The role of interferon in interference and auto-interference elicited by Newcastle disease virus.

Newcastle disease virus (NDV) strains interfere in different degree with the growth of the velogenic NDV strain Texas GB (homologous interference) and Sindbis virus (heterologous interference) in chick embryo fibroblast cells. Homologous interference was elicited by interferon-producing live or UV-inactivated strains and non-interferon-producing live or beta-propiolactone-inactivated strains and it was not influenced by actinomycin D. Thus, interferon had apparently no role in homologous interference of NDV. The growth of Sindbis virus was, however, much more inhibited by interferon-producing live or UV-inactivated NDV strains than with non-inducing ones and the interference was reversible by actinomycin D. Thus heterologous interference is apparently mediated by interferon. In chicken cells infected with the mesogenic NDV strain H, virus yields were 50 to 100 times lower at multiplicities of infection above 0.1 p.f.u./cell than below it. The interferon formed during infection played no role in auto-interference, but may well be held responsible for the mild cytopathic effect observed.