Persistent infection of cells in culture by respiratory syncytial virus.

The virus-cell relationship of RS virus and the HEp-2 cell line has been examined. The production of cytopathic effect (c.p.e.) on HEp-2 cells has been found to be dependent upon the passage level of the cell line. Cells at lower passage levels exhibit c.p.e. in the form of syncytium formation, while those at higher passage levels no longer exhibit this effect. Cells infected at higher passage levels are covertly infected and continue to produce large amounts of infectious virus which remains cell-associated. On continued passage, these cells remain infected with virus but show no c.p.e. and release little if any infectious virus into the medium. Examination of the RNA species present in infected cells revealed that similar species are present in both the overtly and covertly infected cells.