Critical contribution of IFN-gamma and NK cells, but not perforin-mediatedcytotoxicity, to anti-metastatic effect of alpha-galactosylceramide

The glycolipid alpha -galactosylceramide (alpha -GalCer), which is presente d by CD1d and specifically activates V alpha 14 NKT cells, exerts a potent anti-metastatic effect when administered in vivo. In this study, we demonst rated that alpha -GalCer administration led to rapid elimination of NKT cel ls by apoptosis in the liver and spleen, after they produced IFN-gamma and IL-4. In contrast, a more prolonged secretion of IFN-gamma was observed by liver and splenic NK cells after alpha -GalCer administration. Cytotoxic ac tivity of liver mononuclear cells was not augmented 3 h after alpha -GalCer administration, but was increased at 24 h when NKT cells were mostly deple ted. The alpha -GalCer-induced cytotoxic activity was abolished in IFN-gamm a -deficient and NK cell-depleted mice as well as CD1-deficient mice, sugge sting that the alpha -Galcer-induced cytotoxicity was mainly mediated by IF N-gamma -activated NK cells. While the alpha -GalCer-induced cytotoxicity i n vitro was mostly perforin dependent, anti-metastatic effect of alpha -Gal Cer was impaired in NK cell-depleted or IFN-gamma -deficient mice but not i n perforin-deficient mice. Collectively, these results indicated that the a nti-metastatic effect of alpha -GalCer is mainly mediated by NK cells, whic h are activated secondarily by IFN-gamma produced by alpha -GalCer-activate d NKT cells, in a perforin-independent manner.