Abrogation of resistance to Theiler's virus-induced demyelination in H-2^b mice deficient in β2-microglobulin

Intracerebral infection of susceptible strains of mice with Theiler's virus, a picornavirus, results in central nervous system demyelination, which is similar to multiple sclerosis. Imunogenetic experiments indicate that the MHC (H-2) and, in particular, the D region that controls class I-restricted immune responses, is an important determinant to development of demyelination. We tested whether disruption of β2-microglobulin (β2-m) would abrogate resistance to demyelinating disease normally observed in H-2^b mice. All (C57BI/6 × 129)F₃ mice transgenic for homozygous β2-m gene disruption (-/-) developed chronic demyelination after Theiler's murine encephalomyelitis virus infection, whereas none of the infected littermates with normal expression of class I MHC (β2-m, +/+) developed demyelination. Demyelinated lesions showed class II MHC expression, macrophages, and TNF but no class I MHC expression or CD8⁺ T cells. No correlation was observed between development of demyelination and delayed-type hypersensitivity responses to virus Ag. Despite the presence of demyelinating lesions, none of the infected β2-m (-/-) mice developed neurologic deficits. Infectious virus and virus Ag persisted in the central nervous systems of infected β2-m (-/-) mice but not in β2-m (+/+) mice. These experiments support the hypothesis that a class I immune response mediated by CD8⁺ T cells is important in resistance to Theiler's murine encephalomyelitis virus-induced demyelination. Development of chronic neurologic deficits as observed in immunocompetent susceptible strains of mice may be dependent on the presence of class I MHC and CD8⁺ T cells.