Mechanism of Interferon Induction by NDV: a Monolayer and Single Cell Study

Newcastle disease virus (NDV) stocks contain three types of particles which were tested for interferon inducing ability: (1) plaque-forming haemagglutinating particles, (2) non-plaque-forming haemagglutinating particles containing RNA and (3) non-plaque-forming haemagglutinating particles which contain no RNA. Single NDV-infected cells were isolated in microdrops and tested for interferon production as measured by protection of 30 ± 6 additional cells from challenge with mengovirus. This technique demonstrated that: (1) essentially every cell can be induced by plaque-forming NDV to produce interferon, (2) neither of the two types of non-plaque-forming haemagglutinating particles were capable of inducing detectable levels of interferon and (3) while infection with a single active virus was sufficient to induce interferon, the efficiency of induction increased with increasing multiplicity. It was concluded that some virus synthetic processes are probably required to initiate induction.