Anti-vaccinia virus effect of M13 bacteriophage DNA

Single-stranded DNA derived from M13 phage was evaluated for antiviral activity in mice infected with vaccinia virus. M13 DNA at a dose as low as 16.7 mg/kg was effective in reducing the number of tail lesions caused by vaccinia virus by more than 90%. A single administration of M13 DNA 1 day before infection was sufficient to reduce significantly the number of tail lesions caused by vaccinia virus. Denatured eukaryotic nucleic acids such as calf thymus DNA and human placenta DNA were not effective. A mixture of nucleotides prepared according to the nucleotides composition of M13 DNA was also ineffective. Within 4 h after the administration of M13 DNA, the serum interferon (IFN, predominantly type beta) titer rose from undetectable levels to as much as approximately 700 IU/ml. IFN was detectable for up to 12 h after the administration of M13 DNA. IFN titers as high as 1050 IU/ml were detected in vitro when M13 DNA was added to spleen cultures. We conclude that at least part of the antiviral activity of M13 DNA can be explained on the basis of IFN induction.