FIG. 7.
Cytokine-secreting splenocytes following challenge infection. IFN-γ (A), IL-2 (B), IL-4 (C), and IL-5 (D) ELISPOT assays. Splenocytes were isolated from immunized mice 4.5 weeks after the final immunization and on day 4 postchallenge, and cytokine-secreting cells were determined by ELISPOT assays after stimulation with HA-specific MHC class I or II peptides. Naive + PR8 indicates naïve mice that received a PR8 challenge, and 10 μg VLP + PR8 indicates influenza VLP-immunized mice that received a PR8 challenge. The spots for cytokine-producing cells from the spleen were counted and expressed based on 1.5 × 106 cells per well. Each column represents the arithmetic mean from six mice per group at each time point. Statistical significance between the values for naïve and VLP-immunized mice (a, P < 0.01; b, P < 0.05) and the values before and after challenge of VLP-immunized mice (c, P < 0.05; d, P < 0.01) is indicated.