Interferon-γ -Like Molecule Induces Ia Antigens on Cultured Mast Cell Progenitors

Persisting (P) cells (murine cells that resemble mast cells and grow continuously in vitro for prolonged periods in the presence of a specific growth factor) did not express detectable levels of Ia antigens (murine class II major histocompatibility antigens) when their growth was supported by partially purified P cell-stimulating factor. However, when these Ia-negative P cells were transferred to medium conditioned by concanavalin A-stimulated spleen cells, Ia antigens appeared within 24 hr. The increase in Ia antigens was due to induction of synthesis of Ia antigens by P cells and not to absorption of Ia antigens from the conditioned medium or selective growth of Ia-positive cells from a low number of Ia-positive cells in the original population. The Ia-inducing activity was also found in supernatants from antigen-stimulated cloned T-cell lines, but not from certain T-cell hybridomas or the T lymphoma EL-4. The presence of Ia-inducing activity correlated with the presence of interferon-γ (IFN-γ ). The gel filtration profiles of IFN-γ activity and Ia-inducing activity were coincident and corresponded to an apparent molecular weight of 40,000-45,000. Both the IFN-γ and Ia-inducing activity were destroyed by treatment at pH 2. These results indicate that IFN-γ or a closely related molecule induces Ia antigens on P cells and suggest that regulation of Ia antigen expression may be an important aspect of the effects of IFN-γ on the immune and hemopoietic systems.