Interferon inducing activity of a 2'-modified doublestranded complex, poly(2'-azido-2'-deoxyinosinic acid) poly(cytidylic acid).

Although the presence of free 2'-hydroxyl groups in both strands of a double-stranded RNA complex has been recognized as one of the major requisites for the interferon inducing activity of double-stranded RNAs, we have found a particular analog of (I)n·(C)n, in which the 2'-hydroxyls of the purine strand were replaced by azido groups [(dIz)n·(C)n], to be exquisitely effective in inducing interferon. Various other 2'-azido analogs, i.e. (dIz)n·(brC)n, (I)n·(dCz)n, (dAz)n·(U)n, (dAz)n·(rT)n and (dAz)n·(dUz)n were inactive as inducers of interferon. Thus we come to the conclusion that the interferon inducing system recognizes total threedimensional conformation of the double-stranded RNA.