Produced by macrophages, IFN-alpha have antiviral activities. Interferon stimulates the production of two enzymes: a protein kinase and an oligoadenylate synthetase. Two forms exist; alpha-4a (shown here) and alpha-4b (PubMed:9335434). They seem to be equally abundant (PubMed:9335434). Belongs to the alpha/beta interferon family.