Theiler's Murine Encephalomyelitis Virus (TMEV) Subgroup Strain‐Specific Infection in Neural and Non‐Neural Cell Lines

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Abstract
GDVII subgroup strains of Theiler's murine encephalomyelitis virus (TMEV) are highly virulent and produce acute polioencephalomyelitis in mice. Neither viral persistence nor demyelination is demonstrated in the few surviving mice. In contrast, DA subgroup strains are less virulent and establish a persistent central nervous system infection which results in demyelinating disease. We previously reported a subgroup‐specific infection in a macrophage‐like cell line, J774‐1 cells; i.e., GDVII strain does not replicate in J774‐1 cells, whereas the DA strain actively replicates in these cells. In addition, this subgroup‐specific virus growth is shown to be related to the presence of L* protein, a 17 kDa protein translated out‐of‐frame of the viral polyprotein from an AUG located 13 nucleotides downstream from the polyprotein's AUG. The present paper demonstrated that this subgroup‐specific infection is observed in murine monocyte/macrophage lineage cell lines, but not in other murine cell lines including neural cells. An RNase protection assay also suggested that L* protein‐related virus growth is regulated at the step of viral RNA replication. As macrophages are reported to be the major cell harboring virus during the chronic demyelinating stage, the activity of L* protein with respect to virus growth in macrophages may be a key factor in clarifying the mechanism(s) of TMEV persistence, which is probably a trigger to spinal cord demyelination.