HEXAMER PALINDROMIC OLIGONUCLEOTIDES WITH 5'-CG-3' MOTIF(S) INDUCE PRODUCTION OF INTERFERON

We have shown previously that 30-mer oligonucleotides containing hexam er palindromic sequences with 5'-CG-3' motif(s) induce interferon (IFN ), activate natural killer (NK) cells, and thus exhibit tumor-regressi ng activity, The present study showed that a hexamer palindromic oligo nucleotide (5'-AACGTT-3') alone induced IFN from mouse spleen cells wh en added with cationic liposomes, Accordingly, 32 kinds of hexamer pal indromic oligonucleotides were tested for their ability to induce IFN in the presence of cationic liposomes, The results show that oligonucl eotides with NACGTN and NTCGAN sequences exhibited the strongest activ ity, ACGCGT and TCGCGA also possessed moderate but significant activit y, In contrast, palindromes without CG motif(s) were devoid of the act ivity, No hexamer oligonucleotides showed the activity when liposomes were absent, A complete palindromic sequence was essential as any sing le base substitution resulted in diminished activity, Among variety of palindromic oligonucleotides of different sizes with an ACGT sequence at the center, the tetramer oligonucleotide was without activity, whe reas the activity of hexamer and longer oligonucleotides was almost eq ually high, These results strongly suggest that the minimal essential structure required for IFN induction is the hexamer palindromic sequen ce with CG motif(s).