Lack of iNOS facilitates MCMV spread in the retina

PURPOSE. The purposes of this study were to identify iNOS-producing retinal cells and to determine whether lack of iNOS facilitates MCMV spread and replication in the retina. METHODS. Immunosuppressed (IS) iNOS^-/- mice or C57BL/6 (wild-type) mice were inoculated with 5 × 10⁴ PFU of MCMV K181 strain (K181) via the supraciliary route. Injected eyes were collected at several times after inoculation and examined by plaque assay for replicating virus, RT-PCR for iNOS RNA, Western blot for iNOS protein and by staining for MCMV early antigen (EA), iNOS, and retinal cell antigens. RESULTS. iNOS mRNA and iNOS proteins were expressed in the MCMV-injected eye of wild-type mice. Most iNOS-producing cells were F4/80-positive, including macrophages, RPE-derived macrophages, and resident microglia. Significantly higher titers of virus were recovered from the injected eyes, and more infected cells were detected in the retina of IS iNOS^-/- mice than in IS wild-type mice. Retinal necrosis and loss of retinal architecture throughout the retina were noted in IS iNOS^-/- mice, whereas cytomegalic cells and retinitis were present only in the peripheral retina of IS wild-type mice. CONCLUSIONS. iNOS produced by macrophages, especially resident macrophages including microglia and RPE derived macrophages, plays an important role in limiting spread of MCMV in the retina.