Table 2.

Strains of influenza A viruses used in this study and their properties

Short name	Influenza A viral strain	Initial titer (pfu/mL)*	Culture conditions; suspension conditions	Notes
WSN	WSN/33 (H1N1)	4.5( ± 0.6) × 106	Tissue; DME-HEPES/10% FBS	Laboratory strain, nonpathogenic
PR8H	PR/8/34 (H1N1)	1.3( ± 0.5) × 108	Egg; HEPES/saline	Human pathogenic; sucrose-gradient purified
PR8L†	PR/8/34 (H1N1)	0.9( ± 0.2) × 106	Egg; HEPES/PBS/saline	Human pathogenic; sucrose-gradient purified
TurkWt	turkey/MN/833/80 (H4N2)	1.0( ± 0.1) × 106	Egg; allantoic fluid	Avian pathogenic
TurkMu	turkey/MN/833/80 (H4N2)	4.3( ± 0.3) × 106	Egg; allantoic fluid	Avian pathogenic; zanamivir-resistant

^*Determined via plaque assay after ribonuclease pretreatment; the titer is that of a 10-μL droplet incubated with slides prior to a 100-fold dilution upon washing. See Materials and Methods for details.

^†An approximately 100-fold dilution of PR8H with PBS