[Studies of the adaptation of influenza viruses to lowered temperatures of replication. II. Studies in vivo].

Swiss white mice were given intranasally suspension of influenza A virus (H3N2) isolated at different period of time and replicated in lowered temperatures in 11 days old chicken embryos. The presence of antigen in lung of animals was detected by IF. They were given the virus replicated at 30 degrees C at different rate depending on strain tested. No distinct differences were observed in haemagglutination inhibition antibody level. On the other hand the level of neuraminidase activity inhibiting antibodies level was significantly higher after giving virus replicated at 30 degrees C than after giving the virus replicated at 37 degrees C. In the case of epidemic strains 4-5 fold fold increase of immunogenicity of neuraminidase component was observed and in the remaining strains immunogenicity of neuraminidase increased 1-5-fold only.