Mice were killed at days 5 to 7 pi (peak of inflammation) or at day 30 pi (during chronic demyelination) and were perfused transcardially with phosphate-buffered saline followed by phosphate-buffered saline containing 4% paraformaldehyde. Brain, spinal cord, eyes, and optic nerve tissues were collected, postfixed in 4% paraformaldehyde overnight, and embedded in paraffin; sections were then stained with hematoxylin and eosin (H&E) to evaluate inflammation and Luxol fast blue to evaluate demyelination. Experiments were repeated at least 3 times with 3 to 5 mice. Areas of demyelination and inflammation were quantified as previously described (8, 11) . All slides were coded and read in a blinded fashion. To confirm expected virulence of the strains used, livers from the infected mice were embedded in paraffin, sectioned at 5 Km, and stained with H&E (5, 12) . The degree of optic nerve inflammation was scored by 2 blinded investigators on a 0-(no inflammation) to 4-point (severe inflammation) scale, as described (8, 11) , during the time of peak inflammation (days 5Y7 pi). Any amount of inflammation (score of 1Y4) was considered positive for optic neuritis.