Theiler's virus persistence in the central nervous system of mice is associated with continuous viral replication and a difference in outcome of infection of infiltrating macrophages versus oligodendrocytes.

Theiler's murine encephalomyelitis virus (TMEV) infection of mice, in which persistent central nervous system (CNS) infection induces Th1 CD4+ T cell responses to both virus and myelin proteins, provides a relevant experimental animal model for MS. During persistence, >10(9) TMEV genome equivalents per spinal cord are detectable by real-time reverse transcription-polymerase chain reaction (RT-PCR). Because of the short half-life of TMEV (<1 day), continual viral replication is needed to sustain these very high TMEV copy numbers. An essential role for macrophages in TMEV persistence has been documented and, although limited by host anti-viral immune responses, TMEV nonetheless spreads during persistence to infect other cells, particularly oligodendrocytes, in which the infection is productive and lytic. Virus factors influencing persistence of TMEV are expression of the out-of-frame L* protein and use of sialic acid co-receptors.