Susceptibility of human SAEC-T clones to infection by different influenza virus strains. A, high (1A5) and low (21E5) susceptibility clones were infected with human influenza (Beijing (H1N1), Panama (H3N2)), H5N1 (Cw/Ky (H5N1), and Ck/Eg (H5N1)) and previously circulating AI viruses (Dk/Hk (H5N3), rDk/Hk-RRKKR-HA, Tk/Ont (H5N9), Dk/Hk (H2N2), Dk/Hk (H4N5), Dk/Hk (H6N2), Wg/Os (H7N7), Tk/Ont (H8N4), and Dk/Hk (H9N2)) at an m.o.i. of 10. Viral infectivity was determined by calculating the percentage of antigen-positive SAEC-T clones after immunostaining at 16 h post-infection. Data are expressed as the mean ± S.D. of more than three independent experiments. B, high susceptibility clone (1A5) and low susceptibility clone (21E5) were infected with recombinant H5N3 (rDk/Hk-Cw/Ky-HA, rDk/Hk-Ck/Eg-HA, rDk/Hk-ThailandHA, rDk/Hk-IndonesiaHA, or rDk/Hk-ShanghaiHA) viruses containing the HA gene from H5N1 (A/crow/Kyoto/53/04 (clade 2.5), A/chicken/Egypt/CL6/07 (clade 2.2.1), A/Thailand/Kan353/04 (clade 1), A/Indonesia/5/05 (clade 2.1.3), or A/Shanghai/1/06 (clade 2.3.4)) at an m.o.i. of 10. Viral infectivity was determined as described in A. Data are expressed as the mean ± S.D. of three independent experiments. C, high susceptibility clone (1A5) and the low susceptibility clone (21E5) were infected with recombinant Dk/Eg (H5N1) (clade 2.2.1), which shows very high amino acid homology (HA, NP, M1, M2, NS2: 100%; another gene: >99.46%) to the H5N1 human isolate A/Egypt/902786/2006 (H5N1) (clade 2.2.1) and with recombinant H5N3 (rDk/Hk-Dk/Eg-HA) viruses containing the HA gene from A/Egypt/902786/2006 (H5N1) at an m.o.i. of 10. Viral infectivity was determined as described in A. Data are expressed as the mean ± S.D. of three independent experiments. The amino acid homology of Ck/Eg (H5N1) (clade 2.2.1) to the human influenza virus A/Egypt/902786/2006 (H5N1) is as follows: M1, M2, and NS1, 100%; another gene, >99.46%.