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O. W. Gramlich, S. C. Joachim, V. D. Stahl, C. Cuny, P. F. Gottschling, N. Pfeiffer, F. H. Grus; Invasion of Activated Microglia Cells in Retina During Slow Progressive Retinal Ganglion Cell Loss in an Experimental Autoimmune Glaucoma Model. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2126.
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© ARVO (1962-2015); The Authors (2016-present)
The Experimental Autoimmune Glaucoma (EAG) model is characterized by retinal ganglion cell (RGC) loss caused by immunization with neuro-retinal antigens. Aim of this study was to examine if microglia activity changes in retina after immunization. Microglia cells, which are generally related to immune response and maintaining homeostatic processes, can be classified in activated and ramified forms based on their morphological shape.
Rats were immunized with bovine retinal ganglion cell-layer homogenate (RGH; n=10) in combination with pertussis toxin (PTX) and incomplete Freund’s adjuvant (IFA). A control group (Co, n=10) received only PTX and IFA. All animals received a half-dose booster immunization after 4 weeks and were sacrificed after 6 weeks. Density of RGCs (cells/mm2) was evaluated in one eye after staining with cresyl. The ionized calcium binding adaptor molecule 1(Iba 1) was used as microglial marker. Microglia was visualized in sagittal cross-sections of the other eye via anti-Iba 1 immunofluorescence and -histochemical staining. Numbers of activated and ramified microglia were put in relation to retinal length (cells/mm) and cell location was recorded. Data was analyzed using ANOVA and t-test.
A significant RGC loss was observed in rats six weeks after immunization with RGH (P=0.006). Mean density of RGCs in control group was 4058 cells/mm2 compared to 3684 cells/mm2 in immunized group.The total amount of retinal microglia (cells/mm) was significantly higher in the immunized group (Co=5, RGH=9.9; P=0.006). In all retinal layers, number of ramified microglia differed not in groups (Co=2.9, RGH=3.5; P=0.48), while activated microglia cells were significantly increased in immunized animals (Co=2.1, RGH=6.2; P=0.0005). The highest amount of activated microglia was found in the ganglion cell layer (Co=1.2, RGH=2.9; P<0.05) and the inner plexiform layer (Co=0.5, RGH=1.4; P<0.05). In the inner nuclear layer, no difference between groups was detectable.
We observed a significant RGC loss and an increased amount of activated microglia, especially in the ganglion cell layer. Findings indicate that RGC loss is linked to the invasion of activated microglia, which might be associated with debris clearance and other neurodegenerative processes known from brain injury animal models.
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