Single-stranded
polynucleotide preparations, which neither induce detectable
interferon nor affect immune responses, suppress development of
antiviral antibodies in mice infected with an avirulent strain of SFV. On a weight basis the
antiviral activity of a mixture of
poly(I) and poly(ho5C)-copolymer is greater than that of
tRNA and similar
antiviral effects are observed against a related virulent strain of SFV. EMC virus causes and avirulent
infection of rats and development of EMC virus
antibodies (routinely determined by assaying the protective effect of rat serum against EMC
virus infection of mice) is suppressed when the rats are treated with
tRNA or the mixture of
poly(I) and poly(ho5C)-copolymer. This suppression of
antibodies to EMC virus appears to reflect reduction of virus replication. Treatments of 6 mg/rat i.p. or i.v. 6 hours before
infection confer essentially the same
antiviral effect as 3 times these
polynucleotide doses administered during 3 days immediately post
infection. These results with avirulent
infections indicate that the previously reported
antiviral effects of the single-stranded
polynucleotides are not simply due to modifications of the tissue pathology which leads to death in the case of virulent
virus infections.