The Role of α-Galactosylceramide-Activated Vα14 Natural Killer T Cells in the Regulation of Th2 Cell Differentiation

Vα14 natural killer T (NKT) cells produce large amounts of both IL-4 and IFN-γ upon stimulation with a ligand, α-galactosylceramide (α-GalCer), and play a crucial role in various immune responses, including allergic diseases. Interestingly, Vα14 NKT cells are not essential for the induction of IgE responses but rather induce suppression of specific IgE production upon activation. The suppression in the IgE production is not detected either in Vα14 NKT cell-deficient mice or in IFN-γ-deficient mice. Thus, activated Vα14 NKT cells are likely to exert a potent suppressive activity on Th2 cell differentiation and subsequent IgE production by producing a large amount of IFN-γ. In marked contrast, little regulatory effect of IL-4 produced by Vα14 NKT cells on Th2 cell differentiation is suggested.