Theiler's murine encephalomyelitis virus (TMEV): the role of a small out-of-frame protein in viral persistence and demyelination.

Theiler's murine encephalomyelitis virus (TMEV) belongs to the genus Cardiovirus of the family Picornaviridae and is divided into two subgroups on the basis of different biological activities. GDVII subgroup strains produce acute and fatal polioencephalomyelitis in mice with no virus persistence. In contrast, DA or TO subgroup strains cause an early nonfatal polioencephalomyelitis. TMEV is thought to be an excellent animal model for the human demyelinating disease, multiple sclerosis. Data suggest that macrophages are a major reservoir harboring the virus. A small out-of-frame protein designated L* is synthesized in DA subgroup strains from an alternative, out-of-frame, initiation site. Studies of a DA mutant virus, having an ACG rather than an AUG and therefore does not synthesize L* protein, demonstrate that this protein is important for virus growth in particular cell types and is critical for DA-induced demyelinating disease and virus persistence. In addition, TMEV can be used as a vector for delivering foreign sequences into the central nervous system.