The role of apoptosis within the retina of coronavirus-infected mice.

Purpose: To evaluate the possible roles of apoptosis in the murine retinopathy induced by coronavirus.

Methods: Mice were inoculated with virus intravitreally. Mouse eyes harvested at varying times after inoculation were evaluated for apoptotic and immunologic events by hematoxylin and eosin staining, immunohistochemical staining, in situ terminal deoxynucleotidyltransferase dUTP nick-end labeling (TUNEL) assay, and electron microscopy. Isolated retinas were analyzed for infectious virus and for expression of apoptosis-associated genes.

Results: The number of apoptotic events was significantly elevated in infected eyes from BALB/c and CD-1 mouse strains, reaching a maximum at days 6 through 10, and returning to normal levels at day 20. The majority of apoptotic cells were observed in the outer nuclear layer of the infected retina. In contrast, few apoptotic cells were observed in normal or mock-injected mouse eyes. Apoptotic events within the retina were associated with the presence of viral antigen, infiltration of CD8(+) T cells, and clearance of infectious virus. Reverse transcription-polymerase chain reaction (RT-PCR) analysis identified the upregulation of Fas ligand (FasL) and granzyme B mRNAs within the infected retinas. The development of apoptosis, regulative gene expression, and viral clearance were similar in both retinal degeneration-susceptible (BALB/c) and -resistant (CD-1) mice.

Conclusions: Retinal apoptosis was associated with retinal inflammation, a decrease in infectious virus, and upregulation of genes associated with CTL killing. These studies indicate that retinal apoptosis may be one of the host mechanisms that contribute to limiting this retinal infection.