Recovery of a Sendai virus variant with temperature-sensitive hemolytic activity from persistently infected cells from mouse brain

A persistently infected cell line designated MB/Sen_AS was established by cultivation of mouse brain cells from four-day-old C3H mice infected intracerebrally at birth with 10⁶ PFU of Sendai virus, strain 52. After 5 passages, 0.16 per cent of Sendai₅₂ antiserum (containing two 50 per cent plaque reducing doses/ml of serum) was introduced into the culture medium. The addition of antiserum was accompanied by a rise in cell-associated viral antigen from a level of 5 per cent antigen positive cells to 100 per cent demonstrable by both intracellular and membrane immunofluorescence. A variant of Sendai₅₂ virus, designated Sendai_AS, was recovered from MB/Sen_AS by inoculation of supernatant medium into chick embryos. Infection of chick embryos at 37° C was abortive. Fifty per cent or less of chick embryos infected at dilutions 10^-1 to 10^-9 yielded detectable virus. Hemagglutination (HA) was weak but could be improved by trypsinization of allantoic fluids. Neuraminidase (NA) activity was barely detectable. Hemolysis (HE) was absent. Propagation of Sendai_AS virus at 33° C showed no change from weak HA and NA activities but HE activity was now apparent which was temperature sensitive. Mortality of infected chick embryos increased to 100 per cent. HE activity and lethality for chick embryos was thermolabile at 45° C.