Bipolar and Horizontal Cells are the Major Targets of Early MCMV Infection in the Inner Retina Following Supraciliary Inoculation of Immunosuppressed Mice

Abstract

Abstract: : Purpose: The aim of this study was to determine which cells in the inner retina are infected during MCMV retinitis. Methods: BALB/c mice were immunosuppressed (IS) with steroid (2 mg methylprednisolone acetate per mouse, i.m. every 4 days) and inoculated with 5 × 10³ PFU of MCMV k181 via the supraciliary route. At intervals after infection, mice were sacrificed. To determine which cells were MCMV-infected, frozen sections of eyes were double stained with FITC labeled MCMV early antigen (EA) and Texas Red-labeled antibodies specific for retinal cells or infiltrating cells including GFAP (glial cells), GLAST (Müller cells), Mac-1 (macrophages/microglia), RPE-65 (RPE cells), CD45 (leukocytes), PKC-α (bipolar cells), Goα (bipolar cells), GLT-1b (rod, cone and bipolar cells), glycine (amacrine cells), GLYT-1 (amacrine cells), NF-200 (horizontal cells), or calbindin (horizontal cells). Results: Many MCMV infected RPE cells were observed as early as day 3 p.i., and the majority of the RPE cells remained in situ. MCMV infected cells and retinitis were noted in the inner retina of IS mice. Early in infection (≤day 7 p.i.), the majority of MCMV infected cells in the inner retina were calbindin positive horizontal cells and PKC-α, Goα or GLT-1b positive bipolar cells. A few GFAP positive or GLAST positive cells were also MCMV infected. More MCMV infected glial cells, including both GFAP positive, GLAST positive Müller cells and GFAP positive, GLAST negative non-Müller glial cells, were observed at day 10 p.i. Late in infection (day 14 p.i.), the majority of MCMV infected cells were glial cells that replaced most of neurons in MCMV infected areas. During the course of the infection, most of MCMV infected cells were not GLT-1b positive rods or cones in the outer nuclear layer, Mac-1+ macrophages or microglia, CD45+ infiltrating leukocytes or glycine positive amacrine cells. Conclusions: These results indicate that in the inner retina: 1) bipolar and horizontal cells are the major targets of early MCMV infection and 2) glial cells are infected as a late event.

Keywords: cytomegalovirus • retinitis • animal model