For the analysis of inflammation and viral antigen expression, the right half of the brain harvested at 5 days postinfection (see above), was fixed in formalin overnight. Formalin-fixed tissue was embedded in paraffin and sectioned sagittally. Immunohistochemical analysis was performed by the avidin-biotin-immunoperoxidase technique (Vector Laboratories, Burlingame, Calif.) using 3,3′-diaminobenzidine as substrate and a 1:20 dilution of a monoclonal antibody (MAb) directed against the nucleocapsid protein (N) of MHV-JHM (MAb clone 1-16-1, kindly provided by Julian Leibowitz, Texas A & M University). Control slides from mice either uninfected or inoculated with rLm-gp33 but not with virus were incubated in parallel. All slides were read in a blinded manner.