Experimental investigation of changes in the antigenic structure of influenza viruses during their persistence.

Systems of persistent influenza infection produced in the cultures of human embryonal kidneys and in the diploid cells of human embryonal lungs under the effect of A/Hong-Kong/1/68 and A/Victoria/35/72 viruses were characterized. The cell systems were studied in the course of 4--3u passages, i. e., from 40 to 289 days. A total of 102 viruses were isolated during the period of observation, out of which 44 were examined for the antigenic profile of HA and NA. The antigenic structure of the initial viruses was preserved in 31 variations isolated while in 13 variants it was pronouncedly and permanently changed. The following mechanisms of the mentioned phenomenon are discussed: mutations, intrapopulation recombinations and integrations.