IFN-αInduced Human 78 kD Protein: Purification and Homologies with the Mouse Mx Protein,Production of Monoclonal Antibodies,and Potentiation Effect of IFN-γ

A 78-kD protein (p78) is induced in human cells in response to interferon (IFN). It appeared as a radioactive spot when newly synthesized proteins from IFN-treated human cells labeled with [³⁵S]methionine were separated in a two-dimensional system and autoradiographed. p78 was induced by IFN-α in normal human fibroblasts, and in some, but not all, established human tumor cell lines. It has been purified to homogeneity from Namalwa cells induced by recombinant IFN-α. Mouse polyclonal and monoclonal antibodies specific to p78 have been produced which allowed its quantitative determination in a Western blot ELISA. Using this method it was also shown that although IFN-γ was a poor inducer of p78, it markedly increased the effect of IFN-α on p78 induction and accumulation. It was also demonstrated that p78 and the protein Mx of influenza-resistant mice, which we purified and characterized earlier (Horisberger and Hochkeppel, J. Biol. Chem. 260, 1730-1733, 1985) share common properties such as size, pI, amino acid composition, antigenic determinant(s), and IFN inducibility.