Characteristics of a persistent respiratory syncytial virus infection in HeLa cells

Persistent infection with respiratory syncytial (RS) virus has been established in HeLa cells. The persistently infected cell line (HeLa_RS) continues to produce virus (RSpi) at low levels after 230 passages during 3 years. The cells are morphologically similar to the parental HeLa cell line, and susceptible to vesicular stomatitis virus, but resist superinfection with standard RS virus (RS_wt). The block in RS_wt replication is not at attachment. Although infectious center and immunofluorescence assays suggested that only 5 to 30% of the cells in the culture were infected, 30 of 32 clones isolated from HeLa_RS contained some cells with virus antigen and 23 of those clones produced virus. All the clones, including the 2 that appeared not to be infected, were more resistant to RS_wt than HeLa. The clones that produced virus were significantly more resistant than the others. RS_pi is a small-plaque mutant, but not a temperature-sensitive mutant, of RS_wt. Although prior infection of HeLa with RS_pi interferes with RS_wt replication, the interference appears not to be caused by defective interfering particles, but by RS_pi virions. RS_pi initiates a persistent infection in HeLa only after a cytolytic phase similar to that which preceded the establishment of HeLa_RS.