Table 1. Wild-type influenza viruses used in this study.
| Virus | Subtype | Abbreviated name | Residue at 226 |
| A/Duck/Hong Kong/149/77 | H9N2 | Dk/HK/149/77 | Gln |
| A/Quail/Hong Kong/A28945/88 | H9N2 | RGQa88a | Gln |
| A/Duck/Hong Kong/Y280/97 | H9N2 | Dk/HK/Y280/97 | Leu |
| A/Chicken/Hong Kong/SF3/99 | H9N2 | Ck/HK/SF3/99 | Leu |
| A/Guinea fowl/Hong Kong/WF10/99 | H9N2 | RGWF10a | Leu |
| A/Quail/Hong Kong/NT16/99 | H9N2 | Qa/HK/NT16/99 | Leu |
| A/Hong Kong/1073/1999 | H9N2 | Hu/HK/1073/99 | Leu |
| A/Chicken/Jordan/554/03 | H9N2 | Ck/Jordan/554/03 | Gln |
| A/Mallard/Potsdam/178-4/83 | H2N2 | Mal/Potsdam/83 | Gln |
| A/Memphis/14/98 | H3N2 | RGMemphis98a | Leu |
a
RGWF10, RGQa88 and RGMemphis98 are WT viruses generated by reverse genetics.