Microbiota-Dependent Activation of an Autoreactive T Cell Receptor Provokes Autoimmunity in an Immunologically Privileged Site.

Activated retina-specific T cells that have acquired the ability to break through the blood-retinal barrier are thought to be causally involved in autoimmune uveitis, a major cause of human blindness. It is unclear where these autoreactive T cells first become activated, given that their cognate antigens are sequestered within the immune-privileged eye. We demonstrate in a novel mouse model of spontaneous uveitis that activation of retina-specific T cells is dependent on gut commensal microbiota. Retina-specific T cell activation involved signaling through the autoreactive T cell receptor (TCR) in response to non-cognate antigen in the intestine and was independent of the endogenous retinal autoantigen. Our findings not only have implications for the etiology of human uveitis, but also raise the possibility that activation of autoreactive TCRs by commensal microbes might be a more common trigger of autoimmune diseases than is currently appreciated.

Endothelial Cell-Specific Inactivation of TSPAN12 (Tetraspanin 12) Reveals Pathological Consequences of Barrier Defects in an Otherwise Intact Vasculature.

Objective- Blood-CNS (central nervous system) barrier defects are implicated in retinopathies, neurodegenerative diseases, stroke, and epilepsy, yet, the pathological mechanisms downstream of barrier defects remain incompletely understood. Blood-retina barrier (BRB) formation and retinal angiogenesis require ß-catenin signaling induced by the ligand norrin (NDP [Norrie disease protein]), the receptor FZD4 (frizzled 4), coreceptor LRP5 (low-density lipoprotein receptor-like protein 5), and the tetraspanin TSPAN12 (tetraspanin 12). Impaired NDP/FZD4 signaling causes familial exudative vitreoretinopathy, which may lead to blindness. This study seeked to define cell type-specific functions of TSPAN12 in the retina. Approach and Results- A loxP-flanked Tspan12 allele was generated and recombined in endothelial cells using a tamoxifen-inducible Cdh5-CreERT2 driver. Resulting phenotypes were documented using confocal microscopy. RNA-Seq, histopathologic analysis, and electroretinogram were performed on retinas of aged mice. We show that TSPAN12 functions in endothelial cells to promote vascular morphogenesis and BRB formation in developing mice and BRB maintenance in adult mice. Early loss of TSPAN12 in endothelial cells causes lack of intraretinal capillaries and increased VE-cadherin (CDH5 [cadherin5 aka VE-cadherin]) expression, consistent with premature vascular quiescence. Late loss of TSPAN12 strongly impairs BRB maintenance without affecting vascular morphogenesis, pericyte coverage, or perfusion. Long-term BRB defects are associated with immunoglobulin extravasation, complement deposition, cystoid edema, and impaired b-wave in electroretinograms. RNA-sequencing reveals transcriptional responses to the perturbation of the BRB, including genes involved in vascular basement membrane alterations in diabetic retinopathy. Conclusions- This study establishes mice with late endothelial cell-specific loss of Tspan12 as a model to study pathological consequences of BRB impairment in an otherwise intact vasculature.

Inflammation and outer blood-retina barrier (BRB) compromise following choroidal murine cytomegalovirus (MCMV) infections.

Purpose: The purpose of this study was to determine whether the blood-retina barrier is compromised by choroidal murine cytomegalovirus (MCMV) infection, using electron microscopy. Methods: BALB/c mice were immunosuppressed with methylprednisolone and monoclonal antibodies to CD4 and CD8. At several time points post-MCMV intraperitoneal inoculation, the eyes were removed and analyzed with western blotting and immunoelectron microscopy for the presence of MCMV early antigen (EA) and the host protein RIP3. Posterior eyecups from RIP3-/- and RIP3+/+ mice were cultured and inoculated with MCMV. At days 4, 7, and 11 post-infection, cultures were collected and analyzed with plaque assay, immunohistochemical staining, and real-time PCR (RT-PCR). Results: MCMV EA was observed in the nuclei of vascular endothelial cells and pericytes in the choriocapillaris. Disruption of Bruch's membrane was observed, especially at sites adjacent to activated platelets, and a few RPE cells containing some enlarged vesicles were found directly beneath disrupted Bruch's membrane. Some virus particles were also observed in the enlarged vesicles of RPE cells. Levels of the RIP3 protein, which was observed mainly in the RPE cells and the basement membrane of the choriocapillaris, were greatly increased following MCMV infection, while depletion of RIP3 resulted in greatly decreased inflammasome formation, as well as expression of downstream inflammation factors. Conclusions: The results suggest that systemic MCMV spreads to the choroid and replicates in vascular endothelia and pericytes of the choriocapillaris during immunosuppression. Choroidal MCMV infection is associated with in situ inflammation and subsequent disruption of Bruch's membrane and the outer blood-retina barrier.

Zika virus infection of cellular components of the blood-retinal barriers: implications for viral associated congenital ocular disease.

BACKGROUND: Ocular abnormalities present in microcephalic infants with presumed Zika virus (ZIKV) congenital disease includes focal pigment mottling of the retina, chorioretinal atrophy, optic nerve abnormalities, and lens dislocation. Target cells in the ocular compartment for ZIKV infectivity are unknown. The cellular response of ocular cells to ZIKV infection has not been described. Mechanisms for viral dissemination in the ocular compartment of ZIKV-infected infants and adults have not been reported. Here, we identify target cells for ZIKV infectivity in both the inner and outer blood-retinal barriers (IBRB and OBRB), describe the cytokine expression profile in the IBRB after ZIKV exposure, and propose a mechanism for viral dissemination in the retina. METHODS: We expose primary cellular components of the IBRB including human retinal microvascular endothelial cells, retinal pericytes, and Müller cells as well as retinal pigmented epithelial cells of the OBRB to the PRVABC56 strain of ZIKV. Viral infectivity was analyzed by microscopy, immunofluorescence, and reverse transcription polymerase chain reaction (RT-PCR and qRT-PCR). Angiogenic and proinflammatory cytokines were measured by Luminex assays. RESULTS: We find by immunofluorescent staining using the Flavivirus 4G2 monoclonal antibody that retinal endothelial cells and pericytes of the IBRB and retinal pigmented epithelial cells of the OBRB are fully permissive for ZIKV infection but not Müller cells when compared to mock-infected controls. We confirmed ZIKV infectivity in retinal endothelial cells, retinal pericytes, and retinal pigmented epithelial cells by RT-PCR and qRT-PCR using ZIKV-specific oligonucleotide primers. Expression profiles by Luminex assays in retinal endothelial cells infected with ZIKV revealed a marginal increase in levels of beta-2 microglobulin (ß2-m), granulocyte macrophage colony-stimulating factor (GMCSF), intercellular adhesion molecule 1 (ICAM-1), interleukin-6 (IL-6), monocyte chemotactic protein-1 (MCP1), and vascular cell adhesion molecule 1 (VCAM-1) and higher levels of regulated upon activation, normal T cell expressed and presumably secreted (RANTES) but lower levels of interleukin-4 (IL-4) compared to controls. CONCLUSIONS: Retinal endothelial cells, retinal pericytes, and retinal pigmented epithelial cells are fully permissive for ZIKV lytic replication and are primary target cells in the retinal barriers for infection. ZIKV infection of retinal endothelial cells and retinal pericytes induces significantly higher levels of RANTES that likely contributes to ocular inflammation.

Modelling experimental uveitis: barrier effects in autoimmune disease.

OBJECTIVE AND DESIGN: A mathematical analysis of leukocytes accumulating in experimental autoimmune uveitis (EAU), using ordinary differential equations (ODEs) and incorporating a barrier to cell traffic. MATERIALS AND SUBJECTS: Data from an analysis of the kinetics of cell accumulation within the eye during EAU. METHODS: We applied a well-established mathematical approach that uses ODEs to describe the behaviour of cells on both sides of the blood-retinal barrier and compared data from the mathematical model with experimental data from animals with EAU. RESULTS: The presence of the barrier is critical to the ability of the model to qualitatively reproduce the experimental data. However, barrier breakdown is not sufficient to produce a surge of cells into the eye, which depends also on asymmetry in the rates at which cells can penetrate the barrier. Antigen-presenting cell (APC) generation also plays a critical role and we can derive from the model the ratio for APC production under inflammatory conditions relative to production in the resting state, which has a value that agrees closely with that found by experiment. CONCLUSIONS: Asymmetric trafficking and the dynamics of APC production play an important role in the dynamics of cell accumulation in EAU.

Retinal Pigment Epithelial Cells Express Antimicrobial Peptide Lysozyme - A Novel Mechanism of Innate Immune Defense of the Blood-Retina Barrier.

Purpose: For this study we aimed to understand if retinal pigment epithelial (RPE) cells express antimicrobial peptide lysozyme as a mechanism to protect the neuroretina from blood-borne pathogens. Methods: The expression of lysozyme in human and mouse RPE cells was examined by RT-PCR or immune (cyto)histochemistry in cell cultures or retinal sections. RPE cultures were treated with different concentrations of Pam3CSK4, lipopolysaccharides (LPS), staphylococcus aureus-derived peptidoglycan (PGN-SA), Poly(I:C), and Poly(dA:dT). The mRNA expression of lysozyme was examined by qPCR and protein expression by ELISA. Poly(I:C) was injected into the subretinal space of C57BL/6J mice and eyes were collected 24 hours later and processed for the evaluation of lysozyme expression by confocal microscopy. Bactericidal activity was measured in ARPE19 cells following LYZ gene deletion using Crispr/Cas9 technology. Results: The mRNA and protein of lysozyme were detected in mouse and human RPE cells under normal conditions, although the expression levels were lower than mouse microglia BV2 or human monocytes THP-1 cells, respectively. Immunohistochemistry showed punctate lysozyme expression inside RPE cells. Lysozyme was detected by ELISA in normal RPE lysates, and in live bacteria-treated RPE supernatants. Treatment of RPE cells with Pam3CSK4, LPS, PGN-SA, and Poly(I:C) enhanced lysozyme expression. CRISPR/Cas9 deletion of lysozyme impaired bactericidal activity of ARPE19 cells and reduced their response to LPS and Poly(I:C) stimulation. Conclusions: RPE cells constitutively express antimicrobial peptide lysozyme and the expression is modulated by pathogenic challenges. RPE cells may protect the neuroretina from blood-borne pathogens by producing antimicrobial peptides, such as lysozyme.

Inflammatory Regulation of CNS Barriers After Traumatic Brain Injury: A Tale Directed by Interleukin-1.

Several barriers separate the central nervous system (CNS) from the rest of the body. These barriers are essential for regulating the movement of fluid, ions, molecules, and immune cells into and out of the brain parenchyma. Each CNS barrier is unique and highly dynamic. Endothelial cells, epithelial cells, pericytes, astrocytes, and other cellular constituents each have intricate functions that are essential to sustain the brain's health. Along with damaging neurons, a traumatic brain injury (TBI) also directly insults the CNS barrier-forming cells. Disruption to the barriers first occurs by physical damage to the cells, called the primary injury. Subsequently, during the secondary injury cascade, a further array of molecular and biochemical changes occurs at the barriers. These changes are focused on rebuilding and remodeling, as well as movement of immune cells and waste into and out of the brain. Secondary injury cascades further damage the CNS barriers. Inflammation is central to healthy remodeling of CNS barriers. However, inflammation, as a secondary pathology, also plays a role in the chronic disruption of the barriers' functions after TBI. The goal of this paper is to review the different barriers of the brain, including (1) the blood-brain barrier, (2) the blood-cerebrospinal fluid barrier, (3) the meningeal barrier, (4) the blood-retina barrier, and (5) the brain-lesion border. We then detail the changes at these barriers due to both primary and secondary injury following TBI and indicate areas open for future research and discoveries. Finally, we describe the unique function of the pro-inflammatory cytokine interleukin-1 as a central actor in the inflammatory regulation of CNS barrier function and dysfunction after a TBI.

The role of commensal microflora-induced T cell responses in glaucoma neurodegeneration.

Over the last decade, new evidence has become increasingly more compelling that commensal microflora profoundly influences the maturation and function of resident immune cells in host physiology. The concept of gut-retina axis is actively being explored. Studies have revealed a critical role of commensal microbes linked with neuronal stress, immune responses, and neurodegeneration in the retina. Microbial dysbiosis changes the blood-retina barrier permeability and modulates T cell-mediated autoimmunity to contribute to the pathogenesis of retinal diseases, such as glaucoma. Heat shock proteins (HSPs), which are evolutionarily conserved, are thought to function both as neuroprotectant and pathogenic antigens of T cells contributing to cell protection and tissue damage, respectively. Activated microglia recruit and interact with T cells during this process. Glaucoma, characterized by the progressive loss of retinal ganglion cells, is the leading cause of irreversible blindness. With nearly 70 million people suffering glaucoma worldwide, which doubles the number of patients with Alzheimer's disease, it represents the most frequent neurodegenerative disease of the central nervous system (CNS). Thus, understanding the mechanism of neurodegeneration in glaucoma and its association with the function of commensal microflora may help unveil the secrets of many neurodegenerative disorders in the CNS and develop novel therapeutic interventions.

Autoimmunity in retinal degeneration: autoimmune retinopathy and age-related macular degeneration.

Autoantibody production is associated with a variety of ocular disorders, including autoimmune retinopathy (AIR) and age-related macular degeneration (AMD). A breakdown of immunologic tolerance (ocular immune privilege), including the blood-retinal barrier, anti-immune and anti-inflammatory proteins, and anterior chamber-associated immune deviation may play important roles in these disorders. Although the exact triggers for ocular autoimmunity are unknown, autoimmune targeting of retinal tissue is clearly associated with and may contribute to the pathogenesis of both AIR and AMD. Autoantibody production has long been associated with AIR, a collection of disorders that includes cancer-associated retinopathy, melanoma-associated retinopathy and non-paraneoplastic autoimmune retinopathy. A growing body of evidence indicates that AMD pathogenesis, too, involves ocular inflammation and autoimmunity. Identification and quantification of autoantibodies produced in patients with AIR and AMD may assist with diagnosis, prognosis, and choice of treatments. Animal models that allow investigation of ocular autoimmunity will also be needed to better understand the disease processes and to develop novel therapies. In this review we discuss ocular immune privilege and potential mechanisms of autoimmunity in the eye. We describe how autoimmunity relates to the pathogenesis of AIR and AMD. We explain how the antigen microarray technique is used to detect autoantibodies in patient serum samples, and discuss how current animal models for AMD can be used to investigate autoimmune pathogenesis. Finally, we outline unanswered questions and exciting areas of future study related to autoimmune retinal degeneration.

[Local and systemic immunological disorders in patients with subretinal proliferation].

IgM, IgG, IgA, and IgE in the subretinal fluid (SRF) of the subpopulational composition of peripheral blood T lymphocytes and the parameters of a leukocyte migration inhibition test (LMIT) were comparatively studied in patients with posttraumatic and regmatogenic retinal detachments (RD) complicated by subretinal proliferation (SP). SRF and blood samples taken from 20 patients with SP of various etiologies were studied. SRF immunoglobulins of classes M, G, A, and E were revealed in all the examinees, their higher levels being noted in patients with long-standing (more than 4 months) and severe recurrent RD. Comparative examinations of patients with regmatogenic and posttraumatic RDs revealed a significantly higher content of T lymphocytes (CD3+), T killers (CD8+), and T helpers (CD4+) in the peripheral blood of patients with regmatogenic RD. The patients of both groups were found to have increased LMIT values with phytohemagglutinin, Con-A and retinal antigen, in Group 2, leukocyte migration inhibition with retinal antigens being much more pronounced than that in Group 1.

Involvement of CCR5 in the passage of Th1-type cells across the blood-retina barrier in experimental autoimmune uveitis.

Although the recruitment of T helper cell type 1 (Th1)/Th2 cells into peripheral tissues is essential for inflammation and the host response to infection, the traffic signals that enable the distinct positioning of Th1/Th2 cells are unclear. We have determined the role of CC chemokine receptor 5 (CCR5) in this using experimental autoimmune uveitis (EAU) as a model system. In EAU, Th1-like cells are preferentially recruited into the retina across the blood-retina barrier, partly as a result of expression of the adhesion molecules P-selectin glycoprotein ligand 1 and lymphocyte function-associated antigen-1 on these cells. CD3+ T cells, infiltrating the retina, also expressed the chemokine receptor CCR5, and CCR5 ligands, macrophage-inflammatory protein-1alpha (MIP-1alpha), MIP-1beta, and regulated on activation, normal T expressed and secreted (RANTES), were strongly expressed in the retina at peak EAU. Th1-like cells, polarized in vitro, expressed high levels of CCR5. The trafficking of these CCR5+ cells was examined by tracking them after adoptive transfer in real time in vivo at an early disease stage using scanning laser ophthalmoscopy. Treatment of the cells with antibody against CCR5 prior to transfer resulted in a reduction in their infiltration into the retina. However, rolling velocity, rolling efficiency, and adherence of the cells to retinal endothelium were not reduced. CCR5 is clearly important for Th1 cell recruitment, and this study demonstrates for the first time in vivo that CCR5 may act at the level of transendothelial migration rather than at the earlier stage of rolling on the endothelium.

Disruption of outer blood-retinal barrier by Toxoplasma gondii-infected monocytes is mediated by paracrinely activated FAK signaling.

Ocular toxoplasmosis is mediated by monocytes infected with Toxoplasma gondii that are disseminated to target organs. Although infected monocytes can easily access to outer blood-retinal barrier due to leaky choroidal vasculatures, not much is known about the effect of T. gondii-infected monocytes on outer blood-retinal barrier. We prepared human monocytes, THP-1, infected with T. gondii and human retinal pigment epithelial cells, ARPE-19, grown on transwells as an in vitro model of outer blood-retinal barrier. Exposure to infected monocytes resulted in disruption of tight junction protein, ZO-1, and decrease in transepithelial electrical resistance of retinal pigment epithelium. Supernatants alone separated from infected monocytes also decreased transepithelial electrical resistance and disrupted tight junction protein. Further investigation revealed that the supernatants could activate focal adhesion kinase (FAK) signaling in retinal pigment epithelium and the disruption was attenuated by FAK inhibitor. The disrupted barrier was partly restored by blocking CXCL8, a FAK activating factor secreted by infected monocytes. In this study, we demonstrated that monocytes infected with T. gondii can disrupt outer blood-retinal barrier, which is mediated by paracrinely activated FAK signaling. FAK signaling can be a target of therapeutic approach to prevent negative influence of infected monocytes on outer blood-retinal barrier.

Organ-specific protection mediated by cooperation between vascular and epithelial barriers.

Immune privilege is a complex process that protects organs from immune-mediated attack and damage. It is accomplished by a series of cellular barriers that both control immune cell entry and promote the development of tolerogenic immune cells. In this Review, we describe the vascular endothelial and epithelial barriers in organs that are commonly considered to be immune privileged, such as the brain and the eye. We compare these classical barriers with barriers in the intestine, which share features with barriers of immune-privileged organs, such as the capacity to induce tolerance and to protect from external insults. We suggest that when intestinal barriers break down, disruption of other barriers at distant sites can ensue, and this may underlie the development of various neurological, metabolic and intestinal disorders.

Involvement of CD44 in leukocyte trafficking at the blood-retinal barrier.

In the present study, we investigated the involvement of CD44 in leukocyte trafficking in vivo at the blood-retinal barrier using experimental autoimmune uveoretinitis (EAU) as a model system. Leukocyte trafficking was evaluated using adoptive transfer of calcein-AM (C-AM)-labeled spleen cells harvested from syngeneic mice at prepeak severity of EAU to mice at a similar stage of disease. CD44 and its ligand hyaluronan were up-regulated in the eye during EAU. CD44-positive leukocytes were found sticking in the retinal venules and postcapillary venules but not in the retinal arterioles nor in mesenteric vessels. Preincubation of in vitro C-AM-labeled leukocytes with anti-CD44 monoclonal antibodies (mAb; IM7) or high molecular weight hyaluronic acid (HA) before transfer significantly suppressed leukocyte rolling but not sticking in retinal venules and also reduced cell infiltration in the retinal parenchyma. Administration of the HA-specific enzyme hyaluronidase to mice before cell transfer also reduced leukocyte infiltration, suggesting that CD44-HA interactions are involved in leukocyte recruitment in EAU. This was further supported by the observation that disease severity was reduced by administration of anti-CD44 mAb (IM7) at the early leukocyte-infiltration stage. Further studies also indicated that CD44 activation was associated with increased levels of apoptosis, and this may also be in part responsible for the reduction in disease severity. These findings demonstrate that CD44 is directly involved in leukocyte-endothelial interaction in vivo and influence the trafficking of primed leukocytes to the retina and their overall survival.

Anandamide rescues retinal barrier properties in Müller glia through nitric oxide regulation.

The blood retinal barrier (BRB) can mitigate deleterious immune response. Dysfunction at the BRB can affect disease progression. Under inflammatory conditions Müller glia produce increased pro-inflammatory factors, like nitric oxide (NO). In this study we describe molecular events at the Müller glia during inflammation which could affect inner BRB properties. Griess assay and 4,5-diaminofluorescein diacetate (DAF-2DA) time-lapse fluorescence were used to measure NO production. Western blot was used to analyze the expression of inducible nitric oxide synthase (iNOS) and mitogen-activated protein kinases (MAPK) components. Lucifer Yellow was used to measure permeability. Griess assay and DAF-2DA time-lapse fluorescence images revealed that lipopolysaccharide (LPS) induced inflammation and increased NO production. In parallel, changes were observed in tight junction proteins, zona occludens 1 (ZO-1), connexin 43 (Cx43), and permeability. This was mediated through activation of iNOS and mitogen-activated protein kinase phosphatase-1 (MKP-1), implicated in immune response. Endocannabinoids can exert a protective and anti-inflammatory effect. Exogenous arachidonoyl ethanolamide (AEA) inhibited NO generation and also abolished LPS-induced increase in permeability. Our work suggests that subtle changes in Müller glia function, which act as part of the BRB, could contribute to retinal health. AEA which can reduce inflammatory cytotoxicity has potential as treatment in several ocular manifestations where the integrity of the BRB is crucial.

Lymphocyte adhesion to cultured endothelial cells of the blood-retinal barrier.

Microvascular endothelial cells derived from the blood-retinal barrier were grown in vitro and various factors affecting the adhesion of syngeneic lymphocytes to these monolayers was evaluated. Under resting conditions 5.3 +/- 0.4% of lymphocytes derived from peripheral lymph nodes (PLN) were found to adhere to the endothelia. Adhesion of resting lymphocytes increased significantly following endothelial treatment with interferon-gamma (IFN-gamma; 11.7 +/- 1.0%), interleukin-1 (IL-1; 14.9 +/- 1.2%), astrocyte conditioned medium (ACM; 12.7 +/- 0.9%) or forskolin (13.9 +/- 1.2%). Lymphocyte activation with concanavalin A (ConA) increased adhesion to 17.0 +/- 0.9% which could be augmented by activating the endothelia with IFN-gamma (22.3 +/- 1.0%), IL-1 (24.0 +/- 1.0%) and ACM (25.7 +/- 1.6%). An antigen-specific CD4+ T cell line exhibited the greatest degree of adhesion, 40.4 +/- 2.5% on resting endothelia, 60.0 +/- 3.0% on IFN-gamma-activated cells and 54.3 +/- 1.4% on IL-1-activated cells. Although CD4+ lymphocytes predominated in the PLN population by 2:1, significantly more CD8+ cells were found to adhere.

Blood-retinal barrier breakdown in experimental coronavirus retinopathy: association with viral antigen, inflammation, and VEGF in sensitive and resistant strains.

Intraocular coronavirus inoculation results in a biphasic retinal disease in susceptible mice (BALB/c) characterized by an acute inflammatory response, followed by retinal degeneration associated with autoimmune reactivity. Resistant mice (CD-1), when similarly inoculated, only develop the early phase of the disease. Blood-retinal barrier (BRB) breakdown occurs in the early phase in both strains, coincident with the onset of inflammation. As the inflammation subsides, the extent of retinal vascular leakage is decreased, indicating that BRB breakdown in experimental coronavirus retinopathy (ECOR) is primarily due to inflammation rather than to retinal cell destruction. Vascular endothelial growth factor (VEGF) is upregulated only in susceptible mice during the secondary (retinal degeneration) phase.

Analysis of immune deviation elicited by antigens injected into the subretinal space.

PURPOSE: To determine whether the subretinal space supports the induction of deviant immune responses to cell-associated and soluble antigens and to elucidate factors influencing the immunologic properties of the subretinal space. METHODS: P815 mastocytoma cells were used as cell-associated antigens and were inoculated into the anterior chamber (AC), the vitreous cavity (VC), the subretinal space, and subconjunctivally in H2-compatible, but minor H-incompatible, BALB/c mice. Ovalbumin, as a soluble antigen, was similarly injected into eyes, after which recipient animals were immunized with ovalbumin and complete Freund's adjuvant. Delayed-type hypersensitivity (DTH) was assessed by ear challenge. To alter the conditions in the subretinal space, the outer blood-retinal barrier was disrupted by compromising retinal pigment epithelial (RPE) cells with a systemic injection of sodium iodate. Immune privilege in the AC was abolished by mild corneal cauterization. RESULTS: Antigen-specific DTH did not develop in mice in which alloantigenic tumor cells or ovalbumin was injected into the AC, the VC, or the subretinal space, and the mice's spleens contained lymphocytes capable of suppressing DTH when adoptively transferred into naive mice. When RPE cells were compromised with sodium iodate, tumor cells or ovalbumin injected into the subretinal space or the VC did not induce immune deviation, although the AC of these eyes still promoted AC-associated immune deviation. By contrast, when immune privilege in the AC was abolished by corneal cauterization, neither tumor cells nor ovalbumin injected into the subretinal space or the VC of eyes elicited immune deviation. CONCLUSIONS: The subretinal space supports immune deviation for histoincompatible tumor cells and soluble protein antigens by actively suppressing antigen-specific DTH. Acute loss of immune privilege in the subretinal space and the VC does not cause loss of privilege in the AC, but abolition of immune privilege in the AC eliminates the capacity of the subretinal space and the VC to support immune deviation to antigens injected locally.

The blood-retinal barrier in experimental autoimmune uveoretinitis (EAU): a review.

The blood-retinal barrier (BRB) is believed to play an important part in the pathogenesis of experimental autoimmune uveoretinitis (EAU). Central to the disease process is the recruitment of inflammatory cells from the circulation, a mechanism that is controlled in part by the BRB. As the disease progresses the BRB becomes disrupted first to small and then to large molecular weight tracers. In these two respects EAU shares many similarities with experimental autoimmune encephalomyelitis (EAE) in which there is dysfunction of the blood-brain barrier (BBB). In EAU, however, the differential roles played by the two barrier sites that comprise the BRB are not clear although some evidence would suggest that it is the retinal endothelium that is initially involved. BRB breakdown in EAU has been found to occur concomitantly with lymphocyte infiltration by mechanisms that remain to be elucidated.