INDUCTION OF NK ACTIVITY IN MURINE AND HUMAN-CELLS BY CPG MOTIFS IN OLIGODEOXYNUCLEOTIDES AND BACTERIAL-DNA

We have recently shown that oligodeoxynucleotides (ODN) containing unm ethylated CpG dinucleotides (CpG motif) can induce B cells to prolifer ate, differentiate, and secrete cytokines. In this study we demonstrat e that CpG motifs contained in ODN as short as 15 bases in length were quite effective at inducing NK cell lytic activity in vitro in both h uman and murine lymphocytes. Such ODN were also effective at inducing NK lytic activity, in vivo, in mice. Experiments designed to determine the cellular and cytokine requirements for NK cell induction revealed that B and T cells are not necessary, that the ODN do not augment the activity of highly purified NK cells, and that the ODN augment NK cel l activity indirectly by inducing the secretion of IL-12, IFN-alpha be ta, and TNF-alpha. Various ODN sequences were prepared to determine th e optimal ODN length, motif, palindrome, backbone modification, and do se requirements. We found no requirement for a palindromic sequence bu t a definite requirement for an unmethylated CpG motif. While necessar y, however, a CpG motif was not sufficient for NK cell induction. Inst ead, there appeared to be stringent requirements for the immediate fla nking bases at the 5' and 3' ends as well as for flanking sequences ou tside the immediate 5' and 3' bases. In particular poly(G) ends seemed to exert a complex qualitative and quantitative effect which could be up- or down-modulating depending on whether the ODN backbone was phos phorothioate modified or not.