Serial sections from optic nerves were stained by the avidin-biotin-immunoperoxidase technique (Vector Laboratories, Burlingame, CA) using 3, 3 ¶ diaminobenzidine as substrate, and antibodies against lymphocytic cell markers, antiviral nucleocapsid antiserum, or the axonal marker antineurofilament antiserum as primary immunoglobulin G antibodies. The sources and dilution of primary antibodies are listed in the Table. Control slides from mock-infected mice were incubated in parallel.