MHV-free, C57BL/6 (B6) mice (Jackson Laboratory, Bar Harbor, ME) were inoculated intracranially at 4 weeks of age with 50% LD 50 dose of RSA59 strain (20,000 plaque forming units) or RSMHV2 (100 plaque forming units), as described previously (4) . Mice were monitored daily for signs of disease. Mock-infected controls were inoculated similarly but with an uninfected cell lysate at a comparable dilution. Animals were killed (3Y5 mice per group) at day 3, days 5 to 7, and day 30 post inoculation (pi). All experimental procedures adhered to guidelines of, and were approved by, the Institutional Animal Care and Use Committee.