FIG. 6.

Mucosal antibody responses following challenge infection. (A) IgG in nasal washes, (B) IgG in trachea, (C) IgG in lung extracts, and (D) IgA in lung extracts. Nasal, trachea, and lung samples were collected 4.5 weeks after the final immunization and on day 4 after challenge infections. ELISAs were used to determine respiratory IgG and IgA antibody levels. Optical density at 450 nm (OD 450) values were obtained from 10-fold-diluted mucosal samples, and results are represented as the arithmetic means plus standard deviations (error bars). Each bar represents the arithmetic mean from six mice per group at each time point. Naïve denotes unimmunized mice, and the other groups are as described in the legend to Fig. 2. M1 VLP represent mice immunized with 40 μg M1 VLPs. PR8 and WSN denote a challenge infection with PR8 and WSN, respectively. None denotes the group of mice without a virus challenge infection. Statistical significance (a, P < 0.01; b, P < 0.05; c, P < 0.05) between the values before and after challenge of VLP-immunized mice is indicated.