ERU affected retinas to 24%. Results pointed to a dysregulation of retinal neurotransmitter release in ERU. Identification of synaptotagmin-1, the first cell membrane associated autoantigen in this spontaneous autoimmune disease, demonstrated that examination of tissue fractions can lead to the discovery of previously undetected novel autoantigens. Further experiments will address its role in ERU pathology.

Osteopontin and fibronectin levels are decreased in vitreous of autoimmune uveitis and retinal expression of both proteins indicates ECM re-modeling

Autoimmune uveitis is an intraocular inflammation that arises through autoreactive T-cells attacking the inner eye, eventually leading to blindness. However, the contributing molecular pathomechanisms within the affected tissues remain as yet elusive. The extracellular matrix (ECM) is a highly dynamic structure that varies tremendously and influences the encompassing tissue. In order to assess ECM re-modeling in autoimmune uveitis, we investigated the expression of ECM molecules fibronectin and osteopontin in vitreous and retina samples. This was carried out in the only spontaneous animal model for human autoimmue uveitis, namely equine recurrent uveitis (ERU) that resembles the human disease in clinical as well as in immunopathological aspects. ERU is a naturally occurring autoimmune disease in horses that develops frequently and has already proved its value to study disease-related pathomechanisms. Western blot analysis of fibronectin and osteopontin in healthy and uveitic vitreous revealed significant reduction of both proteins in uveitis. Immunohistochemical expression of fibronectin in healthy retinas was restricted to the inner limiting membrane abutting vimentin positive Müller cell endfeet, while in uveitic sections, a disintegration of the ILM was observed changing the fibronectin expression to a dispersed pattern extending toward the vitreous. Retinal expression of osteopontin in control tissue was found in a characteristic Müller cell pattern illustrated by co-localization with vimentin. In uveitic retinas, the immunoreactivity of osteopontin in gliotic Müller cells was almost absent. The ability of Müller cells to express fibronectin and osteopontin was additionally shown by immunocytochemistry of primary cultured equine Müller cells and the equine Müller cell line eqMC-7. In conclusion, severe ECM re-modeling in autoimmune uveitis reported here, might affect the adhesive function of fibronectin and thus the anchoring of Müller cell endfeet to the ILM. Furthermore, the absence of osteopontin in gliotic Müller cells might represent reduced neuroprotection, an osteopontin attribute that is intensively discussed.

Characterization of cytokines associated with Th17 cells in the eyes of horses with recurrent uveitis

OBJECTIVE

Equine recurrent uveitis (ERU) is a spontaneous disease that is the most common cause of blindness in horses, affecting up to 15% of the horse population. Th17 cells are a major cell population driving the pathogenesis in several mouse models of autoimmune inflammation, including experimental autoimmune uveitis. The purpose of this study is to investigate the role a Th17 cell-mediated response plays in the pathogenesis of ERU.

PROCEDURE

Banked, Davidson's-fixed equine globes histopathologically diagnosed with ERU (n = 7) were compared immunohistochemically with healthy control globes (n = 7). Immunohistochemical staining was performed using a pan-Leptospira antibody and antibodies against IL-6, IL-17, and IL-23. Additionally, immunostaining was performed for T-cell (CD3) and B-cell (CD79α) markers. Specificity of immunoreactivity was confirmed by western blot analysis.

RESULTS

Immunohistochemical staining was positive for IL-6, IL-17, and IL-23 within the cytoplasm of nonpigmented ciliary epithelial cells and mononuclear inflammatory cells infiltrating the iris, and ciliary body of ERU horses (n = 7) but negative in controls (n = 7). ERU-affected eyes were CD3 positive (n = 7) and CD79α negative (n = 7). Staining for Leptospira was negative in all ERU and control globes.

CONCLUSIONS

Strong immunoreactivity for IL-6, IL-17, and IL-23, in conjunction with the fact that T lymphocytes are the predominating inflammatory cells present in ERU, suggests that IL-17-secreting helper T-cells play a role in the pathogenesis of ERU. These findings suggest that horses with ERU may serve as a naturally occurring animal model for autoimmune uveitis.

Ocular immunology in equine recurrent uveitis

Equine recurrent uveitis (ERU) is a disease with high prevalence and relevance for the equine population, since it results in blindness. Over the last decade, important advancements have been made in our understanding of the underlying immune responses in this disease. ERU is mediated by an autoaggressive Th1 response directed against several retinal proteins. Interphotoreceptor-retinoid binding protein (IRBP) and cellular retinaldehyde-binding protein (CRALBP) are capable to induce ERU-like disease in experimental horses, with the unique possibility to activate relapses in a well-defined manner. Further, proteomic evidence now suggests that retinal Mueller glial cells (RMG) may play a fatal role in uveitic disease progression by directly triggering inflammation processes through the expression and secretion of interferon-gamma. Ongoing relapses in blind eyes can be associated with stable expression of the major autoantigens in ERU retinas. This review briefly summarizes the most significant developments in uveitis immune response research.