HA protein-specific IFN-γ (A) and IL-4 (B) ELISPOT. Splenocytes harvested from mice 3, 5 or 7 days after vaccination were stimulated with HA protein for 18 h and scored in ELISPOT assays for IFN-γ and IL-4 producing cells. The values represent the averages of triplicate wells of 4 mice, and are expressed as means ± SD. The results were expressed as the number of SFC per 106 input cells. * Significant difference (p < 0.05).