The alpha interferons are involved in virus resistance in target cells for these viruses. They are known to block cell proliferation and to regulate MHC class I antigen expression. The IFNα family has over 20 genes and pseudogenes in two families (I and II), one with a mature length of 166aa and one of 172aa. Cells producing IFNα are lymphocytes, monocytes, macrophages and cell lines such as Namalwa and KGI. Bioassays for IFNα include cytopathic effect blocking, by viruses such as VSV, SFV and BMCV, on their target cells. A number of receptors for IFNα are now known and seem to be expressed on most cell types. N27 is specific for human IFNα2 and does not cross react with human IFNα1. N27 reacts with linear peptide 43aa-53aa, placing the epitope outside the immunodominant regions I and II. Positive control: Human IFNα2, Namalwa and KGI cells. Pair: N39