Assessment of neutralizing antibody and HI antibody titers in HA1-Fc- and HA1-Fdc-vaccinated mouse sera.

<p>Sera were collected at 10 days post-last vaccination. PBS was used as the negative control. (A) Neutralizing antibody titers against HA of heterologous (HK-HA, 1194-HA, QH-HA and XJ-HA) and homologous (AH-HA) strains of H5N1 pseudovirus. The data are presented as mean 50% neutralizing antibody titer (NT₅₀) ±SD from five mice per group. * indicates significant difference (<i>P</i><0.05) between HA1-Fc and HA1-Fdc vaccination groups. (B) Neutralizing antibody titers against heterologous strains (HK/156, VN/1194 and SZ/406H) of H5N1 live virus. The titers of neutralizing antibodies were determined as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0016555#s4" target="_blank">Materials and Methods</a>, and are presented as mean NT₅₀±SD of five mice per group. (C) HI antibody titers against heterologous strains (HK/156, VN/1194 and SZ/406H) of H5N1 live virus. The HI titers were determined as the highest serum dilution indicating hemagglutinating activity, and are expressed as mean ± SD of five mice per group.