Mechanism of demyelination in JHM virus encephalomyelitis: Electron microscopic studies

Weanling mice were given intraperitoneal inoculations of the neurotropic, JHM strain of mouse hepatitis virus, the virulence of which had been altered by repeated mouse passages. Five to seven days later many animals developed hind leg paralysis. The pathology consisted of an acute encephalomyelitis with patchy demyelinating lesions in the brain stem and spinal cord. Virus particles, consistent with the appearance of corona viruses, were found in the cytoplasm of cells that were identified as oligondendrocytes by demonstrating connections of their plasma membranes with myelin lamellae. Following the degeneration of oligodendrocytes the myelin sheaths disintegrated or were stripped off intact axons by cytoplasmic tongues of polymorpho- and mononuclear leucocytes that intruded between myelin lamellae. The findings indicate that JHM virus has an affinity for oligodendrocytes in weanling mice and that demyelination occurs subsequently to the degeneration of the infected oligodendrocytes.