Characteristics of a respiratory syncytial virus persistently infected macrophage-like culture

A persistently infected culture obtained from immortalized murine macrophage-like cells, which survived respiratory syncytial virus (RSV) infection at multiplicity of one, was established and characterized. The presence of RSV through the passages was confirmed and monitored by (a) detection of infectious virus by TCID50/ml, (b) defective particles by viral infectivity interference and buoyant density determinations, (c) cell surface antigen by indirect immunofluorescence and FACS, and (d) expression of a viral gene by RT-PCR. Moreover, cell morphology changes by comparison of macrophage area and perimeter were determined. A second culture was obtained by cell cloning out of this culture, and a third culture was established by superinfection with the original virus, in which 92–95% of the macrophages expressed viral antigen without cell destruction and released defective particles but low levels of infectious virus. Although the three cultures maintained the characteristics of persistently infected cells, concentrations of released infectious virus, defective particles, and percentages of cells bearing viral antigen varied. RSV persistently infected murine macrophage cultures provide an in vitro model to study viral–macrophage interaction and to allow the experimental use of a cell important in disseminating the infection. In addition, due to the wide array of cellular and humoral reagents in the mouse, studies on immunologic aspects of viral immunity are facilitated.