(A, B) Cytokine production by peptide-specific CD4 T cells. DR1 and B10 mice were infected intranasally with PR8. Enriched CD4 T cells from the MedLN were analyzed on day 10 after infection. Frequencies of CD4 T cells secreting IL-2, IFN-γ, or IL-4 were determined by ELISpot assay after in vitro stimulation with antigen-presenting cells and individual 17-mer peptides. Peptide designations (x-axis) include the viral proteins of origin (NP, M1, and NS1). Results are normalized to spot counts per 106 CD4 T cells and are shown as the mean ± range for 2 independent experiments. Cells from at least three mice were pooled for each experiment. (C, D) Proportions of peptide-specific CD4 T cells secreting IL-2, IFN-γ, or IL-4. Results are compiled from the data shown in A and B. The mean ± range is shown for the two independent experiments.