Figure 5.

The M2 protein contains an epitope recognized by CD8⁺ T cells. (A) Each 15-aa peptide from a panel of overlapping peptides encompassing the entire M2 protein was incubated with pooled splenocytes harvested from two BALB/c mice 18 days p.i. The percentage of CD8⁺ T cells producing IFN-γ in response to each peptide was measured by flow cytometry. Data are representative of two independent experiments. Phorbol 12-myristate 13-acetate plus ionomycin stimulation resulted in production of IFN-γ by 47% of CD8⁺ T cells (not shown). (B) IFN-γ production by splenocytes from a BALB/c mouse (representative of three mice tested) at 18 days p.i. in response to the 9-mer peptide GFNKLRSTL (M2_91–99) that is present within peptides 18–20 in A; staining with an isotype-matched control antibody is also shown (Right). Splenocytes from uninfected mice did not respond to M2_91–99 (not shown). (C) A CD8⁺ CTL line kills S11 cells (●) and BALB/c 3T3 cells pulsed with M2_91–99 (■), but not unpulsed 3T3 cells (□). Results are from a standard 5-hr ⁵¹Cr-release assay (32) at various effector to target (E:T) ratios and are representative of six independent experiments.