EPITOPE SELECTION IN MAJOR HISTOCOMPATIBILITY COMPLEX CLASS I-MEDIATED PATHWAY IS AFFECTED BY THE INTRACELLULAR-LOCALIZATION OF AN ANTIGEN

We analyzed the mode of antigen presentation of an endogenous antigen localized in the cytoplasm or in the mitochondria. Pseudomonas aerugin osa PAO leucine-, isoleucine-, valine-binding protein (LIVAT-BP) encod ed by the braC gene was used as a model antigen. Using mouse BALB/3T3 cells, we established two LIVAT-BP transfectants by transfection of a plasmid harboring the intact braC or braC gene fused with the mitochon drial transport signal derived from the yeast COXIV gene. One of the r esulting transfectants, BC-15, expressed LIVAT-BP in the cytoplasm, wh ile YZ-710 cells expressed LIVAT-BP in the mitochondria. The splenic e ffector cells derived from BALB/c mice primed with BC-15 cells exhibit ed cytotoxic T lymphocyte (CTL) activity against BC-15 cells, but not against YZ-710 cells, whereas splenic effector cells primed with YZ-71 0 cells exhibited CTL activity against YZ-710 cells, but not against B C-15 cells. Neither group of splenic effector cells showed CTL activit y against parental BALB/3T3 cells. These CTL belonged to the CD8(+) al pha beta T cell subset. Furthermore, we observed that the CTL activity against BC-15 cells or YZ-710 cells was blocked with anti-H2-K-d mAb, but not with anti-H2-D-d or H2-L(d) mAb. The CTL against BC-15 or YZ- 710 cells could kill parental BALB/3T3 cells in the presence of peptid es produced by alkali lysis of the LIVAT-BP, suggesting that these CTL indeed recognized the peptide(s) derived from LIVAT-BP. We determined that the epitope for the CTL against BC-15 cells was QYGEGIATEV, corr esponding to residues 162-171, and that the epitope recognized by the CTL against YZ-710 cells was GYKLIFRTI, corresponding to residues 123- 131 of LIVAT-BP, respectively. Thus, we show here that epitope selecti on for MHC class I expression is affected by the intracellular localiz ation of the antigenic protein.