Regulation, counter-regulation, and immunotherapy of autoimmune responses to immunologically privileged retinal antigens

CDCP1 regulates retinal pigmented epithelial barrier integrity for the development of experimental autoimmune uveitis

Cub domain-containing protein 1 (CDCP1) is a protein that is highly expressed on the surface of many cancer cells. However, its distribution in normal tissues and its potential roles in nontumor cells are poorly understood. We found that CDCP1 is present on both human and mouse retinal pigment epithelial (RPE) cells. CDCP1-KO mice developed attenuated retinal inflammation in a passive model of autoimmune uveitis, with disrupted tight junctions and infiltrating T cells detected in RPE flat mounts from WT but not CDCP1-KO mice during EAU development. Mechanistically, we discovered that CDCP1 on RPE cells was upregulated by IFN-γ in vitro and after EAU induction in vivo. CD6 stimulation induced increased RPE barrier permeability of WT but not CDCP1-knockdown (CDCP1-KD) RPE cells, and activated T cells migrated through WT RPE monolayers more efficiently than the CDCP1-KD RPE monolayers. In addition, CD6 stimulation of WT but not the CDCP1-KD RPE cells induced massive stress fiber formation and focal adhesion disruption to reduce cell barrier tight junctions. These data suggest that CDCP1 on RPE cells interacts with CD6 on T cells to induce RPE cytoskeleton remodeling and focal adhesion disruption, which open up the tight junctions to facilitate T cell infiltration for the development of 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.

Abrogation of Rbpj attenuates experimental autoimmune uveoretinitis by inhibiting IL-22-producing CD4+ T cells

Experimental autoimmune uveoretinitis (EAU) is an organ-specific T cell-mediated disease induced by immunizing mice with interphotoreceptor retinoid binding protein (IRBP). Autoaggressive CD4(+) T cells are the major pathogenic population for EAU. We investigated the contribution of Notch signaling in T cells to EAU pathogenesis because Notch signaling regulates various aspects of CD4(+) T cell functions. Rbpj is required for Notch signaling, and Rbpj deficiency in T cells inhibited EAU disease severity. The amelioration of EAU in T cell-specific Rbpj-deficient mice correlated with low levels of IL-22 production from CD4(+) T cells, although IRBP-specific CD4(+) T cell proliferation and Th17 differentiation were unaffected. Administration of recombinant IL-22 during the late phase, but not the early phase, of EAU increased EAU clinical scores in T cell-specific Rbpj-deficient mice. Notch inhibition in mice immunized with IRBP with a γ-secretase inhibitor (GSI) suppressed EAU progression, even when GSI was administered as late as 13 days after IRBP immunization. Our data demonstrate that Rbpj/Notch-mediated IL-22 production in T cells has a key pathological role in the late phase of EAU, and suggest that Notch blockade might be a useful therapeutic approach for treating EAU.

Therapeutic dosing of fingolimod (FTY720) prevents cell infiltration, rapidly suppresses ocular inflammation, and maintains the blood-ocular barrier

Fingolimod (FTY720) is an FDA-approved therapeutic drug with efficacy demonstrated in experimental models of multiple sclerosis and in phase III human multiple sclerosis trials. Fingolimod prevents T-cell migration to inflammatory sites by decreasing expression of the sphingosine-1 phosphate receptor normally required for egress from secondary lymphoid tissue. As a preclinical model of human uveitis, experimental autoimmune uveoretinitis permits assessment of immunotherapeutic efficacy. Murine experimental autoimmune uveoretinitis is induced by activation of retinal antigen-specific CD4(+) T cells that infiltrate the eye. High-dose fingolimod treatment administered before disease onset reduces ocular infiltration within hours of administration and suppresses clinicopathologic expression of experimental autoimmune uveoretinitis. In the present investigation of the efficacy of fingolimod treatment for established disease, single-dose treatment was effective and immunosuppressive ability was maintained through a dose range, demonstrating significant and rapid reduction in CD4(+) cell infiltration at clinically relevant therapeutic doses of fingolimod. A repeated-treatment regimen using a dose similar to that in current multiple sclerosis patient protocols significantly reduced infiltration within 24 hours of administration; importantly, repeated doses did not compromise the vascular integrity of the blood-ocular barrier. On withdrawal of fingolimod, drug-induced remission was lost and recrudescence of clinical disease was observed. These results support a strong therapeutic potential for fingolimod as an acute rescue therapy for the treatment of ocular immune-mediated inflammation.

Protective effect of pristane on experimental autoimmune uveitis

This study evaluates the effects of pristane and phytol, two mineral oils with pro-oxidative effects, on the course of experimental autoimmune uveitis. C57BL6 mice were immunized with IRBP1-20 peptide emulsified in CFA and treated five days prior to immunization with phytol or with pristane or with PBS as control. Administration of pristane reduces the incidence and severity of IRBP-induced uveitis as demonstrated by the decrease in vasculitis and inflammatory foci in fundus and by a reduction in histological damages and leukocyte infiltration compared to untreated or phytol-treated mice. The protective effect observed is associated with a decreased activation of peripheral CD4+ and CD8+ T lymphocytes and a decrease in the intensity of the Th1 and Th17 autoimmune response to IRBP in pristane-treated mice compared to control mice, as evidenced by the decreased production of IFNγ and IL17 by IRBP-specific lymphocytes from lymph nodes draining the site of immunization and by the increased production of anti-IRBP IgG1 over IgG2a. In addition, HUVEC and ARPE-19 cells incubated with the sera of mice treated with pristane presented a reduced production of H(2)O(2). The benefit of lowering the systemic oxidative stress by pristane in the course of EAU was confirmed by injecting the antioxidant NAC in IRBP-immunized mice. As pristane, NAC decreased clinical and histological inflammation of the retina and preserved the integrity of the hemato-retinal barrier. Finally, the protective effect of pristane on the development of EAU suggests that some mineral oils may represent a new therapeutic strategy in human uveitis.

A hapten generated from an oxidation fragment of docosahexaenoic acid is sufficient to initiate age-related macular degeneration

The protein adduct carboxyethylpyrrole (CEP) is present in age-related macular degeneration (AMD) eye tissue and in the blood of AMD patients at higher levels than found in age-matched non-AMD tissues. Autoantibodies to CEP are also higher in AMD blood samples than in controls. To test the hypothesis that this hapten is causally involved in initiating an inflammatory response in AMD, we immunized C57BL/6J mice with mouse serum albumin (MSA) adducted with CEP. Immunized mice develop antibodies to CEP, fix complement component-3 in Bruch's membrane, accumulate drusen below the retinal pigment epithelium during aging, show decreased a- and b-wave amplitudes in response to light, and develop lesions in the retinal pigment epithelium mimicking geographic atrophy, the blinding end-stage condition characteristic of the dry form of AMD. Inflammatory cells are present in the region of lesions and may be actively involved in the pathology observed. We conclude that early immunization of mice with CEP-adducted MSA sensitizes these animals to the ongoing production of CEP adducts in the outer retina where DHA is abundant and the conditions for oxidative damage are permissive. In response to this early sensitization, the immune system mounts a complement-mediated attack on the cells of the outer retina where CEP adducts are formed. This animal model for AMD is the first that was developed from an inflammatory signal discovered in eye tissue and blood from AMD patients. It provides a novel opportunity for dissecting the early pathology of AMD and the immune response contributing to this disorder. The availability of a mouse with a mechanistically based AMD-like disease that progresses rapidly is highly desirable. Such a model will allow for the efficient preclinical testing of the much-needed therapeutics quickly and inexpensively.

Systemic and local anti-C5 therapy reduces the disease severity in experimental autoimmune uveoretinitis

Activation of complement occurs during autoimmune retinal and intraocular inflammatory disease as well as neuroretinal degenerative disorders. The cleavage of C5 into fragments C5a and C5b is a critical event during the complement cascade. C5a is a potent proinflammatory anaphylatoxin capable of inducing cell migration, adhesion and cytokine release, while membrane attack complex C5b-9 causes cell lysis. Therapeutic approaches to prevent complement-induced inflammation include the use of blocking monoclonal antibodies (mAb) to prevent C5 cleavage. In these current experiments, the rat anti-mouse C5 mAb (BB5.1) was utilized to investigate the effects of inhibition of C5 cleavage on disease progression and severity in experimental autoimmune uveoretinitis (EAU), a model of organ-specific autoimmunity in the eye characterized by structural retinal damage mediated by infiltrating macrophages. Systemic treatment with BB5.1 results in significantly reduced disease scores compared with control groups, while local administration results in an earlier resolution of disease. In vitro, contemporaneous C5a and interferon-gamma signalling enhanced nitric oxide production, accompanied by down-regulation of the inhibitory myeloid CD200 receptor, contributing to cell activation. These experiments demonstrate that C5 cleavage contributes to the full expression of EAU, and that selective C5 blockade via systemic and local routes of administration can suppress disease. This presents great therapeutic potential to protect against tissue damage during autoimmune responses in the retina or inflammation-induced degenerative disease.

TNFR1-dependent regulation of myeloid cell function in experimental autoimmune uveoretinitis

Experimental autoimmune uveoretinitis is an autoimmune disease induced in mice, which involves the infiltration of CD11b(+) macrophages and CD4(+) T cells into the normally immune-privileged retina. Damage is produced in the target organ following the activation of Th1 and Th17 T cells and by the release of cytotoxic mediators such as NO by activated macrophages. The majority of immune cells infiltrating into the retina are CD11b(+) myeloid cells, but, despite the presence of these APCs, relatively limited numbers of T cells are observed in the retina during the disease course. These T cells do not proliferate when leukocytes are isolated from the retina and restimulated in vitro, although they do produce both IFN-gamma and IL-17. T cell proliferation was restored by depleting the myeloid cells from the cultures and furthermore those isolated myeloid cells were able to regulate the proliferation of other T cells. The ability of macrophages to regulate proliferation depends on activation by T cell-produced IFN-gamma and autocrine TNF-alpha signaling in the myeloid cells via TNFR1. In the absence of TNFR1 signaling, relative T cell expansion in the retina is increased, indicating that regulatory myeloid cells may also act in vivo. However, TNFR1 signaling is also required for macrophages, but not T cells, to migrate into the target organ. Thus, in TNFR1 knock out mice, the amplification of autoimmunity is limited, leading to resistance to experimental autoimmune uveoretinitis induction.

A suppressive oligodeoxynucleotide inhibits ocular inflammation

Synthetic oligodeoxynucleotides (ODN) expressing 'suppressive' TTAGGG motifs down-regulate a variety of proinflammatory and T helper type 1 (Th1)-mediated pathological immune responses. The ability of the archetypal suppressive ODN A151 to inhibit ocular inflammation was examined in two murine models: experimental autoimmune uveitis, induced by immunization with a retinal antigen, interphotoreceptor retinoid-binding protein (IRBP) and adoptively transferred ocular inflammation, induced by transferring Th1 cells specific to hen egg lysozyme (HEL) into recipient mice that express HEL in their eyes. A151 treatment suppressed the inflammation in both models. In addition, A151 inhibited IRBP-specific cytokine production and lymphocyte proliferation in mice immunized with IRBP. These findings suggest that suppressive ODN affects both afferent and efferent limbs of the immunopathogenic process and may be of use in the treatment of autoimmune ocular inflammation.

Inhibitory peptide analogs derived from a major uveitogenic epitope protect from antiretinal autoimmunity by inducing type 2 and regulatory T cells

We identified inhibitory peptide analogs (IPAs), capable of immunomodulating experimental autoimmune uveitis (EAU), induced in B10.RIII mice by immunization with the retinal antigen interphotoreceptor-binding protein in CFA. Alanine-substituted peptides of the major pathogenic epitope, residues 161-180, were synthesized. They were tested for immunogenicity, cross-reactivity with the native 161-180 epitope, pathogenicity, and ability to prevent EAU when given in IFA before EAU challenge with native murine (m)161-180. Two peptides, 169A and 171A, were unable to elicit disease but cross-reacted with m161-180 by lymphocyte proliferation. Mice pretreated with either of the substituted peptides failed to develop EAU after challenge with the native epitope, m161-180, and had reduced cellular responses by lymphocyte proliferation and by delayed hypersensitivity. Their cytokine response profile to m161-180 showed reduced antigen-specific IFN-gamma and IL-17, whereas IL-4, IL-5, IL-10, and IL-13 from IPA-protected mice were increased, and serum antibody titers to m161-180 revealed reduced IgG2a and elevated IgG1 isotypes, suggesting a Th2 shift in the response. Protection was transferable with lymphoid cells from protected donors to naïve recipients, who were subsequently immunized for EAU. Thus, IPA pretreatment prevents induction of EAU by skewing the response to a subsequent uveitogenic challenge with the native peptide to a nonpathogenic phenotype, as well as by eliciting transferable regulatory cells.

Autoimmune Uveitis Elicited with Antigen-Pulsed Dendritic Cells Has a Distinct Clinical Signature and Is Driven by Unique Effector Mechanisms: Initial Encounter with Autoantigen Defines Disease Phenotype

Human autoimmune uveitis is a heterogeneous group of potentially blinding ocular diseases in which most patients who exhibit immunity recognize the same retinal Ag. It is represented by the model of experimental autoimmune uveitis (EAU) induced in mice by immunization with retinal Ag in CFA. Murine EAU is characterized by a Th1/Th17 response pattern, which may not represent all types of human uveitis. We report in this study a new model of EAU induced by injection of matured dendritic cells loaded with a uveitogenic retinal peptide. Dendritic cell-induced EAU demonstrated unique characteristics compared with traditional EAU in terms of clinical manifestations, the nature of the inflammatory infiltrating cells, the cytokine response profile, and a strict requirement for IFN-gamma, whereas IL-17 appeared to play a minor role. Disease was self-limiting, but could be reinduced with the same Ag in CFA, albeit with reduced severity, suggesting post-recovery resistance. Our study demonstrates in a disease setting that the context in which the same autoantigen is initially presented to the immune system precipitates distinct forms of pathology via a distinct pathogenic pathway on the same genetic background. These findings may shed new light on the complex biology and the heterogeneous nature of human uveitis, and provide an alternative model for uveitic diseases of immune origin.

Advances in immunology: from bench to bedside--a symposium at the 2005 Annual Meeting of the Federation of Clinical Immunology Societies (FOCIS), Boston, MA, USA

The American Uveitis Society sponsored a symposium at the recent 2005 Annual FOCIS meeting in Boston, MA, USA, that was organized by the authors of this report. The symposium was designed to bring together several leaders in the broad field of immunology and investigators in ocular immunology to discuss three interrelated areas of interest: (i) animal models of ocular inflammation; (ii) interface of innate and adaptive immunity; and (iii) immune regulation. A brief summary of the salient points of the symposium is given.

SOCS5 mRNA levels in peripheral blood mononuclear cells (PBMC): a potential bio-marker for monitoring response of uveitis patients to Daclizumab therapy

Uveitis is an intraocular inflammatory disease mediated by Th1 lymphocytes. Therapy for severe uveitis is frequently long-term immunosuppression using systemic corticosteroids and cytotoxic agents, but side effects make long-term therapy difficult. Long-term humanized anti-interleukin-2 (IL-2) receptor alpha (Daclizumab) therapy has few side effects and is as effective as standard immunosuppression for treating severe uveitis. However, it is necessary to carefully monitor levels of activated T cells in the eye to allow prompt re-institution of standard immunosuppressive therapy to non-responders to Daclizumab therapy. Suppressors of cytokine signaling (SOCS) are feedback regulators of Th1/Th2 cytokines. SOCS5 and SOCS3 are preferentially expressed in Th1 and Th2 cells, respectively, and are thought to be lineage markers for T-helper cells. In this study, we have investigated whether SOCS3 or SOCS5 expression can serve as surrogate markers of T-cell levels in the eye. Compared to healthy volunteers, SOCS5 mRNA is significantly elevated in PBMC of uveitis patients while SOCS3 is decreased. However, after Daclizumab therapy SOCS5 mRNA level is significantly decreased, suggesting that SOCS5 mRNA can be used as diagnostic tool to monitor therapeutic response of uveitis patients. Our data also suggest that SOCS5 may serve as a new therapeutic target for uveitis and other autoimmune diseases.