Interphotoreceptor retinoid binding protein peptide-induced uveitis in B10.RIII mice: characterization of disease parameters and immunomodulation

TNF-α in Uveitis: From Bench to Clinic

Uveitis is an inflammation of the iris, ciliary body, vitreous, retina, or choroid, which has been shown to be the first manifestation of numerous systemic diseases. Studies about the immunopathogenesis and treatment of uveitis are helpful to comprehend systemic autoimmune diseases, and delay the progression of systemic autoimmune diseases, respectively. Tumor necrosis factor-alpha (TNF-α), a pleiotropic cytokine, plays a pivotal role in intraocular inflammation based on experimental and clinical data. Evidence of the feasibility of using anti-TNF-α agents for uveitis management has increased. Although there are numerous studies on TNF-α in various autoimmune diseases, the pathological mechanism and research progress of TNF-α in uveitis have not been reviewed. Therefore, the objective of this review is to provide a background on the role of TNF-α in the immunopathogenesis of uveitis, as well as from bench to clinical research progress, to better guide TNF-α-based therapeutics for uveitis.

Caffeic acid phenethyl ester lessens disease symptoms in an experimental autoimmune uveoretinitis mouse model

Experimental autoimmune uveoretinitis (EAU) is an autoimmune disease that models human uveitis. Caffeic acid phenethyl ester (CAPE), a phenolic compound isolated from propolis, possesses anti-inflammatory and immunomodulatory properties. CAPE demonstrates therapeutic potential in several animal disease models through its ability to inhibit NF-κB activity. To evaluate these therapeutic effects in EAU, we administered CAPE in a model of EAU that develops after immunization with interphotoreceptor retinal-binding protein (IRBP) in B10.RIII and C57BL/6 mice. Importantly, we found that CAPE lessened the severity of EAU symptoms in both mouse strains. Notably, treated mice exhibited a decrease in the ocular infiltration of immune cell populations into the retina; reduced TNF-α, IL-6, and IFN-γ serum levels: and inhibited TNF-α mRNA expression in retinal tissues. Although CAPE failed to inhibit IRBP-specific T cell proliferation, it was sufficient to suppress cytokine, chemokine, and IRBP-specific antibody production. In addition, retinal tissues isolated from CAPE-treated EAU mice revealed a decrease in NF-κB p65 and phospho-IκBα. The data identify CAPE as a potential therapeutic agent for autoimmune uveitis that acts by inhibiting cellular infiltration into the retina, reducing the levels of pro-inflammatory cytokines, chemokine, and IRBP-specific antibody and blocking NF-κB pathway activation.

Oral delivery of ACE2/Ang-(1-7) bioencapsulated in plant cells protects against experimental uveitis and autoimmune uveoretinitis

Hyperactivity of the renin-angiotensin system (RAS) resulting in elevated Angiotensin II (Ang II) contributes to all stages of inflammatory responses including ocular inflammation. The discovery of angiotensin-converting enzyme 2 (ACE2) has established a protective axis of RAS involving ACE2/Ang-(1-7)/Mas that counteracts the proinflammatory and hypertrophic effects of the deleterious ACE/AngII/AT1R axis. Here we investigated the hypothesis that enhancing the systemic and local activity of the protective axis of the RAS by oral delivery of ACE2 and Ang-(1-7) bioencapsulated in plant cells would confer protection against ocular inflammation. Both ACE2 and Ang-(1-7), fused with the non-toxic cholera toxin subunit B (CTB) were expressed in plant chloroplasts. Increased levels of ACE2 and Ang-(1-7) were observed in circulation and retina after oral administration of CTB-ACE2 and Ang-(1-7) expressing plant cells. Oral feeding of mice with bioencapsulated ACE2/Ang-(1-7) significantly reduced endotoxin-induced uveitis (EIU) in mice. Treatment with bioencapsulated ACE2/Ang-(1-7) also dramatically decreased cellular infiltration, retinal vasculitis, damage and folding in experimental autoimmune uveoretinitis (EAU). Thus, enhancing the protective axis of RAS by oral delivery of ACE2/Ang-(1-7) bioencapsulated in plant cells provide an innovative, highly efficient and cost-effective therapeutic strategy for ocular inflammatory diseases.

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 T_reg 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.

Lesional-targeting of neuroprotection to the inflammatory penumbra in experimental multiple sclerosis

Progressive multiple sclerosis is associated with metabolic failure of the axon and excitotoxicity that leads to chronic neurodegeneration. Global sodium-channel blockade causes side effects that can limit its use for neuroprotection in multiple sclerosis. Through selective targeting of drugs to lesions we aimed to improve the potential therapeutic window for treatment. This was assessed in the relapsing-progressive experimental autoimmune encephalomyelitis ABH mouse model of multiple sclerosis using conventional sodium channel blockers and a novel central nervous system-excluded sodium channel blocker (CFM6104) that was synthesized with properties that selectively target the inflammatory penumbra in experimental autoimmune encephalomyelitis lesions. Carbamazepine and oxcarbazepine were not immunosuppressive in lymphocyte-driven autoimmunity, but slowed the accumulation of disability in experimental autoimmune encephalomyelitis when administered during periods of the inflammatory penumbra after active lesion formation, and was shown to limit the development of neurodegeneration during optic neuritis in myelin-specific T cell receptor transgenic mice. CFM6104 was shown to be a state-selective, sodium channel blocker and a fluorescent p-glycoprotein substrate that was traceable. This compound was >90% excluded from the central nervous system in normal mice, but entered the central nervous system during the inflammatory phase in experimental autoimmune encephalomyelitis mice. This occurs after the focal and selective downregulation of endothelial p-glycoprotein at the blood-brain barrier that occurs in both experimental autoimmune encephalomyelitis and multiple sclerosis lesions. CFM6104 significantly slowed down the accumulation of disability and nerve loss in experimental autoimmune encephalomyelitis. Therapeutic-targeting of drugs to lesions may reduce the potential side effect profile of neuroprotective agents that can influence neurotransmission. This class of agents inhibit microglial activity and neural sodium loading, which are both thought to contribute to progressive neurodegeneration in multiple sclerosis and possibly other neurodegenerative diseases.

Tumour necrosis factor-mediated macrophage activation in the target organ is critical for clinical manifestation of uveitis

Clinically available anti-tumour necrosis factor (TNF) biologics, which inhibit both soluble (sTNF) and transmembrane forms (tmTNF) of TNF, eliminating all TNF signalling, have successfully treated autoimmune diseases including uveitis. These have potentially serious side effects such as reactivation of latent Mycobacterium tuberculosis and, therefore, more specific inhibition of TNF signalling pathways may maintain clinical efficacy while reducing adverse effects. To determine the effects of specific pharmacological inhibition of sTNF on macrophage activation and migration, we used a mouse model of uveitis (experimental autoimmune uveoretinitis; EAU). We show that selective inhibition of sTNF is sufficient to suppress EAU by limiting inflammatory CD11b(+) macrophages and CD4(+) T cell migration into the eye. However, inhibition of both sTNF and tmTNF is required to inhibit interferon-γ-induced chemokine receptor 2, CD40, major histocompatibility complex class II and nitric oxide (NO) up-regulation, and signalling via tmTNF is sufficient to mediate tissue damage. In confirmation, intravitreal inhibition of sTNF alone did not suppress disease, and inflammatory cells that migrated into the eye were activated, generating NO, thus causing structural damage to the retina. In contrast, intravitreal inhibition of both sTNF and tmTNF suppressed macrophage activation and therefore disease. We conclude that sTNF is required for inflammatory cell infiltration into target tissue, but at the tissue site inhibition of both sTNF and tmTNF is required to inhibit macrophage activation and to protect from tissue damage.

Immunosuppressive activity of a novel peptide analog of α-melanocyte stimulating hormone (α-MSH) in experimental autoimmune uveitis

Autoimmune uveitis is an inflammatory disorder of the eye that can lead to pain and vision loss. Steroids and immunosuppressive drugs are currently the only therapeutics for uveitis and have serious ocular and systemic toxicities. Therefore, safer alternative therapeutics are desired. Alpha-melanocyte stimulating hormone (α-MSH) is a neuropeptide that suppresses effector T cell functions, induces regulatory T cells and has beneficial effects in certain autoimmune and transplant models. A novel d-amino acid peptide analog of native α-MSH (dRI-α-MSH) was produced that was protected from protease digestion and had increased selectivity for the melanocortin-1 receptor. Systemic delivery of the dRI-α-MSH analog dramatically suppressed disease progression and retained retinal architecture in the experimental autoimmune uveitis (EAU) model. Local delivery by periorbital injection was equally effective. Importantly, treatment with the novel dRI-α-MSH analog suppressed uveitis with a similar magnitude to the corticosteroid, dexamethasone. Data indicate that the novel dRI-α-MSH analogs show anti-inflammatory activities and have potential therapeutic use in uveitis and other autoimmune diseases.

Clinical review: Anti-TNFalpha therapies in uveitis: perspective on 5 years of clinical experience

Despite a lack of robust evidence, anti-TNF therapies are in wide use for the treatment of noninfectious ocular inflammatory diseases. There is a clear rationale, based on mechanistic and preclinical efficacy data, for their use in posterior segment intraocular inflammation. However, their increasing use for other indications has been largely extrapolated from the benefit observed in autoinflammatory and autoimmune systemic diseases. Given their cost and the potential for significant adverse events, this review highlights the evidence for their continued use, possibilities for switching anti-TNF agents, and ways of reducing the risk of therapy.

Sequence 168 to 177 of interphotoreceptor retinoid-binding protein (IRBP) is an antigenic epitope for autoreactive CD8 T cells in the B10RIII mouse

We previously demonstrated that a significant proportion of interphotoreceptor retinoid-binding protein (IRBP)-specific uveitogenic T cells in the C57BL/6 mouse and Lewis rat express CD8. The aims of this study were to determine whether some of the IRBP-specific T cells in the B10RIII mouse also express CD8 and whether CD8 and CD4 IRBP-specific T cells in the B10RIII mouse recognize a different or the same antigenic epitope. Our results show that autoreactive CD8 T cells were abundant in B10RIII mice immunized with the uveitogenic peptide IRBP161-180. Using multimers of recombinant H-2D(r) molecules, we also showed that the binding of the H-2D(r) fusion protein to IRBP161-180-expanded CD8 T cells was dependent on the peptide complexed with the recombinant molecules. The use of a panel of truncated peptides showed that the truncated 10-mer peptide, IRBP168-177, retained the ability to bind to, and stimulate, IRBP161-180-specific CD8 T cells after complexing with a dimeric MHC class I (H-2D(r)) molecule. Finally, adoptive transfer of IRBP161-180-specific T cells stimulated with IRBP168-177 consistently induced mild, but significant, EAU in naïve B10RIII mice.

Monoclonal antibody-mediated CD200 receptor signaling suppresses macrophage activation and tissue damage in experimental autoimmune uveoretinitis

Macrophage responses are regulated by multiple secreted factors as well as by cell surface receptors, including the inhibitory signals resulting from ligation of myeloid CD200 receptors (CD200R) by the widely distributed CD200. In the absence of CD200, animals display increased susceptibility to autoimmunity and earlier onset aggressive autoimmune disease. In these current experiments, an agonist monoclonal rat anti-mouse CD200R (DX109) antibody delivered a negative signal to bone marrow-derived macrophages, which suppressed interferon (IFN)gamma-mediated nitric oxide (NO) and interleukin-6 production. Experimental autoimmune uveoretinitis (EAU) was used as a model of organ-specific autoimmunity in the eye, a tissue with extensive neuronal and endothelial CD200 expression. In mice lacking CD200 (CD200(-/-)), increased numbers of retina-infiltrating macrophages displaying heightened NO responses were observed during EAU. In addition, we aimed to suppress disease by maintaining tonic suppression of macrophage activation via CD200R. Systemically administered DX109 monoclonal antibody suppressed EAU despite maintained T-cell proliferation and IFNgamma production. Furthermore, locally administered DX109 monoclonal antibody resulted in an earlier resolution of disease. These experiments demonstrate that promoting CD200R-mediated signaling can successfully prevent full expression of IFNgamma-mediated macrophage activation and protect against tissue damage during autoimmune responses.

S-nitrosoglutathione Prevents Interphotoreceptor Retinoid-Binding Protein (IRBP161–180)-Induced Experimental Autoimmune Uveitis

PURPOSE

Experimental autoimmune uveitis (EAU), an animal model of human uveitis, is an organ-specific autoimmune disease mediated by various inflammatory cytokines. In particular, tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta and interferon (IFN)-gamma are known to play a role in its pathogenesis. S-nitrosothiol S-nitrosoglutathione (GSNO), a slow nitric oxide (NO) donor, was reported to have beneficial effects in inflammatory disease in ischemia-reperfusion injury. The efficacy of GSNO treatment on interphotoreceptor retinoid-binding protein (IRBP)-induced EAU was investigated, using functional, histologic, and immunologic readouts.

METHODS

Mice were immunized with a single injection of IRBP(161180) peptide to induce EAU, followed by a daily treatment with GSNO (1 mg/kg). Electroretinogram (ERG) analysis, histopathology, and immunologic responses to IRBP were analyzed. The effects of GSNO treatment on the antigen-specific T-cell recall responses and their cytokine production were determined.

RESULTS

A single immunization of IRBP(161180) peptide led to significant structural damage of the retina and concomitant elimination of ERGs. Daily oral GSNO treatment from days 1-14 following immunization was found to be effective against IRBP-induced EAU. Histopathologic and ERG analysis both demonstrated significant retinal protection in GSNO-treated mice. The GSNO treatment of EAU animals significantly attenuated the levels of TNF-alpha, IL-1beta, IFN-gamma, and IL-10 in retinas, as measured by quantitative real-time polymerase chain reaction analysis. The splenocytes isolated from EAU- and GSNO-treated mice had lower antigen-specific T-cell proliferation in response to IRBP protein, and their cytokine production was inhibited.

CONCLUSIONS

The oral administration of GSNO significantly suppressed the levels of inflammatory mediators in the retinas of EAU mice. This suppression was associated with the maintenance of normal retinal histology and function. These results clearly demonstrated the therapeutic potential of GSNO in EAU, and provide new insights for the treatment of human uveitis.

A selective role for the TNF p55 receptor in autocrine signaling following IFN-gamma stimulation in experimental autoimmune uveoretinitis

IFN-gamma stimulates macrophage activation and NO production, which leads to destruction of the retina in experimental autoimmune uveoretinitis. In this study, we investigate the mechanism of disease resistance in TNF p55 receptor-deficient animals. We show that although T cell priming is relatively unaffected, macrophages lacking the TNF p55 receptor fail to produce NO following IFN-gamma stimulation because of a requirement for autocrine TNF-alpha signaling through the TNF p55 receptor. In contrast to the impaired activation of NO synthesis, MHC class II up-regulation was indistinguishable in wild-type and TNFRp55-/- mice stimulated with IFN-gamma. These defects could be overcome by stimulating macrophages with LPS. Together, these results show that selected aspects of IFN-gamma activation are controlled by autocrine secretion of TNF-alpha, but that this control is lost in the presence of signals generated by pathogen-associated molecular patterns recognizing receptors.

The effects of atorvastatin in experimental autoimmune uveitis

AIM

To investigate the effect of atorvastatin (Lipitor), a commonly used drug for dyslipidaemia in experimental autoimmune uveitis (EAU).

METHODS

48 B10-RIII mice were immunised with human interphotoreceptor retinoid binding protein (IRBP) peptide p161-180. They were divided into three groups of 16 each and treated orally once daily for 14 days; group one received phosphate buffered saline (control group), group two received 1 mg/kg of atorvastatin (low dose group), and group three received 10 mg/kg (high dose). On day 14 lymph nodes, spleens, and right eyes were harvested. RNA was extracted from lymph nodes for RNase protection assay (RPA) to determine proinflammatory (IL-1 alpha and IL-1 beta), Th1 (TNF-alpha, IL-2, IL-12), and Th2 (IL-4, IL-5, and IL-10) cytokine levels. Protein was extracted from spleens for western blot to detect the expression of phosphorylated signal transducer and activator of transcription (STAT) 4 and STAT6. The severity of inflammation in enucleated eyes was graded by a masked observer. Paired t test was performed for the mean difference in histological scoring between treated groups and the immunised control group.

RESULTS

Surprisingly, atorvastatin did not modulate the immune response. The proinflammatory cytokines, IL-1 alpha and IL-1 beta, and Th1 cytokines, TNF-alpha and IL-2, were upregulated equally in control and atorvastatin treated groups. IL-12 and Th2 cytokines were not upregulated in all three groups. Western blot analysis showed high levels of phosphorylated STAT4, but not STAT6 protein in the control and atorvastatin treated groups. Mean differences in histological scoring between treated groups and the immunised control group were not statistically significant.

CONCLUSIONS

Atorvastatin treatment had no effect on Th1 and Th2 cytokine transcription. Although histological grading suggested mildly decreased inflammation in the high dose treated group, the equivalence of cytokine expression in all groups suggests that the statins may not modulate IRBP induced uveoretinitis.

Suppression of autoimmune retinal disease by lovastatin does not require Th2 cytokine induction

Intraocular inflammatory diseases are a common cause of severe visual impairment and blindness. In an acute mouse model of autoimmune retinal disease, we demonstrate that treatment with the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, lovastatin, suppresses clinical ocular pathology, retinal vascular leakage, and leukocytic infiltration into the retina. Efficacy was reversed by coadministration of mevalonolactone, the downstream product of 3-hydroxy-3-methylglutaryl coenzyme A reductase, but not by squalene, which is distal to isoprenoid pyrophosphate metabolites within the cholesterol biosynthetic pathway. Lovastatin treatment (20 mg/kg/day i.p.) over 7 days, which resulted in plasma lovastatin hydroxyacid concentrations of 0.098 +/- 0.03 microM, did not induce splenocyte Th2 cytokine production but did cause a small reduction in Ag-induced T cell proliferation and a decrease in the production of IFN-gamma and IL-10. Thus, it is possible to dissociate the therapeutic effect of statins in experimental autoimmune uveitic mice from their activity on the Th1/Th2 balance. Statins inhibit isoprenoid pyrophosphate synthesis, precursors required for the prenylation and posttranslational activation of Rho GTPase, a key molecule in the endothelial ICAM-1-mediated pathway that facilitates lymphocyte migration. Consistent with inhibition of leukocyte infiltration in vivo, lovastatin treatment of retinal endothelial cell monolayers in vitro leads to inhibition of lymphocyte transmigration, which may, in part, account for drug efficacy. Unlike lovastatin, atorvastatin treatment showed little efficacy in retinal inflammatory disease despite showing significant clinical benefit in experimental autoimmune encephalomyelitis. These data highlight the potential differential activity of statins in different inflammatory conditions and their possible therapeutic use for the treatment of human posterior uveitis.

The role of tumour necrosis factor (TNF-alpha) in experimental autoimmune uveoretinitis (EAU)

The pleiotropic cytokine tumour necrosis factor-alpha (TNF-alpha) is released from cells that include macrophages and T-cells during inflammatory responses, orchestrating the initiation of further leucocytic infiltration via adhesion molecule upregulation, dendritic cell maturation and survival, macrophage activation and driving Th1 T-cells responses within tissues. Exposure to TNF also plays a role in maintaining tissue homeostasis, particularly relating to resident cell responses of both microglia and retinal pigment epithelium. Depending on the balance between duration and dose of TNF exposure, an environment where full expression of inflammatory and autoimmune responses within tissues may occur. In experimental autoimmune uveoretinitis (EAU), increased tissue concentrations of TNF facilitate the on-going T-cell effector responses and macrophage activation. These are responsible for targeted and bystander tissue damage and can be suppressed by anti-TNF therapies, in particular, those directed at the p55 TNF receptor. The ability to suppress disease experimentally has led to the successful translation of anti-TNF therapy for treatment of uveitis in cohort studies and phase I/II trials where, additionally, altered peripheral blood CD4(+) T-cell profiles can be demonstrated following each treatment.

Cannabinoids inhibit neurodegeneration in models of multiple sclerosis

Multiple sclerosis is increasingly being recognized as a neurodegenerative disease that is triggered by inflammatory attack of the CNS. As yet there is no satisfactory treatment. Using experimental allergic encephalo myelitis (EAE), an animal model of multiple sclerosis, we demonstrate that the cannabinoid system is neuroprotective during EAE. Mice deficient in the cannabinoid receptor CB1 tolerate inflammatory and excitotoxic insults poorly and develop substantial neurodegeneration following immune attack in EAE. In addition, exogenous CB1 agonists can provide significant neuroprotection from the consequences of inflammatory CNS disease in an experimental allergic uveitis model. Therefore, in addition to symptom management, cannabis may also slow the neurodegenerative processes that ultimately lead to chronic disability in multiple sclerosis and probably other diseases.