IDENTIFICATION OF 9 INTERFERON-ALPHA SUBTYPES PRODUCED BY SENDAI VIRUS-INDUCED HUMAN PERIPHERAL-BLOOD LEUKOCYTES

The human interferon-alpha (IFN-alpha) family is encoded by 13 differe nt functional genes, and including all cloned sequence variants there are 28 potential IFN-alpha proteins. To find out which of the describe d sequences are expressed in normal human leucocytes, we have isolated and partly characterized the components of a highly purified IFN-alph a preparation produced by Sendai virus-induced human peripheral blood leucocytes, The identification protocol consisted of N-terminal sequen cing and mass mapping of the proteins separated by reverse-phase HPLC and/or SDS/PAGE. The highly purified leucocyte IFN-alpha preparation w as found to contain at least nine different IFN-alpha species: IFN-alp ha 1a, IFN-alpha 2b, IFN-alpha 4b, IFN-alpha 7a, IFN-alpha 8b, IFN-alp ha 10a, IFN-alpha 14c, IFN-alpha 17b and IFN-alpha 21b. IFN-alpha 1a w as the major subtype, comprising approx. 30% of total leucocyte IFN-al pha. IFN-alpha 14c, the only subtype containing potential N-glycosylat ion sites, was shown to be glycosylated at Asn-72. Molecular mass dete rmination of the intact proteins by electrospray ionization MS showed that there are no other post-translational modifications in the IFN-al pha subtypes than the glycosylation of IFN-alpha 2b and IFN-alpha 14c. Only one sequence variant was found for each subtype, suggesting that the other described gene sequences represent allelic variants or muta tions that are more rarely found in the general population.