Natural killer T cells from interleukin‐4‐deficient mice are defective in early interferon‐γ production in response to α‐galactosylceramide

Discovery of the natural killer (NK) T cell‐specific ligand, α‐galactosylceramide (α‐GalCer) has enabled us to investigate the functional regulation of NKT cells. However, the detailed mechanism of cytokine production by NKT cells remains to be elucidated. Here we evaluated the role of interleukin (IL)‐4 in the production of interferon (IFN)‐γ from NKT cells using IL‐4‐deficient C57BL/6 mice (IL‐4 −/– mice). Administration of α‐GalCer into wild‐type C57BL/6 mice caused the production of both IFN‐γ and IL‐4 in serum or cytoplasm within 4 h of the injection. Unexpectedly, however, IL‐4 −/– mice‐derived NKT cells did not produce any IFN‐γ at early phase after primary stimulation with α‐GalCer. Because NKT cells from IL‐4 −/– mice produced IFN‐γ when they were stimulated secondarily with α‐GalCer in vitro for 72 h, NKT cells from IL‐4 −/– mice were not completely genetically deficient for IFN‐γ production. To elucidate which cells, NKT cells or dendritic cells (DC), were responsible for the deficiency in IFN‐γ production in IL‐4 −/– mice, we carried out an add‐back experiment using purified NKT cells and DC, which were prepared from either wild‐type mice or IL‐4 −/– mice. NKT cells from wild‐type mice produced IFN‐γ when they were cocultured with DC prepared from either wild‐type or IL‐4 −/– mice, whereas NKT cells from IL‐4 −/– mice did not produce IFN‐γ by coculturing with DC from either wild‐type or IL‐4 −/– mice. These results indicate that NKT cells, not DC, were responsible for the deficiency in IFN‐γ production in IL‐4 −/– mice. Thus, IL‐4 is required for the activation of NKT cells to produce IFN‐γ in response to α‐GalCer. ( Cancer Sci 2007; 98: 721–725)