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T.A. Albini, R.C. Wang, B. Reiser, E. Zamir, G.S. Wu, N.A. Rao; Microglial Stability and Repopulation in Retinas of Radiated Bone Marrow Chimeric Lewis Rats. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5293.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Retinal microglia are thought to be renewed either by in situ proliferation of resident microglia or by transformation of bone marrow–derived monocytes that take up residence in the retina. The contribution of recent bone marrow–derived monocytes to the uninflammed retina is not well defined. The present study sought to determine repopulation of microglia by bone marrow–derived monocytes in adult retinas in bone marrow chimeric rats. Methods: Chimeric (Y→X) Lewis rats were constructed by transplanting 5 x 107 male bone marrow cells into the recipient female rat, which had been lethally irradiated with 1000 rads using a Cesium–135 γ irradiator. After establishment of chimerism (60 days from bone marrow transplantation), chimeras were sacrificed at 8, 10, 12, 30 and 52 weeks, and retina, brain, lung, and spleen samples were collected. DNA was extracted with Easy DNA kit and quantified by 260–nm absorption. Exactly 1 µg DNA was used for PCR. Y–positive cells in chimeric animals were detected by PCR amplification of a Y–chromosome specific 104–bp fragment using the following primers: 5'–CATCGAAGGGTTAAAGTGCCA–3'(5'primer) and 5'–ATAGTGTGTAGGTTGTTGTCC–3'(3'primer). The amplified product (Y–104 bp) was confirmed by agarose gel electrophoresis using 100–bp DNA ladder as the molecular weight marker. Results: Using the male–female splenic DNA mixture, this PCR protocol detected 1 ng of male DNA in 1 µg of female DNA (0.1%) and could detect 0.01% male cells (1:10,000) in the mixture of male and female cells. There was a rapid repopulation of hematopoietic tissues such as spleen (at 8 weeks) and, to a lesser extent, lung (at 30 weeks) in Y→X bone marrow transplantation. This repopulation was absent in the brain parenchyma and retina until 52 weeks post–transplantation. Conclusion: These data indicate that resident microglia in the retina, much like those in the brain, are stable in number in the retinal compartment (up to one year), and repopulation by bone marrow–derived cells may be delayed for a year. Since these retinas are free of inflammation, the presence of bone marrow–derived nucleated cells in the retina most likely reflects the influx of monocytes. Bone marrow–chimeric rats offer a biologic model to study the role of resident microglia in retinal degenerations and uveoretinitis.
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