In contrast, there was significant disruption and degeneration of axons in chronically infected SJL/J mice (Rivera-Quinones et al., 1998) . These findings indicate Infected β2m +/+ mice do not exhibit demyelination, whereas the extent and distribution of demyelinated lesions is qualitatively similar in class I-deficient mice (β2m −/− ), SJL/J mice, and class II-deficient mice (Ab 0 ).