On the study of Sendai virus hemolysis. I. Complete Sendai virus lacking in hemolytic activity.

The hemolytic activity of Sendai virus was examined with samples collected at various times after infection of the embryonated eggs. The virus obtained just after the end of the one-step growth cycle (early harvest) was shown to exhibit no hemolytic activity, whereas it expressed full activity of cell fusion and infectivity. Incubation at 36°, freezing and thawing, or sonic treatment enabled the early harvests to be hemolytic. Conversion of the virus from the nonhemolytic state to a hemolytic one was always followed by the alteration of the virus envelope so that it became permeable to the uranyl acetate stain used for the negative staining (UA-particle). The degree of hemolysis and the number of UA-particles of the early harvest increased as freezing and thawing was repeated while the degree of cell fusion and infectivity was decreasing. On the basis of these findings, it was concluded that Sendai virus with intact envelope does not exhibit hemolysis, while it has the potential activity to do so.