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H. Zeng, W. Green, M. Tso; Activation of Microglia in Human Retinitis Pigmentosa . Invest. Ophthalmol. Vis. Sci. 2005;46(13):513.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Photoreceptor degeneration is frequently accompanied by the activation of retinal microglia. We examined retinal microglial cells with different markers and observed their activation in the patients with retinitis pigmentosa (RP) . Methods:Paraffin sections were prepared from 22 human eyes with RP and 14 normal eyes. Immunolabeling of retinal microglial cells was performed using monoclonal antibodies MHC Class II, CD45 and CD68. Results: In the normal retina, few ramified microglial cells were distributed in the inner retinal layers. No microglial cells extended beyond the middle limiting membrane. In eyes with RP, numerous hypertrophic activated microglia were noted in the inner retinal layers at the equatorial region. These cells infiltrated the degenerated photoreceptor cell layer. In the macula, microglial activation was present in three manners in different RP patients: In the advanced RP patients with poor central vision, microglia were markedly activated in the inner retina, infiltrating the outer nuclear layer (ONL) with thinning of the photoreceptor cell layer. In the RP patients with well preserved central vision, marked activation of microglia was seen in the inner retinal layers, yet few infiltrated the ONL. In the third group of RP patients, the macula was mostly spared of activated microglia in spite of marked photoreceptor degeneration in the equator. In addition, marked microglial activation was seen in the optic nerves. Labeled microglial cells was also noted in the epiretinal membranes. MHC Class II and CD45 were expressed by both parenchymal and perivascular microglia, while CD68 positive microglial cells often appeared around the blood vessels. Conclusions: In RP, activated microglia in the retina and optic nerve was observed. Microglial activation in RP is a form of novel inflammatory reaction in response to the retinal degeneration. We postulate that degenerative rod cells produce chemokines which activate the microglia in the inner retina. The activated microglia may invade the ONL and remove the rod cell debris. However, the cytotoxic cytokines produced by the microglia may damage the cone cells, ganglion cells and optic nerve.
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