Are accessory molecules implicated in activation of T cells at the blood-retinal barrier?

Microglia in the mouse retina alter the structure and function of retinal pigmented epithelial cells: a potential cellular interaction relevant to AMD

BACKGROUND

Age-related macular degeneration (AMD) is a leading cause of legal blindness in the elderly in the industrialized word. While the immune system in the retina is likely to be important in AMD pathogenesis, the cell biology underlying the disease is incompletely understood. Clinical and basic science studies have implicated alterations in the retinal pigment epithelium (RPE) layer as a locus of early change. Also, retinal microglia, the resident immune cells of the retina, have been observed to translocate from their normal position in the inner retina to accumulate in the subretinal space close to the RPE layer in AMD eyes and in animal models of AMD.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we examined the effects of retinal microglia on RPE cells using 1) an in vitro model where activated retinal microglia are co-cultured with primary RPE cells, and 2) an in vivo mouse model where retinal microglia are transplanted into the subretinal space. We found that retinal microglia induced in RPE cells 1) changes in RPE structure and distribution, 2) increased expression and secretion of pro-inflammatory, chemotactic, and pro-angiogenic molecules, and 3) increased extent of in vivo choroidal neovascularization in the subretinal space.

CONCLUSIONS/SIGNIFICANCE

These findings share similarities with important pathological features found in AMD and suggest the relevance of microglia-RPE interactions in AMD pathogenesis. We speculate that the migration of retinal microglia into the subretinal space in early stages of the disease induces significant changes in RPE cells that perpetuate further microglial accumulation, increase inflammation in the outer retina, and fosters an environment conducive for the formation of neovascular changes responsible for much of vision loss in advanced AMD.

Immunomodulation of experimental autoimmune uveoretinitis: a model of tolerance induction with retinal antigens

Experimental autoimmune uveoretinitis (EAU) is a CD4+ T-lymphocyte mediated inflammation of the uveal tract and retina. As a model of human posterior uveitis it permits further understanding of the underlying immunopathogenesis of uveitis. It also allows for preclinical trials of immunosuppressive therapies and in vivo assessment of alternative strategies for immunointervention. This review highlights possible immunostrategic modalities which prevent the initiation or perpetuation of the immune response, and in particular reports on the novel effect of intranasal induction of tolerance with retinal antigens, prior to immunisation with retinal antigens. The mechanisms and potential application of this 'natural' method of immunosuppression in the treatment of autoimmune disease are discussed.

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.

Antigen processing and presentation in the eye: a review

The recognition event between self-antigen, the MHC and the T cell receptor has become the target for potential immunotherapy of T cell mediated autoimmune disease. For this approach to succeed in uveoretinitis, uniformity in T cell receptor usage, restricted MHC usage and limited epitope recognition by individuals would be required. In this study we have shown that despite clonal heterogeneity of response to multideterminate retinal extract antigens, proliferation to the antigens tested was restricted by the IA MHC class II molecule. Different patterns of reactivity to retinal antigens in the presence of various protease inhibitors was observed. Natural processing of IRBP appears to be complex, requiring a number of enzymes to generate immunogenic fragments, in contrast, for S-antigen, plasmin alone may suffice. The RPE cells which are potential processors and presenters of retinal antigens produce PGE2 and may act as suppressors of ocular inflammation.