Characterization of the reproduction of influenza A epidemic viruses in cell cultures.

Two influenza A epidemic viruses with different indices of virulence for humans have been compared with respect to their reproduction in human embryo kidney (HEK), human embryo lung (HEL), and chick embryo kidney (CEK) cell cultures. It has been shown that the highly virulent for humans A/Victoria/35/72 (H3N2) strain reproduced intensively in HEK and HEL cells irrespective of the inoculated dose (multiplicity of infection = 1 EID50 per cell and of 0.001 EID50 per cell, respectively). Efficient infection of a moderately virulent virus A/Bangkok/1/79 (H3N2) was registered in these cell cultures only after addition of trypsin to the maintenance medium. The viruses tested exhibited essentially no difference as to the intensity of their reproduction in CEK cell culture whose sensitivity remained unchanged after addition of trypsin to the maintenance medium.