Demonstration of the presence of a specific interferon-γ receptor on murine astrocyte cell surface

Interferon gamma (IFN-γ) is a pleiotropic lymphokine produced by T-lymphocytes which acts as a soluble mediator in immunological reactions. In addition to several immune target cells, such as monocytes and macrophages, it acts on the principal glial population, the astrocytes, inducing Ia antigen expression. We have developed a binding assay for (125)I-labeled recombinant murine IFN-γ, and show that, using this assay, IFN-γ interacts with a single specific receptor on the murine astrocyte cell membrane. The binding is specific and saturable and it takes place with a K(d) = 1.64 × 10(−9) M, with 11,100 receptor molecules per astrocytic cell. The binding shows, as for macrophages, species specificity. Using an immune assay including rabbit antibodies to IFN-γ and (125)I-labeled protein A, we have demonstrated an internalization of the ligand. This is an energy-dependent process, as around 50% of the bound IFN-γ is endocytosed after 4 h at 37°C when cultures are maintained in complete culture medium.