These are loosely named for their source, e.g., secreted by leukocyte or fibroblast cells or in response to viral or other immune challenge. It was originally presumed that cells secreted only one type of interferon. A newer, more commonly used, nomenclature system is based on initial characterization of the types of interferon produced by different cell types. The term 'alfa' is often used when referring to commercial alpha interferon products, e.g., in FDA proper names. Within each interferon class, interferons share considerable homology, i.e., their nucleotide and amino acid sequences are very similar.
Recombinant interferons are essentially pure single subspecies protein.
The mechanisms by which interferons exert antitumor and antiviral activities are not clearly understood. However, it is believed that they direct antiproliferative action against tumor cells, inhibit virus replication, and modulate host immune response which play important roles in their antitumor and antiviral activity. As a consequence, preclinical evaluation of interferon products has largely involved in vitro experiments with human cells and some in vivo experiments. Because of its species-restricted activity, it has not been possible to demonstrate antitumor activity of interferon products in immunologically intact syngeneic tumor model systems, where effects on the host immune system would be observable. However, antitumor activity has been repeatedly demonstrated, e.g., with mouse interferon alpha in transplantable mouse tumor systems.