The interferons (IFNs) are a group of proteins produced by cells of all vertebrate animals in response to a variety of stimuli. The ability to stimulate antiviral resistance, which was the first observed property of the IFNs, is still of great interest and remains the basic criterion by which the interferons are measured 1 (even into the most recent era of radioimmunoassay systems). It is the recent clinical uses of these substances as antineoplastic agents that has brought them to the attention of clinicians and the public in general. The IFN molecules exert their effects, much as hormones do, by attaching to specific receptors on other cells of the same species. Once attached, the IFNs induce cells to undergo a series of biochemical changes that renders them resistant to further virus propagation. To be an IFN, a substance must be a protein devoid of accompanying nucleic acid or endotoxin (both of which are interferon inducers). Treated cells must undergo de novo RNA and protein synthetic activity to acquire antiviral resistance.
