Oligodendrocytes and their myelin-plasma membrane connections in JHM mouse hepatitis virus encephalomyelitis.

Mice infected with JHM strain of mouse hepatitis virus develop a demyelinating encephalomyelitis. Myelin sheaths are stripped off axons by invading macrophages after degeneration of the infected oligodendrocytes. The derivation of the virus from granular cytoplasmic particles that condense around and bud into endoplasmic reticulum is demonstrated. The infected oligodendrocytes undergo hypertrophic changes prior to degeneration. Hypertrophic cells are characterized by abundant microtubules, filaments, mitochondria, aggregates of electron-dense particles, and numerous, unusual plasma membrane connections to myelin lamellae. Vacular and hydropic changes are prominent in degenerating cells. The significance of finding infected oligodendrocytes with altered myelin-plasma membrane connections is discussed with reference to the pathogenesis of recurrent, postinfectious demyelination known to develop subsequent to acute virus infections.