Abstract: The invention relates to purified proteins induced in human cells by interferon .alpha. or .beta., RNAs, DNAs and hybrid vectors coding for said proteins, hosts transformed with such a hybrid vector, processes for the preparation and purification of these proteins, DNAs, vectors and hosts, monoclonal antibodies specific to these proteins, monoclonal antibody derivatives, hybridoma cell lines secreting these monoclonal antibodies, the use of the monoclonal antibodies and their derivatives in the qualitative and quantitative determination of these proteins, test kits containing the monoclonal antibodies, and pharmaceutical preparations containing said proteins. A protein of the invention shows antiviral properties ascribed to interferons and may be a valuable indicator of the cell response to an interferon therapy.