FIG 4.

Increased H5-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 virus (wild type [WT]) 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 (PR8 reassortant) virus (n = 3 mice per dose). At 21 days postchallenge, sera were collected from the mice that survived the infection. IgG against recombinant H5 from A/Vietnam/1203/04 was measured in pre- and postchallenge sera. Prechallenge H5-reactive IgG levels are shown as an average of all the primed mice from a single group at a specific time point (light blue bars). Postchallenge H5-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 blue bars). Antibody levels are expressed as area under the curve (AUC). The mean plus SEM is plotted for each group.