Immunization and sample collection scheme.

<p>Four groups of mice, each consisted of 28, were immunized with either PBS, recombinant HA alone, HA plus C48/80 (10 µg) or CT (0.1 µg). Twenty mice were used for challenge with lethal dose of A/California/04/2009 live virus on 21 days after initial immunization and monitored for diseases (n = 10) and viral and pathological investigation in lung tissues (n = 10). The remaining eight were used for either cytokine production from stimulated spleenocytes (n = 3) or long-term antibody response (n = 5).