Role of?-Galactosylceramide- activated V?14 Natural Killer T Cells in the Regulation of Allergic Diseases

Vα14 natural killer T (NKT) cells produce large amounts of both IL-4 and IFN-γ upon stimulation with a ligend, α-galactosylceramide (α-GalCer), and play a crucial role in various immune responses, including allergic reac-tions. Interestingly, Vα14 NKT cells are not essential for the induction of specific IgE response but they instead tend to induce suppression of specific IgE upon α-GalCer activation in vivo. The suppression in the IgE produc-tion is not detected either in Vα14 NKT cell-deficient mice or in IFN-γ-deficient mice. Therefore, activated Vα14 NKT cells are able to exert a potent suppressive activity on Th2 cell differentiation and subsequent IgE produc-tion by producing a large amount of IFN-γ. In an OVA-induced asthma model, α-GalCer administration inhibited airway inflammation and airway hyperreactivity by IFN-γ from activated Vα14 NKT cells, thus suggesting the negative regulation of Th2-responses by the activated Vα14 NKT cells