A hybrid between a resistant and a susceptible strain of mouse alters the pattern of Theiler's murine encephalomyelitis virus-induced white matter disease and favors oligodendrocyte-mediated remyelination

Theiler's murine encephalomyelitis virus (TMEV) produces a chronic disease in its natural host, the mouse, characterised by primary inflammatory demyelination of the spinal cord. This viral infection is considered a very good model for human MS because the pathogenesis of myelin injury is mediated through the host immune response. Susceptibility and/or resistance to the demyelinating disease depend on multiple genes both in and outside the major histocompatibility complex (MHC). The pathological lesions in animals with different degrees of susceptibility vary in both their severity and in their ability to become remyelinated. In general, animals with intermediate levels of susceptibility show the best potential for remyelination. Most crosses of susceptible animals with resistant strains carrying the H-2b haplotype are resistant with only a couple of exceptions. One such exception is the (SJL/J x C57L/J)F1 hybrid, which is susceptible to the disease. To study whether the resistant genotype of C57L/J mice could modify the phenotypic expression of pathological lesions characteristic of the highly susceptible SJL/J mouse, we performed a light microscopical and ultrastructural study of the spinal cord of both parental strains and their F1 progeny. We focused particularly on the relationship between severity of inflammation, and especially macrophage infiltration, and the subsequent remyelinating potential of lesions. The results show a dramatic difference between the ability to remyelinate lesions by infected SJL/J mice vs similarly infected (SJL/L x C57L/J)F1 hybrids, and suggest an important influence by resistant genes in modulating the phenotypic expression of disease, including the ability to stimulate oligodendroglia-mediated remyelination.