Quantitative, not qualitative, differences in CD8⁺ T cell responses to Theiler's murine encephalomyelitis virus between resistant C57BL/6 and susceptible SJL/J mice

Theiler's murine encephalomyelitis virus (TMEV) infection of the CNS induces an immune-mediated demyelinating disease in susceptible mouse strains and serves as a relevant infection model for human multiple sclerosis. However, it is not yet clear what immunological parameters determine the susceptibility of SJL/J mice compared to resistant mice. We have here compared the TMEV-specific CD8⁺ T cell responses in highly susceptible SJL/J mice with those of highly resistant C57BL/6 mice. Our results clearly indicate that the levels of initial responses of infiltrating CD8⁺ T cells to viral capsid proteins are higher in resistant C57BL/6 mice compared to susceptible SJL/J mice. However, the level of virus-specific CD8⁺ T cells was much more rapidly reduced in resistant C57BL/6, resulting in a higher CD8⁺ T cell level in SJL/J mice later in viral infection. The activation states, cytokine production, as well as the cytolytic function of the CD8⁺ T cells were similar to each other in these mice. These results suggest that an initial induction of a vigorous CD8⁺ T cell response to TMEV is critically important for the resistance to virally induced demyelinating disease.