aAPC/MP1 can naturally process and present MP1 peptide via A2 on the cell surface in a proteasome-dependent way. (A-B) MP1^58-66-specific IFN-γ ELISPOT analysis. (A) MP1^58-66-specific CD8⁺ T cells were stimulated with aAPC/EGFP, aAPC/MP1, or without any APCs in the presence or absence of indicated peptides. (B) APCs were pretreated with lactacystin and acid to inhibit the processing and presentation of endogenous peptides. Then, IFN-γ ELISPOT was performed in the presence or absence of lactacystin. The results are expressed as mean ± SD.