Role of the immune response in age-dependent resistance of mice to encephalitis due to Sindbis virus.

One- to eight-week-old mice were studied after subcutaneous inoculation of Sindbis virus. Local replication at the site of inoculation, transient viremia, and invasion of the brain were found in mice of all ages, although the quantities of virus were greater in younger mice. Death occurred in 100% of one-week-old mice, 28% of two-week-old mice, and none of the mice four weeks old or older. Pathologic examination of the brains on day 7 after infection revealed a mononuclear inflammatory infiltrate in all mice, with evidence of necrosis in the youngest. Neutralizing antibody was present by day 3 and reached high titers by day 6 in all age groups. Specific stimulation of cells from the draining lymph node by Sindbis virus antigen was also demonstrable by day 6 in all groups. There was no evidence for a primary role of humoral or cellular immune responses in the age-dependent resistance of mice to infection with Sindbis virus.