Intraocular Inflammatory Disease Research Articles

Uveitis: Molecular Pathogenesis and Emerging Therapies.

The profound impact that vision loss has on human activities and quality of life necessitates understanding the etiology of potentially blinding diseases and their clinical management. The unique anatomic features of the eye and its sequestration from peripheral immune system also provides a framework for studying other diseases in immune privileged sites and validating basic immunological principles. Thus, early studies of intraocular inflammatory diseases (uveitis) were at the forefront of research on organ transplantation. These studies laid the groundwork for foundational discoveries on how immune system distinguishes self from non-self and established current concepts of acquired immune tolerance and autoimmunity. Our charge in this review is to examine how advances in molecular cell biology and immunology over the past 3 decades have contributed to the understanding of mechanisms that underlie immunopathogenesis of uveitis. Particular emphasis is on how advances in biotechnology have been leveraged in developing biologics and cell-based immunotherapies for uveitis and other neuroinflammatory diseases.

Efficacy and safety of suprachoroidal triamcinolone injection in horses with poorly responsive equine recurrent uveitis.

Equine recurrent uveitis (ERU), a chronic, immune-mediated intraocular inflammatory disease, is a common cause of blindness in horses. The severity and recurrent nature of ERU makes it difficult to treat with current therapeutics leading to a poor visual prognosis. The suprachoroidal space (SCS), a potential space between the choroid and sclera surrounding the ocular posterior segment, offers a promising alternative site for drug application to the eye. Corticosteroid administration within this space is hypothesized to be safe and effective at controlling intraocular inflammation, especially in horses with poorly responsive ERU. Horses with active, poorly responsive ERU. A retrospective study was performed with 29 horses (36 total eyes) that received SCS injection of triamcinolone acetonide (TA) with ERU not well controlled with standard uveitis treatment. A standardized ocular inflammation score (OIS) was used to assess inflammation at the time of injection and at follow-ups. Standardized OIS revealed a significant decrease in ocular inflammation over time after SCS TA administration (p<.004). Adverse effects after injections occurred in <20% of the horses at follow-up, but some of these effects were attributed to chronic inflammation prior to effective treatment, long-term topical corticosteroid use, or complications from hospitalization rather than the SCS injections. Most horses (86.7%) in this study remained visual greater than 3months after SCS injection. Based on these results, SCS TA injections appear to be a safe and possible effective treatment modality for managing poorly responsive ERU; further clinical study is warranted.

A clinical study of anterior uveitis at India

Purpose: To evaluate the etiological pattern, treatment, and its outcome and complications of anterior uveitis. Uveitis, a complex intraocular inflammatory disease, results from several etiological entities. The cause of inflammation might be an infectious agent or trauma, but in most cases, the underlying mechanism appears to be autoimmune in nature.[1] Methods: A prospective clinical study was done in the department of ophthalmology at a general hospital in Jaipur, during July 2017 to June 2018. All patients between 20 and 80 years of age clinically presenting with anterior uveitis were studied. A thorough clinical evaluation followed by investigations was done to determine etiology. Patients were put on specific and nonspecific treatment and were followed up for a period of 6 months. Complications were noted. Results: The etiology of uveitis remained unknown in most cases (42%). The most common cause was observed to be blunt trauma (20%) followed by phacolytic (12%). Most cases responded well to treatment. The most common complication was posterior persistent synechiae (23.64%), and cataract was the second common (14.54%). Conclusion: Etiological diagnosis remains undetermined in majority of cases. A thorough examination and investigation is required in each case to facilitate a final diagnosis. Prompt treatment ensures good visual outcome. Ocular morbidity is common in chronic and recurrent cases.

Protein Biomarkers in Uveitis.

The diseases affecting the retina or uvea (iris, ciliary body, or choroid) generate changes in the biochemical or protein composition of ocular fluids/tissues due to disruption of blood-retinal barrier. Ocular infections and inflammations are sight-threatening diseases associated with various infectious and non-infectious etiologies. Several etiological entities cause uveitis, a complex intraocular inflammatory disease. These causes of uveitis differ in different populations due to geographical, racial, and socioeconomic variations. While clinical appearance is sufficiently diagnostic in many diseases, some of the uveitic entities manifest nonspecific or atypical clinical presentation. Identification of biomarkers in such diseases is an important aid in their diagnostic armamentarium. Different diseases and their different severity states release varying concentrations of proteins, which can serve as biomarkers. Proteomics is a high throughput technology and a powerful screening tool for serum biomarkers in various diseases that identifies proteins by mass spectrometry and helps to improve the understanding of pathogenesis of a disease. Proteins determine the biological state of a cell. Once identified as biomarkers, they serve as future diagnostic and pharmaceutical targets. With a potential to redirect the diagnosis of idiopathic uveitis, ocular proteomics provide a new insight into the pathophysiology and therapeutics of various ocular inflammatory diseases. Tears, aqueous and vitreous humor represent potential repositories for proteomic biomarkers discovery in uveitis. With an extensive proteomics work done on animal models of uveitis, various types of human uveitis are being subjected to proteome analysis for biomarker discovery in different ocular fluids (vitreous, aqueous, or tears).

Discrimination of dissociated lymphoma cells from leukocytes by Raman spectroscopy

Diagnosis of intraocular lymphoma is difficult. Among the hurdles in the diagnosis are the variety of reactive inflammatory and ischemic changes among intraocular lymphoma patients. Thus, a novel diagnostic method is desired such that lymphoma cells can be distinguished by the signals intrinsic to the cells, not by those from the surrounding tissues with reactive changes. Raman spectroscopy is a technique that can detect intrinsic signals from each cell. Therefore, Raman spectroscopy is a good candidate for an intraocular evaluation technology that could contribute to improve the diagnosis of intraocular lymphoma. In this study, we tested whether the intrinsic Raman signals from malignant lymphoma cells, in the absence of surrounding tissue, were sufficient for the discrimination of malignant lymphoma cells from leukocytes. We acquired spectra from dissociated lymphoma cells, along with spectra from normal B cells and other leukocytes involved in intraocular inflammatory diseases. We analysed the spectra using principal component analyses and quadratic discriminant analyses. We found that Raman spectra from dissociated cells without confounding tissues showed high discriminating ability, regardless of the variation due to day-to-day differences and donor differences. The present study demonstrates the possible effectiveness of Raman spectroscopy as a tool for intraocular evaluation.

Characterization of Clinical and Immune Responses in an Experimental Chronic Autoimmune Uveitis Model

Autoimmune uveitis is a sight-threatening intraocular inflammatory disease. For >30 years, the mouse model of experimental autoimmune uveitis has been employed to investigate disease mechanisms and test immunotherapeutic approaches. However, inflammation in this model is self-limited, and does not replicate the chronic, insidious nature prevalent in the human disease. Herein, a robust and reliable model of chronic autoimmune uveitis was developed and characterized in two strains of wild-type mice by modifying interphotoreceptor retinoid-binding protein dose and peptide fragments from conventional experimental autoimmune uveitis models. In both of these murine strains, immunization with our modified protocols resulted in a slowly progressive uveitis, with retinal scars and atrophy observed in the chronic stage by fundoscopy. Optical coherence tomography demonstrated decreased retinal thickness in chronic autoimmune uveitis mice, and electroretinography showed significantly reduced amplitudes of dark-adapted a- and b-waves and light-adapted b-waves. Histologic examination revealed prominent choroiditis with extensive retinal damage. Flow cytometry analysis showed substantially increased numbers of CD44hiIL-17+IFN-γ- memory T-helper 17 (Th17) cells in the retina, cervical lymph nodes, inguinal lymph nodes, and spleen. These data establish new modified protocols for inducing chronic uveitis in wild-type mice, and demonstrate a predominant memory Th17 cell response, suggesting an important role for memory Th17 cells in driving chronic inflammation in autoimmune uveitis.

Hypomethylation of Notch1 DNA is associated with the occurrence of uveitis.

Uveitis is a serious intra-ocular inflammatory disease that can lead to visual impairment even blindness worldwide. Notch signaling can regulate the differentiation of naive CD4+ T cells, influencing the development of uveitis. DNA methylation is closely related to the autoimmune diseases. In this study, we measured the Notch1 DNA methylation level, determined the Notch1 and related DNA methylases mRNA expression and evaluated the ratio of T helper type 17 regulatory T cell (Th17/Treg ) in peripheral blood mononuclear cells (PBMCs) from uveitis patients and normal control subjects; we also tested the levels of relevant inflammatory cytokines in serum from the participants. Results indicated that compared with those in normal control individuals, the expression of ten-eleven translocation 2 (TET2) and Notch1 mRNA is elevated in uveitis patients, whereas the methylation level in Notch1 DNA promotor region [-842 ~ -646 base pairs (bp)] is down-regulated, and is unrelated to anatomical location. Moreover, the Th17/Treg ratio is up-regulated in PBMCs from uveitis patients, accompanied by the elevated levels of proinflammatory cytokines [e.g. interleukin (IL)-2, IL-6, IL-17 and interferon (IFN)-γ] in serum from uveitis patients. These findings suggest that the over-expression of TET2 DNA demethylase may lead to hypomethylation of Notch1, activate the Notch1 signaling, induce naive CD4+ T cells to differentiate theTh17 subset and thus disturb the balance of the Th17/Treg ratio in uveitis patients. Overall, hypomethylation of Notch1 DNA is closely associated with the occurrence of uveitis. Our study preliminarily reveals the underlying mechanism for the occurrence of uveitis related to the hypomethylation of Notch1 DNA, providing a novel therapeutic strategy against uveitis in clinical practice.

Genomewide Association Study of Acute Anterior Uveitis Identifies New Susceptibility Loci.

PurposeAcute anterior uveitis (AAU) is a common intraocular inflammatory disease. AAU occurs in 30% to 50% of patients with ankylosing spondylitis (AS), and both conditions are strongly associated with human leukocyte antigen (HLA)-B27, implying a shared etiology. This study aims to apply genomewide association study (GWAS) to characterize the genetic associations of AAU and their relationship to the genetics of AS.MethodsWe undertook the GWAS analyses in 2752 patients with AS with AAU (cases) and 3836 patients with AS without AAU (controls). There were 7,436,415 single-nucleotide polymorphisms (SNPs) available after SNP microarray genotyping, imputation, and quality-control filtering.ResultsWe identified one locus associated with AAU at genomewide significance: rs9378248 (P = 2.69 × 10−8, odds ratio [OR] = 0.78), lying close to HLA-B. Suggestive association was observed at 11 additional loci, including previously reported AS loci ERAP1 (rs27529, P = 2.19 × 10−7, OR = 1.22) and NOS2 (rs2274894, P = 8.22 × 10−7, OR = 0.83). Multiple novel suggestive associations were also identified, including MERTK (rs10171979, P = 2.56 × 10−6, OR = 1.20), KIFAP3 (rs508063, P = 5.64 × 10−7, OR = 1.20), CLCN7 (rs67412457, P = 1.33 × 10−6, OR = 1.25), ACAA2 (rs9947182, P = 9.70 × 10−7, OR = 1.37), and 5 intergenic loci. The SNP-based heritability is approximately 0.5 for AS alone, and is much higher (approximately 0.7) for AS with AAU. Consistent with the high heritability, a genomewide polygenic risk score shows strong power in identifying individuals at high risk of either AS with AAU or AS alone.ConclusionsWe report here the first GWAS for AAU and identify new susceptibility loci. Our findings confirm the strong overlap in etiopathogenesis of AAU with AS, and also provide new insights into the genetic basis of AAU.

Comparison of the Vitreous Fluid Bacterial Microbiomes between Individuals with Post Fever Retinitis and Healthy Controls.

Ocular microbiome research has gained momentum in the recent past and has provided new insights into health and disease conditions. However, studies on sight threatening intraocular inflammatory diseases have remained untouched. In the present study, we attempted to identify the bacterial microbiome associated with post fever retinitis using a metagenomic sequencing approach. For this purpose, bacterial ocular microbiomes were generated from vitreous samples collected from control individuals (VC, n = 19) and individuals with post fever retinitis (PFR, n = 9), and analysed. The results revealed 18 discriminative genera in the microbiomes of the two cohorts out of which 16 genera were enriched in VC and the remaining two in PFR group. These discriminative genera were inferred to have antimicrobial, anti-inflammatory, and probiotic function. Only two pathogenic bacteria were differentially abundant in 20% of the PFR samples. PCoA and heatmap analysis showed that the vitreous microbiomes of VC and PFR formed two distinct clusters indicating dysbiosis in the vitreous bacterial microbiomes. Functional assignments and network analysis also revealed that the vitreous bacterial microbiomes in the control group exhibited more evenness in the bacterial diversity and several bacteria had antimicrobial function compared to the PFR group.

Attenuation of experimental autoimmune uveoretinitis in mice by IKKβ inhibitor IMD-0354

Uveitis is a sight-threatening intraocular inflammatory disease that accounts for almost 10% of blindness worldwide. NF-κB signaling plays pivotal roles in inflammatory diseases. We have reported that IMD-0354, which inhibits NF-κB signaling via selective blockade of IKK-β, suppresses inflammation in several ocular disease models. Here, we examined the therapeutic effect of IMD-0354 in an experimental autoimmune uveoretinitis (EAU) model, a well-established animal model for endogenous uveitis in humans. Systemic administration of IMD-0354 significantly suppressed the clinical and histological severity, inflammatory edema, and the translocation of NF-κB p65 into the nucleus of retinas in EAU mice. Furthermore, IMD-0354 treatment significantly inhibited the levels of several Th1/Th17-mediated pro-inflammatory cytokines in vitro. Our current data demonstrate that inhibition of IKKβ with IMD-0354 ameliorates inflammatory responses in the mouse EAU model, suggesting that IMD-0354 may be a promising therapeutic agent for human endogenous uveitis.

Intraocular Biopsy and ImmunoMolecular Pathology for "Unmasking" Intraocular Inflammatory Diseases.

Intraocular inflammation can hide a variety of eye pathologies. In 33% of cases, to obtain a correct diagnosis, investigation of the intraocular sample is necessary. The combined analyses of the intraocular biopsy, using immuno-pathology and molecular biology, point to resolve the diagnostic dilemmas in those cases where history, clinical tests, and ophthalmic and systemic examinations are inconclusive. In such situations, the teamwork between the ophthalmologist and the molecular pathologist is critically important to discriminate between autoimmune diseases, infections, and intraocular tumors, including lymphoma and metastases, especially in those clinical settings known as masquerade syndromes. This comprehensive review focuses on the diagnostic use of intraocular biopsy and highlights its potential to enhance research in the field. It describes the different surgical techniques of obtaining the biopsy, risks, and complication rates. The review is organized according to the anatomical site of the sample: I. anterior chamber containing aqueous humor, II. iris and ciliary body, III. vitreous, and IV. choroid and retina. We have excluded the literature concerning biopsy for choroidal melanoma and retinoblastoma, as this is a specialized area more relevant to ocular oncology.

Construct a diagnostic thinking for intraocular inflammatory diseases

The etiology of intraocular inflammatory disease and its diagnosis is complicated. Currently available and newly emerging systemic and ocular examinations are of important to determine etiology of intraocular inflammatory disorders. But there also exists multiple misunderstanding, and the strategy of their application is not well defined, or even exaggerated. Unprincipled or randomly selection of auxiliary examination would not help for etiology determination, but bring unnecessary pain and economic burden to patients. Establishment of diagnosis thinking of intraocular inflammatory disease is helpful to standardize the diagnosis process of the disease, improve the diagnostic efficiency, and relief patients from the pain and financial burden that caused by too many useless examinations. Key words: Endophthalmitis/diagnosis; Editorial

Targeted over-expression of S100B in the retina of transgenic mice induced exacerbated experimental autoimmune uveitis

Abstract S100B, originally found in glial cells (astrocyte and microglial cells), acts as an intracellular Ca++-sensor and an extracellular regulator protein. Its neuronal trophic or toxic effect on cells might be dependent on its cellular concentrations. Human uveitis is an intraocular inflammatory disease of infectious or autoimmune etiology and neuroinflammatory responses orchestrated by retinal microglia cells are implicated in exacerbation of uveitis. The S100B protein is predominantly secreted by glial cells in central nerve system (CNS). In this study we examined whether S100B protein plays a role in regulating inflammatory responses in the neuroretina. To this end we generated retinal S100B transgenic mice and investigated whether experimental autoimmune uveitis (EAU) would be exacerbated in these transgenic mice. We monitored EAU progression and severity by fundoscopy and ERG (Electroretinogram)and found that over-expression of S100B+ promoted retinal inflammatory responses and vision loss during EAU. Results of FACS and ELISA analysis did not indicate significant difference in the numbers of uveitogenic Th1 and Th17 cells in the draining lymph-nodes. However, significant amounts of pathogenic Th1 and Th17 cells were detected in the retina of S100B transgenic mice. Conversely, the numbers of IL-10-producing CD4+Foxp3+Treg cells in the retina was significantly decreased in the S100B transgenic mice. These results suggest that S100B can serve as a biomarker for ocular inflammatory diseases.

Outcomes of treatment with sirolimus for non-infectious uveitis: a meta-analysis and systematic review.

BackgroundUveitis is a group of intraocular inflammatory diseases whose primary treatment involves immunosuppression. Although corticosteroids (CSs) remain the mainstay therapy, sirolimus is among the recently studied immunomodulatory drugs for treating noninfectious uveitis (NIU).ObjectiveThe aim of this review was to assess and summarize the updated evidence on the outcomes of treatment with sirolimus for NIU.Materials and methodsTwo reviewers conducted a systematic search on November 5, 2018, of electronic databases (EMBASE, MEDLINE, and The Cochrane Library) and clinical trial registers having no restrictions on language or publication date. The primary outcome was uveitis activity as measured by vitreous haze (VH), while the secondary outcomes included central macular thickness (CMT), best-corrected visual acuity (BCVA), CS-sparing effect, IOP elevation, and other adverse events. A meta-analysis was conducted on selected studies with appropriate clinical and methodological homogeneity.ResultsSeven studies were included and reviewed. Four randomized clinical trials were eligible for meta-analysis: SAVE 2013, One-year outcomes of the SAVE study, SAVE 2 2016, SAKURA 2016. The pooled proportions of inflammation control (VH improvement) were 38% (95% CI 16.19%–62.66%) during a 6-month follow-up and 49.97% (95% CI 16.19%–83.03%) during a 6- to 12-month follow-up with the latter showing a significantly higher response rate (p=0.0472). BCVA improvement was 62.2% (95% CI 33.17%–87.11%) during a 6-month follow-up and 56.86% (95% CI 20.91%–89.05%) during a 6- to 12-month follow-up with no significant difference between the two (p=0.3705). Increased IOP remained at 7.11% (95% CI 3.46%–12.68%) for both a 6-month follow-up and up to a 12-month follow-up duration. The CS-sparing effect of sirolimus was also well demonstrated. A reduction in CMT was observed, and only minor drug-related adverse events were reported in all the studies reviewed.ConclusionThis review provided evidence that sirolimus is a promising treatment option for controlling inflammatory activity, improving visual acuity, and sparing CS use with minor adverse events for NIU.

Evaluation of controlled-release triamcinolone acetonide-loaded mPEG-PLGA nanoparticles in treating experimental autoimmune uveitis

Uveitis is a recurrent, sight-threatening intraocular inflammatory disease and is treated with glucocorticoids in clinical practice. In the present study, methoxypoly(ethyleneglycol)-poly(dl-lactide-co-glycolic acid) (mPEG-PLGA) nanoparticles in combination with triamcinolone acetonide (TA) were fabricated using a modified double emulsification method. Further, we characterized the TA-loaded nanoparticles, and investigated the effects of TA-loaded nanoparticles on experimental autoimmune uveitis rats, including histopathological examination and the alterations in interleukin (IL)-17 and IL-10 at mRNA and protein levels in either aqueous humor or serum. As a result, the TA-loaded nanoparticles were a well-defined spherical shape with a mean particle size of 82 nm. The in vitro release profile showed that the TA-loaded nanoparticles could sustain for more than 45 days, and possessed higher anti-inflammatory effects compared to TA alone after pathological examination, resulting in decreased IL-17 and elevated IL-10 levels in both aqueous humor and serum. Based on these findings, it can be concluded that TA-loaded mPEG-PLGA nanoparticles can potentially provide a better anti-inflammatory effect in treating chronic and recurrent uveitis in clinical practice.

UVEOGENE: An SNP database for investigations on genetic factors associated with uveitis and their relationship with other systemic autoimmune diseases.

Uveitis is an intraocular inflammatory disease which can lead to serious visual impairment. Genetic factors have been shown to be involved in its development. However, few databases have focused on the information of associations between single nucleotide polymorphisms (SNPs) and uveitis. To discover the exact genetic background of uveitis, we developed an SNP database specific for uveitis, “UVEOGENE,” which includes 370 genes and 918 SNPs covering 14 uveitis entities and 40 populations from 286 PubMed English‐language papers. Stratification analyses by gender, HLA status, and different clinical features were also extracted from the publications. As a result, 371 associations were judged as “statistically significant.” These associations were also shared with Global Variome shared Leiden Open Variation Database (LOVD) (https://databases.lovd.nl/shared/genes). Based on these associations, we investigated the genetic relationship among three widely studied uveitis entities including Behcet's disease (BD), Vogt–Koyanagi–Harada (VKH) disease, and acute anterior uveitis (AAU). Furthermore, “UVEOGENE” can be used as a reliable and informative resource to identify similarities as well as differences in the genetic susceptibility among uveitis and other autoimmune diseases. UVEOGENE is freely accessible at http://www.uvogene.com.

Persistent Activation of STAT3 Pathway in theRetina Induced Vision Impairment and Retinal Degenerative Changes in Ageing Mice.

Neurotrophic factors can promote the survival of degenerating retinal cells through the activation of STAT3 pathway. Thus, augmenting STAT3 activation in the retina has been proposed as potential therapy for retinal dystrophies. On the other hand, aberrant activation of STAT3 pathway is oncogenic and implicated in diverse human diseases. Furthermore, the STAT3/SOCS3 axis has been shown to induce the degradation of rhodopsin during retinal inflammation. In this study, we generated and used mice with constitutive activation of STAT3 pathway in the retina to evaluate the safety and consequences of enhancing STAT3 activities in the retina as a potential treatment for retinal degenerative diseases. We show that long-term activation of the STAT3 pathway can induce retinal degenerative changes and also exacerbate uveitis and other intraocular inflammatory diseases. Mechanisms underlying the development of vision impairment in the STAT3c-Tg mice derived in part from STAT3-mediated inhibition of rhodopsin and overexpression of SOCS3 in the retina. These results suggest that much caution should be exercised in the use of STAT3 augmentation therapy for retinal dystrophies.

TMP778, a selective inhibitor of RORγt, suppresses experimental autoimmune uveitis development, but affects both Th17 and Th1 cell populations.

Experimental autoimmune uveitis (EAU), an animal model for severe intraocular inflammatory eye diseases, is mediated by both Th1 and Th17 cells. Here, we examined the capacity of TMP778, a selective inhibitor of RORγt, to inhibit the development of EAU, as well as the related immune responses. EAU was induced in B10.A mice by immunization with interphotoreceptor retinoid-binding protein (IRBP). Treatment with TMP778 significantly inhibited the development of EAU, determined by histological examination. In addition, the treatment suppressed the cellular immune response to IRBP, determined by reduced production of IL-17 and IFN-γ, as well as lower percentages of lymphocytes expressing these cytokines, as compared to vehicle-treated controls. The inhibition of IFN-γ expression by TMP778 is unexpected in view of this compound being a selective inhibitor of RORγt. The observation was further confirmed by the finding of reduced expression of the T-bet (Tbx21) gene, the transcription factor for IFN-γ,by cells of TMP778-treated mice. Thus, these data demonstrate the capacity of TMP778 to inhibit pathogenic autoimmunity in the eye and shed new light on its mode of action in vivo.

Epigenetics, microbiota, and intraocular inflammation: New paradigms of immune regulation in the eye.

Sight threatening immune responses that damage the eye characterize intraocular inflammatory diseases. These diseases including uveitis and age-related macular degeneration are worryingly common and quality of life shattering. Genetic studies in past decades significantly advanced our understanding of the etiology of these devastating diseases. Unfortunately, patient genetics alone failed to adequately explain disease origin, susceptibility, and progression. Non-genetic factors such as the epigenetic regulation of ocular diseases and the environmental factors triggering intraocular inflammation offer new insight into intraocular inflammatory disorders. Importantly, mounting evidence is signaling that dysbiosis of human microbiota leads to rapid epigenomic reprograming of host cells and results in the onset of many diseases. In this review, we discuss how epigenetic mechanisms and microbiota may cooperate to initiate and perpetuate ocular inflammation. Lastly, we propose that the discovery of intraocular microbiota presents a significant shift in thought affecting current approaches to the diagnosis, treatment, and prevention of intraocular inflammatory diseases such as uveitis and age-related macular degeneration. The geographical and genetic background difference in both disease presentation and genetic association of intraocular inflammatory diseases may be due to the variation of intraocular microbiota.

Gut microbiota linked to autoimmune uveitis.

Autoimmune uveitis is a group of intraocular inflammatory diseases that arise without known infectious etiology. Uveitis is one of the leading causes of blindness in the developed world and is responsible for up to 15% of severe visual handicap. The disease affects population of working age and has a significant impact on public health. Patients often show detectable immune responses to unique retinal proteins such as retinal arrestin and interphotoreceptor retinoid binding protein (IRBP), which are involved in visual function, and particular HLA haplotypes have been associated with disease, supporting the autoimmune nature (1). Although anecdotal evidence suggested a link between microbial infections and uveitis, our understanding of the etiology of disease, its driving mechanisms and treatment options are still limited. Animal models have been instrumental to advance our understanding on pathogenesis of uveitis. A ‘classic’ uveitis model in mice is referred as experimental autoimmune uveitis (EAU), involving active immunization with IRBP in complete Freund’s adjuvant (CFA) that contains heat-killed Mycobacterium tuberculosis . Co-administration of bacterial adjuvants is required to activate innate immune cells and create the proinflammatory milieu to induce adaptive immune responses and to trigger the autoimmune effector pathway (1). However, unlike experimental diseases in the animal models, most cases of human autoimmune uveitis cannot be connected to an exposure of the immune system to ocular antigens that are present behind the blood retinal barrier. These target antigens in uveitis are sequestered inside the eye and are not expressed in the periphery (2), but retina-specific T cells that would recognize them must be activated to enter the eye to drive pathology in uveitis. This presents a paradox and raises a fundamental question: where and how do autoreactive T cells, that can recognize retinal antigens and trigger uveitis, first become activated?