Epitope selection in major histocompatibility complex class I‐mediated pathway is affected by the intracellular localization of an antigen

Abstract

We analyzed the mode of antigen presentation of an endogenous antigen localized in the cytoplasm or in the mitochondria. Pseudomonas aeruginosa PAO leucine-, isoleucine-, valine-binding protein (LIVAT-BP) encoded 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 mitochondrial transport signal derived from the yeast COXIV gene. One of the resulting transfectants, BC-15, expressed LIVAT-BP in the cytoplasm, while YZ-710 cells expressed LIVAT-BP in the mitochondria. The splenic effector cells derived from BALB/c mice primed with BC-15 cells exhibited cytotoxic T lymphocyte (CTL) activity against BC-15 cells, but not against YZ-710 cells, whereas splenic effector cells primed with YZ-710 cells exhibited CTL activity against YZ-710 cells, but not against BC-15 cells. Neither group of splenic effector cells showed CTL activity against parental BALB/3T3 cells. These CTL belonged to the CD8+ alphabeta T cell subset. Furthermore, we observed that the CTL activity against t 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 peptides 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, corresponding 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 selection for MHC class I expression is affected by the intracellular localization of the antigenic protein.

Proteasome-independent HLA-B27 Ligands Arise Mainly from Small Basic Proteins

“…Some but no dramatic differences in the cellular origin of the parental proteins were apparent. It was remarkable that a number of proteasomeindependent ligands arose from mitochondrial proteins of the respiratory chain, raising the interesting possibility of a putative mitochondrial processing of these ligands, in line with previous speculations (68) and with the finding that the same protein expressed in the cytosol or in the mitochondria produced different MHC class I-restricted peptide epitopes (69). In addition, proteasome-independent ligands derived from internal sequences of secreted proteins were not found.…”

Similar as well as distinct MHC class I-binding peptides are generated by exogenous and endogenous processing of hepatitis B virus surface antigen

“…Processing of antigen in mitochondria and in the cytosol has been shown to generate different repertoires of antigenic epitopes; this was demonstrated using cells that express a bacterial protein either in mitochondria or in the cytoplasm [26]. Furthermore, human CTL recognize epitopes of the EBV-derived nuclear antigen EBNA1 that are apparently processed only in the alternative pathway: human CD8 + CTL lines recognize EBNA1 epitopes in the context of HLA-B35.01 or HLA-A2.03 on cells when the nuclear antigen is supplied as an exogenous antigen but not when the targets express endogenous EBNA1 [27].…”

Enhanced Immunogenicity of Mitochondrial-Localized Proteins in Cancer Cells

“…In contrast, DNGR-1, which was previously shown to be involved in the cross-presentation of cellassociated antigens (37), appeared not to be involved in the crosspresentation of mitochondrial OVA. Previous papers have provided insights into the mechanisms by which mitochondrial-derived proteins may intersect the antigen processing and presentation pathway (15,16). However, these papers fail to demonstrate whether mitochondrial antigenic proteins can be efficiently taken up by DCs in vivo and cross-presented to antigen-specific CD8 þ T cells.…”

“…Yamazaki and colleagues have demonstrated that cytoplasmic versus mitochondrial localization of antigenic protein LIVAT-BP determines which portions of the protein are selected as antigenic epitopes for CD8 þ T-cell recognition (16). Although these results are of interest, this paper falls short of distinguishing whether antigen location modulates: (i) in vivo cross-priming of T-cell responses; (ii) proteasome-dependent degradation of the antigenic protein; and (iii) tumor growth.…”

“…Previous studies have described the effect of subcellular localization of protein antigens on direct presentation of T-cell epitopes (13)(14)(15)(16).…”