Observations regarding the role of MHC class I in resistance vs. susceptibility to viral persistance and demyelination were made in recombinant inbred strains of the C57BL background (Rodriguez and David, 1985; Rodriguez et al., 1986) , and the immunodominant VP2 121-130 peptide response was observed only in H-2 b mice (Fig. 14) . The hypothesis probably does not explain the mechanism of demyelination and neurological deficit in susceptible strains such as SJL/J mice (H-2 s haplotype).