Production of a monoclonal antibody directed against an interferon-induced 56,000-dalton protein and its use in the study of this protein.

Interferon (IFN) treatment of cells induces the synthesis of several new proteins. A hybridoma cell line producing monoclonal antibody to the IFN-induced 56,000-dalton protein has been developed. The IFN-induced 56,000-dalton protein is synthesized by a variety of different cells and in response to IFN-alpha, IFN-beta, and IFN-gamma. The induction of this protein is dependent on de novo RNA synthesis, since its induction is inhibited if actinomycin D and the IFNs are added to the cells simultaneously. Labeling of IFN-treated cells at 4-h intervals at various times after the addition of the IFNs reveals that the synthesis of the 56,000-dalton protein in IFN-alpha-treated cells peaks within 12 h after the addition of the IFN and is no longer enhanced 20 h after exposure to the IFN. In contrast, IFN-gamma-treated cells continue to show an enhanced synthesis of this IFN-induced protein even after 20 h of exposure to the IFN. Thus, the synthesis of the IFN-induced 56,000-dalton protein is regulated differently by the different IFNs. When cells are treated with IFN-alpha or IFN-gamma in the presence of cycloheximide, and actinomycin D is added prior to the removal of the cycloheximide, the cells produce the IFN-induced 56,000-dalton protein and develop an antiviral state in response to both IFN-alpha and IFN-gamma. These results demonstrate that the synthesis of the 56,000-dalton protein is not dependent on the synthesis of an intermediary protein and that the establishment of an antiviral state occurs in the absence of multiple transcriptional events.