FIG 5.

Increased stalk-specific antibodies in B-H1-primed mice pre- and post-H5N1 challenge. Mice were primed with B-H1, B-H3, or B/Yamagata/16/88 (wild-type [WT]) virus or treated with PBS (n = 60/group). At 90, 180, 270, or 360 days postpriming, sera from all the mice were collected. Mice were challenged with 10¹, 10², 10³, 10⁴, or 10⁵ PFU/mouse of H5N1 A/Vietnam/1203/04 virus (n = 3 mice per dose). At 21 days postchallenge, sera were collected from the mice that survived the infection. Specific IgG against the chimeric HA cH6/1, was measured in pre- and postchallenge sera. Prechallenge stalk-reactive IgG levels are shown as an average of all the primed mice from a single group at a specific time point (light brown bars). Postchallenge stalk-reactive IgG levels are shown as an average of the primed mice from a single group at a specific time point and receiving the indicated dose of H5N1 virus (dark brown bars). Antibody levels are expressed as area under the curve (AUC). The mean plus SEM is plotted for each group.