Age-dependent resistance to viral encephalitis: Studies of infections due to sindbis virus in mice

Resistance to Sindbis-virus encephalitis was studied in mice of various ages. Resistance developed abruptly during the second week of life in mice that received either intracerebral or subcutaneous inoculation. In weanling mice, limited replication of virus occurred in the inoculated tissues, and staining with fluorescent antibody showed that the same types of cells became infected in weanlings as in newborns. In weanling mice, infection did not spread; this limitation of viral replication and dissemination was evident by 24 hr. The development of neutralizing antibody at three days and of mononuclear cell infiltrates at four to five days did not appear to determine resistance. Furthermore, fibroblasts from weanling mice were grown in vitro and were found to be resistant to infection, whereas fibroblasts derived from newborn mice were susceptible.