Figure 2.

pH1N1 antibody responses in previously naive ferrets are dominated against Sa antigenic site of HA. (A) HAI assays were completed using viruses possessing either wild-type A/California/07/2009 HA or A/California/07/2009 HA with G158E or K133N mutations. HAI assays were performed with sera isolated from ferrets 14 d after infection with the A/California/07/2009 pH1N1 strain. Fold change for each mutant virus (WT HAI titer/mutant HAI titer) is shown here. Each triangle represents an individual sera sample, and the mean is indicated with a line. HAI titers using the G158E mutant virus are lower compared with HAI titers using the WT virus, as determined using a paired Student’s t test on log₂ transformed data (*, P = 0.016). Data are representative of three independent experiments. (B) Direct flow cytometry-based antibody (Ab) binding assays were completed using pooled anti-sera. pH1N1-infected MDCK cells were incubated with ferret anti-sera, and antibody binding was determined after addition of a FITC anti-ferret antibody. Data are representative of three independent experiments.