Characterization of a neurologic disease induced by a polytropic murine retrovirus: evidence for differential targeting of ecotropic and polytropic viruses in the brain.

A variety of ecotropic murine leukemia viruses cause neurodegenerative disease. We describe here the clinical and histopathological features of a neurologic disease induced by a polytropic murine leukemia virus, FMCF98. Clinical disease was dominated by hyperexcitability and ataxia, and the histopathology was characterized primarily by astrocytosis and astrocytic degeneration. The viral envelope gene harbored the determinants of neurovirulence, since the chimeric virus Fr98E, which contained the envelope gene of FMCF98 on a background of the nonneurovirulent virus FB29, caused a similar disease. The disease caused by Fr98E differed from that induced by the coisogenic neurovirulent ecotropic virus FrCasE in clinical presentation, histopathology, and distribution of virus in the central nervous system. Since Fr98E contains a polytropic envelope gene and FrCasE contains an ecotropic envelope gene, these phenotypic differences appeared to be determined by envelope sequences and may reflect differences in virus receptor usage in the central nervous system.