Effect of fluorocarbon treatment on Newcastle disease virus.

Full hemolytic activity in Newcastle disease virus (NDV) suspensions is not obtained without pretreatment of the virus by techniques such as freezing and thawing or extensive dialysis (Granoff and Henle, J. Immunol. 75:322, 1954). Girardi (Virology 9:488, 1959) has reported that fluorocarbon treatment unmasks polyoma virus hemagglutinin. Results are reported here which show that fluorocarbon treatment may also be used to unmask the NDV hemolysin. Fluorocarbon treatment of virus suspensions was accomplished by mixing equal volumes of allantoic fluid, containing the L. Kansas or NK strains of NDV, and Genetron 113 (trichlorotrifluoroethane). This mixture was stirred at the slowest speed in a Virtis 23 homogenizer for 10 min and then centrifuged to separate the two phases. Hemolysis of chicken red cells (RBC) was measured by mixing 1.0 ml of virus suspension with 3.0 mnl citrate saline or 3.0 ml of a 1:120 dilution of NDVr antiserum in citrate saline. This mixture w-as incubated for 1 hr at 37 C, and then 1.0 ml of 4% w-ashed RBC was added and incubation continued for 1 hr. The suspensions were then centrifuged to remove unlysed cells and the optical density of the supernatant fluid was measured at 550 m,u. Hemagglutinin end point titrations were carried out using twofold dilution series in spot plates to which 2 drops of 4% w-ashed RBC were added. Plaque titrations weree madle by inoculating chick embryo fibroblast tissue cultures, which were incubated with a nutrient agar overlay after infection. Genetron-treated .NK virus suspensions showed greater than ten times as much henmolytic activity as untreated fluids (Table 1). Samples run in parallel series, with and without antiserum, indi930 [VOL. 83