FIG. 4.

Secondary CD8⁺ T-cell immune response. Recall responses were determined in single-cell populations obtained from mediastinal lymph nodes draining the respiratory tracts of 8-week-old mice challenged with Sing-WT virus 4 weeks after primary immunization with the indicated viruses. Single-cell populations were assessed for influenza virus-specific IFN-γ-secreting CD8⁺ T cells in an ELISPOT assay. The mean numbers of antigen-specific IFN-γ-secreting cells ± the standard errors of the means for triplicate cultures are shown. The differences between the ca Sing and ca Sing-IL-2 responses are significant (P < 0.01).