Model for trafficking of NK and NK T cells in vivo. Under normal conditions, the homing of NK and NK T cells to the BM is Gαi- and CXCR4-dependent. The homing of NK and NK T cells to the BM is important for both BM transplantation and the GVL effect. Upon activation with IL-2, NK and NK T cells up-regulate the cell-surface expression of the receptor CXCR3 and down-regulate the expression of CXCR4. This may direct the cells to sites of inflammation, such as virally infected livers, where the chemokines CXCL9 and CXCL10 are highly expressed.