Generation and characterization of monoclonal antibodies specific for the human IFN-γ receptor

Purified preparations of the human IFN-γR derived from placental membranes were used to produce receptor-specific murine mAb. Supernatants from growth-positive wells were screened for their ability to block binding of ¹²⁵I-IFN-γ to human placental membranes. Ten inhibitory cultures were identified. Two of these (GIR-208 and GIR-301) abrogated all binding of radioligand to either intact placental membranes or soluble, purified IFN-γR. Three others (GIR-72, 76 and 94) showed moderate blocking activity (65, 59, and 49%, respectively) whereas the remaining five (GIR-57, 67, 83, 109, and 153) blocked binding to a low but significant extent (20 to 40%). Specificity experiments demonstrated that the antibodies reacted with the receptor and not the ligand (IFN-γ). None of the antibodies reacted with IFN-γ by ELISA. Moreover, GIR-208 and GIR-301, but not isotype-matched controls, identified the receptor by Western blot analysis. GIR-208 and GIR-301 also completely abrogated binding of ¹²⁵I-IFN-γ to either mononuclear phagocytes (U937) or human fibroblasts (WISH). Competition experiments revealed that GIR-208 and GIR-301 recognized similar epitopes on the IFN-γR and that these (or this) epitopes were identical to or linked to the ligand binding site of the receptor. In addition, both antibodies inhibited development of IFN-γ-dependent anti-viral activity in WISH cells in a dose-dependent fashion. These data thus indicate that the IFN-γR expressed on human placental cells, mononuclear phagocytes, and fibroblasts are similar.