IFNs are routinely produced in E.coli or in CHO cells. Very easy and cheap to produce. The type I interferon gene families may have evolved from a common ancestor, but now are not closely related. The three classes are quite distinct, antibodies to one group not cross reacting with the other. All vertebrates produce interferons, and all appear to produce the three major classes.
Most interferons are very species specific.
E.g. mouse and rat show little cross reactivity, as do human and rodent, or chick and duck. However human and bovine alpha interferons do cross react, and monkey and human interferons are mutually protective. Basis of host specificity lies in the presence of specific receptor sites. Radio-immune assay based on monoclonal antibody very useful. Plaque assay inhibition is still most sensitive assay.