Mutations at positions 186 and 194 in the HA gene of the 2009 H1N1 pandemic influenza virus improve replication in cell culture and eggs

Table 1 Effect of variations at residues 186 and 194 of A/CA/04/2009 HAs on reactivity with post-infection ferret sera

HAI titer with selected ferret sera¹
Virus designation	RG15	A/CA/04	A/CA/07	Normal
vF8	320, 640²	1280, 2560	1280, 2560	<40, <40
vF9	160, 320	640, 1280	640, 1280	<40, <40
vF10	320, 320	5120, 2560	5120, 2560	<40, <40
A/CA/04/2009	160, 160	640, 640	640, 640	<40, <40
A/PR/8/34	<40, <40	<40, <40	<40, <40	<40, <40

¹ H1N1 immune ferret sera were obtained from CDC. Ferrets were infected with RG15 (IDCDC RG15, a reverse genetics virus containing the A/TX/05/2009 HA [A/TX/05/2009 × A/PR/8/34], A/CA/04 (A/CA/04/2009, Lot # 2009-082, CDC#2009712049), or A/CA/07 (A/CA/07/2009, Lot #2009-089, CDC#2009712112). Normal (un-infected ferret) sera was obtained from Alpha Diagnostics Intl., Inc.
² Data shown are from two experiments in which all four sera were checked in parallel with all five antigens.
HAI tests were performed by standard methods using guinea pig red blood cells, receptor-destroying enzyme-treated serum, and 4 HA units of antigen [25].

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