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Updated: Apr 28, 2026
Retinal Pigment Epithelium Transplantation in a Non-human Primate Model for Degenerative Retinal Diseases
Published on: June 14, 2021
Retinal pigment epithelium cells alter the pro-inflammatory response of retinal microglia to TLR-3 stimulation
Alexa Klettner1, Timothy Hamann, Karen Schlüter
1Institute of Ophthalmology, University of Kiel, University Medical Center, Kiel, Germany.
Purpose:
Microglia are the local cells of the innate immunity in the retina. Toll-like receptor (TLR) 3 is a receptor of the innate immune system, recognizing viral double-stranded RNA. Retinal pigment epithelium (RPE) cells express TLR-3 and react to TLR-3 stimulation. In this study, we investigated the effect of TLR-3-activated RPE on microglia.
Methods:
Primary porcine RPE cells were prepared from freshly prepared pigs' eyes. Retinal microglia were prepared from porcine retina. Expression of the microglia marker Iba1 was evaluated using immunocytochemistry. RPE cells were treated with polyinosinic/polycytidylic acid (Poly I:C; 100 ng/ml, 1 μg/ml, 10 μg/ml, 100 μg/ml) for 24 hr. Either the supernatant was applied to microglia for 6 or 24 hr or microglia cells were directly treated with Poly I:C for 6 and 24 hr. Expression of interleukin (IL)-1ß, IL-6, tumour necrosis factor (TNF)α, IL-10, Cox2 and iNOS was evaluated in quantitative PCR. Phagocytosis was evaluated with a microscope-based and a fluoroscan-based phagocytosis assay.
Results:
Retinal pigment epithelium (RPE) cells induce the expression of IL-6, IL-1ß and IL-10 in microglia cells. Microglia cells respond to Poly I:C stimulation in a concentration-dependent manner with the induction of IL-1ß, IL-6, TNFα, Cox2, iNOS and, to a lesser degree, IL-10. Stimulation of microglia cells with supernatant of Poly I:C-treated RPE cells further elevated IL-6, IL-1ß and Cox2 expression, while it reduced the expression of iNOS. No changes in phagocytosis could be detected.
Conclusions:
TLR-3-activated RPE exacerbates inflammatory response of microglia in a differentiated manner. This indicates that viral infections in the RPE may have a proinflammatory influence on retinal microglia.
Insights
Activated retinal pigment epithelium (RPE) cells exacerbate microglial inflammatory responses. This suggests viral infections impacting RPE may promote retinal inflammation.
Area of Science:
- Ophthalmology
- Immunology
- Cell Biology
Background:
- Microglia are retinal innate immune cells.
- Toll-like receptor (TLR) 3 recognizes viral double-stranded RNA.
- Retinal pigment epithelium (RPE) cells express TLR-3 and respond to its stimulation.
Purpose of the Study:
- To investigate the effect of TLR-3-activated RPE on retinal microglia.
- To understand the role of RPE-microglia interaction in retinal inflammation.
Main Methods:
- Primary porcine RPE cells and retinal microglia were isolated.
- RPE cells were stimulated with polyinosinic/polycytidylic acid (Poly I:C).
- Microglia were exposed to Poly I:C or RPE supernatant; inflammatory gene expression and phagocytosis were assessed.
Main Results:
- RPE cells induced IL-6, IL-1ß, and IL-10 expression in microglia.
- Poly I:C stimulation of microglia increased inflammatory markers (IL-1ß, IL-6, TNFα, Cox2, iNOS).
- RPE supernatant amplified IL-6, IL-1ß, and Cox2 in microglia while reducing iNOS; phagocytosis remained unchanged.
Conclusions:
- TLR-3-activated RPE exacerbates microglial inflammatory responses.
- Viral infections affecting RPE may promote a proinflammatory state in retinal microglia.
