The human interferon-α (IFN-α) family is encoded by 13 different functional genes, and including all cloned sequence variants there are 28 potential IFN-α proteins. To find out which of the described sequences are expressed in normal human leucocytes, we have isolated and partly characterized the components of a highly purified IFN-α preparation produced by Sendai virus-induced human peripheral blood leucocytes. The identification protocol consisted of N-terminal sequencing and mass mapping of the proteins separated by reverse-phase HPLC and/or SDS/PAGE. The highly purified leucocyte IFN-α preparation was found to contain at least nine different IFN-α species: IFN-α1a, IFN-α2b, IFN-α4b, IFN-α7a, IFN-α8b, IFN-α10a, IFN-α14c, IFN-α17b and IFN-α21b. IFN-α1a was the major subtype, comprising approx. 30% of total leucocyte IFN-α. IFN-α14c, the only subtype containing potential N-glycosylation sites, was shown to be glycosylated at Asn-72. Molecular mass determination of the intact proteins by electrospray ionization MS showed that there are no other post-translational modifications in the IFN-α subtypes than the glycosylation of IFN-α2b and IFN-α14c. Only one sequence variant was found for each subtype, suggesting that the other described gene sequences represent allelic variants or mutations that are more rarely found in the general population.

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