Preferential induction of protective T cell responses to Theiler's virus in resistant (C57BL/6 X SJL)F1 mice

Infection of the central nervous system (CNS) with Theiler's murine encephalomyelitis virus (TMEV) induces an immune-mediated demyelinating disease in susceptible mouse strains such as SJL/J (H-2^s) but not in strains such as C57BL/6 (H-2^b). In addition, it has been shown that (C57BL/6 X SJL/J)F1 mice (F1 mice), which carry both resistant and susceptible MHC haplotypes (H-2^b/s), are resistant to both viral persistence and TMEV-induced demyelinating disease. In this study, we further analyzed the immune responses underlying the resistance of F1 mice. Our study shows that the resistance of F1 mice is associated with a higher level of the initial virus-specific H-2^b-restricted CD8⁺ T cell responses than of the H-2^s-restricted CD8⁺ T cell responses. In contrast, pathogenic Th17 responses to viral epitopes are lower in F1 mice than in susceptible SJL/J mice. Dominant effects of resistant genes expressed in antigen-presenting cells of F1 mice on regulation of viral replication and induction of protective T cell responses appear to play a crucial role in disease resistance. Although the F1 mice are resistant to disease, the level of viral RNA in the CNS was intermediate between those of SJL/J and C57BL/6 mice, indicating the presence of a threshold of viral expression for pathogenesis.