Pathological alterations of ependyma and choroid plexus after experimental cerebral infection of mice with Sendai virus.

The effects of intracerebral inoculation of Sendai virus into young adult mice were investigated by immunofluorescence, light, and electron microscopy. Immunofluorescence of virus-specific antigens was maximal on the third day after inoculation, revealing infection of leptomeninges, ependyma, and choroid plexus. Histologically, meningitis, ependymitis, and choroiditis occurred between the second and third days. The choroiditis was associated with formation of vacuoles within the cytoplasm of epithelial cells. The vacuoles reached diameters up to 50 micrometer. The ubiquitous vacuolization of plexus epithelia resulted in a honeycomb-like pattern. Opaque viral inclusions were visible within the cytoplasm of choroidal and ependymal epithelium as well as in mononuclear inflammatory cells. On electron microscopy, they were composed of intracytoplasmic nucleocapsid accumulations. Viria lay free between microvilli of plexus epithelial cells, and budding virus structures were observed at cellular surfaces. Occasionally, complete viria occurred in the cytoplasm of plexus epithelial cells and were surrounded by a unit membrane from which they appeared to arise by budding. The formation of this small cavity can be interpreted as the first stage of vacuole formation.