Effects of a heat-labile factor(s) in normal serum on the interferon-inducing activity of Newcastle disease virus (NDV). Brief report.

The effect of fresh serum on the interferon-inducing activity of Newcastle disease virus (NDV) was studied. Infectivity in fertile eggs, hemolytic activity in human erythrocytes and interferon-inducing activity in mouse L cells and mouse spleen cells were all reduced by treatment of NDV with fresh serum from humans or guinea pigs, while hemagglutinating (HA) activity remained unchanged. The interferon-inducing ability of UV-inactivated NDV was also similarly reduced after treatment with serum. The serum effects were decreased by heating at 56 degrees C for 30 minutes or the addition of 10 mM EDTA. These results suggest that a heat-labile serum factor(s) such as complement or certain enzyme(s) reduced the hemolytic activity and consequently the penetrating activity of NDV, and that interferon-inducing activity was related to the hemolytic but not to the HA activity of NDV particles. Thus, it was concluded that the hemolytic activity of NDV was necessary for interferon induction in both mouse L cells and mouse spleen cells.