Abstract
Interferons are proteins of cellular origin capable of conferring virus resistance to vertebrate cells. Most cells do not produce interferons except in response to proper stimulation. Clearly, the stimulation of interferon production encompasses two phenomena. When stimulated, some cell systems produce their interferons by synthesizing new proteins. Other cell systems do not require the synthesis of new proteins to produce interferons, and still other cell systems may produce interferons by both means. Before much can be learned from the detailed study of the nature of the molecules which stimulate interferons, the type of phenomenon which the stimulus induces must be identified. Chick embryo tissues apparently make interferons by synthesizing new proteins. Many viruses stimulate interferon production in chick embryo tissues. Data available suggest that neither the protein nor nucleic acid moieties of the added virions act as inducing molecules. Also, double-stranded replicative form is probably not responsible. It is suggested that the inducer molecule may be cellular in nature and may be produced in response to a wide variety of insults among which are viral infections.