Expression of Ia antigen on retinal pigment epithelium in experimental autoimmune uveoretinitis

Microbiome and Inherited Retinal Degenerations

Inherited retinal degenerations (IRDs) represent a genetically and clinically heterogeneous group of progressive and visually debilitating disorders that can lead to irreversible visual loss. Our understanding of IRD pathogenesis at both the genetic and cellular levels has increased tremendously over the past two decades, but the exact pathogenic mechanisms remain incompletely understood. Enhanced understanding of the pathophysiology of these diseases can result in new treatment targets. Alterations in the human gut microbiome play a key role in the pathogenesis of many ocular and nonocular diseases, such as age-related macular degeneration, neurologic and metabolic disorders, and autoimmune conditions. The gut microbiome regulates the susceptibility of mice to develop experimental autoimmune uveitis, a model for autoimmune disease of the posterior portion of the eye elicited by the systemic response to retinal antigens. Because of the mounting evidence in favor of a role for local and systemic inflammatory and autoimmune-mediated components to IRD pathogenesis, this review presents the current knowledge of gut microbiome in IRDs and discusses the association between possible changes in gut microbiome and pathogenesis of these diseases, with special attention to their possible contribution to the inflammatory underpinnings of IRDs.

The double-edged sword of inflammation in inherited retinal degenerations: Clinical and preclinical evidence for mechanistically and prognostically impactful but treatable complications

We present retrospective data from our clinical research efforts of the past several years alongside a review of past and current clinical and preclinical data independently by several investigators supporting our clinical evidence for the importance of inflammation in inherited retinal degenerations (IRDs). We show how inflammation is a complicating factor in IRDs but, if recognized and managed, also a great opportunity to mitigate disease severity immediately, improve patient prognosis and quality of life, extend the treatment windows for gene-specific and agnostic therapeutic approaches, mitigate the impact of inflammatory complications on the accurate estimate of vision changes in IRD natural history studies, improve the chances of safer outcomes following cataract surgery, and potentially reduce the likelihood of inflammatory adverse events and augment the efficacy of viral vector-based treatment approaches to IRDs. Manuscript contribution to the field. Inflammation has been suspected to be at play in IRDs since the beginning of the 1900s and became a research focus through the early 1990s but was then largely abandoned in favor of genetic-focused research. Thanks to regained cognizance, better research tools, and a more holistic approach to IRDs, the recent reappraisal of the role of inflammation in IRDs has brought back to the surface its importance. A potential confounder in natural history studies and a limiting factor in clinical trials if not accounted for, inflammation can be managed and often offers an opportunity for immediately improved prognosis and outcomes for IRD patients. We present our retrospective clinical evidence for connections with a measurable secondary autoimmune component that can develop in IRDs and contribute to vision loss but is at least in part treatable. We also present ample lines of evidence from the literature corroborating our clinical observations at the preclinical level.

Blocking the inflammasome: A novel approach to treat uveitis

Uveitis is a complex ocular inflammatory disease often accompanied by bacterial or viral infections (infectious uveitis) or underlying autoimmune diseases (non-infectious uveitis). Treatment of the underlying infection along with corticosteroid-mediated suppression of acute inflammation usually resolves infectious uveitis. However, to develop more effective therapies for non-infectious uveitis and to better address acute inflammation in infectious disease, an improved understanding of the underlying inflammatory pathways is needed. In this review, we discuss the disease aetiology, preclinical in vitro and in vivo uveitis models, the role of inflammatory pathways, as well as current and future therapies. In particular, we highlight the involvement of the inflammasome in the development of non-infectious uveitis and how it could be a future target for effective treatment of the disease.

MHC class II expression and potential antigen-presenting cells in the retina during experimental autoimmune uveitis

Background

Controversy exists regarding which cell types are responsible for autoantigen presentation in the retina during experimental autoimmune uveitis (EAU) development. In this study, we aimed to identify and characterize the retinal resident and infiltrating cells susceptible to express major histocompatibility complex (MHC) class II during EAU.

Methods

EAU was induced in C57BL/6 mice by adoptive transfer of autoreactive lymphocytes from IRBP1-20-immunized animals. MHC class II expression was studied by immunostainings on eye cryosections. For flow cytometry (FC) analysis, retinas were dissected and enzymatically digested into single-cell suspensions. Three MHC class II⁺ retinal cell populations were sorted by FC, and their RNA processed for RNA-Seq.

Results

Immunostainings demonstrate strong induction of MHC class II expression in EAU, especially in the inner retina at the level of inflamed vessels, extending to the outer retinal layers and the subretinal space in severely inflamed eyes. Most MHC class II⁺ cells express the hematopoietic marker IBA1. FC quantitative analyses demonstrate that MHC class II induction significantly correlates with disease severity and is associated with upregulation of co-stimulatory molecule expression. In particular, most MHC class II^hi cells express co-stimulatory molecules during EAU. Further phenotyping identified three MHC class II⁺ retinal cell populations: CD45⁻CD11b⁻ non-hematopoietic cells with low MHC class II expression and CD45⁺CD11b⁺ hematopoietic cells with higher MHC class II expression, which can be further separated into Ly6C⁺ and Ly6C⁻ cells, possibly corresponding to infiltrating macrophages and resident microglia. Transcriptome analysis of the three sorted populations leads to a clear sample clustering with some enrichment in macrophage markers and microglial cell markers in Ly6C⁺ and Ly6C⁻ cells, respectively. Functional annotation analysis reveals that both hematopoietic cell populations are more competent in MHC class II-associated antigen presentation and in T cell activation than non-hematopoietic cells.

Conclusion

Our results highlight the potential of cells of hematopoietic origin in local antigen presentation, whatever their Ly6C expression. Our work further provides a first transcriptomic study of MHC class II-expressing retinal cells during EAU and delivers a series of new candidate genes possibly implicated in the pathogenesis of retinal autoimmunity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0915-5) contains supplementary material, which is available to authorized users.

TNFα suppresses IFNγ-induced MHC class II expression on retinal pigmented epithelial cells cultures

PURPOSE

One major consequence of retinal pigment epithelium (RPE) cell activation during autoimmune uveitis is the induction of MHC II molecules expression at their surface. IFNγ is regarded as the main cytokine involved in this induction. As TNFα plays a central role in autoimmune uveitis, we investigated its effects on IFNγ-mediated MHC II induction on RPE cells.

METHODS

Retinal pigment epithelium cells (ARPE-19) were stimulated with IFNγ, TNFα and the anti-TNFα antibody infliximab. The expression of MHCII and ICAM-1 was analysed by flow cytometry. The activation and expression of IRF-1 and STAT-1, two proteins involved in IFNγ-signalling pathway, were analysed by WB. Class II transactivator (CIITA) expression was monitored by qRT-PCR and immunoprecipitation.

RESULTS

TNFα inhibits IFNγ-induced MHC II expression on ARPE cells in a dose-dependent manner. Infliximab completely reverses the inhibitory effect of TNFα. We did not observe an inhibitory effect of TNFα on the expression of ICAM-1 induced by IFNγ. Similarly, IFNγ-induced STAT1 phosphorylation and IRF1 expression were not affected by TNFα. On the contrary, we found that TNFα suppresses IFNγ-induced CIITA mRNA accumulation and protein expression.

CONCLUSION

TNFα inhibits IFNγ-induced MHC II expression in RPE cells. This inhibitory effect was reversed by infliximab and was not because of a global inhibition of IFNγ -mediated RPE cell activation but rather to a specific down-regulation of CIITA expression. Those findings are consistent with the role of TNFα in the resolution of inflammation and might help to elucidate the complex development of autoimmune uveitis.

Cytokine modulation of costimulatory molecules on human fetal retinal pigment epithelial cells

PURPOSE

Experiments were performed to evaluate the effect of various pro- and anti-inflammatory cytokines on the human fetal retinal pigment epithelium's (HFRPE) expression of major histocompatibility complex (MHC) and costimulatory molecules.

METHODS

Pure cultures of HFRPE cells were isolated. HFRPE cells were incubated in the presence of Interferon-gamma (IFN-gamma), IFN-beta, Tumor Necrosis Factor-alpha (TNF-alpha), Interleukin-1beta (IL-1beta), Tumor Growth Factor-beta (TGF-beta), and a combination of IFN-gamma and TGF-beta (pre-incubation and simultaneously incubated). The expression of MHC class I and class II, Intercellular cell adhesion molecule (ICAM-1), B7-1 (CD80), and B7-2 (CD86) molecules was quantitatively analyzed by flow cytometry.

RESULTS

The cultured HFRPE cells expressed high levels of MHC class I and low levels of MHC class II and ICAM-1 molecules. After culture with the above mentioned cytokines, IFN-gamma up-regulated the HFRPE's expression of MHC class II and ICAM-1. IFN-beta and IL-beta1 only up-regulated the expression of ICAM-1. TGF-beta was unable to suppress the up-regulatory effect of IFN-gamma in HFRPE cells (pre-incubated and simultaneously incubated). The other cytokines did not have any significant effect on HFRPE's expression of MHC I and II or the selected costimulatory molecules.

CONCLUSIONS

Our findings indicate that TGF-beta cannot suppress up-regulating effects of IFNgamma- on HFRPE's expression of MHC and costimulatory molecules. Overall, the weak or lack of expression of costimulatory molecules after stimulation with various cytokines further confirms that HFRPE cells are weak antigen presenting cells.

Uveitis: what do we know and how does it help?

Uveitis essentially means intraocular inflammation and encompasses a wide variety of different disorders. This includes both mild and severe types of inflammation affecting different parts of the eye. Histologically, all uveitis is characterized by an influx of lymphocytes into the affected tissue. In all types these lymphocytes are predominantly of the CD4 type, whether the disorder is mild or blinding, giving no clue as to why. New studies comparing cells in ocular fluids taken from inflamed eyes with different types of inflammation have, for the first time, shown a difference in the cytokine profile, so that in visually benign disease interleukin 10 levels are higher than in those which are blinding.The potential for this in terms of therapy is discussed.

Expression of interferon-gamma in the lens exacerbates anterior uveitis and induces retinal degenerative changes in transgenic Lewis rats

Interferon-gamma (IFN-gamma) is a pleiotropic cytokine that has been implicated in immunopathogenic mechanisms of a number of inflammatory diseases of autoimmune or infectious disease etiology. However, its exact role is still a matter of debate. In experimental mouse models, IFN-gamma has been shown to exacerbate autoimmune thyroiditis, insulin-dependent diabetes mellitus, and autoimmune neuritis while it confers protection against experimental allergic encephalomyelitis and experimental uveitis. In this study, we generated transgenic rats with constitutive expression of IFN-gamma in the eye to study its paracrine effects and to investigate whether local production of IFN-gamma also confers protection against uveitis in the rat species. We show here that chronic exposure of ocular cells to IFN-gamma results in apoptotic death of retinal ganglion cells, development of chronic choroiditis, formation of retinal in-foldings, and activation of proinflammatory genes. In contrast to its protective systemic effect in the mouse, constitutive secretion of IFN-gamma in the rat eye was found to predispose the development of severe anterior uveitis and induction of retinal degenerative processes that impair visual acuity. Our data underscore the danger in extrapolation of cytokine effects in the mouse to humans without corroborating evidence in other species.

IL-4 potentiates IL-1beta- and TNF-alpha-stimulated IL-8 and MCP-1 protein production in human retinal pigment epithelial cells

PURPOSE

Human retinal pigment epithelial (HRPE) cells are involved in ocular inflammation by secretion of chemokines such as IL-8 and MCP-1. It has been shown in this and other laboratories that interleukin-1 beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) are potent inducers of HRPE IL-8 and MCP-1 secretion. The induced IL-8 and MCP-1 expression is often modulated by other proinflammatory factors in a synergistic manner. Modulation of IL-8 and MCP-1 production by interleukin-4 (IL-4), a important mediator in Th2-mediated immunity, and granulocyte/macrophage-colony-stimulating factor (GM-CSF), one of the cytokines secreted by HRPE has been reported in non-ocular cells. The aim of the present investigation was to study effects of these two cytokines alone or in combination with IL-1beta or TNF-alpha on HRPE IL-8 and MCP-1 generation.

METHODS

The primary culture of HRPE cells was stimulated with various doses of IL-4, GM-CSF, IL-1beta and TNF-alpha alone or in combination for 8 or 24 hr. The supernatants were subjected to enzyme-linked immunosorbent assay (ELISA) for IL-8 and MCP-1. The mRNAs were isolated from the corresponding cells for Northern blot analysis.

RESULTS

IL-1beta and TNF-alpha induced dose-dependent increases in HRPE IL-8 and MCP-1 secretion with maximal stimulation observed at 2-5 ng/ml. IL-4 alone (100 ng/ml) resulted in a slight increase of MCP-1 and IL-8 secretion. When IL-4 was co-administrated with IL-1beta or TNF-alpha, two to three-fold increases in IL-8 and MCP-1 were observed over the maximal levels induced by IL-1beta or TNF-alpha alone. Northern blot analyses revealed that IL-4 did not alter the steady-state MCP-1 mRNA stimulated by IL-1beta and TNF-alpha, or alter the IL-8 mRNA stimulated by TNF-alpha, although the IL-1beta-induced IL-8 mRNA was slightly enhanced by higher concentrations of IL-4 (100 ng/ml).

CONCLUSION

The synergistic action by IL-4 occurs predominately at the post-transcriptional level. In contrast to IL-4, GM-CSF alone or in combination with IL-1beta or TNF-alpha did not generate additional secretion of HRPE IL-8 and MCP-1. HRPE IL-8 and MCP-1 gene expression and protein production are stimulated by IL-1beta or TNF-alpha through pathways differentially modulated by IL-4 and GM-CSF.

Localization of IgG in the normal and dystrophic rat retina after laser lesions

PURPOSE

To test the hypothesis that access to extravasated plasma protein IgG may influence photoreceptor survival following laser photocoagulation and to determine whether this correlates with the retinal glial reaction.

METHODS

A total of 45 rats (18 Royal College of Surgeons (RCS) dystrophic and 18 RCS-rdy+ congenic control) were used for this experiment. Nine non-lasered littermates of same age were used as controls. The superior retinas of postnatal day 23 rats were irradiated with a grid pattern of 40 argon green laser lesions of 50 microm in diameter and two powers (150 and 300 mW) for 0.2 s. At various times after laser lesions (up to 14 days), animals were perfused, the retinas snap frozen and sectioned on a cryostat. A one-step immunohistochemical technique was used by incubating with rabbit anti-rat IgG conjugated directly to horseradish peroxidase. Adjacent sections were processed using an antibody to glial fibrillary acidic protein (GFAP) by the standard avidin-biotin complex method.

RESULTS

The labelling pattern for extravasated IgG after laser lesion was very similar in both RCS and RCS-rdy+ rat retinas. At 6, 12 and 24 h after lesions, IgG immunoreactivity (IR) was very intense in the lesion core and flanks. The outer plexiform layer (OPL) and photoreceptor inner segments provided a ready pathway for lateral spread of IgG. However, in the outer nuclear layer (ONL), IgG localization was much more restricted. Despite very intense IgG IR in the ONL of the coagulated lesion core, there was always a very sharply delineated boundary where the label abruptly halted. The GFAP labelling in both RCS dystrophic and RCS-rdy+ congenic control rat retinas showed that this boundary was between normal and necrotic cells because there was a core where GFAP was not produced by Müller cells. By 2 days after lesions, the coagulated cells in the lesion core were being removed by phagocytic cells that were IgG IR. Labelled phagocytic cells were also found among the inner and outer segment region on the lesion flanks. There was still IgG IR in the lesion, but the label was faint. No IgG IR was found in the retina at 3, 4, 7 and 14 days after lesions. Absorption control with pure rat IgG showed the label to be specific.

CONCLUSIONS

The extravasated IgG was derived from the choroidal circulation because at no stage was IgG localized around the retinal vasculature. The IgG labelling was surprisingly widespread and, therefore, did not correlate with photoreceptor sparing, although it preceded the widespread Müller cell expression of GFAP and may, therefore, trigger glial reaction.

Immunohistochemical studies in equine recurrent uveitis (ERU)

Despite extensive clinical research, the etiology of equine recurrent uveitis (ERU) is still unknown. After an immunologic pathogenesis was established in recurrent uveitis in humans, a similar pathogenic mechanism was assumed to exist in ERU. To investigate whether immunopathologic mechanisms are involved in ERU, 20 eyes of 15 horses with ERU were examined immunohistochemically with a T cell marker, B cell marker, and anti-major histocompatibility complex (MHC) class II antibodies. Twenty-six eyes of 20 horses were used for investigation of MHC class II antigen expression in normal equine eyes. In 18 eyes of 14 horses, the number of T cells in the inflammatory cell population within the uvea was assessed. In 16/18 eyes (89%), the T lymphocyte fraction was > 70%. This cell population was distributed mostly in a diffuse manner throughout the uvea and also within the mantle zone of follicular lymphocytic aggregates. Foci of B lymphocytes could be found within the center of follicular aggregates in three eyes. The expression of MHC class II antigen on resident ocular cells was evaluated in 10 eyes of six horses with ERU. An increase of MHC class II antigen expression in the trabecular meshwork and on the nonpigmented ciliary epithelium was noted as was a deviant expression on proliferating Müller cells and retinal pigment epithelial cells. The predominance of T cells in the inflammatory infiltrates supports the central role of a cell-mediated immune response. Furthermore, the observation of a deviant MHC class II expression on resident ocular cells suggests that aberrant immune regulation may play a role in the pathogenesis of ERU.

Selective IL-10 inhibition of HLA-DR expression in IFN-gamma-stimulated human retinal pigment epithelial cells

PURPOSE

Human RPE cells express HLA-DR antigens, bind leukocytes via ICAM-1, and secrete IL-8 and MCP-1, which attract and activate leukocytes. Since little is known concerning endogenous cytokines that may alter ocular immunologic and inflammatory mechanisms, we investigated whether IL-10, an immunosuppressive cytokine, modulates these HRPE features.

METHODS

IL-10 effects on HLA-DR and ICAM-1 were examined by HRPE exposures to: (1) IFN-gamma (10-1000 U/ml) + IL-10 (1-100 U/ml) and (2) IL-10 pre-incubation followed by IFN-gamma + IL-10. Immunohistochemistry for HLA-DR and ICAM-1 was graded by masked observers. Flow cytometric analysis quantitated HRPE HLA-DR and ICAM-1. Effects of IL-10 on IL-1 beta (0.2 or 2 ng/ml)-, or TNF-alpha (0.2 or 2 ng/ml)-induced IL-8 and MCP-1 secretion and gene expression were assessed using enzyme-linked immunosorbent assay (ELISA) and Northern blot analysis.

RESULTS

HLA-DR expression, detected by immunohistochemistry and flow cytometric analysis, showed dose-dependent increases to IFN-gamma. IL-10 pre-/co-incubation, but not co-incubation alone, markedly reduced HLA-DR expression, but did not modulate constitutive or IFN-gamma-induced ICAM-1. IL-10 alone did not induce MCP-1 or IL-8 secretion or steady-state mRNA expression, nor modulate IL-1 beta-, TNF-alpha- or IFN-gamma-induced IL-8 or MCP-1.

CONCLUSIONS

This study suggests that HRPE HLA-DR antigens are selectively inhibited by IL-10, but the timing of IL-10 exposure may be crucial.

Immunocytochemical study of retinal diode laser photocoagulation in the rat

AIM

To determine the nature of the cellular infiltrate, alterations in cell adhesion molecules, and MHC II antigen expression in the rat retina following diode laser retinal photocoagulation.

METHOD

20 normal Lister rats underwent diode laser photocoagulation of the retina. Frozen sections from eyes enucleated at 0, 1, 5, 13, and 33 days post laser were examined for T cells (R7.3), CD4 T cells (W3/25), activated CD4 T cells (OX-40), CD8 T cells (OX-8), B cells (OX-33), and macrophages (OX-42), MHC II antigen (OX-6), and E-Selectin-1, VCAM-1, and ICAM-1.

RESULTS

Retinal diode laser photocoagulation stimulated a wound healing response in the outer retina and choroid. The cellular infiltrate included macrophages and activated CD4 T cells at 13 and 33 days post laser. Glial cells in the inner plexiform and inner nuclear layers expressed MHC II antigen at 24 hours only. ICAM-1 antigen was induced in RPE cells and in Muller cells in the inner retina at all time intervals post laser and intense staining for ICAM-1 was present around intraretinal migrated cells at 13 and 33 days post laser. VCAM-1 antigen expression was induced in the choroidal vascular endothelium and RPE at 13 and 33 days after laser as was E-Selectin-1 antigen expression which was also evident focally at the external limiting membrane in association with migrated cells adjacent to the burn.

CONCLUSIONS

These results suggest that alterations in cell adhesion molecules may regulate the migration and activation of retinal pigment epithelium, macrophages and CD4 T cells at the outer blood-retinal barrier and choroid following diode laser photocoagulation of the normal Lister rat retina.

Expression of interleukin-15 and its receptor by human fetal retinal pigment epithelial cells

PURPOSE

IL-15 and IL-15 receptor expression was measured in retinal pigment epithelial (RPE) cells to support a possible role of IL-15 in ocular inflammatory and immune responses.

METHODS

Reverse transcription-coupled polymerase chain reaction (RT-PCR) and Northern blot analysis of IL-15 mRNA in previously characterized non-transformed and simian virus (SV)-40 transformed human fetal RPE cells were carried out. Biological activities of IL-15 produced by the RPE cells were assayed by co-culture with IL-15 responsive cells. Expression of the IL-15 receptor (IL-15R) alpha, IL-2R beta and gamma chains were examined by RT-PCR.

RESULTS

Both non-transformed and SV-40 transformed human fetal RPE cells express IL-15, a T cell growth factor which has similar biological activities to IL-2, and the expression of IL-15 is enhanced by interferon-gamma (IFN-gamma) or tumor necrosis factor-alpha (TNF-alpha) stimulation. In addition, transcripts for all three IL-15 receptor components (IL-15R alpha, IL-2R beta and IL-2R gamma) were detected in these cells.

CONCLUSIONS

RPE cells produce IL-15, which may play an important role in ocular immune and inflammatory responses by stimulating infiltrated T cells and RPE cells via paracrine and autocrine loops, respectively.

The influence of penetrating keratoplasty and cyclosporin A therapy on MHC class II (Ia)-positive cells in the rat iris and choroid

BACKGROUND

The presence of Ia-positive cells (MHC class II equivalent) has been previously reported in the iris and choroid of various species. They have been reported to have both round and dendritic morphologies; the latter may represent classic dendritic cells, potent antigen-presenting cells (APCs). It is possible that the dendritic-like cells play a important role in (auto)immune processes of uveal and other ocular tissues. Using the flat or whole mount technique, the distribution of Ia-positive cells in the rat iris and choroid was investigated following penetrating keratoplasty (PKP) and following treatment with cyclosporin A (CsA).

METHODS

Lewis (LW) rats received corneal buttons from Lewis-Brown Norway (LW-BN) donors and were randomly assigned to the following groups: (i) operated, untreated (n = 24); (ii) operated, CsA-treated (10 mg/kg i.m.; n = 22). Controls were groups (iii) normal LW rats (n = 13); (iv) unoperated, CsA-treated (16 days' treatment; n = 8); (v) anterior perforation of the anterior chamber (n = 3); (vi) eight corneal sutures only (n = 4); (vii) syngeneic operated (LW to LW; n = 4). Animals of groups (i) and (ii) were killed on the 5th, 9th and 13th postoperative days and on appearance of the corneal rejection (group i, day 13; group ii, day 16). Both eyes were enucleated, immediately fixed, and iris-choroid flat mounts were examined for Ia-positive cells using APAAP immunohistochemistry.

RESULTS

In the normal Lewis rat iris, scattered Ia-positive cells of both nondendritic and dendritic morphology were observed. CsA treatment in the unoperated rat did not result in a significant decrease in the percentage of dendritic cells in the iris or choroid. Anterior chamber perforation, the placement of sutures in the cornea and syngeneic PKP resulted in a moderate increase in iris Ia-positive cells. Allogeneic transplantation resulted in a large increase in both types of Ia-positive cells, particularly on day 13 with corneal rejection. In group ii, an initial decrease in Ia-positive cells until day 13 was observed; upon rejection (day 16), the histological picture was similar to that of untreated animals. Alterations in the operated choroid were also apparent following CsA treatment.

CONCLUSION

Corneal transplantation in the Lewis rat results in an increase in Ia-positive cells in the iris; CsA therapy can delay but not prevent this reaction. Changes in choroidal Ia-positive cells following PKP were not apparent, their numbers being affected only by CsA treatment following grafting.

Flow cytometric identification of a minority population of MHC class II positive cells in the normal rat retina distinct from CD45lowCD11b/c+CD4low parenchymal microglia

AIMS

This study aimed to isolate and classify by flow cytometry, the cell surface phenotype of microglia in the normal rat retina with a view to identifying putative antigen presenting cells (APC) within the retina, which has to date not been possible by immunohistochemistry.

METHODS

Normal rat retinal microglia were isolated and classified using a modification of an isolation technique employing graduated Percoll density gradient cell separation and flow cytometric phenotypic criteria used for CNS microglia.

RESULTS

Retinal microglia can be defined by flow cytometry on the basis of their CD45lowCD11b/c+CD4low cell surface expression. Constitutive MHC class II expression in the normal rat retina was confined almost exclusively to a very minor population of cells expressing neither low (microglia) nor high levels of CD45. Three colour flow cytometric analysis confirmed that these MHC class II positive cells were ED2+.

CONCLUSIONS

Using this sensitive isolation technique we have identified the cell surface characteristics of ramified, resident microglia, and found that they do not constitutively express MHC class II. There is, however, constitutive MHC class II expression on a phenotypically distinct population of cells (CD45low/highED2+). We propose these cells are the counterpart of the perivascular macrophages found in the CNS which present antigen to extravasating T cells, although their exact retinal location can only be confirmed by immunohistochemical analysis. The role of parenchymal microglia as APC remains undefined. Future isolation of microglia and putative perivascular cells using this technique will help identify the role these cells play in the initiation and perpetuation of immune responses within the retina.

Immunohistochemical studies on melanin associated antigen (MAA) induced experimental autoimmune anterior uveitis (EAAU)

Experimental autoimmune anterior uveitis (EAAU), a model of uveitis induced by sensitization to melanin associated antigen (MAA) derived from the iris and ciliary body, closely resembles human acute anterior uveitis. The immunopathogenesis of EAAU was studied by immunohistochemical detection of immune cells and the expression of Ia, ICAM-1 and LFA-1 antigens. Male Lewis rats were immunized with bovine MAA, mixed with CFA and pertussis toxin in the hind foot pad. Animals were examined daily by slit-lamp biomicroscopy and serially sacrificed up to 30 days. Immunohistology of the enucleated eyes was performed with monoclonal antibodies W3/25 (CD4), OX-8 (CD8), ED2 (macrophage), OX-33 (B cell), OX-6 (Ia), IA29 (ICAM-1) and WT.1 (LFA-1). During each stage of EAAU, CD4+ T cells predominated over both CD8+ T cells and macrophages in the uvea. Very few B cells were detected during each stage of EAAU. EAAU could not be induced by the adoptive transfer of sera obtained from immunized animals. Low levels of constitutive ICAM-1 and Ia were observed. An increase in ICAM-1 expression was first noted on the epithelial cells of the uveal tract and RPE on day 9 post immunization and preceded LFA-1 and Ia upregulation by approximately 2 days. The immunopathogenesis of EAAU appears to be linked to the presence of the CD4+ T cells.

CD4+ lymphocyte involvement in ocular Behçet's disease

Despite extensive study, the pathogenic mechanisms of Behçet's disease remain uncertain. The ocular inflammation caused by this disease is severe, often causing significant visual loss and, although the nature of the cellular infiltrate has been examined in many of the involved organs, the infiltrating cells in inflamed eyes have not. To investigate the mechanisms involved in perpetuating the ocular inflammation, five enucleated eyes from patients with Behçet's disease were examined by immunohistochemical staining using a panel of monoclonal and polyclonal antibodies. Control eyes from patients with chronic intraocular inflammation from other causes were also examined. Cellular infiltrates were a consistent finding in choroid and periretinal scar tissue, formed almost entirely by mononuclear cells. T lymphocytes were found to predominate (largely the CD4+ subset). B lymphocytes and NK cells were infrequent findings but macrophages were present in significant numbers. No complement or immunoglobulin deposits were found. Infiltrating lymphocytes and macrophages were HLA DR positive. Retinal vascular and retinal pigment epithelium were only occasionally positive. Our findings suggest that cell mediated immunity, rather than immune complex deposition is responsible for the perpetuation of the ocular inflammation in Behçet's disease and that CD4+ T lymphocytes play a central role in this.

Experimental autoimmune pinealitis in the rat: ultrastructure and quantitative immunocytochemical characterization of mononuclear infiltrate and MHC class II expression

Lewis rats immunized with Peptide M (an oligopeptide epitope of the S-antigen protein) developed experimental autoimmune uveoretinitis (EAU) and experimental autoimmune pinealitis (EAP). Temporal changes in mononuclear infiltrate to the pineal gland were quantitated by computer image analysis of sections immunostained with monoclonal antibodies to specific mononuclear populations. T helper/inducer cells (W3/25+) and monocyte/macrophages (OX-42+) were elevated during the early phases of inflammation (day 15) while cytotoxic/suppressor T cells (OX-8+) were elevated at days 15 and 21. Expression of MHC class II (OX-6) was markedly enhanced on pineal glia, but was not present on vascular endothelia during EAP. Ultrastructurally, many capillaries exhibited thickenings of the endothelia and basal lamina. EAP had little effect on the fine structure of pinealocytes and glia and there was little evidence of cellular destruction by day 21, in contrast to the extensive retinal destruction resulting from EAU. These findings suggest fundamental differences between EAU and EAP related to mechanisms of antigen processing/recognition in autoimmune diseases. Our study further indicates the importance of EAP as a model to investigate neuroendocrine-immune interactions.

Retinal antigen specific lymphocytes, TCR-gamma delta T cells and CD5+ B cells cultured from the vitreous in acute sympathetic ophthalmitis

CD5+ B lymphocytes and TCR gamma-delta T lymphocytes, phenotypes implicated in the pathogenesis of autoimmune disease, were isolated from the vitreous in a case of acute sympathetic ophthalmitis. These cells were obtained using a method which allows the selective maintainance in vitro of in vivo activated T lymphocytes. Dual colour flow cytometry showed that after 3 days culture in IL-2 containing medium 61% of cells were CD5/CD19 + ve and 41% CD3/TCR gamma delta + ve. Of the total CD3 + ve population, 15% were gamma/delta negative. These cells formed a population which also responded in a proliferation assay to retinal antigens. Histologically the eye showed a marked mononuclear cell infiltration of the retina, ciliary body and choroid. Granulomatous lesions within the choroid contained lymphocytes, plasma cells and multinucleate giant cells. Immunocytochemistry showed lymphocyte populations to be predominantly CD2 + ve CD3 + ve T lymphocytes of the CD4 sub-set. Distribution of monocytes/macrophages throughout the lesions and restriction of B-lymphocytes to granulomata were all consistent with a DTH type reaction. Despite immunosuppressive therapy, the expression of activation antigens HLA-DR and ICAM-1 on infiltrating and resident ocular tissue cells was high, although IL-2 receptor (CD25) expression was virtually absent. Flow cytometric analysis of peripheral blood cells prior to treatment with Cyclosporin-A showed systemic activation of lymphocytes, with high levels of HLA-DR and CD25 expression and a raised CD4/CD8 ratio.

Experimental autoimmune anterior uveitis (EAAU). II. Dose-dependent induction and adoptive transfer using a melanin-bound antigen of the retinal pigment epithelium

Retinal pigment epithelial cell fractions have been investigated for their capacity to induce experimental uveitis. Cells of the dark (melanotic) and light areas of the bovine RPE have subsequently been extracted by buffer, Triton X-100, sodium dodecyl sulfate (SDS), and treated with various reagents in order to study some characteristics of the antigen. The SDS-insoluble melanotic fraction, consisting of spindle-shaped, mature melanin granules, proved to be the most uveitogenic preparation. Using pertussis toxin as coadjuvant, 1 microgram of melanin-protein (3.4 x 10(6) granules) was able to induce experimental autoimmune anterior uveitis (EAAU) in Lewis rats. The pathogenic activity of the responsible pathogen (PEP-X) was not diminished by SDS, nor eliminated by mildly alkaline SDS or formic acid treatment. However, HCl-deproteinized granules were not uveitogenic. The results show that PEP-X is a highly stable melano-antigen that is probably covalently bound to the granule surface. This is the first time that a melanin-bound antigen has been demonstrated to evoke specific autoaggressive activity. EAAU could adoptively be transferred by sensitized and in vitro stimulated CD4 T-lymphocytes. The evoked inflammation started 3-4 days after injection, was similar to those induced by immunization, and consisted mainly of severe iridocyclitis accompanied by dense flare and cells in the anterior chamber. Choroiditis developed in severe cases of EAAU but no inflammation was detected in the retina, pineal gland or other organs of these rats. EAAU could not be transferred by serum. Immunized PVG rats and guinea-pigs did not develop ocular inflammation. In monkeys a high dose of antigen evoked a very mild EAAU accompanied by choroiditis. In view of its characteristics, EAAU may be a new model for human anterior uveitis.

Association between mast cells and the development of experimental autoimmune uveitis in different rat strains

To study the role of anterior uveal mast cells in experimental autoimmune uveitis (EAU), the mast cells in the iris and ciliary body of Lewis rats, Brown Norway (BN) rats, and their F1 hybrids (LBNF1) were quantitated in normal rats and during the induction period of EAU. The mean baseline mast cell number was 68.9 +/- 10.8 per anterior uvea for Lewis rats, 0.3 +/- 0.2 for BN rats, and 4.6 +/- 0.6 for LBNF1 rats. Detectable mast cells in the anterior uvea of S-Ag-immunized Lewis rats decreased to 60% of control at 6 days postimmunization, recovered to 80% at 10 days, and dropped again to 16% at 13 days, with disease onset around 14 days. In Lewis rats that were adoptively transferred with a uveitogenic T-lymphocyte line, a profound drop in anterior uveal mast cell numbers occurred in the eyes with early signs of EAU, 3 days after the transfer. The decrease in detectable mast cells is consistent with mast cell degranulation. The data suggest that anterior mast cells participate in the immunopathogenesis of EAU and may influence the genetic susceptibility to EAU.

Experimental autoimmune uveoretinitis (EAU) versus experimental allergic encephalomyelitis (EAE): a comparison of T cell-mediated mechanisms

EAU is a model of ocular inflammatory disease. EAU resembles another T cell-mediated autoimmune disease--experimental allergic encephalomyelitis--since both have increased expression of MHC class II molecules in the target tissue, can be adoptively transferred by activated CD4+ T cells and are inhibited by cyclosporin A. The immunological findings will be compared to find out if the same cellular mechanisms are involved in both diseases.

CD68 antigen expression by human retinal pigment epithelial cells

Although a primary role of the retinal pigment epithelium (RPE) is the phagocytosis of aged outer segment membranes, the RPE may also phagocytize particulates via several specific receptors that are characteristically present on mononuclear phagocytes of bone marrow origin. In recent immunophenotypic studies, CD68 monoclonal antibodies (mAb) have been shown to react selectively with a specific 110 kDa cytoplasmic glycoprotein present in mononuclear phagocytes from various sources. Designated as anti-macrophage antibodies that react with this macrophage-associated antigen, CD68 antibodies are now widely used for immunohistochemical identification of mononuclear phagocytes. Using a panel of CD68 mAb (KP1, EMB11, Ki-M6, Y1/82A, and Y2/131) we performed immunohistochemistry on three cytospin preparations of freshly isolated human RPE cells, three primary human RPE cultures, and 12 human RPE cell lines maintained in culture for up to 40 passages. Cytospin preparations of freshly isolated RPE cells demonstrated heavy reactivity in 5% of cells. Five- to 7-day-old primary RPE cultures exhibited uniform, heavy staining of all cells. Strong immunohistochemical reactivity persisted in all 12 cell lines at various passages up to and including passage 40. Stimulation of cultured RPE cells with interferon-gamma (100 U ml-1) for 24 and 48 hr did not produce observable differences in CD68 staining. RPE cells failed to stain when control mAb or mouse serum were substituted for the primary antibody. The constitutive expression of CD68 by neuroectodermally-derived RPE cells extends their immunophenotypic similarities with mesenchymally-derived mononuclear phagocytes and provides an additional antigenic marker to identify RPE cells in vitro.

Immunopathology of experimental autoimmune uveoretinitis in primates

The eyes and pineal glands from 10 monkeys immunized with S-antigen were studied using routine histopathological and immunohistochemical techniques. Seven out of 10 animals developed uveitis between 19 and 33 days after the initial immunization. Histopathology of the eyes harvested 70 days after immunization showed moderate to marked uveoretinitis, subretinal fibrosis, retinal necrosis and gliosis. The pineal glands demonstrated chronic pinealitis. The infiltrating cells were both CD3 and CD19/CD22 lymphocytes with a ratio of 1.4 in the eye and 2.2 in the pineal gland. The ratio of CD4 to CD8 lymphocytes was 1.5:1. MHC Class II antigens and adhesion molecule (ICAM-1) were observed on resident cells. The influx of B lymphocytes and the formation of subretinal fibrosis differentiate the disease in the monkey from that in the rat and mouse. These findings are similar to Vogt-Koyanagi-Harada syndrome and subretinal fibrosis with uveitis syndrome in human.

Suppression of experimental autoimmune uveoretinitis by prazosin, an alpha 1-adrenergic receptor antagonist

S-antigen (S-Ag)-induced experimental autoimmune uveoretinitis (EAU) was suppressed in Lewis and PVG rats by treatment beginning 4 days post immunization with prazosin, a specific alpha 1-adrenergic receptor antagonist. A significant suppression of EAU was observed at clinical and histological levels in both treated groups compared to a severe EAU which developed in controls. Fluorescein angiography showed no leakage of dye from the optic disc of a treated PVG rat presenting no ocular inflammation by clinical examination. The treatment had no effect on the titer of anti-S-Ag antibodies. Perivascular infiltrates of T-lymphocytes and macrophages together with alterations of blood-retinal barrier permeability are early events in EAU. Prazosin, by acting on the vascular alpha 1-adrenoreceptors, inhibits vasospasm, preserves blood-retinal-barrier integrity and prevents vascular edema and early inflammatory cell infiltration observed in EAU.

Immunohistologic study of epiretinal membranes in proliferative vitreoretinopathy

We performed an immunohistologic study on 11 specimens of epiretinal membranes surgically obtained from patients who had rhegmatogenous retinal detachment with proliferative vitreoretinopathy. Immunostaining procedures were used to identify immunoglobulin and complement deposits, to visualize class II antigen expression by proliferating cells, and to determine eventual infiltration by cells of the immune system. Diffuse deposits of IgG, IgA, IgE, C1q, C3c, and C3d were found in epiretinal membranes, whereas numerous cells, including glial or pigmented epithelial cells, expressed HLA-DR and HLA-DQ antigens. Some macrophages and B or T8 lymphocytes were identified. These results suggest activation of the immune system during the course of proliferative vitreoretinopathy. Class II antigen expression could be dependent upon growth-promoting factors and interferon gamma and could play a crucial role in this immune reaction, which resulted in immunoglobulin deposition and activation of complement. However, the eventual role of immune phenomena in the extension of proliferative processes remains to be determined.

Pathology of experimental autoimmune uveoretinitis in mice

The histopathology and immunopathology of murine experimental autoimmune uveoretinitis (EAU) following active immunization with the interphotoreceptor retinoid-binding protein (IRBP) were studied. The methods used included conventional light microscopy and immunoperoxidase staining. Lesions were located mainly in the uvea and the retina and were characteristically focal. The prominent histopathologic findings in the retina were vasculitis, granuloma, retinal fold, focal serous detachment, and loss of photoreceptors. Granulomas, formation of Dalen-Fuchs nodules, inflammatory cellular infiltration and increase in the thickness of the choroid and ciliary body were frequent findings. Subretinal neovascularization occurred in 10% of the experimental animals. Mild to moderate inflammation was also noted in the vitreous. The predominant infiltrating cells in the retinal and uveal granuloma and the Dalen-Fuchs nodules were macrophages. In contrast, the predominant infiltrating cell types in the vitreous were T helper/inducer lymphocytes. T suppressor/cytotoxic cells were rarely seen. Expression of Ia antigens on the ocular cells was confined to the immediate area of the inflammatory sites. The kinetics of histopathology showed two peaks at the 5th and 10th week after immunization, suggesting a relapsing course of the disease.

Evaluation of Ia expression in rat ocular tissues following inoculation with interferon-gamma

It is becoming increasingly clear that IFN-gamma is a potent immunoregulatory protein which influences MHC class II (Ia) antigen expression and cellular functions of B cells, T cells, NK cells and macrophages. During the past 5 yr our laboratory has provided evidence that IFN-gamma modulates class II antigens on retinal cells (retinal pigment epithelial cells, endothelial cells) and is localized within the eye during human inflammatory conditions. In this study we evaluate the direct effect of IFN-gamma on ocular tissue. Lewis rats were inoculated intravitreally or under the retina with either recombinant IFN-gamma (20,000 U) or saline. At 2 hr, 1, 2 and 6 days postinoculation, the eyes were removed and frozen sections were evaluated by immunocytochemical staining with monoclonal anti-Ia antibodies and an irrelevant monoclonal anti-T cell antibody. Saline treated tissue and tissue removed 2 hr after IFN-gamma inoculation showed no significant staining for Ia antigens. However, eyes evaluated 24 hr after IFN-gamma inoculation revealed Ia expression on a variety of ocular cells localized in the conjunctiva and anterior segment, such as conjunctival epithelium, keratocytes, iris epithelium, ciliary epithelium and choroidal cells. In the retina, retinal pigment epithelial (RPE) cells were Ia positive only when IFN-gamma was injected directly under the retina. In conjunction with Ia expression, two striking changes were noted. An iritis was seen and infiltrating cells were detected in the inner retinal layers. Both of these phenomena have been observed in certain inflammatory eye diseases. These studies clearly substantiate the concept that IFN-gamma can regulate class II antigens in the eye and thus may perpetuate immune reactivity in this site.

FR900506 (FK506) and 15-deoxyspergualin (15-DSG) modulate the kinetics of infiltrating cells in eyes with experimental autoimmune uveoretinitis

In order to evaluate two new immunosuppressive agents, FR900506 (FK 506) and 15-Deoxyspergualine (15-DSG), the kinetics of infiltrating cells in the eyes of Lewis rats with experimental autoimmune uveoretinitis (EAU) were studied. Rats were immunized with retinal S-antigen and treated with different doses of either FK 506 or 15-DSG. The inflammatory ocular tissues obtained at various intervals during the process of EAU were examined using an immunoperoxidase technique. The results were compared with those eyes developing EAU without treatment or with suboptimal doses or a suboptimal dose of Cyclosporine (CsA). Both FK 506 and 15-DSG, like CsA, delayed the cellular kinetics during the course of EAU. However, FK 506 had the greatest effect on the kinetics of T lymphocyte subsets by causing the greatest increase in the recruitment time of the T suppressor/cytotoxic population. FK506 treatment resulted not only in the highest inhibition of expression of IL-2 receptors on T cells, but also in the prevention of the expression of MHC class II antigens on ocular resident cells. Treatment with 15-DSG resulted in general immunosuppression on various infiltrating inflammatory cells.

Proliferative vitreoretinopathy membranes. An immunohistochemical study

Proliferative vitreoretinopathy (PVR) is the leading cause of failure after retinal detachment surgery. Therefore, both the extracellular matrix and cellular components of preretinal membranes from 23 eyes with PVR were characterized immunohistochemically. The membrane stroma was composed primarily of types I, II, and III collagen. Laminin and both heparan sulfate proteoglycans and collagens types IV and V were co-distributed in discrete regions within the stroma. Glial and retinal pigment epithelial (RPE) cell populations were identified in these membranes using specific immunohistochemical markers as was a small but significant macrophage population. Double-labeling experiments indicated that RPE cells in these membranes expressed the class II histocompatibility antigen HLA-DR, although neither the RPE monolayer in situ nor cultured RPE cells was HLA-DR positive unless induced by gamma interferon. Only rare isolated vascular endothelial cells were detected in 5 of the 23 membranes.

In vitro phenotypic and functional characterization of human pigment epithelial cell lines

We have characterized human retinal pigment epithelium (HRPE) for the expression of cell surface antigens. Primary HRPE cultures, established cell lines, and freshly brushed pigment epithelial cells all express HLA-ABC but not HLA-DR antigens. However, both primary cultures and established cell lines can be induced by gamma interferon stimulation to express HLA-DR in a dose dependent manner. Only freshly brushed HRPE cells express Fc, and no cells demonstrated the presence of C3b. Our results show that HRPE cells change in culture, as reflected by the loss of Fc receptors, but retain the ability to synthesize HLA-ABC spontaneously and HLA-DR upon stimulation.

Experimental autoimmune uveitis (EAU): immunophenotypic analysis of inflammatory cells in chorio retinal lesions

Using a panel of monoclonal antibodies to guinea pig leukocyte antigens we have examined the phenotype of inflammatory cells present in focal chorio-retinal lesions developing in guinea pigs during S-antigen induced experimental autoimmune uveitis (EAU). The earliest choroidal infiltrates of T cells appeared to be T helper (Th) cells but in choroidal foci of inflammatory cells and in early retinal lesions, where rod outer segment lysis had occurred, the presence of a Pan T negative, T cytotoxic/suppressor (T c/s) positive population of effector cells was identified. In areas of more extensive retinal damage, the ratio of putative Th to T c/s cells was 1.1. The observation that B cell numbers increased progressively to become the predominant cell type in end state lesions, supports the concept that these may be the major suppressor cell population in guinea pigs. Infiltrating inflammatory cells and capillary endothelial cells express Class I and Class II antigen, however retinal pigment epithelium and Mullers cells did not express Class I or Class II antigens.

Anti-Ia antibody diminishes ocular inflammation in experimental autoimmune uveitis

An experimental model of inflammatory eye disease, experimental autoimmune uveitis (EAU), was established by injecting rats in the footpad with S-antigen in complete Freund's adjuvant. This model system was used to evaluate the role of major histocompatibility complex (MHC) class II antigens (Ia) in the pathogenesis of this T cell mediated disease. One day prior to S-antigen priming, rats were injected with either anti-Ia antibodies or with mouse ascites. Clinical and histopathological analysis of eyes from rats treated with anti-Ia antibody showed less ocular inflammation as well as a delay in onset of EAU when compared to controls (p = 0.01). Furthermore, immunocytochemical evaluation demonstrated that tissue obtained from animals receiving anti-Ia therapy also expressed less Ia antigen, as well as a diminution in the number of infiltrating macrophages and lymphocytes. These data show that anti-Ia treatment significantly modifies the course of EAU in the rat. In addition, this study suggests that MHC class II antigen expression may be involved in the initiation and continuation of immune responses that results in ocular inflammatory diseases.

Immunopathologic study of Vogt-Koyanagi-Harada syndrome

We studied an enucleated eye from a patient with a 30-year history of Vogt-Koyanagi-Harada syndrome using both conventional and immunohistochemical techniques. Clinically, the eye was in the end stage of Vogt-Koyanagi-Harada syndrome, and was characterized by the absence of inflammation, large areas of chorioretinal scarring, and pigmentary changes. Histopathologic examination showed marked retinal gliosis, extensive chorioretinal adhesion and scar formation, migration of pigment into the retina, and severe retinal pigment epithelial changes. However, foci of mild to moderate nongranulomatous inflammation of the uvea were observed. These foci contained infiltrating cells that were mainly T lymphocytes with B lymphocyte aggregates at the center. Scattered macrophages were also noted in the uvea and retina. These findings suggest that both the cell-mediated and humoral immune arms may play roles in the pathogenesis of Vogt-Koyanagi-Harada syndrome.

Interferons and autoimmunity

Autoimmunity can be accelerated in several genetically prone murine models and can even be induced in normal mice by treatment with interferon (IFN) or IFN-inducers. Several cases of IFN-induced autoimmune disease in humans also have been observed; however, more striking is the fact that some of the clinical manifestations in autoimmune diseases and many of the immunological aberrations can be mediated or enhanced by IFN. The finding of high levels of circulating IFN in many patients may be highly significant in that respect, and the characterization of the predominant type of IFN as an unusual acid-labile IFN-alpha may indicate an infectious etiologic agent in autoimmunity, since this peculiar IFN was mostly associated with viral infections in vivo or in vitro. The induction of MHC class II antigens on previously HLA-DR or Ia negative cells appears to be caused primarily by IFN-gamma and may have a central role in the pathogenesis of autoimmunity in susceptible individuals. Such aberrant HLA-DR expression on nonlymphoid cells can be detected early in the disease in the target organs of many varied autoimmune conditions and may trigger a cascade of self-directed, uncontrolled immune response in conjunction with other factors.

Immune mechanisms in autoimmune ocular disease

Aberrant expression of Class II MHC antigens (Ia) by non-immune cells is considered to be an important mechanism in the pathogenesis of autoimmune disease processes including those affecting the eye. It is suggested that circulating autoreactive T-cells are directed to their target organ as a result of aberrant expression of Ia antigens by the vascular endothelium of that organ. This hypothesis was tested in this study using two different models of severe ocular inflammation, induced by either S-antigen or bovine serum albumin (BSA). The retinal vascular endothelium becomes Ia + in S-antigen induced inflammation but not in inflammation induced by BSA. The accumulation in the eye of a T-cell line, ThS, specific for an ocular antigen (S-antigen), was compared in the two types of ocular inflammation and compared to that of another T-cell line, ThP, specific for a non-ocular antigen (PPD). In S-antigen induced inflammation, there was much greater accumulation of ThS than ThP whereas in BSA induced inflammation, both T-cell lines accumulated to the same extent but more than in uninflamed eyes. These results suggest that when the retinal vascular endothelium expresses Ia antigens during an inflammatory process, autoreactive T-cells will be specifically retained in the eye as a result of this and perpetuate the autoimmune destructive process.

Pharmacologic effects on the expression of class II histocompatibility antigen in experimental endotoxin-induced uveitis

Systemic dexamethasone, cyclosporine A, colchicine, indomethacin, and cobra venom factor were administered to Lewis rats that were then challenged with 100 micrograms of Salmonella typhimurium endotoxin. The effects of these five pharmacologic agents in endotoxin-induced uveitis were studied by analyzing their effects on ocular inflammation and on the expression of class II antigen of the major histocompatibility complex (MHC) on the epithelium of the ciliary body and iris. All the agents used in our study exhibited anti-inflammatory effects but only dexamethasone was able to inhibit significantly the expression of Ia antigen on the uveal epithelium. This demonstrates a dissociation between the inflammation and class II antigen expression and supports our previous data that class II antigen presentation may precede the inflammatory infiltrates. The alteration of ocular inflammation and especially the variation of Ia antigen expression in the uveal tissue may provide insight into the mechanism of action and the success of different pharmacologic agents used in the treatment of uveitis.

Organ-resident, nonlymphoid cells suppress proliferation of autoimmune T-helper lymphocytes

Local presentation of autoantigen by organ-resident cells inappropriately expressing Ia determinants has been implicated in organ-specific autoimmunity. Experimental autoimmune uveoretinitis, induced in rats by immunization with retinal soluble antigen, is used as a model of organ-specific autoimmunity. In an in vitro system derived from this model, uveitogenic rat T-helper lymphocytes specific to the retinal soluble antigen, or control T-helper lymphocytes reactive to the purified protein derivative of tuberculin, were cocultured with Ia-expressing syngeneic retinal glial cells (Müller cells) in the presence of specific antigen. Antigen presentation was not apparent under ordinary culture conditions, and the Müller cells profoundly suppressed the proliferative response of primed T-helper lymphocytes to antigen presented on conventional antigen-presenting cells, as well as their subsequent interleukin-2 (IL-2)-dependent expansion. Suppression of proliferation was accompanied by inhibition of IL-2 production in response to antigen, as well as by reduction in high-affinity IL-2 receptor expression, and proceeded via a contact-dependent mechanism. These results suggest a role for locally acting suppression mechanisms in immune regulation and maintenance of tissue homeostasis.

Histopathologic and immunohistopathologic features of subretinal fibrosis and uveitis syndrome

We studied histopathologic and immunohistopathologic features of an eye from a patient who had hypopigmented choroidal lesions with subsequent development of progressive subretinal fibrotic tissue associated with minimal signs of vitreal inflammation. A 24-year-old woman had a rapid and severe onset of the disease, which led to blindness within a few months despite treatment with corticosteroids and cyclophosphamide. Histopathologic studies disclosed a marked gliotic retina and thick subretinal fibrotic tissue as well as a granulomatous lymphocytic infiltration in the choroid. Electron microscopy demonstrated that the subretinal tissue was derived from retinal pigment epithelial cells. The immunoperoxidase staining showed similar proportions of T and B lymphocytes, indicating a relative increase of B cells. There was a predominance of the helper/inducer T lymphocyte subset in the infiltrating area. The Müller cells in the retina expressed class II antigens of the major histocompatibility complex.

Cyclosporine and dexamethasone inhibit T-lymphocyte MHC class II antigens and IL-2 receptor expression in experimental autoimmune uveitis

Results of recent studies indicated that a monoclonal ART18 antibody recognizes the receptor sites or closely related structures for IL-2 on activated rat T-cells. The major histocompatibility complex (MHC) class II (Ia) antigens (RT1B and RT1D in rat), detected with OX6 antibody, and OX17 antibody, may be present on activated rat T-cells. In the present report, we examined the effect of corticosteroids and cyclosporine (CsA) on the expression of IL-2 receptors and Ia antigens by the T-cells, which constituted the major cellular component of the ocular infiltration during the period of peak ocular inflammatory activity in experimental autoimmune uveoretinitis (EAU). Lewis rats immunized with retinal S-antigen (S-Ag) and treated for a limited time with suboptimal doses of either CsA or Dexamethasone (Dex) subsequently developed EAU. The inflamed ocular tissues were studied using an immunoperoxidase staining technique. CsA treatment resulted not only in the inhibition of IL-2 receptors on T-cells, but also in the prevention of the induction of Ia antigen expression on T-cells and other non-lymphoid cells. Dex treatment resulted in less inhibition of the expression of both class II antigens and IL-2 receptor by the infiltrating T-cells.

Immunohistochemical analysis of experimental autoimmune uveoretinitis (EAU) induced by interphotoreceptor retinoid-binding protein (IRBP) in the rat

Experimental autoimmune uveoretinitis (EAU) was induced in rats by immunization with bovine interphotoreceptor retinoid-binding protein (IRBP) and studied by immunohistochemistry. In general, the IRBP induction of inflammatory cellular components and expression of immune-related antigens on various non-lymphoid cells resembled those provoked by S-antigen (S-Ag). However, differences were found between the two diseases, including: 1) The increase in T suppressor/cytotoxic cells occurred in IRBP EAU more rapidly than in S-Ag EAU. 2) Fewer numbers of non-lymphoid cells expressed major histocompatibility complex class II surface antigens in IRBP EAU than in S-Ag EAU. The immunopathogenic mechanism of EAU induced by these two retinal antigens are discussed.

Expression of class II antigen in endotoxin induced uveitis

Uveitis can be induced by systemic or intravitreal administration of endotoxin (lipopolysaccharide, LPS). In this study we correlated the expression of class II antigens (la in rat) of the Major Histocompatibility Complex (MHC), with this experimental model of uveitis. Ia antigen was detected by immunohistochemistry using the Avidin-Biotin-Peroxidase Complex (ABC) method and the monoclonal antibody OX6. Ia antigen was not expressed in normal eyes. However, Ia was expressed in the anterior uvea epithelial cells in all eyes with LPS induced uveitis. This study demonstrates that the ocular Ia expression is a localized process in the anterior uvea in response to systemic or intravitreal LPS. This response appears to be distinct from the action of LPS on macrophage Ia expression, where LPS has been shown to inhibit the induction of Ia antigen in macrophages by gamma interferon.