The majority of infiltrating CD8⁺ T cells in the central nervous system of susceptible SJL/J mice infected with Theiler's virus are virus specific and fully functional

Theiler's virus infection of the central nervous system (CNS) induces an immune-mediated demyelinating disease in susceptible mouse strains, such as SJL/J, and serves as a relevant infectious model for human multiple sclerosis. It has been previously suggested that susceptible SJL/J mice do not mount an efficient cytotoxic T-lymphocyte (CTL) response to the virus. In addition, genetic studies have shown that resistance to Theiler's virus-induced demyelinating disease is linked to the H-2D major histocompatibility complex class I locus, suggesting that a compromised CTL response may contribute to the susceptibility of SJL/J mice. Here we show that SJL/J mice do, in fact, generate a CD8⁺ T-cell response in the CNS that is directed against one dominant (VP3_159-166) and two subdominant (VP1_11-20 and VP3_173-181) capsid protein epitopes. These virus-specific CD8⁺ T cells produce gamma interferon (IFN-γ) and lyse target cells in the presence of the epitope peptides, indicating that these CNS-infiltrating CD8⁺ T cells are fully functional effector cells. Intracellular IFN-γ staining analysis indicates that greater than 50% of CNS-infiltrating CD8⁺ T cells are specific for these viral epitopes at 7 days postinfection. Therefore, the susceptibility of SJL/J mice is not due to the lack of an early functional Theiler's murine encephalomyelitis virus-specific CTL response. Interestingly, T-cell responses to all three epitopes are restricted by the H-2K^S molecule, and this skewed class I restriction may be associated with susceptibility to demyelinating disease.