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 IFNalppha family has over .. genes and pseudogenes in two families (I and II), one with a mature length of 166aa and one of 172aa. Cells producing IFNalpha are lymphocytes, monocytes, macrophages and cell lines such as Namalwa and KGI. Bioassays for IFNalpha include cytopathic effect blocking, by viruses such as VSV, SFV and BMCV, on their target cells. A number of receptors for IFNalpha are now known and seem to be expressed on most cell types. N39 is specific for INFalpha(II) and does not crossreact with INFalpha(I).Synonyms: IFN-alpha 2, Interferon alpha-A, LeIF A