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Dale Gregerson, Neal Heuss, Mark Pierson, Kim Ramil Montaniel, Scott McPherson, Thien Sam; Interactions Between Dendritic Cells, Microglia, and Retinal Ganglion Cells Following Injury to the Optic Nerve. Invest. Ophthalmol. Vis. Sci. 2013;54(15):438. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Cells of the immune system are known to play roles in the loss of neurons due to injury or disease. While the actions of microglia (MG) are being studied by many labs, there has been less effort devoted to other immune cells, including dendritic cells (DC). We have detected the close, physical contact between dendritic cells and retinal ganglion cell (RGC) axons following an optic nerve crush (ONC), and are working to learn if these DC play a role in promoting survival or death in the RGC.
A unilateral optic nerve crush was used to provide the RGC injury. RGC were visualized and/or counted by retrograde staining with Fluorogold injected into the superior colliculus, or immunostaining for B3-tubulin. DC were detected by their expression of green fluorescent protein (GFP) from the CD11c promoter, and deleted by treatment with diphtheria toxin (DTx) based on expression of the diphtheria toxin receptor (DTR) on the same CD11c promoter. MG were distinguished by their expression of CD11b, and absence of detectable GFP. Fluorescence microscopy, flow cytometry, fundoscopy, and H&E staining were used to detect, count and characterize the cells and their responses to the ONC injury. Multiple strains of transgenic and knockout mice were used to promote the study of the cellular responses.
The earliest detection of close association of GFP+ cells with RGC axons was at 3 days post-injury, with the frequency rising quickly after that. The relative number of GFP+ DC in close contact with RGC axons was much greater than found for the MG. Depletion of DC in CD11c-DTR/GFP mice via DTx treatment promoted RGC survival after an ONC injury. RGC survival after an ONC was enhanced in MyD88/TRIF double knockout mice relative to wt controls. Association of GFP+ DC with axons was associated with the loss of RGC.
These results extend the influence of myeloid cells of the innate immune system to include CD11b+ dendritic cells, previously shown to be substantially recruited from circulating progenitors, in addition to the MG and macrophages investigated by multiple other labs. Depletion of the DC gave a moderate, but significant enhancement of RGC survival at 4 wks post-injury. Since the RGC in mice deficient in MyD88 and TRIF, known to signal from toll-like receptors to NF-kB, were found to better survive the injury, ligands and specific TLR are being sought.
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