Papovavirus detection by electron microscopy in the brain of an elderly patient without overt progressive multifocal leukoencephalopathy.

Virions resembling papovavirus were demonstrated in glial cells in the brain of an aged patient without overt progressive multifocal leukoencephalopathy. The patient was not in a severely immunocompromised state. On histological examination, only a few tiny incomplete necrotic foci were found in the subcortical area. These foci were widely dispersed. Rare, swollen oligodendroglial cells and astrocytes in which papovavirus capsid protein (VP-1) was demonstrated immunohistochemically were present around the foci. The two typical types of virus particles i.e. 35 to 40 nm round particles and elongated particles, were observed in the nuclei of the swollen glial cells. The latter were in the minority. Distinct crystals were also found in the nuclei. The centre-to-centre distance of the particles in the crystals, about 40 nm, and the electron-opaque spots of the round-shaped virions and of the elongated particles, were indicative of structural subunits of papovavirus capsids. This case provides further evidence that papovavirus, possibly JC virus, may be reactivated in the brains of aged patients who are not in an immunocompromised state.