The development of antibody to the interferon-induced indoleamine 2,3-dioxygenase and the study of the regulation of its synthesis.

Interferon (IFN) treatment of cells induces the synthesis of several new proteins. Antibody to the IFN-induced 42,000 dalton protein has been prepared and used in the study of this protein. The synthesis of the 42,000 dalton protein is dependent on de novo RNA synthesis, as its induction can be blocked if actinomycin D and the IFN are added to the cells simultaneously. Several lines of evidence suggest that the IFN-induced 42,000 dalton protein is the IFN-induced indoleamine 2,3-dioxygenase (IDO). These are as follows: 1) antibody to the 42,000 dalton protein neutralizes the activity of the IDO; 2) examination of a variety of cell lines reveals a correlation between the presence of this protein and the presence of the IDO; and 3) the induction of both the IDO and the 42,000 dalton protein is blocked under conditions in which the IFN treatment is performed in the presence of cycloheximide, and actinomycin D is added to the cells prior to the removal of the cycloheximide. A study of a variety of cell lines has revealed that the induction of the IDO occurs primarily in response to IFN-gamma. Peripheral blood mononuclear cells (PBMC) were the only cell population in which IFN-alpha and IFN-gamma were observed to produce the IDO. The IDO activity induced in IFN-alpha and IFN-gamma treated PBMC is neutralized by antibody to the 42,000 dalton protein, thus demonstrating that the IDO activity induced in these cells by IFN-alpha and IFN-gamma is mediated by the same molecule or antigenically related molecules. Fractionation of the PBMC populations reveals that it is the monocyte that produces the IFN-induced IDO.