CD4⁺ T-cell plasticity in non-infectious retinal inflammatory disease

Non-infectious uveitis (NIU) is a potentially sight-threatening disease. Effector CD4+ T cells, especially interferon-γ-(IFNγ) producing Th1 cells and interleukin-17-(IL-17) producing Th17 cells, are the major immunopathogenic cells, as demonstrated by adoptive transfer of disease in a model of experimental autoimmune uveitis (EAU). CD4+FoxP3+CD25+ regulatory T cells (Tregs) were known to suppress function of effector CD4+ T cells and contribute to resolution of disease. It has been recently reported that some CD4+ T-cell subsets demonstrate shared phenotypes with another CD4+ T-cell subset, offering the potential for dual function. For example, Th17/Th1 (co-expressing IFNγ and IL-17) cells and Th17/Treg (co-expressing IL-17 and FoxP3) cells have been identified in NIU and EAU. In this review, we have investigated the evidence as to whether these ‘plastic CD4+ T cells’ are functionally active in uveitis. We conclude that Th17/Th1 cells are generated locally, are resistant to the immunosuppressive effects of steroids, and contribute to early development of EAU. Th17/Treg cells produce IL-17, not IL-10, and act similar to Th17 cells. These cells were considered pathogenic in uveitis. Future studies are needed to better clarify their function, and in the future, these cell subsets may in need to be taken into consideration for designing treatment strategies for disease

Adhesion Molecule Targeted Therapy for Non-Infectious Uveitis

Non-infectious uveitis (NIU) is an inflammatory eye disease initiated via CD4+ T-cell activation and transmigration, resulting in focal retinal tissue damage and visual acuity disturbance. Cell adhesion molecules (CAMs) are activated during the inflammatory process to facilitate the leukocyte recruitment cascade. Our review focused on CAM-targeted therapies in experimental autoimmune uveitis (EAU) and NIU. We concluded that CAM-based therapies have demonstrated benefits for controlling EAU severity with decreases in immune cell migration, especially via ICAM-1/LFA-1 and VCAM-1/VLA-4 (integrin) pathways. P-selectin and E-selectin are more involved specifically in uveitis related to vasculitis. These therapies have potential clinical applications for the development of a more personalized and specific treatment. Localized therapies are the future direction to avoid serious systemic side effects

Experimental Autoimmune Uveitis: An Intraocular Inflammatory Mouse Model

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

Immune-Mediated Retinal Vasculitis in Posterior Uveitis and Experimental Models: The Leukotriene (LT)B4-VEGF Axis

Retinal vascular diseases have distinct, complex and multifactorial pathogeneses yet share several key pathophysiological aspects including inflammation, vascular permeability and neovascularisation. In non-infectious posterior uveitis (NIU), retinal vasculitis involves vessel leakage leading to retinal enlargement, exudation, and macular oedema. Neovascularisation is not a common feature in NIU, however, detection of the major angiogenic factor—vascular endothelial growth factor A (VEGF-A)—in intraocular fluids in animal models of uveitis may be an indication for a role for this cytokine in a highly inflammatory condition. Suppression of VEGF-A by directly targeting the leukotriene B4 (LTB4) receptor (BLT1) pathway indicates a connection between leukotrienes (LTs), which have prominent roles in initiating and propagating inflammatory responses, and VEGF-A in retinal inflammatory diseases. Further research is needed to understand how LTs interact with intraocular cytokines in retinal inflammatory diseases to guide the development of novel therapeutic approaches targeting both inflammatory mediator pathways

Classical dendritic cells mediate fibrosis directly via the retinoic acid pathway in severe eye allergy

Fibrosis is a shared end-stage pathway to lung, liver, and heart failure. In the ocular mucosa (conjunctiva), fibrosis leads to blindness in trachoma, pemphigoid, and allergy. The indirect fibrogenic role of DCs via T cell activation and inflammatory cell recruitment is well documented. However, here we demonstrate that DCs can directly induce fibrosis. In the mouse model of allergic eye disease (AED), classical CD11b(+) DCs in the ocular mucosa showed increased activity of aldehyde dehydrogenase (ALDH), the enzyme required for retinoic acid synthesis. In vitro, CD11b(+) DC-derived ALDH was associated with 9-cis-retinoic acid ligation to retinoid x receptor (RXR), which induced conjunctival fibroblast activation. In vivo, stimulating RXR led to rapid onset of ocular mucosal fibrosis, whereas inhibiting ALDH activity in DCs or selectively depleting DCs markedly reduced fibrosis. Collectively, these data reveal a profibrotic ALDH-dependent pathway by DCs and uncover a role for DC retinoid metabolism

Leukotriene B4 (LTB4) and its receptor in Experimental Autoimmune Uveitis (EAU) and in human retinal tissues: clinical severity and LTB4-dependence of retinal Th17 cells

Nomacopan, a drug originally derived from tick saliva, has dual functions of sequestering leukotriene B4 (LTB4) and inhibiting complement component 5 (C5) activation. It was demonstrated that nomacopan provides therapeutic benefit in experimental autoimmune uveitis (EAU). The longer-acting forms of nomacopan were more efficacious in mouse EAU models and the long-acting variant that inhibited only LTB4 was at least as effective as the long-acting variant that inhibited both C5 and LTB4, preventing structural damage to the retina and a significant reduction of effector Th17 cells and inflammatory macrophages. Increased levels of LTB4 and C5a (produced upon C5 activation) were detected during disease progression. Retinal activated lymphocytes were shown to express LTB4 receptors (R) in vitro and in inflamed draining lymph nodes (dLN). Levels of LTB4R-expressing retinal active/inflammatory macrophages were also increased. Within the dLN CD4+T cell population, 30% expressed LTB4R+ following activation in vitro, while retinal infiltrating cells expressed LTB4R and C5aR. Validation of expression of those receptors in human uveitis and healthy tissues suggests that infiltrating cells could be targeted by inhibitors of the LTB4-BLT1 pathway as a novel therapeutic approach. In conclusion, this study provides novel data on intraocular LTB4 and C5a in EAU, their associated receptor expression by retinal infiltrating cells in mouse and human tissues and in attenuating EAU via the dual inhibitor nomacopan

Aldehyde dehydrogenase inhibition blocks mucosal fibrosis in human and mouse ocular scarring

Mucous membrane pemphigoid (MMP) is a systemic mucosal scarring disease, commonly causing blindness, for which there is no antifibrotic therapy. Aldehyde dehydrogenase (ALDH) family 1 is upregulated in both ocular MMP (OMMP) conjunctiva and cultured fibroblasts. Application of the ALDH metabolite, retinoic acid (RA), to normal human conjunctival fibroblasts in vitro induced a diseased phenotype. Conversely, application of ALDH inhibitors, including disulfiram, to OMMP fibroblasts in vitro restored their functionality to that of normal controls. ALDH1 is also upregulated in the mucosa of the mouse model of scarring allergic eye disease, used here as a surrogate for OMMP, in which topical application of disulfiram decreased fibrosis in vivo. These data suggest that progressive scarring in OMMP results from ALDH/RA fibroblast autoregulation, that the ALDH1 subfamily has a central role in immune-mediated ocular mucosal scarring, and that ALDH inhibition with disulfiram is a potential, and readily translatable, antifibrotic therapy

Autoimmune and autoinflammatory mechanisms in uveitis

The eye, as currently viewed, is neither immunologically ignorant nor sequestered from the systemic environment. The eye utilises distinct immunoregulatory mechanisms to preserve tissue and cellular function in the face of immune-mediated insult; clinically, inflammation following such an insult is termed uveitis. The intra-ocular inflammation in uveitis may be clinically obvious as a result of infection (e.g. toxoplasma, herpes), but in the main infection, if any, remains covert. We now recognise that healthy tissues including the retina have regulatory mechanisms imparted by control of myeloid cells through receptors (e.g. CD200R) and soluble inhibitory factors (e.g. alpha-MSH), regulation of the blood retinal barrier, and active immune surveillance. Once homoeostasis has been disrupted and inflammation ensues, the mechanisms to regulate inflammation, including T cell apoptosis, generation of Treg cells, and myeloid cell suppression in situ, are less successful. Why inflammation becomes persistent remains unknown, but extrapolating from animal models, possibilities include differential trafficking of T cells from the retina, residency of CD8(+) T cells, and alterations of myeloid cell phenotype and function. Translating lessons learned from animal models to humans has been helped by system biology approaches and informatics, which suggest that diseased animals and people share similar changes in T cell phenotypes and monocyte function to date. Together the data infer a possible cryptic infectious drive in uveitis that unlocks and drives persistent autoimmune responses, or promotes further innate immune responses. Thus there may be many mechanisms in common with those observed in autoinflammatory disorders