MPO T-cell epitopes in C57BL/6 mice. (A) Overlapping peptides (89 20-mers) spanning the entire mouse MPO sequence were used to immunize groups of mice. Pro, proregion peptides (1–17); Light, light chain peptides (18–31). H1 (32–46), H2 (47–61), H3 (62–76), and H4 (77–89) are heavy chain peptides. Splenocytes were restimulated ex vivo with each third of the immunizing pool (x axis), and responses were measured by IFN-γ ELISPOT assay (mean number of spots minus baseline). Each dot represents the mean response from an individual mouse, and results are representative of two independent experiments with a minimum of four mice per group. (B) Groups of mice were immunized with one of the five strongest responding pools of peptides (peptides 7–12, 23–27, 52–56, 57–61, or 62–66) and draining LN cells were restimulated ex vivo with individual peptides (x axis). Each dot represents the mean response from an individual mouse, and results are representative of two independent experiments with a minimum of four mice per group.