The classification and biological functions of the interferons

There are three main types of interferon, now designated α, β and γ. Human interferons-α exist as many subtypes, probably more than 26. These are chemically quite closely related, but each has a unique chemical composition and biological properties. Preparations of interferon-α derived from stimulated peripheral blood leukocytes or lymphoblastoid cell lines contain mixtures of these sub-types; individual sub-types can be obtained by expression of the human gene concerned in bacteria. Human interferon-β shows about 30% chemical homology with the interferons-α. The natural product is glycosylated, and there is only one molecular species. Natural interferon-γ, also a glycoprotein, has the same non-specific antiviral properties as other types of interferon, but shows little, if any, chemical homology. Recombinant interferons-β and -γ have also been prepared by application of gene cloning techniques and expression in E. coli. These proteins are not glycosylated, and differ in their pharmacokinetic behaviour from the natural human proteins. In nature, interferons are normally formed and act locally. If relatively large amounts are administered in order to produce systemic effects, there are dose-related side effects which resemble an attack of influenza.