[Role of individual genes in expression of phenotypic properties of the cold-adapted strain A/Leningrad/134/47/57 (H2N2)-a donor of attenuation of live influenza vaccine].

The influenza A/Leningrad/134/47/57 (H2N2) (A/Len/47) cold-adapted virus expresses the ability to reproduce at 25 degrees C (the ca phenotype) and inability to reproduce at 40 degrees C (the ts phenotype). It was attenuated for mice. Reassortants of this donor virus with the genes coding for the surface glycoproteins from the epidemic viruses, i.e. hemagglutinin (HA) and neuraminidase (NA), have been shown to be attenuated, immunogenic and genetically stable. We made attempts to reveal the influence of individual genes from the A/Len/47 ca virus on the expression of some phenotypic properties. Different "single-gene" reassortants were created and investigated using the influenza A/PR/8/34 (H1N1) virus as another parent with the opposite phenotypic properties, i.e. lack of ca+ and ts+ phenotypes and high virulence for mice. We managed to obtain "single-gene" reassortants with PB1, NA and NS genes at this stage of the work. None of them (probably including the M gene as well) could determine the ca or ts phenotypes, nor could the presence of the NA and NS genes from the strain A/Len/47 influence these properties. However, our findings show that the combined influence (synergism) of the PB1 and NS genes from the ca donors results in the ts phenotype of the reassortants. Significant role of the NS gene for attenuation of influenza viruses in mice has been revealed.