In this report we present a protocol that allows the investigator to generate a mouse model of intraocular uveitis. More commonly referred to as experimental autoimmune uveitis (EAU), this established model captures many aspects of human disease. Herein, we will describe how to induce and monitor disease progression using several readouts.
Experimental Autoimmune Uveitis (EAU) is driven by immune cells responding to self-antigens. Many features of this non-infectious, intraocular inflammatory disease model recapitulate the clinical phenotype of posterior uveitis affecting humans. EAU has been used reliably to study the efficacy of novel inflammatory therapeutics, their mode of action and to further investigate the mechanisms that underpin disease progression of intraocular disorders. Here, we provide a detailed protocol on EAU induction in the C57BL/6J mouse – the most widely used model organism with susceptibility to this disease. Clinical assessment of disease severity and progression will be demonstrated using fundoscopy, histological examination and fluorescein angiography. The induction procedure involves subcutaneous injection of an emulsion containing a peptide (IRBP1-20) from the ocular protein interphotoreceptor retinoid binding protein (also known as retinol binding protein 3), Complete Freund's Adjuvant (CFA) and supplemented with killed Mycobacterium tuberculosis. Injection of this viscous emulsion on the back of the neck is followed by a single intraperitoneal injection of Bordetella pertussis toxin. At the onset of symptoms (day 12-14) and under general anesthesia, fundoscopic images are taken to assess disease progression through clinical examination. These data can be directly compared with those at later timepoints and peak disease (day 20-22) with differences analyzed. At the same time, this protocol allows the investigator to assess potential differences in vessel permeability and damage using fluorescein angiography. EAU can be induced in other mouse strains – both wildtype or genetically modified – and combined with novel therapies offering flexibility for studying drug efficacy and/or disease mechanisms.
This protocol will demonstrate how to induce Experimental Autoimmune Uveitis (EAU) in the C57BL/6J mouse by a single subcutaneous injection of a retinal antigen in an emulsified adjuvant. Methods for monitoring and assessing disease progression will be detailed through fundoscopic imaging and histological examination, with measurement parameters outlined within. In addition, fluorescein angiography, a technique for examining retinal blood vessel structure and permeability will be discussed.
This EAU model recapitulates central features of non-infectious posterior uveitis in humans with regards to clinicopathologic characteristics and the basic cellular and molecular mechanisms that drive disease. EAU is mediated by Th1 and/or Th17 subsets of self-reactive CD4+T lymphocytes, as shown in adoptive transfer experiments and with IFNγ-depleted mice1. Much of our understanding of the potential roles for these cells in uveitis comes from studying EAU2 where both Th1 and Th17 cells are detected within the retinal tissues3. Often, EAU is used as a preclinical model to assess the utility of novel therapies in attenuating disease. Therapeutic approaches that have successfully modulated EAU disease have shown some efficacy in the clinic and reached FDA approved status. Examples of these are groups of immunoregulatory drugs such as the T cell-targeting therapies: cyclosporine, FK-506, and rapamycin4,5,6. Recently, interventions targeting novel pathways have also been explored in this model to investigate both mechanism and effect on disease outcome. These include targeting transcriptional regulation through chromatin reader Bromodomain Extra-Terminal (BET) proteins and P-TEFb inhibitors3. Moreover, more conventional approaches such as a VLA-4 inhibitor have recently demonstrated suppression in EAU via modulation of effector CD4+ T cells7. In addition, targeting Th17 cells with TMP778, a RORγt inverse agonist, has also been found to significantly suppress EAU8. Furthermore, this model offers an opportunity to study chronic autoimmune inflammation in the retina and the accompanying underlying mechanisms such as lymphocyte priming.
The primary readouts for EAU preclinical studies are clinical assessment by performing retinal fundoscopy imaging and less frequently, by assessing retinal integrity by Optical Coherence Tomography (OCT). Retinal histopathological evaluation and immunophenotyping of retinal cells by flow cytometry are then undertaken at termination. Fundoscopy is an easy-to-use live imaging system that allows for rapid and reproducible clinical assessment of the whole retina. For immunohistochemical assessments, the techniques are based on the preparation of retinal sections that allow us to study tissue architecture for the degree of inflammation and structural damage9. The assessment criteria and conventional scoring systems, for all techniques used, will be outlined within this protocol. The extent of damage recorded using fundoscopic imaging often closely correlates with histological changes. This dual approach to monitoring and assessing disease severity affords greater sensitivity and more reliable measurement outcomes.
EAU is a well-established, commonly used model for preclinical testing and investigation of immune-mediated eye disease. This model is reliable and reproducible with >95% disease incidence and generates comprehensive data that can be used to validate or repudiate new therapies for the treatment of intraocular inflammatory disease that represents a major cause of working-age blindness worldwide10.
All experiments were performed in accordance with the UK Animals (Scientific Procedures) Act of 1986, and institutional Animal Welfare and Ethical Review Body (AWERB) guidelines.
1. Housing C57BL/6J mice
2. Immunization of C57BL/6 mice
3. Clinical Evaluation – Mouse Fundus Examination
NOTE: Clinical disease is to be scored using fundus examination, via bright-field live imaging using a fundoscope and Discover software used for visualization.
4. Fluorescein angiography
5. Clinical Disease Scoring
6. Histology and Histological Scoring
In this protocol, we describe a step-by-step method for inducing a model of experimental autoimmune uveitis (EAU) by immunizing mice with a uveitogenic retinal peptide derived from IRBP. The assessment of disease employing widely used and readily accessible approaches are covered although these are not exclusive and may be added to, or partially replaced, by other imaging techniques. The first signs of EAU in C57BL/6J mice can be detected two weeks post-immunization and peak disease reached within three weeks as illustrated in Figure 1. Fundoscopic changes are classified during disease progression as inflammatory changes, which include retinal tissue, vascular and optic disc inflammation, and retinal structural damage (Figure 2) in addition to histological changes based on infiltrating immune cells and structural damage. These clinical and histopathological changes can be detected for up to 85 days post immunization, and graded and scored for evaluation proposes to study disease progression. In order to avoid unintentional bias in the qualitative visual scoring, the images should be evaluated by more than one expert and scorers require to be blinded to the treatment groups.
We show here how the clinical and histological scoring systems (Table 1 and Table 2) guide scientists to quantify EAU severity, to validate the efficacy of treatments and to explore the mechanism of drug action. Vascular leakage is also a pathological feature of the model and in human uveitis. We are showing examples of vascular leakage of fluorescein (Figure 3) as another method for assessing disease in this model.
Figure 1. Schematic timeline of clinical and histological disease progression in IRBP1-20 induced EAU. A timeline marking the onset of infiltration and progression of IRBP1-20 induced EAU towards peak disease. From immunisation, the first signs of clinical disease, as detected by fundoscopic imaging and histopathological analysis, falls between days 12-14. The disease will then continue to progress, according to these parameters, until a peak is reached around day 21-23. Please click here to view a larger version of this figure.
Figure 2. Representative fundoscopic images correlating with histological sections at different stages of IRBP1-20 induced EAU disease in C57BL/6J mice. Clinical fundoscopic and corresponding tissue images of C57BL/6J from the same animal immunised with IRBP1-20 peptide. (A and B) fundoscopic images and histological sections of eye obtained from healthy and CFA injected mice. Retina has no sign of inflammation and corresponding histology sections show preserved retinal layers. (C) Fundoscopic image of eye obtained from C57BL/6J mouse 14 days post immunization demonstrate classic signs of EAU, presenting with severe optic disc swelling in the early stage of disease, corresponding histology shows infiltrating immune cells into vitreous space. (D) Fundoscopic images of eye obtained from C57BL/6J mouse 21 days post immunization shows signs of vessel cuffing and infiltrating immune populations. Histology data demonstrates severe structural changes by retinal folding (yellow arrows). V= vessel, O= optic disk, R=retina, L=lens, Vit=vitreous, iO= inflamed optic disk, iV= inflamed vessel, iR= inflamed retina, i= infiltrating cells in vitreous, RFs=retinal folds. Please click here to view a larger version of this figure.
Figure 3. Representative images of fluorescent angiography taken using Micron III imaging system at peak disease. C57BL/6J mice were injected subcutaneously with 2% fluorescein and images taken at various timepoints after circulation of the tracer. (A) CFA only control mouse taken at 1.5- and 7-minutes post fluorescein administration. (B) Representative images of IRBP1-20 immunized mice taken 1.5 and 7 minutes, respectively, after receiving fluorescein. White arrow indicates vessel leakage. Please click here to view a larger version of this figure.
Score | Optic Disc | Retinal Vessels | Retinal Tissue Infiltrate | Structural Damage | ||||
1 | Minimal Inflammation | 1-4 mild cuffings | 1-4 small lesions or 1 linear lesion | Retinal lesions or retinal atrophy involving ¼ to ¾ retina area | ||||
2 | Mild inflammation | >4 mild cuffings or 1-3 moderate cuffing | 5-10 small lesions or 2-3 linear lesions | Pan retinal atrophy with multiple small lesions (scars) or <3 linear lesions (scars) | ||||
3 | Moderate inflammation | >3 moderate cuffings | >10 small lesions or >3 linear lesions | Pan retinal atrophy with >3 linear lesions or confluent lesions (scars) | ||||
4 | Severe inflammation | >1 severe cuffing | Linear lesion confluent | Retinal detachment with folding | ||||
5 | * Not visible (white out or extreme detachment) | * Not visible (white out or extreme detachment) | * Not visible (white out or extreme detachment) | * Not visible (white out or extreme detachment) |
Table 1. Conventional clinical scoring scale for evaluating EAU clinical disease severity. Table showing criteria used to evaluate the extent of disease severity in mice immunised with IRBP1-20. Scores were allocated according to the hallmarks outlined above being visible on the fundus images, each eye was given a total score out of twenty. * Due to the obscuration of infiltrate and retinal detachment inside the posterior chamber cannot be assessed. Table adapted with permission from Xu H., et al., 20088.
Grade | Criteria |
0 | No change |
0.5 (trace) | Mild inflammatory cell infiltration. No tissue damage |
1 | Infiltration; retinal folds and focal retinal detachments; few small granulomas in choroid and retina, perivasculitis |
2 | Moderate infiltration; retinal folds, detachments and focal photoreceptor cell damage; small to medium sized granulomas, perivasculitis and vasculitis |
3 | Medium to heavy infiltration; extensive retinal folding with detachments, moderate photoreceptor cell damage; medium sized granulomatous lesions; subretinal neovascularization |
Table 2. Histologically scoring EAU
Table showing criteria used to evaluate the severity of EAU based on histopathological features of disease. Scores were allocated according to the hallmarks outlined above on H&E staining, each eye was given a total score out of four. Table adapted with permission from Agarwal et al. 201311.
Experimental animal models are necessary tools for studying disease pathogenesis and preclinical testing of novel therapeutic paradigms. In the current protocol, we have discussed a methodology for inducing, monitoring, and scoring EAU, an experimental model of intraocular inflammatory uveitis. This EAU model has more than 95% disease incidence when all procedures are performed according to the protocol outlined herein, and results in the development of chronic, monophasic EAU. To achieve this incidence level, we stress the importance of antigen preparation and injection of the emulsion, both of which are detailed above. The main features of EAU in animals are retinal and/or choroidal inflammation, retinal vasculitis, photoreceptor destruction and loss of vision, all of which represent many essential clinicopathological features of human posterior uveitis12. Much of the understanding of the basic cellular and molecular mechanisms involved in uveitis derived from the induced EAU model as described herein. EAU can be induced in mice13 and rats11 by active immunization with retinal antigens that are recognized by lymphocytes. These retinal antigens take many forms; IRBP (for mice) or retinal soluble antigen (S-Ag) for rats. Inducing EAU on a C57BL/6J background generates a more chronic form of the disease, with peak pathology observed three weeks post-immunization. By comparison, applying retinal antigen to a B10RIII background14 induces an acute-monophasic and clinically severe form of EAU where peak pathology typically presents within two weeks of induction, and disease subsides by week 3.
Different IRBP epitopes have been tested in C57BL/6J mice and IRBP1-20 peptide has proven to be a reproducible model with a high incidence and severity levels. Recently a new uveitogenic epitope of IRBP, amino acid residues 651 to 670 of human IRBP have been reported to induce EAU with a higher clinical incidence and severe disease manifestation11 and may be used in preference should this meet the scientific objectives. Since the impact of gut commensal microbiota and the activation of autoreactive T cell receptors (TCRs) is known to interfere with the onset of disease when applying different antigens15, we recommend for beginners in this field to use either hIRBP1-20 or hIRBP651-670 peptides at a dose titrated between 300-500 µg in order to achieve a reliable model. Indeed, variability in this model has been documented elsewhere with reports highlighting the importance of differences between housing systems and the microbiome which might impact disease severity and incidence15. Thus, more or less peptide antigen and pertussis toxin may be required.
There are a number of other models to which our described analysis can be performed. These include spontaneous uveitis that progresses in IRBP T cell receptor (TCR) transgenic (R161H) mice where ocular inflammation develops by 5-6 weeks of age16. EAU can also be adoptively induced by transferring uveitogenic effector CD4+T cells. Activated, IRBP-specific CD4+T cells derived from primed mice can be used as a source of effector cells3,11. This model represents the effector phase of the disease while avoiding the complexities of using CFA in the inducible model.
Further to this, there are many advantages to using ocular inflammatory models as appropriate tools to investigate other inflammatory diseases, in particular, those with effector Th1 and Th17 subset pathology. The main advantages to using this model are the non-invasive and quantifiable methods for monitoring disease development and progression, which are fundoscopy and angiography. These non-invasive imaging systems allow easy access to neuronal tissues, that would otherwise be concealed behind protective anatomical barriers. Additional methods for monitoring disease progression include the application of OCT imaging, which is more sensitive than fundoscopic imaging in detecting cellular infiltrates, especially at the early stage of EAU onset. The technique allows multi-layer cross- and horizontal-sectional visualizations of the retina longitudinally and in a non-invasive fashion. In vivo OCT imaging adds information on retinal thickness that could not be obtained by fundoscopic and histological examinations17. Increasingly, the availability of even more sophisticated non-invasive imaging techniques, such as adaptive optics scanning laser ophthalmoscopy and multimodal imaging tools will further advance our capacity to investigate this disease in small rodents. Furthermore, the ability to dissect and isolate resident and infiltrating cell populations for deeper analysis of immunophenotypes, using techniques such as flow cytomety, affords great opportunities to deliver insightful information.
There are a few established scoring systems based on clinical criteria obtained from fundoscopy8,9,18. Whilst these differ slightly between ophthalmology research centers, all are reliable, correlate with histopathological features and are capable of accurately reflecting the severity of disease. In the current study, we refer to the scoring system developed by Xu et al.8. This system offers a more detailed assessment approach with greater numbers of clinical measurement parameters. It comprises a maximum score of 20 which introduces a wider window for scoring than alternative systems limited to a maximum of 5. This is more important for further exploration within therapeutic approaches. Minimising operator error, however, is critical when using such a refined and detailed set of parameters and may require careful training of the operator and independent validation of the interpretation.
Here, we present a protocol to induce EAU in female C57BL/6 mice as there is an increased incidence of women : men 1.4:1 presenting with uveitis in the clinical setting. Nevertheless, the sex of the mice used for inducing autoimmune disease should be considered as this may affect the cytokine milieu11, and also reveal important differences in the way they respond to therapeutic intervention. Another consideration is the age of the mice at disease induction. For example, we have studied age-dependency of susceptibility in B10RIII mice and concluded that mice over 8 weeks of life have a lower incidence of EAU (unpublished study from our group).
In conclusion, animal models of intraocular disease have provided an invaluable tool to study human posterior uveitis and have facilitated development of novel therapies such as CsA. However, no animal model by itself reproduces the full spectrum of human uveitis, as each has unique characteristics that make it suitable for studying particular aspects of the disease. This EAU model is induced by autoimmunity through the application of IRBP peptide supplemented with adjuvants which trigger innate immune responses. However, it is not known if all forms of posterior uveitis in humans are autoimmune and if antigenic mimicry is a triggering factor. In addition, it is not clear whether there is an association with infection in triggering human uveitis. Nonetheless, the model described herein is a useful and reproducible generic model that can be used to glean useful information regarding aetiology, pathogenesis and therapy of this sight-threatening disease.
The authors have nothing to disclose.
JG was awarded a UCL Impact Studentship and Rosetrees Trust funding to support CB. VC was in receipt of a research collaborative grant from Akari Therapeutics Inc. We would like to thank UCL Institute of Ophthalmology, Biological Service Unit especially Ms Alison O'Hara and her team for their technical support.
antisedan | ZOETIS, USA | for waking up | |
Complete Freund’s Adjuvant; CFA | Sigma, UK | F5881 | for immunisation |
Domitor | Orion Pharma, Finland | for anesthesia | |
Flourescein | Sigma, UK | F2456 | for Angiography |
IRBP1-20 | Chamberidge peptide, UK | peptide;antigen | |
Ketamine | Orion Pharma, Finland | for anesthesia | |
Micron III | Phoenix Research, USA | for fundoscopy | |
Mouse Serum | Sigma, UK | M5905 | for immunisation |
Mycobacterium terberculosis | Sigma, UK | 344289 | for immunisation |
Pertussis Toxin | Sigma, UK | P2980 | for immunisation |
phenylephrine hydrochloride 2.5% | Bausch & Lomb UK | PHEN25 | for dilation |
Tropicamide 1% | SANDOZ | for dilation | |
Viscotears | WELDRICKS Pharmacy, UK | 2082642 | for eye lubrication |