Autoimmune uveitis is a sight-threatening ocular inflammatory condition in which the retina and uveal tissues become a target of autoreactive immune cells. While microglia have been studied extensively in autoimmune uveitis, their exact function remains uncertain. The objective of the current study was to determine whether resident microglia are necessary and sufficient to initiate and amplify retinal inflammation in autoimmune uveitis. In this study, we clearly demonstrate that microglia are essential for initiating infiltration of immune cells utilizing a murine model of experimental autoimmune uveoretinitis (EAU) and the recently identified microglia-specific marker P2ry12. Initiating disease is the primary function of microglia in EAU, since eliminating microglia during the later stages of EAU had little effect, indicating that the function of circulating leukocytes is to amplify and sustain destructive inflammation once microglia have triggered disease. In the absence of microglia, uveitis does not develop, since leukocytes cannot gain entry through the blood-retinal barrier, illustrating that microglia play a critical role in regulating infiltration of inflammatory cells into the retina.

SignificancePhotoreceptor cell death resulting from retinal detachment (RD) causes significant visual loss. While the immune system is activated during RD, its role is still unclear. Microglia are resident immune cells in the retina and are thought to be either protective or deleterious in response to neuronal injury, suggesting context-dependent effects. Here, we demonstrate that microglia limit retinal damage during acute injury, since microglial ablation led to increased photoreceptor death. Microglial morphological–activation changes triggered their migration into injured tissue where they formed intimate connections with infiltrating immune cells and phagocytized injured photoreceptors. These findings provide insight into the microglial response and function during RD, indicating microglia promote photoreceptor survival during acute phase injury by removing potentially damaging cell debris.

Vascular endothelial growth factor and also angiogenin, IP-10, MCP-1, MIP-1β, and Mig may be related to the pathogenesis of age-related macular degeneration. Intravitreal bevacizumab injection increases inflammatory cytokine levels, suggesting the induction of an inflammatory process.

High intraocular VEGF level at the time of primary vitrectomy in patients with PDR was identified as a significant risk factor for postoperative early VH.

Purpose. Aryl hydrocarbon receptor (AHR) has been identified as a regulator of CD25(+)CD4(+) regulatory T-cell (T(reg)) and Th17 cell differentiation in mice, and activation of AHR by its ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces functional T(reg) cells. In this study, the authors examined whether the AHR-mediated effect of TCDD suppresses mouse experimental autoimmune uveitis (EAU) by inducing T(reg) cell differentiation. Methods. C57BL/6 mice were injected with TCDD 1 day before immunization with human interphotoreceptor retinoid-binding protein peptide 1-20 (hIRBP-p), and the severity of EAU was assessed clinically and histopathologically. Immunologic responses of draining lymph node cells and splenocytes to hIRBP-p and anti-CD3 monoclonal antibody (mAb) were assessed by T-cell proliferation and cytokine production. In addition, differentiation of Foxp3(+) T cells and their immunosuppressive roles in TCDD-injected mice were evaluated. Results. TCDD injection increased Foxp3(+) T cells in the lymph nodes and in the spleen. Development of EAU was completely suppressed by TCDD injection, and suppression was abolished by treatment with anti-CD25 mAb before TCDD injection. Both lymphocytes and splenocytes obtained from TCDD-injected mice immunized with hIRBP-p failed to produce IFN-gamma and IL-17 on stimulation with hIRBP-p, and the failure of IL-17 production was observed even when stimulated with anti-CD3 mAb. However, this protocol did not interfere with IL-10 production and T-cell proliferation response when assessed on stimulation with anti-CD3 mAb. Conclusions. Activation of AHR by TCDD markedly suppressed autoimmune uveoretinitis through mechanisms that expand CD25(+)Foxp3(+) T(reg) cells and interfere with the activation of Th1 and Th17 cells.

Age-related macular degeneration (AMD) is the most common cause of blindness for individuals age 50 and above in the developed world. Abnormal growth of choroidal blood vessels, or choroidal neovascularization (CNV), is a hallmark of the neovascular (wet) form of advanced AMD and leads to significant vision loss. A growing body of evidence supports a strong link between neovascular disease and inflammation. Metabolites of long-chain polyunsaturated fatty acids derived from the cytochrome P450 (CYP) monooxygenase pathway serve as vital second messengers that regulate a number of hormones and growth factors involved in inflammation and vascular function. Using transgenic mice with altered CYP lipid biosynthetic pathways in a mouse model of laser-induced CNV, we characterized the role of these lipid metabolites in regulating neovascular disease. We discovered that the CYP-derived lipid metabolites epoxydocosapentaenoic acids (EDPs) and epoxyeicosatetraenoic acids (EEQs) are vital in dampening CNV severity. Specifically, overexpression of the monooxygenase CYP2C8 or genetic ablation or inhibition of the soluble epoxide hydrolase (sEH) enzyme led to increased levels of EDP and EEQ with attenuated CNV development. In contrast, when we promoted the degradation of these CYP-derived metabolites by transgenic overexpression of sEH, the protective effect against CNV was lost. We found that these molecules work in part through their ability to regulate the expression of key leukocyte adhesion molecules, on both leukocytes and endothelial cells, thereby mediating leukocyte recruitment. These results suggest that CYP lipid signaling molecules and their regulators are potential therapeutic targets in neovascular diseases.

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Vascular endothelial growth factor, interleukin-8, monocyte chemotactic protein-1, interferon-inducible protein-10, and monokine induced by interferon-gamma were expressed at high levels locally in ocular tissues in diabetic retinopathy, and these cytokines may form a network and interact to impact the pathogenesis of the disease.