TABLE 1.

Receptor specificities of H1N1 influenza A viruses^a

Virus	Hemagglutination titer by use of erythrocytes containing:b
	Native linkage	NeuAcα2,3Gal	NeuAcα2,6Gal
Human
A/USSR/77	512	0	512
A/Lackland/78	128	0	64
A/Brazil/78	256	0	16
A/Baylor/3724/81	64	0	64
A/Chile/83	128	0	64
A/Taiwan/1/86	64	0	64
A/Singapore/6/86	256	0	128
Duck
A/duck/Alberta/35/76	1,024	2,048	0
A/duck/Bavaria/1/77	32	32	0
A/mallard/Alberta/740/80	128	128	128
A/mallard/Tennessee/11464/85	16	16	0
Swine
Classic
A/swine/Iowa/15/30	16	0	8
A/swine/Wisconsin/1/61	128	0	64
A/swine/Hokkaido/2/81	64	0	32
Avian-like
A/swine/Belgium/1/79	128	128	128
A/swine/Finland/55/80	256	128	128
A/swine/Netherlands/3/80	256	64	32
A/swine/Belgium/1/83	1,024	512	512
A/swine/Italy-Vir/383/84	8	4	8
A/swine/Italy-Vir/492/85	32	0	64
A/swine/Italy-Vir/547/85	64	0	64
A/swine/Netherlands/12/85	32	0	2
A/swine/Italy-Vir/671/87	16	0	8

^aErythrocyte preparations included unmodified cells (native linkage) and sialidase-treated cells which were enzymatically resialylated, as described earlier (32, 33), so that they contained the terminal NeuAcα2,3Gal or the NeuAcα2,6Gal linkage on cell surface oligosaccharides. Native (unmodified) and asialo (sialidase-treated) cells were used as controls. Although the amounts of incorporated sialic acid varied among the erythrocyte preparations used, they remained within the previously reported ranges: NeuAcα2,3Gal, 98 to 164 nmol/ml; NeuAcα2,6Gal, 20 to 50 nmol/ml (10, 32, 33). 

^bHemagglutination titers are expressed as the reciprocal of the maximal dilution required to give complete agglutination (0 = ≤2). All virus samples presented hemagglutination titers of ≤2 when asialo cells were used (data not shown).