Ocular infection with a murine neurovirulent retrovirus does not cause retinal degeneration

The developing eyes of CFW/D mice inoculated at birth with a neurovirulent mutant (ts1) of Moloney murine leukemia virus (MoMuLV), nonneurovirulent wild type (wt) MoMuLV, and conditioned virus-free medium were studied comparatively by immunohistochemistry, lectin histochemistry, and light microscopy. Cellular targets for viral antigen expression in the eye were identical in both ts1 and wt MoMuLV-infected mice. Viral antigen first was observed in endothelial cells of the retina and subsequently spread in a spatial and temporal pattern consistent with normal vascularization of the developing retina. The virus also was observed in (1) epithelial cells of the bulbar and palpebral conjunctiva, ora ciliaris retinae, and lacrimal gland; (2) endothelial cells of the ciliary body, iris, choroid, and sclera; (3) amacrine cells of the retina; and (4) smooth muscle cells and endothelia of the periocular muscle. Although ts1 MoMuLV induced a spongiform encephalopathy in the brain and spinal cord, structural lesions were not observed in the retina or other ts1 MoMuLV-infected ocular structures; differentiation of the retina was normal. The lectin Ricinus communis agglutinin-I (RCA-I) labeled (1) endothelial cells of the hyaloid vessels, tunica vasculosa lentis, retina, ciliary body, iris, choroid, and sclera; (2) epithelial cells of the cornea, bulbar and palpebral conjunctiva, ora ciliaris retinae, and lacrimal gland; (3) smooth muscle cells and endothelia of the periocular muscle; (4) inner segments of the photoreceptor layer; and (5) amacrine cells of the retina. The retina did not contain RCA-I-labeled cells with morphologic features comparable the RCA-I-positive microglial cells in the central nervous system (CNS). Previous studies showed that ts1 MoMuLV-induced lesions in the brain and spinal cord correlated with the infection and activation of resident RCA-I-positive microglial cells. These ocular studies suggested that retinal lesions may not occur in ts1 MoMuLV- infected mice because there is an absence of appropriate targets cells (RCA- I-positive microglial cells) suitable for pathologic virus infection.