The complement activation molecule C5a has been found in the eye and is implicated in the pathogenesis of ocular inflammatory diseases. In this study, the authors sought to investigate C5a's effects on human retinal pigment epithelial (RPE) cells and peripheral blood mononuclear cells (PBMCs), and on the interaction between RPE cells and PBMCs.
Arising retinal pigment epithelia cell line-19 and PBMCs isolated from healthy donors were used in this study. Western blot, real-time PCR and cell surface receptor staining were used to detect C5a receptor expression. Real-time PCR was used to detect cytokine mRNA expression. A thiazolyl blue tetrazolium bromide assay was used to detect cell viability. Cells were stained with Annexin V and 7-aminoactinomycin D for an apoptosis assay. Cell proliferation was measured using a tritiated thymidine incorporation assay.
C5a receptors were present on RPE cells, and receptor expression was increased by pro-inflammatory cytokines. C5a suppressed RPE cells' production of transforming growth factor β2, an important immunosuppressive agent in the eye. In addition, the viability of RPE cells was decreased in the presence of C5a, and this effect was not due to apoptosis. C5a increased proliferation of PBMCs and upregulated their production of pro-inflammatory cytokines. Finally, C5a decreased RPE cells' ability to suppress immune cell proliferation.
The results provide a direct link between complement activation and intraocular inflammation. This line of information may help to understand the mechanism of the pathogenesis of intraocular inflammatory diseases. Moreover, the authors show that a close, reciprocal interaction between the innate immune system and the adaptive immune system may be involved in the development of such diseases.
[Show abstract][Hide abstract] ABSTRACT: Age-related macular degeneration (AMD) is a disease of the outer retina, characterized most significantly by atrophy of photoreceptors and retinal pigment epithelium accompanied with or without choroidal neovascularization. Development of AMD has been recognized as contingent on environmental and genetic risk factors, the strongest being advanced age. In this review, we highlight pathogenic changes that destabilize ocular homeostasis and promote AMD development. With normal aging, photoreceptors are steadily lost, Bruch's membrane thickens, the choroid thins, and hard drusen may form in the periphery. In AMD, many of these changes are exacerbated in addition to the development of disease-specific factors such as soft macular drusen. Para-inflammation, which can be thought of as an intermediate between basal and robust levels of inflammation, develops within the retina in an attempt to maintain ocular homeostasis, reflected by increased expression of the anti-inflammatory cytokine IL-10 coupled with shifts in macrophage plasticity from the pro-inflammatory M1 to the anti-inflammatory M2 polarization. In AMD, imbalances in the M1 and M2 populations together with activation of retinal microglia are observed and potentially contribute to tissue degeneration. Nonetheless, the retina persists in a state of chronic inflammation and increased expression of certain cytokines and inflammasomes is observed. Since not everyone develops AMD, the vital question to ask is how the body establishes a balance between normal age-related changes and the pathological phenotypes in AMD.
Progress in Retinal and Eye Research 08/2013; 37. DOI:10.1016/j.preteyeres.2013.07.003 · 8.73 Impact Factor
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