Activation of natural killer T cells by NK-4, a criptocyanine dye]

We previously reported that oral administration of NK-4, a criptocyanine dye, enhances interleukin (IL)-12-dependent interferon (IFN)-gamma production by lipopolysaccharide (LPS)-stimulated mouse splenocytes. These findings raised a possibility that NK-4 potentiated IFN-gamma production by T cells, natural killer (NK) cells or natural killer T (NKT) cells in response to IL-12 produced by macrophage and dendritic cells. To explore this possibility, we first analyzed percentages of T, NK or NKT cells in splenocytes of mice that were administered NK-4 orally for three days. The percentage of NKT cells in splenocytes from NK-4-treated mice was significantly (p<0.05) increased compared to vehicle-treated mice. When splenocytes were stimulated with a-galactosylceramide (alpha-GalCer), an NKT cell ligand, IFN-gamma production by splenocytes from NK-4-treated mice tended to increase, while no difference in the IL-4 production and proliferation were observed between the vehicle- and NK-4-treated mice. When IFN-gamma/IL-4 ratios were calculated in individual mice, the ratios were significantly (p<0.05) elevated in NK-4-treated mice. Furthermore, IL-12 production by alpha-GalCer-stimulated splenocytes from NK-4-treated mice was also significantly (p<0.05) increased. These results suggest that oral administration of NK-4 increases the population of type I NKT cells with potent IFN-gamma-producing activities. Since IL-12 and IFN-gamma have been shown to play important roles in anti-tumor immunity as well as in the defence against bacterial infection, our results further imply that NK-4 may provide a potential therapeutic tool in cancer immunotherapy.