Reinfection of mice with respiratory syncytial virus.

A BALB/c model of respiratory syncytial virus infection has been developed in which high-titered replication occurs in lung, immunological infiltrates in lung can be detected histologically, and illness can be consistently reproduced. The immunodeterminants of RSV reinfection in this system were investigated by rechallenging mice with RSV early (less than 2 months after primary infection) and late (16 to 21 months after primary infection) and correlating illness and titer of RSV isolated from lungs and noses with RSV-specific serological responses and lung histology. After early rechallenge, RSV was cleared within 24 hours from both nose and lung. After late rechallenge, RSV was isolated at 72 hours from nose in 21/24 mice, but from lung in only 5/24 mice. Isolation of RSV from lung after rechallenge was associated with low RSV-specific antibody titers measured by ELISA and plaque-reduction neutralization. The presence of lymphocyte aggregates around the bronchovascular bundles was associated with inability to isolate RSV from lung and lack of illness. The basophilic lymphocytes were small and uniform in size with dense nuclei and a small amount of cytoplasm. These studies demonstrate that nasal and pulmonary reinfection with RSV is possible in mice after late rechallenge. The studies also indicate the potential importance of RSV-specific antibody in protecting lung from reinfection.