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

Enhanced ROS Production and Mitochondrial Metabolic Shifts in CD4+ T Cells of an Autoimmune Uveitis Model

Equine recurrent uveitis (ERU) is a spontaneously occurring autoimmune disease and one of the leading causes of blindness in horses worldwide. Its similarities to autoimmune-mediated uveitis in humans make it a unique spontaneous animal model for this disease. Although many aspects of ERU pathogenesis have been elucidated, it remains not fully understood and requires further research. CD4+ T cells have been a particular focus of research. In a previous study, we showed metabolic alterations in CD4+ T cells from ERU cases, including an increased basal oxygen consumption rate (OCR) and elevated compensatory glycolysis. To further investigate the underlying reasons for and consequences of these metabolic changes, we quantified reactive oxygen species (ROS) production in CD4+ T cells from ERU cases and compared it to healthy controls, revealing significantly higher ROS production in ERU-affected horses. Additionally, we aimed to define mitochondrial fuel oxidation of glucose, glutamine, and long-chain fatty acids (LCFAs) and identified significant differences between CD4+ T cells from ERU cases and controls. CD4+ T cells from ERU cases showed a lower dependency on mitochondrial glucose oxidation and greater metabolic flexibility for the mitochondrial oxidation of glucose and LCFAs, indicating an enhanced ability to switch to alternative fuels when necessary.

The use of shotgun label-free quantitative proteomic mass spectrometry to evaluate the inflammatory response in aqueous humor from horses with uveitis compared to ophthalmologically healthy horses

OBJECTIVE

The objective of this study was to use shotgun label-free tandem mass spectrometry (LF-MS/MS) to evaluate aqueous humor (AH) from horses with uveitis (UH) compared to ophthalmologically healthy horses (HH).

ANIMALS STUDIED

Twelve horses diagnosed with uveitis based on ophthalmic examination and six ophthalmologically healthy horses (postmortem) purchased for teaching purposes.

PROCEDURES

All horses received a complete ophthalmic examination and physical exam. Aqueous paracentesis was performed on all horses and AH total protein concentrations were measured with nanodrop (TPn) and refractometry (TPr). AH samples were analyzed with shotgun LF-MS/MS and proteomic data were compared between groups using Wilcoxon rank-sum test.

RESULTS

A total of 147 proteins were detected, 11 proteins had higher abundance in UH, and 38 proteins had lower abundance in UH. Proteins with higher abundance included apolipoprotein E, alpha-2-macroglobulin (A2M), alpha-2-HS-glycoprotein, prothrombin, fibrinogen, complement component 4 (C4), joining chain for IgA and IgM, afamin, and amine oxidase. There were positive correlations between TPn (p = .003) and TPr (p = .0001) compared to flare scores.

CONCLUSION

Differential abundance of A2M, prothrombin, fibrinogen, and C4 indicate upregulation of the complement and coagulation cascade in equine uveitis. Proinflammatory cytokines and the complement cascade have potential as therapeutic targets for equine uveitis.

Unveiling Differential Responses of Granulocytes to Distinct Immunostimulants with Implications in Autoimmune Uveitis

The perception of circulating granulocytes as cells with a predetermined immune response mainly triggered by pathogens is evolving, recognizing their functional heterogeneity and adaptability, particularly within the neutrophil subset. The involvement of these cells in the pathophysiology of autoimmune uveitis has become increasingly clear, yet their exact role remains elusive. We used an equine model for autoimmune-mediated recurrent pan-uveitis to investigate early responses of granulocytes in different inflammatory environments. For this purpose, we performed differential proteomics on granulocytes from healthy and diseased horses stimulated with IL8, LPS, or PMA. Compared to healthy horses, granulocytes from the recurrent uveitis model significantly changed the cellular abundance of 384 proteins, with a considerable number of specific changes for each stimulant. To gain more insight into the functional impact of these stimulant-specific proteome changes in ERU pathogenesis, we used Ingenuity Pathway Analysis for pathway enrichment. This resulted in specific reaction patterns for each stimulant, with IL8 predominantly promoting Class I MHC-mediated antigen processing and presentation, LPS enhancing processes in phospholipid biosynthesis, and PMA, clearly inducing neutrophil degranulation. These findings shed light on the remarkably differentiated responses of neutrophils, offering valuable insights into their functional heterogeneity in a T-cell-driven disease. Raw data are available via ProteomeXchange with identifier PXD013648.

Preliminary evaluation of safety and migration of immune activated mesenchymal stromal cells administered by subconjunctival injection for equine recurrent uveitis

Introduction

Equine recurrent uveitis (ERU), an immune mediated disease characterized by repeated episodes of intra-ocular inflammation, affects 25% of horses in the USA and is the most common cause of glaucoma, cataracts, and blindness. Mesenchymal stromal cells (MSCs) have immunomodulatory properties, which are upregulated by preconditioning with toll-like receptor agonists. The objective was to evaluate safety and migration of TLR-3 agonist polyinosinic, polycytidylic acid (pIC)-activated MSCs injected subconjunctivally in healthy horses prior to clinical application in horses with ERU. We hypothesized that activated allogeneic MSCs injected subconjunctivally would not induce ocular or systemic inflammation and would remain in the conjunctiva for >14 days.

Methods

Bulbar subconjunctiva of two horses was injected with 10 × 106 pIC-activated (10 μg/mL, 2 h) GFP-labeled MSCs from one donor three times at two-week intervals. Vehicle (saline) control was injected in the contralateral conjunctiva. Horses received physical and ophthalmic exams [slit lamp biomicroscopy, rebound tonometry, fundic examination, and semiquantitative preclinical ocular toxicology scoring (SPOTS)] every 1-3 days. Systemic inflammation was assessed via CBC, fibrinogen, and serum amyloid A (SAA). Horses were euthanized 14 days following final injection. Full necropsy and histopathology were performed to examine ocular tissues and 36 systemic organs for MSC presence via IVIS Spectrum. Anti-GFP immunohistochemistry was performed on ocular tissues.

Results

No change in physical examinations was noted. Bloodwork revealed fibrinogen 100-300 mg/dL (ref 100-400) and SAA 0-25 μg/mL (ref 0-20). Ocular effects of the subjconjucntival injection were similar between MSC and control eyes on SPOTS grading system, with conjunctival hypermia, chemosis and ocular discharge noted bilaterally, which improved without intervention within 14 days. All other ocular parameters were unaffected throughout the study. Necropsy and histopathology revealed no evidence of systemic inflammation. Ocular histopathology was similar between MSC and control eyes. Fluorescent imaging analysis did not locate MSCs. Immunohistochemistry did not identify intact MSCs in the conjunctiva, but GFP-labeled cellular components were present in conjunctival phagocytic cells.

Discussion

Allogeneic pIC-activated conjunctival MSC injections were well tolerated. GFP-labeled tracking identified MSC components phagocytosed by immune cells subconjunctivally. This preliminary safety and tracking information is critical towards advancing immune conditioned cellular therapies to clinical trials in horses.

Elastin stabilization prevents impaired biomechanics in human pulmonary arteries and pulmonary hypertension in rats with left heart disease

Pulmonary hypertension worsens outcome in left heart disease. Stiffening of the pulmonary artery may drive this pathology by increasing right ventricular dysfunction and lung vascular remodeling. Here we show increased stiffness of pulmonary arteries from patients with left heart disease that correlates with impaired pulmonary hemodynamics. Extracellular matrix remodeling in the pulmonary arterial wall, manifested by dysregulated genes implicated in elastin degradation, precedes the onset of pulmonary hypertension. The resulting degradation of elastic fibers is paralleled by an accumulation of fibrillar collagens. Pentagalloyl glucose preserves arterial elastic fibers from elastolysis, reduces inflammation and collagen accumulation, improves pulmonary artery biomechanics, and normalizes right ventricular and pulmonary hemodynamics in a rat model of pulmonary hypertension due to left heart disease. Thus, targeting extracellular matrix remodeling may present a therapeutic approach for pulmonary hypertension due to left heart disease.

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.

The mounted alloimmunity of the iris-ciliary body devotes a hotbed of immune cells for corneal transplantation rejection

Graft rejection is still the major obstacle causing corneal transplantation failure. However, the underlying pathogenesis remains largely unclear. The iris-ciliary body (I-C) is enriched with blood vessels and various immune cell populations, presumably predisposed to be involved in corneal transplantation rejection. After penetrating keratoplasty, compared to the normal (Nor) and syngeneic (Syn) groups, I-C tissues in the allogeneic (Allo) group displayed stronger alloimmune responses, with more infiltrations of CD45⁺ inflammatory cells and CD3⁺ lymphocytes, increased transcriptional levels of pro-inflammatory cytokines, and elevated NF-κB activity. This histopathology was similar to the pathological alterations of corneal allografts. Angiography analysis revealed the abnormal vasculature in the iris during allograft rejection, characterized by vasodilatation, increased vessel density, and vascular permeability. While, immunofluorescence staining showed the intact tight junction of the posterior iris epithelium. In vitro, human microvascular endothelial cells (HMECs) stimulated by tumor necrosis factor-α (TNF-α) showed an increased Evans blue (EB)-albumin leakage, with lower expression of zonula occludens-1 (ZO-1) and Occludin. The increased EB-albumin leakage, up-regulated NF-κB activity, and reduced expression of ZO-1 and Occludin could be partially reversed after cyclosporine A (CsA) administration. In contrast, the barrier function in primary mouse iris pigment epithelial cells (IPEs) after TNF-α treatment remained largely unchanged. These findings revealed the vigorous alloimmunity in I-C tissues, characterized with impaired vascularization but intact posterior epithelial barrier in the iris, which allowed proteins and immune cells to be exudated from the front surface of I-C tissues, and facilitated immune reaction in the anterior chamber, thereby contributing to aggravated corneal transplantation rejection.

Open label safety and efficacy pilot to study mitigation of equine recurrent uveitis through topical suppressor of cytokine signaling-1 mimetic peptide

Equine recurrent uveitis (ERU) is a painful and debilitating autoimmune disease and represents the only spontaneous model of human recurrent uveitis (RU). Despite the efficacy of existing treatments, RU remains a leading cause of visual handicap in horses and humans. Cytokines, which utilize Janus kinase 2 (Jak2) for signaling, drive the inflammatory processes in ERU that promote blindness. Notably, suppressor of cytokine signaling 1 (SOCS1), which naturally limits the activation of Jak2 through binding interactions, is often deficient in autoimmune disease patients. Significantly, we previously showed that topical administration of a SOCS1 peptide mimic (SOCS1-KIR) mitigated induced rodent uveitis. In this pilot study, we test the potential to translate the therapeutic efficacy observed in experimental rodent uveitis to equine patient disease. Through bioinformatics and peptide binding assays we demonstrate putative binding of the SOCS1-KIR peptide to equine Jak2. We also show that topical, or intravitreal injection of SOCS1-KIR was well tolerated within the equine eye through physical and ophthalmic examinations. Finally, we show that topical SOCS1-KIR administration was associated with significant clinical ERU improvement. Together, these results provide a scientific rationale, and supporting experimental evidence for the therapeutic use of a SOCS1 mimetic peptide in RU.

Ex Vivo and In Vitro Analysis Identify a Detrimental Impact of Neutrophil Extracellular Traps on Eye Structures in Equine Recurrent Uveitis

Equine recurrent uveitis (ERU) is a common ocular disease of horses and described as a model for human autoimmune uveitis. This immune-mediated, inflammatory condition progressively destroys the eye, ultimately leading to blindness. Genetic and autoimmune factors, next to infections with Leptospira, are discussed as key factors in the pathogenesis. Furthermore, a release of neutrophil extracellular traps (NETs) by activated neutrophils is involved. NETs are composed of decondensed chromatin and proteins that can immobilize invading pathogens. However, if NETs accumulate, they can contribute to detrimental autoimmune processes. Thus, we aimed to investigate the impact of NETs in ERU patients. Therefore, we quantified several NET-markers (cell-free DNA, nucleosomes, citrullinated histone H3, histone-myeloperoxidase complexes, interleukin-17, equine cathelicidin 1 and DNase I activity) and NET-autoantibodies in sera and vitreous body fluids (VBF) of ERU-diseased horses and correlated the data with the disease status (signalment, ERU scores and Leptospira infection status). NET markers were detected to varying degrees in VBF of diseased horses, and partially correlated to disease severity and the presence of Leptospira spp. Cell-free DNA and nucleosomes as NET markers correlate with ERU severity in total and VBF scores, despite the presence of active DNases. Additionally, a significant correlation between fundus affection in the eye and NET autoantibodies was detectable. Therefore, we further investigated the influence of VBF samples from equine patients and isolated NETs on the blood-retina barrier in a cell culture model. VBF of diseased horses significantly induced cytotoxicity in retinal pigment epithelial cells. Moreover, partially digested NETs also resulted in cytotoxic effects. In the presence of lipopolysaccharide (LPS), the main component of the leptospiral surface, both undigested and completely digested NETs were cytotoxic. Correlations between the ERU-scores and Leptospira were also calculated. Detection of leptospiral DNA, and antibody titers of the serovar Grippotyphosa correlated with disease severity. In addition, a correlation between Leptospira and several NET markers was observed in VBF. Altogether, our findings suggest a positive correlation between NET markers with disease severity and involvement of Leptospira in the VBF of ERU-diseased horses, as well as a cytotoxic effect of NETs in eyes.

The Usefulness of Mesenchymal Stem Cells beyond the Musculoskeletal System in Horses

Simple Summary

The main target of mesenchymal stem cell therapy in horses has long been the locomotor system, because these athletic animals commonly suffer from tendon and joint lesions. Originally, mesenchymal stem cells were thought to act by just differentiating into the cells of the injured tissue. However, these cells are also able to regulate and stimulate the body’s own repair mechanisms, opening the door to many applications in inflammatory and immune-mediated disorders in both animals and humans. In horses, beyond their traditional application in the musculoskeletal system, these cells have been studied for ophthalmologic pathologies such as corneal ulcers or immune-mediated processes, and for reproductive disorders such as endometritis/endometrosis. Their potential has been explored for equine pathologies very similar to those affecting people, such as asthma, metabolic syndrome, aberrant wound healing, or endotoxemia, as well as for equine-specific pathologies such as laminitis. Current evidence is still preliminary, and further research is needed to clarify different aspects, although research performed so far shows the promising potential of mesenchymal stem cells to treat a wide variety of equine pathologies, some of which are analogous to human disorders. Therefore, advancements in this path will be beneficial for both animals and people.

Abstract

The differentiation ability of mesenchymal stem cells (MSCs) initially raised interest for treating musculoskeletal injuries in horses, but MSC paracrine activity has widened their scope for inflammatory and immune-mediated pathologies in both equine and human medicine. Furthermore, the similar etiopathogenesis of some diseases in both species has advanced the concept of “One Medicine, One Health”. This article reviews the current knowledge on the use of MSCs for equine pathologies beyond the locomotor system, highlighting the value of the horse as translational model. Ophthalmologic and reproductive disorders are among the most studied for MSC application. Equine asthma, equine metabolic syndrome, and endotoxemia have been less explored but offer an interesting scenario for human translation. The use of MSCs in wounds also provides a potential model for humans because of the healing particularities in both species. High-burden equine-specific pathologies such as laminitis have been suggested to benefit from MSC-therapy, and MSC application in challenging disorders such as neurologic conditions has been proposed. The available data are preliminary, however, and require further development to translate results into the clinic. Nevertheless, current evidence indicates a significant potential of equine MSCs to enlarge their range of application, with particular interest in pathologies analogous to human conditions.

The Fecal Bacterial Microbiota in Horses with Equine Recurrent Uveitis

The objective of this study was to describe and compare the fecal bacterial microbiota of horses with equine recurrent uveitis (ERU) and healthy horses using next-generation sequencing techniques. Fecal samples were collected from 15 client-owned horses previously diagnosed with ERU on complete ophthalmic examination. For each fecal sample obtained from a horse with ERU, a sample was collected from an environmentally matched healthy control with no evidence of ocular disease. The Illumina MiSeq sequencer was used for high-throughput sequencing of the V4 region of the 16S rRNA gene. The relative abundance of predominant taxa, and alpha and beta diversity indices were calculated and compared between groups. The phyla Firmicutes, Bacteroidetes, Verrucomicrobia, and Proteobacteria predominated in both ERU and control horses, accounting for greater than 60% of sequences. Based on linear discriminant analysis effect size (LEfSe), no taxa were found to be enriched in either group. No significant differences were observed in alpha and beta diversity indices between groups (p > 0.05 for all tests). Equine recurrent uveitis is not associated with alteration of the gastrointestinal bacterial microbiota when compared with healthy controls.

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.

The Potential of Mesenchymal Stem Cells to Treat Systemic Inflammation in Horses

One hallmark of mesenchymal stem cells (MSCs) is the ability to differentiate into multiple tissue types which assists in tissue regeneration. Another hallmark of MSCs is their potent anti-inflammatory and immunomodulatory properties and the potential to treat inflammatory, immune-mediated, and ischemic conditions. In equine practice, MSCs have shown efficacy in the treatment of musculoskeletal disorders such as tendinopathy, meniscal tears and cartilage injury. However, there are many equine disease processes and conditions that may benefit from the immunomodulatory properties of MSCs. Examples include conditions associated with overwhelming acute inflammatory response such as systemic inflammatory response syndrome to chronic diseases characterized by a prolonged low level of inflammation such as equine asthma and recurrent uveitis. For the acute inflammatory response processes, there is often high morbidity and mortality with no effective immunomodulatory treatment to prevent the overwhelming synthesis of proinflammatory mediators. For chronic inflammatory disease processes, frequently long-term corticosteroid treatment is the therapeutic mainstay, with serious potential complications. Thus, there is an unmet need for alternative anti-inflammatory treatments for both acute and chronic illnesses in horses. While MSCs show promise for such conditions, much research is needed before a clinically safe and effective treatment will be available. Optimal MSC tissue source, patient vs. donor source (autologous vs. allogeneic) and cell growth conditions need to be determined for each problem. For immediate use, allogeneic MSC treatments is preferable, but immune tolerance and adequate safety require further study. MSC collection and cryopreservation from horses before they are injured or ill, whether from umbilical cord tissue, bone marrow or adipose might become more widespread. Once these fundamental approaches to treating specific diseases with MSCs are determined, the route of administration, dose and timing of administration also need to be studied. To provide a framework for development of MSC immunomodulatory treatments, this article reviews the current understanding of equine MSC anti-inflammatory and immunomodulatory properties and proposes how MSC therapy may be further developed to treat acute onset systemic inflammatory processes and chronic inflammatory diseases.

Neutrophil Extracellular Traps in the Pathogenesis of Equine Recurrent Uveitis (ERU)

Equine recurrent uveitis (ERU) is considered one of the most important eye diseases in horses and typically appears with relapsing inflammatory episodes without systemic effects. Various disorders have been described as an initial trigger, including infections. Independent of the initiating cause, there are numerous indications that ERU is an immune-mediated disease. We investigated whether neutrophil extracellular traps (NETs) are part of the ERU pathogenesis. Therefore, vitreous body fluids (VBF), sera, and histological sections of the eye from ERU-diseased horses were analyzed for the presence of NET markers and compared with horses with healthy eyes. In addition, NET formation by blood derived neutrophils was investigated in the presence of VBF derived from horses with healthy eyes versus ERU-diseased horses using immunofluorescence microscopy. Interestingly, NET markers like free DNA, histone-complexes, and myeloperoxidase were detected in higher amounts in samples from ERU-diseased horses. Furthermore, in vitro NET formation was higher in neutrophils incubated with VBF from diseased horses compared with those animals with healthy eyes. Finally, we characterized the ability of equine cathelicidins to induce NETs, as potential NET inducing factors in ERU-diseased horses. In summary, our findings lead to the hypothesis that ERU-diseased horses develop more NETs and that these may contribute to the pathogenesis of ERU.

Clinical, Pathological, and Ethical Considerations for the Conduct of Clinical Trials in Dogs with Naturally Occurring Cancer: A Comparative Approach to Accelerate Translational Drug Development

The role of comparative oncology in translational research is receiving increasing attention from drug developers and the greater biomedical research community. Pet dogs with spontaneous cancer are important and underutilized translational models, owing to dogs' large size and relative outbreeding, combined with their high incidence of certain tumor histotypes with significant biological, genetic, and histological similarities to their human tumor counterparts. Dogs with spontaneous tumors naturally develop therapy resistance and spontaneous metastasis, all in the context of an intact immune system. These fundamental features of cancer biology are often lacking in induced or genetically engineered preclinical tumor models and likely contribute to their poor predictive value and the associated overall high failure rate in oncology drug development. Thus, the conduct of clinical trials in pet dogs with naturally occurring cancer represents a viable surrogate and valuable intermediary step that should be increasingly incorporated into the cancer drug discovery and development pipeline. The development of molecular-targeted therapies has resulted in an expanded role of the pathologist in human oncology trials, and similarly the expertise of veterinary pathologists will be increasingly valuable to all phases of comparative oncology trial design and conduct. In this review, we provide a framework of clinical, ethical, and pathology-focused considerations for the increasing integration of translational research investigations in dogs with spontaneous cancer as a means to accelerate clinical cancer discovery and drug development.

Horses with equine recurrent uveitis have an activated CD4+ T-cell phenotype that can be modulated by mesenchymal stem cells in vitro

Equine recurrent uveitis (ERU) is an immune‐mediated disease causing repeated or persistent inflammatory episodes which can lead to blindness. Currently, there is no cure for horses with this disease. Mesenchymal stem cells (MSCs) are effective at reducing immune cell activation in vitro in many species, making them a potential therapeutic option for ERU. The objectives of this study were to define the lymphocyte phenotype of horses with ERU and to determine how MSCs alter T‐cell phenotype in vitro. Whole blood was taken from 7 horses with ERU and 10 healthy horses and peripheral blood mononuclear cells were isolated. The markers CD21, CD3, CD4, and CD8 were used to identify lymphocyte subsets while CD25, CD62L, Foxp3, IFNγ, and IL10 were used to identify T‐cell phenotype. Adipose‐derived MSCs were expanded, irradiated (to control proliferation), and incubated with CD4⁺ T‐cells from healthy horses, after which lymphocytes were collected and analyzed via flow cytometry. The percentages of T‐cells and B‐cells in horses with ERU were similar to normal horses. However, CD4⁺ T‐cells from horses with ERU expressed higher amounts of IFNγ indicating a pro‐inflammatory Th1 phenotype. When co‐incubated with MSCs, activated CD4⁺ T‐cells reduced expression of CD25, CD62L, Foxp3, and IFNγ. MSCs had a lesser ability to decrease activation when cell‐cell contact or prostaglandin signaling was blocked. MSCs continue to show promise as a treatment for ERU as they decreased the CD4⁺ T‐cell activation phenotype through a combination of cell‐cell contact and prostaglandin signaling.

Leptospirosis: An important infectious disease in North American horses

North American horses are commonly exposed to Leptospira organisms. Leptospira Bratislava is the most common infecting serovar but this serovar has not been confirmed to cause clinical disease in North American horses. Leptospira Pomona type kennewicki is responsible for most of the clinical diseases (leptospirosis) in North American horses. Leptospirosis is most commonly associated with diseases of the placenta and fetus, the kidneys and the eyes in horses. In-utero infections in pregnant mares may result in abortion, neonatal illness or birth of an antibody positive healthy foal. Acute renal failure in younger horses and recurrent uveitis in adult horses are other well documented clinical syndromes of leptospirosis. Abortions, neonatal disease and acute renal failure are caused by a subacute infection, while horses with Leptospira associated recurrent uveitis develop ocular disease months or years after the initial Leptospira infection. Diagnosis of Leptospirosis is made by a combination of antigen or antibody testing methods. Mares that abort following Leptospira infection have no additional clinical signs at the time of abortion but may shed the offending Leptospira spp. in the urine for several weeks. Antibiotic treatments are sometimes used in hopes of decreasing Leptospira shedding in infected horses or prophylactically in exposed pregnant mares but documentation of efficacy is lacking. Horses with Leptospira - associated acute renal failure can be successfully treated with antibiotics and supportive care. Recurrent uveitis is commonly associated with leptospirosis in North American horses and although horses may have chronic intraocular infection triggering an immune disease, systemic antimicrobial therapy has not been effective in eliminating the organism from the eye. An equine approved Leptospira Pomona type kennewicki vaccine is now available in North America.

Detection of intraocular Leptospira spp. by real-time polymerase chain reaction in horses with recurrent uveitis in Belgium

BACKGROUND

Equine recurrent uveitis (ERU) has been associated with Leptospira spp. infection. No information exists concerning the prevalence of Leptospira-associated ERU in Belgium and about the sensitivity of detection of Leptospira in different ocular media.

OBJECTIVES

To establish the prevalence of intraocular Leptospira spp. in ERU-affected and healthy eyes of horses examined at the Equine Clinic of the University of Liège by real-time PCR and to compare the results of the aqueous and vitreous humour of the same eye.

STUDY DESIGN

Cross-sectional.

METHODS

Sixty-six eyes from 59 client-owned horses with a diagnosis of equine recurrent uveitis (ERU-group) were studied from May 2015 to December 2017. Fifty healthy eyes from 28 euthanised horses for unrelated reasons examined during the same period were included in the control group. Intraocular fluids (aqueous and/or vitreous humours) from ERU-affected eyes were sampled and analysed by real-time PCR for Leptospira spp. Aqueous and vitreous humours from the control group were processed in the same way.

RESULTS

Both groups were comparable regarding age, sex, eye sampled (OS/OD), humours sampled (aqueous/vitreous humour) but not regarding breeds, with an over-representation of Warmbloods and Appaloosas in the ERU-group. The prevalence of Leptospira spp. was 30.3% (20/66 eyes) in the ERU-group. Leptospira spp. DNA was identified in 11 aqueous and 17 vitreous humours with eight horses testing positive in both humours, nine horses testing positive for vitreous humour alone and third horses for aqueous humour alone. The phi-correlation between aqueous and vitreous humour Leptospira-PCR results is 0.47 suggesting a low association. All the control eyes were negative.

MAIN LIMITATIONS

The diagnostic method selected for this study (lipL32 qPCR) did not allow identification of the serovars.

CONCLUSIONS

Leptospirosis is a potential cause of ERU in Belgium. Testing both intraocular media is advised whenever possible. The Summary is available in Spanish - see Supporting Information.

Proliferative and inflammatory factors in the vitreous of patients with proliferative diabetic retinopathy

PURPOSE

The purpose was to measure the concentrations of various cytokines and growth factors (including vascular endothelial growth factor [VEGF] and pigment epithelium-derived factor [PEDF]) in the vitreous of patients with proliferative diabetic retinopathy (PDR) and to investigate interaction between inflammatory and proliferative factors in the genesis of PDR. Materials and Methods : Vitreous samples from 32 eyes with PDR and 25 eyes without diabetes mellitus and signs of DR (control) were collected. Vitreous concentrations of VEGF, PEDF, monocyte chemotactic protein-1 (MCP-1), interleukin-4 (IL-4), IL-6, IL-8, IL-10, IL-17A, and secretory immunoglobulin A (sIgA) were simultaneously measured using enzyme-linked immunoassay. Results : Vitreous levels of VEGF, PEDF, IL-17A, IL-6, IL-8, IL-4, and sIgA were significantly (Π < 0.05) higher in eyes with PDR compared to control. The concentration of VEGF was more than 17-times higher than in control, and the concentration of PEDF was not changed oppositely and was also higher (1.45-times) compared to control, that may indicate disturbances of compensatory mechanisms in angiogenesis regulation in PDR. Significant (Π < 0.05) positive correlations were observed between vitreous concentrations of VEGF and IL-17ΐ (r = 0.45), VEGF and IL-8 (r = 0.48), VEGF and IL-4 (r = 0.51), PEDF and IL-17ΐ (r = 0.48), PEDF and IL-8 (r = 0.59), MCP-1 and PEDF (r = 0.72), MCP-1 and IL-8 (r0 = 0.45), IL-4 and IL-17ΐ (r = 0.65), IL-4 and IL-8 (r = 0.71), IL-8 and IL-17ΐ (r = 0.59).

CONCLUSIONS

Significantly raised levels of inflammatory and proliferative factors and numerous positive correlations between them may demonstrate a significant role of activation of vascular proliferation and local inflammation in the pathogenesis of PDR.

Cytokine and chemokine profiles of aqueous humor and serum in horses with uveitis measured using multiplex bead immunoassay analysis

OBJECTIVE

To determine whether horses with clinically diagnosed Equine Recurrent Uveitis (ERU) and those with Leptospirosis infection have a specific cytokine profile in their aqueous humor (AH) and serum that differs from horses with uveitis secondary to other ocular inflammatory processes and from horses with normal eyes.

ANIMALS STUDIED

Twenty-five client-owned horses with uveitis that were presented to the North Carolina State University Ophthalmology Service, and four University-owned horses without history or clinical signs of ocular disease.

PROCEDURE

Samples of AH and serum were obtained from horses with ERU (n=13), acute or non-recurrent uveitis (UV; n=7), uveitis secondary to infectious keratitis (IK; n=5), and normal eyes (N; n=4). Cytokine levels in AH and serum were quantified using a multiplex bead immunoassay. Leptospiral antibody titers in serum and AH and PCR for Leptospiral DNA in AH were performed.

RESULTS

In the AH of horses with ERU, increased levels of IL-1a, IL-4, IL-6, IL-8, IL-12p70, FGF-2, G-CSF, and RANTES were measured compared to UV, IK and N eyes, but the differences were not significant. However, IL-10 was significantly higher in ERU eyes compared to IK and N (P=0.029; 0.013), and IP-10 in ERU eyes was significantly higher than in UV and N (P=0.004). Furthermore, MCP-1 was significantly higher in ERU than N (P=0.04). In the serum, increased levels of IL-1a, IL-4, IL-6, IL-8, IL-12p70, fractalkine, and G-CSF were measured in horses with ERU, but the levels were not significantly higher than those observed in UV, IK, or N horses. However, serum IP-10 levels in horses with ERU were significantly higher than in UV and N horses (P=0.005) and MCP-1 levels were significantly higher in ERU than N (P=0.03). Horses with marked ocular inflammation had significantly higher serum levels of G-CSF, IL-1a, fractalkine, IL-13, IL-4, IL-17a, IL-12p70, IFN-γ, and MCP-1. Elevated IL-10 in AH was significantly associated with disease chronicity, both overall and in ERU eyes (P=0.049), and in horses with positive ocular leptospiral titers or leptospiral PCR, significant elevations of IL-10 (P=0.0018; 0.0032) and IP-10 (P=0.0342; 0.043) were detected in the AH compared to leptospiral negative eyes.

CONCLUSIONS

The anti-inflammatory cytokine IL-10 and the pro-inflammatory cytokine IP-10 appear to play an important role in ERU. Further studies are needed to further clarify and characterize cytokine profiles of specific ocular inflammatory diseases, but multiplex bead immunoassay technology shows promise as a diagnostically valuable tool.

Multiple etiologies of equine recurrent uveitis--A natural model for human autoimmune uveitis: A brief review

Equine recurrent uveitis (ERU) has various etiologies, with Leptospira infection and genetic predisposition being the leading risk factors. Regardless of etiology, expression of ocular proteins associated with maintenance of the blood-ocular barrier is impaired in ERU. The recurring-remitting cycle of ERU repeatedly disrupts the blood-ocular barrier, allowing the previously immune-privileged ocular environment to become the site of a progressive local autoimmune pathology that ultimately results in tissue destruction and vision loss. The immune-mediated process involves humoral and cellular mechanisms. Intraocular antibodies either produced in the eye or that leak through the blood-ocular barrier, are often present at higher levels than in serum and react with antigens in ocular tissue of horses with ERU. Ocular infiltration of auto-aggressive lymphocytes occurs with each uveitis episode and is the most crucial contributor to inflammation and eye damage. Recurring uveitis episodes may be initiated when epitopes of an ocular antigen become visible to the immune system (intramolecular spreading) or another autoantigen (intermolecular spreading), resulting in a new inflammatory reaction.

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.

Characterization of amyloid in equine recurrent uveitis as AA amyloid

Two horses with chronic uveitis and histological lesions consistent with equine recurrent uveitis (ERU) were examined. Microscopical findings in the ciliary body included deposits of amyloid lining the non-pigmented epithelium, intracytoplasmic, rod-shaped, eosinophilic inclusions and intraepithelial infiltration of T lymphocytes. Ultrastructural examination of the ciliary body of one horse confirmed the presence of abundant extracellular deposits of non-branching fibrils (9-11 nm in diameter) consistent with amyloid. Immunohistochemistry revealed strong positive labelling for AA amyloid and mass spectrometry showed the amyloid to consist primarily of serum amyloid A1 in both cases. The findings suggest that localized, intraocular AA amyloidosis may occur in horses with ERU.

A genome-wide association study identifies risk loci to equine recurrent uveitis in German warmblood horses

Equine recurrent uveitis (ERU) is a common eye disease affecting up to 3-15% of the horse population. A genome-wide association study (GWAS) using the Illumina equine SNP50 bead chip was performed to identify loci conferring risk to ERU. The sample included a total of 144 German warmblood horses. A GWAS showed a significant single nucleotide polymorphism (SNP) on horse chromosome (ECA) 20 at 49.3 Mb, with IL-17A and IL-17F being the closest genes. This locus explained a fraction of 23% of the phenotypic variance for ERU. A GWAS taking into account the severity of ERU, revealed a SNP on ECA18 nearby to the crystalline gene cluster CRYGA-CRYGF. For both genomic regions on ECA18 and 20, significantly associated haplotypes containing the genome-wide significant SNPs could be demonstrated. In conclusion, our results are indicative for a genetic component regulating the possible critical role of IL-17A and IL-17F in the pathogenesis of ERU. The associated SNP on ECA18 may be indicative for cataract formation in the course of ERU.