Critical contribution of IFN-γ and NK cells, but not perforin-mediated cytotoxicity, to anti-metastatic effect of α-galactosylceramide

The glycolipid α-galactosylceramide (α-GalCer), which is presented by CD1d and specifically activates Vα14 NKT cells, exerts a potent anti-metastatic effect when administered in vivo. In this study, we demonstrated that α-GalCer administration led to rapid elimination of NKT cells by apoptosis in the liver and spleen, after they produced IFN-γ and IL-4. In contrast, a more prolonged secretion of IFN-γ was observed by liver and splenic NK cells after α-GalCer administration. Cytotoxic activity of liver mononuclear cells was not augmented 3 h after α-GalCer administration, but was increased at 24 h when NKT cells were mostly depleted. The α-GalCer-induced cytotoxic activity was abolished in IFN-γ-deficient and NK cell-depleted mice as well as CD1-deficient mice, suggesting that the α-Galcer-induced cytotoxicity was mainly mediated by IFN-γ-activated NK cells. While the α-GalCer-induced cytotoxicity in vitro was mostly perforin dependent, anti-metastatic effect of α-GalCer was impaired in NK cell-depleted or IFN-γ-deficient mice but not in perforin-deficient mice. Collectively, these results indicated that the anti-metastatic effect of α-GalCer is mainly mediated by NK cells, which are activated secondarily by IFN-γ produced by α-GalCer-activated NKT cells, in a perforin-independent manner.