Table 3.

Role of the cell culture-selected Q136K substitution in NA-mediated binding of recombinant A(H3N2) viruses.

Source of NA	NA amino acid at residue				Infectivity (log10 IU/ml)	Hemagglutination titer (HAU/50 μl)				NA-mediated binding
						Turkey RBCsa		Guinea pig RBCs
	136	148	150	439		− Oseb	+ Ose	− Ose	+ Ose
A/Victoria/361/2011	Q	T	R	R	8.1 ± 0.3	128	<2	512	2	Yes
	Q	T	R	T	8.2 ± 0.1	<2	<2	<2	<2	No
	K	T	R	T	7.7 ± 0.1	64	<2	256	<2	Yes
A/Texas/50/2012	Q	T	H	T	7.6 ± 0.3	<2	<2	<2	<2	No
	Q	T	H	R	8.0 ± 0.3	128	<2	512	2	Yes
	K	T	H	T	6.7 ± 0.1	32	<2	128	2	Yes
A/Switzerland/9715293/2013	Q	T	R	T	7.8 ± 0.3	<2	<2	<2	<2	No
	Q	T	H	R	7.9 ± 0.3	128	<2	512	2	Yes
	K	T	R	T	6.6 ± 0.3	32	<2	128	2	Yes

Recombinant PR8-based A(H3N2) viruses containing the NAs of the designated viruses were generated. Amino acid sequence at indicated positions were substituted (boldface) by site-directed mutagenesis.

^aRBCs, red blood cells.

^bOseltamivir, 20 nM.