ABILITY OF OLIGONUCLEOTIDES WITH CERTAIN PALINDROMES TO INDUCE INTERFERON-PRODUCTION AND AUGMENT NATURAL-KILLER-CELL ACTIVITY IS ASSOCIATEDWITH THEIR BASE LENGTH

A synthetic 30-mer single-stranded oligodeoxyribonucleotide with a hex amer palindrome, AACGTT, induced IFN production and augmented NK activ ity in murine splenocytes. This effect does not appear to result from an antisense mechanism but rather is due to the palindrome. To clarify the required minimal size of the nucleotide, 10 kinds of 12- to 30-me r nucleotides were examined. Immunostimulatory activity of oligonucleo tides 18 bases or more in length was observed and was proportional to the base length, with a maximum at 22-30 bases. On the other hand, the oligonucleotides 16 bases or less in length were not active even if t hey possessed the palindromic sequence. These results indicate that th e immunostimulatory activity of oligonucleotides with certain palindro mic sequences requires an oligonucleotide at least 18 bases long.