The aim of this study was to examine the effect of cytokines on different subsets of NK cells, while especially focusing on CD16− CD56dim cells and CD16− CD56bright cells. When human peripheral blood mononuclear cells (PBMC) were cultured with a combination of IL‐2, IL‐12 and IL‐15 for several days, a minor population of CD56bright NK cells expanded up to 15%, and also showed potent cytotoxicities against various cancer cells. Sorting experiments revealed that unconventional CD16− CD56+ NK cells (CD16− CD56dim NK cells and CD16− CD56bright NK cells, both of which are less than 1% in PBMC) much more vigorously proliferated after cytokine stimulation, whereas predominant CD16+ CD56dim NK cells proliferated poorly. In addition, many of the resting CD16− CD56bright NK cells developed into CD16+ CD56bright NK cells, and CD16− CD56dim NK cells developed into CD16− CD56bright NK cells and also further into CD16+ CD56bright NK cells by the cytokines. CSFE label experiments further substantiated the proliferation capacity of each subset and the developmental process of CD16+ CD56bright NK cells. Both CD16− CD56dim NK cells and CD16− CD56bright NK cells produced large amounts of IFN‐γ and Fas‐ligands. The CD16+ CD56bright NK cells showed strong cytotoxicities against not only MHC class I (−) but also MHC class I (+) tumours regardless of their expression of CD94/NKG2A presumably because they expressed NKG2D as well as natural cytotoxicity receptors. The proliferation of CD16+ CD56bright NK cells was also induced when PBMC were stimulated with penicillin‐treated Streptococcus pyogenes, thus suggesting their role in tumour immunity and bacterial infections.

We recently reported that the direct antitumor effectors in the liver induced by α-galactosylceramide (α-GalCer) are NK cells that are activated by the IFN-γ produced from NK1.1 Ag+ T cells (NKT cells) specifically stimulated with α-GalCer, whereas NKT cells cause hepatocyte injury through the Fas-Fas ligand pathway. In the present study, we investigated how mouse age affects the α-GalCer-induced effect using young (6-wk-old), middle-aged (30-wk-old), and old (75-wk-old) mice. The serum IFN-γ and IL-4 concentrations as well as alanine aminotransferase levels after the α-GalCer injection increased in an age-dependent manner. An α-GalCer injection also induced an age-dependent increase in the Fas ligand expression on liver NKT cells. Under the stimulus of α-GalCer in vitro, the liver mononuclear cells from old and middle-aged mice showed vigorous proliferation, remarkable antitumor cytotoxicity, and enhanced production of both IFN-γ and IL-4 in comparison to those of young mice, all of which were mediated mainly by NK1.1+ cells. Furthermore, liver mononuclear cells from old mice stimulated with α-GalCer showed a more potent Fas-Fas ligand-mediated cytotoxicity against primary cultured hepatocytes than did those from young mice. Most α-GalCer-injected old mice, but no young mice, died, while anti-IFN-γ Ab pretreatment completely inhibited mouse mortality. However, α-GalCer-induced hepatic injury did not improve at all by anti-IFN-γ Ab treatment, and the Fas-ligand expression of liver NKT cells did not change. Taken together, the synthetic ligand-mediated function of NKT cells is age-dependently up-regulated, and the produced IFN-γ is responsible for α-GalCer-induced antitumor immunity and the mouse mortality, while hepatic injury was unexpectedly found to be independent of IFN-γ.

Background: The role of telomerase activation in the expression and/or maintenance of drug resistance is not clearly understood. Therefore, we investigated the relationships, among the telomerase activity, telomere length and the expression of multidrug resistance genes in colorectal cancer cell lines cultivated with anti-cancer drugs.

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