Cytotoxicity in glioma cells due to interleukin-12 and interleukin-18—stimulated macrophages mediated by interferon-γ regulated by nitric oxide

Abstract

Object. Interleukin (IL)-12 and IL-18 synergistically mediate antitumor responses through the production of interferon-γ (IFNγ) by T and natural killer (NK) cells. Recently, it has been reported that macrophages stimulated with these cytokines also produce IFNγ, which led the authors to investigate the antiglioma activity of macrophages stimulated by the combination of these cytokines in vitro. Methods. Dish-adherent peritoneal exudate cells, which had been elicited in thioglycollate broth as a source of macrophages, were used in the experiment. The murine glioma cell lines VM-glioma and 203G were labeled with [3H]thymidine for a cytotoxicity assay of macrophages. In response to the combined stimulation by IL-12 and IL-18, macrophages expressed potent cytotoxic activity against glioma cells in association with increasing production of IFNγ and nitric oxide (NO). Inhibitors of NO abrogated the cytotoxic activity of the macrophages, which had been induced by IL-12 and IL-18, despite the increase in IFNγ production. Neutralization of IFNγ or use of macrophages obtained from IFNγ gene-knockout mice markedly reduced not only cytotoxic activity, but also NO production. Depletion of T and NK cells from the macrophage population, which was achieved using antibody plus complement treatment, slightly reduced macrophage activities, suggesting that these are the main effector cells, although T and NK cells may partially participate in this cytotoxicity. Conclusions. Macrophages stimulated with IL-12 and IL-18 produced IFNγ and NO, which in turn mediated the antiglioma response. Therefore, macrophages as well as T and NK cells play an important role in antitumor responses stimulated by IL-12 and IL-18.