Growth Characteristics and Cytopathogenic Effects of Influenza A and B in Cultures of Human Embryo Tissues

Abstract

Recently isolated strains of influenza A and B have been propagated by serial passages in cultures of human embryo lung and kidney. Titers of infectious or hemagglutinating virus of either type were equivalent in kidney cultures. Comparable titers were found in lung cultures inoculated with influenza B, but were much lower in those infected with influenza A. Influenza A strains propagated in cultures of human tissues agglutinated human type O erythrocytes at a higher titer than fowl erythrocytes at 4°C and did not agglutinate the latter cells at 24°C unless passaged in the chick embryo. Influenza B strains propagated in either system agglutinated both kinds of erythrocytes similarly. The antigenic composition of influenza A or B as determined by hemagglutination-inhibition was not significantly altered by passages in human tissue culture or in the chick embryo. Incremental rates of tissue culture lines of influenza viruses were greater in kidney cultures than in the amniotic sac, and in both the influenza A strain was the faster. Growth of influenza B was similar in cultures of lung or kidney. More tissue culture propagated virus was required to infect the allantoic sac than the amniotic sac and hemagglutinating titers were lower in the former. For determinations of titers of infectivity, periods of growth were required which varied according to the virus and the system utilized; i.e., influenza A propagated in kidney cultures 2 days in the latter and 3 days in the amniotic sac, and its chick embryo adapted counterpart 2 days in that host; influenza B propagated in lung cultures 4 days in the latter as well as in the amniotic sac, and the chick embryo line 3 days in that host. The results of infectivity titrations of the tissue culture line of influenza A were higher in kidney cultures than in the amniotic sac, while the reverse was found with the influenza B virus propagated in lung cultures and titrated in the latter system and in the amniotic sac. Five passages with influenza A and nine passages with influenza B in the chick embryo did not significantly alter the characteristics of either in human tissue culture. Titers of PR₈ and Lee, however, were lower than those of the latter virus in human lung cultures. Cytopathogenic effects accompanied multiplication of influenza A and B viruses in human embryo kidney cultures and influenza B in lung cultures.