Respiratory syncytial virus infects and abortively replicates in the lungs in spite of preexisting immunity.

Respiratory syncytial virus (RSV) is a major cause of bronchiolitis and viral pneumonia in young children and a serious health risk in immunocompromised individuals and the elderly. Immunity to RSV is not completely understood. In this work, we established a method for monitoring RSV infection by real-time PCR and applied this method for analysis of RSV replication in vivo in the cotton rat model in naïve animals and in animals rendered immune to RSV by prior RSV infection. We found that even though no virus could be isolated from the lungs of RSV-challenged immune animals, RSV infection in fact took place and an accumulation of viral RNA transcripts was observed. This type of replication, therefore, can be termed "abortive," as RSV is capable of entering the cells in the lungs of immune animals, yet the production of progeny viruses is impaired. Similar patterns of RSV gene expression gradient were observed between naïve and reinfected animals, indicating that the skewing of mRNA gradient of viral gene expression, a mechanism documented during latent infection by other viruses, is not likely to be responsible for abortive replication of RSV during reinfection. We found that passive administration of antibodies to RSV prevents productive infection normally accompanied by viral release in the lung, but it does not prevent abortive replication of the virus. To the best of our knowledge, this is the first evidence of abortive replication of RSV in vivo.