Spread of MCMV Through Müller Cells and Horizontal Cells Following Supraciliary Inoculation

Abstract

Abstract: : Purpose: Following supraciliary inoculation of MCMV into immunosuppressed (IS) mice, the choroid and RPE are the initial sites of infection followed by spread of virus to the inner nuclear layer. The aim of this study was to determine how the MCMV spreads in the inner retina. Methods: IS mice (2mg methylprednisolone acetate per mouse, i.m. every 4 days) were inoculated with 5 × 10³ PFU of MCMV K181 via the supraciliary route. At intervals after infection, mice were sacrificed. Sections of injected eyes were examined by electron microscopy and by staining for MCMV early antigen (EA), late antigen (LA) and antigens representing different retinal cells including GLAST, GFAP, Lectin, GO–α, Calbindin, Glycine, GABA and NF. Results: Beginning on day 3 p.i., virus infected cells were observed in the choroid and RPE; virus–infected cells were observed in the inner retina on day 5 p.i. Many MCMV infected horizontal cells and bipolar cells were observed on day 5–7 p.i. Staining for GFAP and viral antigens indicated that virus spread from the RPE and photoreceptor layer to the inner retina through Müller cells. Staining for Calbindin and viral antigens demonstrated that virus spread horizontally in the retina through horizontal cells. Some MCMV–infected cells in the inner retina were located near lectin–stained retinal vasculature, but lectin+ EA+ double stained cells were rarely observed in the inner retina. Electron microscopic examination revealed viral particles in the choroid, RPE and inner nuclear layer. Although viral particles were also observed in the endothelium of the retinal vessels and in the nearby retinal cells, the lining of swollen endothelial cells remained intact. Both apoptotic and necrotic cells were seen in the inner retina by electron microscopy. Apoptotic cells were characterized by the presence of cell shrinkage, condensation of chromatin and cytoplasm, and necrotizing cells exhibited margination of chromatin, neatly apposed to the inner nuclear membrane and marked lytic changes in cytoplasm and organelles. Conclusions: Following supraciliary inoculation, MCMV spreads from the RPE and photoreceptors to the inner retina through Müller cells and spreads horizontally in the inner retina through horizontal cells. Both necrosis and apoptosis of retinal cells contributes to the pathology associated with MCMV retinitis.

Keywords: cytomegalovirus • AIDS/HIV • retinitis