Persistent infection of oligodendrocytes in Theiler's virus‐induced encephalomyelitis

Mice infected with Theiler's murine encephalomyelitis virus (TMEV) develop a chronic relapsing demyelinating myelitis. To determine the localization of viral antigen in infected cells of the spinal cord, we studied TMEV‐infected SJL/J mice using immunoelectron microscopic peroxidase‐antiperoxidase techniques. Viral antigens were expressed in the cytoplasm of neurons and astrocytes 4 and 11 days postinfection. At 28 days postinfection, macrophages astrocytes, and oligodendrocytes showed viral antigen in their cytoplasm. At 45, 83, 270, and 360 days postinfection, most infected cells were oligodendrocytes as revealed ultrastructurally by immunoperoxidase staining of prominent glial loops that connect with myelin lameliae. Some of these sheaths also showed Schmidt‐Lanterman incisures that stained for viral antigen. Virus could be recovered at low titers for the duration of the illness. The findings indicate that TMEV induces persistent infection of oligodendrocytes which could then become the target of immune‐mediated injury resulting in demyelination.