Virus isolaAntigenic stability of viruses propagated in different cell lines
After three passages in each of the three MDCK cell lines, antigenic characteristics of the viruses were determined by HI test. HI titers of tested viruses were compared with those obtained with the reference virus, and the number of viruses with significant reduction of HI titers relative to homologous titers of the reference viruses are shown in Table 3. HI titers obtained from the different viruses with a given antiserum were within ≤4-fold of the titer its homologous antigen, indicating that a majority of viruses propagated in any of the three cell lines were antigenically similar to the reference viruses. However, ≥4-fold differences in HI titers were observed among several viruses isolated from MDCK cell lines. Interestingly, most of the ≥4-fold HI titer differences were observed among the H3N2 viruses followed by H1N1 viruses. The majority of influenza B viruses isolated from the three MDCK cell lines showed HI titer differences