The Tmevp3 locus controls the load of Theiler's virus RNA during persistent infection of the mouse central nervous system (CNS). We identified a candidate gene at this locus, Tmevpg1, by using a positional cloning approach. Tmevpg1 and its human ortholog, TMEVPG1, are expressed in the immune system and encode what appears to be a noncoding RNA. They are located in a cluster of cytokine genes that includes the genes for gamma interferon and one or two homolog of interleukin-10. We now report that Tmevpg1 is expressed in CNS-infiltrating immune cells of resistant B10.S mice, but not in those of susceptible SJL/J mice, following inoculation with Theiler's virus. The pattern of expression of Tmevpg1 is the same in B10.S mice and in SJL/J mice congenic for the resistant B10.S haplotype of Tmevp3. Nineteen polymorphisms were identified when the Tmevpg1 genes of B10.S and SJL/J mice were compared. Interestingly, Tmevpg1 is down regulated after in vitro stimulation of murine CD4 ؉ or CD8 ؉ splenocytes, whereas Ifng is up regulated. Similar patterns of expression of TMEVPG1 and IFNG were observed in human NK cells and CD4 ؉ and CD8 ؉ T lymphocytes. Therefore, Tmevpg1 is a strong candidate gene for the Tmevp3 locus and may be involved in the control of Ifng gene expression.After intracranial inoculation, the DA strain of Theiler's virus replicates for approximately 2 weeks in neurons of the mouse brain and spinal cord, regardless of the mouse's genetic background. Some genetically resistant mice clear the infection at this stage. Others, which are susceptible to persistence of the infection, remain infected for life (26). However, in this case, the virus does not persist in neurons. Instead, it is found in glial cells of the white matter of the spinal cord. Persistent infection of the white matter induces chronic inflammation and primary demyelination similar to those seen in multiple sclerosis (25). Susceptibility to viral persistence varies greatly among inbred strains of mice. The viral genome load during persistent infection is controlled mainly by the H2D class I gene (4-6, 24). However, the SJL/J strain is the only inbred strain among 16 examined for which the viral genome load is greater than that predicted by its H2 s haplotype (13). Studies of bone marrow chimeras of the SJL/J and B10.S strains, which both bear an H2 s haplotype, showed that susceptibility loci with major effects on persistence are expressed in cells of the immune system (3). Some non-H2 susceptibility loci were mapped by using a backcross and congenic mice between the SJL/J and B10.S strains. Two susceptibility loci, Tmevp2 and Tmevp3, were located on chromosome 10 close to the Ifng locus (8, 12). However, immunological studies indicated that the Ifng gene does not explain the effects of the Tmevp2 or the Tmevp3 locus (30). Instead, the Tmevpg1 gene was recently identified by positional cloning of the Tmevp3 locus. It is located telomeric to a cluster of cytokines, which includes the Ifng and IL-22/Il-Tif genes (36). Tmevpg1 has six exons and ap...

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