Rat Peritoneal Mast Cells Produce IFN-γ Following IL-12 Treatment but Not in Response to IgE-Mediated Activation

Mast cells have been reported to secrete a wide range of immunoregulatory cytokines following IgE-mediated activation and to play an important role in allergic inflammation. We have previously demonstrated that mast cells can also produce certain cytokines following activation with bacterial LPS or prostanoids without preformed mediator release. IL-12 is a potent inducer of IFN-γ production by T cells and NK cells, and is thought to play a critical role in determining the nature of the local immune response to infection. We here report that highly purified peritoneal mast cells from Brown Norway rats will produce IFN-γ in response to IL-12 without significant histamine release. IFN-γ protein was detected by ELISA in supernatants of mast cells cultured with 2 U/ml recombinant mouse IL-12 for between 6 and 24 h. The production of IFN-γ was dependent on the dose of IL-12 and was significantly inhibited by concurrent treatment with IL-10 or PGE₂. Supernatants from IL-12-stimulated mast cells induced MHC class II expression on the mouse epithelial cell line, MODE-K, by an IFN-γ-dependent mechanism. Peritoneal mast cells cultured following activation with anti-IgE or LPS, under conditions that will induce the production of IL-6, demonstrated no detectable protein production of IFN-γ. We conclude that mast cells are capable of contributing to the IFN-γ response to IL-12, but substantial mast cell IFN-γ production does not occur as a result of IgE-mediated activation. These observations have important implications for the role of the mast cell in local immune regulation.