Identification of interferon-alpha 7, -alpha 14, and -alpha 21 variants in the genome of a large human population.

The genes for type I interferon (IFN), which include 14 IFN-alpha genes, 1 IFN-beta gene, 1 IFN-omega gene, and a number of IFN-omega pseudogenes, are clustered on human chromosome 9. Among IFN-alpha genes, a number of variants have been reported. Three variants of IFN-alpha 7 (IFN-alpha 7a, IFN-alpha 7b, and IFN-alpha 7c) and IFN-alpha 14 (IFN-alpha 14a, IFN-alpha 14b, and IFN-alpha 14c) and two variants of IFN-alpha 21 (IFN-alpha 21a and IFN-alpha 21b) are identified. The variants differ from each other by base changes in the coding region and can be distinguished by selective restriction enzyme analysis and DNA sequencing. We have used polymerase chain reaction (PCR) with IFN species-specific oligonucleotide primers for amplification of IFN-alpha 7, IFN-alpha 14, and IFN-alpha 21 gene sequences. Genomic DNA obtained from over 28,000 normal healthy individuals were collected in six pools for PCR amplification. To identify the presence of variant sequences, the resulting PCR products of specific IFN-alpha genes were analyzed by restriction endonuclease digestion and DNA sequencing, with a limit of detection of minor components to 1% and 10%, respectively. The results show that only one variant form for each of IFN-alpha 7, IFN-alpha 14, and IFN-alpha 21, namely, IFN-alpha 7a, IFN-alpha 14c, and IFN-alpha 21b, is detectable in the genomic DNA of the population examined. Similar results were obtained from the analysis of a human myeloblastoid cell line, KG-1.