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Human transporters associated with antigen processing (TAPs) select epitope precursor peptides for processing in the endoplasmic reticulum and presentation to T cells.

Lauvau G, Kakimi K, Niedermann G, Ostankovitch M, Yotnda P, Firat H, Chisari FV, van Endert PM - J. Exp. Med. (1999)

Bottom Line: Antigen presentation by major histocompatibility complex (MHC) class I molecules requires peptide supply by the transporters associated with antigen processing (TAPs), which select substrates in a species- and, in the rat, allele-specific manner.Conflicts between TAPs and MHC preferences for COOH-terminal peptide residues in rodent cells strongly reduce the efficiency of MHC class I antigen presentation.Therefore, the previously reported aminopeptidase activity in the ER can also act on TAP-translocated peptides.

View Article: PubMed Central - PubMed

Affiliation: Institut National de la Santé et Recherche Medicale (INSERM) U25, Hôpital Necker, 75015 Paris, France.

ABSTRACT
Antigen presentation by major histocompatibility complex (MHC) class I molecules requires peptide supply by the transporters associated with antigen processing (TAPs), which select substrates in a species- and, in the rat, allele-specific manner. Conflicts between TAPs and MHC preferences for COOH-terminal peptide residues in rodent cells strongly reduce the efficiency of MHC class I antigen presentation. Although human TAP is relatively permissive, some peptide ligands for human histocompatibility leukocyte antigen class I molecules are known to possess very low TAP affinities; the significance of these in vitro findings for cellular antigen presentation is not known. We studied two naturally immunodominant viral epitopes presented by HLA-A2 that display very low affinities for human TAP. Low TAP affinities preclude minimal epitope access to the endoplasmic reticulum (ER) and assembly with HLA-A2 in vitro, as well as presentation by minigene-expressing cells to cytotoxic T lymphocytes. However, NH(2)-terminally but not COOH-terminally extended epitope variants with higher TAP affinities assemble in vitro and are presented to cytotoxic T lymphocytes with high efficiency. Thus, human TAP can influence epitope selection and restrict access to the ER to epitope precursors. Analysis of TAP affinities of a panel of viral epitopes suggests that TAP selection of precursors may be a common phenomenon for HLA-A2-presented epitopes. We also analyzed HLA-A2-eluted peptides from minigene-expressing cells and show that an NH(2)-terminally extended variant with low A2 binding affinity undergoes ER processing, whereas another with high affinity is presented unmodified. Therefore, the previously reported aminopeptidase activity in the ER can also act on TAP-translocated peptides.

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Efficiency of presentation of minigene-expressed minimal epitopes and Nt-extended precursors to specific CTL lines. Target cells were sensitized by synthetic peptides, by vaccinia viruses corresponding to different forms of epitopes indicated in the panels, or by control viruses, and lysis by CTL lines specific for the indicated epitopes was measured. Symbols indicate target cell sensitization by the following reagents: ▵, synthetic peptide corresponding to minimal epitope; ⋄, irrelevant vaccinia virus; ♦, vaccinia virus expressing the appropriate full-length HBV protein; □, vaccinia-expressed short epitope preceded by the E3/19K signal sequence; •, vaccinia-expressed short epitope; ○, vaccinia-expressed, Nt-extended precursor peptide. (A) Lysis of JY target cells by a patient-derived CTL line. (B) Lysis of Jesthom cells by a line derived by in vitro immunization. (C) Lysis of T2 cells by the same line as in B. (D and E) Lysis of JY cells by two CTL lines derived from different acutely HBV-infected patients.
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Figure 5: Efficiency of presentation of minigene-expressed minimal epitopes and Nt-extended precursors to specific CTL lines. Target cells were sensitized by synthetic peptides, by vaccinia viruses corresponding to different forms of epitopes indicated in the panels, or by control viruses, and lysis by CTL lines specific for the indicated epitopes was measured. Symbols indicate target cell sensitization by the following reagents: ▵, synthetic peptide corresponding to minimal epitope; ⋄, irrelevant vaccinia virus; ♦, vaccinia virus expressing the appropriate full-length HBV protein; □, vaccinia-expressed short epitope preceded by the E3/19K signal sequence; •, vaccinia-expressed short epitope; ○, vaccinia-expressed, Nt-extended precursor peptide. (A) Lysis of JY target cells by a patient-derived CTL line. (B) Lysis of Jesthom cells by a line derived by in vitro immunization. (C) Lysis of T2 cells by the same line as in B. (D and E) Lysis of JY cells by two CTL lines derived from different acutely HBV-infected patients.

Mentions: As shown in Fig. 5, CTL lines recognizing epitope pol 575-83 killed target cells much more efficiently when these expressed the Nt-extended precursor 573-85 than cells expressing the minimal peptide 575-83. Lysis of cells expressing the precursor was similar to lysis of cells pulsed with short synthetic peptides or expressing full-length pol protein, whereas cells expressing the minimal epitope were hardly recognized at all in an experiment with a CTL line from a patient (Fig. 5 A). A similar although less dramatic difference in recognition was obtained with two CTL lines obtained by in vitro immunization (Fig. 5 B and data not shown). In contrast, one of these lines recognized TAP-deficient T2 cells expressing the two epitope forms with equal, intermediate efficiency, demonstrating that more efficient sensitization by expression of the precursor form was due to TAP-mediated ER access of this epitope variant (Fig. 5 C).


Human transporters associated with antigen processing (TAPs) select epitope precursor peptides for processing in the endoplasmic reticulum and presentation to T cells.

Lauvau G, Kakimi K, Niedermann G, Ostankovitch M, Yotnda P, Firat H, Chisari FV, van Endert PM - J. Exp. Med. (1999)

Efficiency of presentation of minigene-expressed minimal epitopes and Nt-extended precursors to specific CTL lines. Target cells were sensitized by synthetic peptides, by vaccinia viruses corresponding to different forms of epitopes indicated in the panels, or by control viruses, and lysis by CTL lines specific for the indicated epitopes was measured. Symbols indicate target cell sensitization by the following reagents: ▵, synthetic peptide corresponding to minimal epitope; ⋄, irrelevant vaccinia virus; ♦, vaccinia virus expressing the appropriate full-length HBV protein; □, vaccinia-expressed short epitope preceded by the E3/19K signal sequence; •, vaccinia-expressed short epitope; ○, vaccinia-expressed, Nt-extended precursor peptide. (A) Lysis of JY target cells by a patient-derived CTL line. (B) Lysis of Jesthom cells by a line derived by in vitro immunization. (C) Lysis of T2 cells by the same line as in B. (D and E) Lysis of JY cells by two CTL lines derived from different acutely HBV-infected patients.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2195672&req=5

Figure 5: Efficiency of presentation of minigene-expressed minimal epitopes and Nt-extended precursors to specific CTL lines. Target cells were sensitized by synthetic peptides, by vaccinia viruses corresponding to different forms of epitopes indicated in the panels, or by control viruses, and lysis by CTL lines specific for the indicated epitopes was measured. Symbols indicate target cell sensitization by the following reagents: ▵, synthetic peptide corresponding to minimal epitope; ⋄, irrelevant vaccinia virus; ♦, vaccinia virus expressing the appropriate full-length HBV protein; □, vaccinia-expressed short epitope preceded by the E3/19K signal sequence; •, vaccinia-expressed short epitope; ○, vaccinia-expressed, Nt-extended precursor peptide. (A) Lysis of JY target cells by a patient-derived CTL line. (B) Lysis of Jesthom cells by a line derived by in vitro immunization. (C) Lysis of T2 cells by the same line as in B. (D and E) Lysis of JY cells by two CTL lines derived from different acutely HBV-infected patients.
Mentions: As shown in Fig. 5, CTL lines recognizing epitope pol 575-83 killed target cells much more efficiently when these expressed the Nt-extended precursor 573-85 than cells expressing the minimal peptide 575-83. Lysis of cells expressing the precursor was similar to lysis of cells pulsed with short synthetic peptides or expressing full-length pol protein, whereas cells expressing the minimal epitope were hardly recognized at all in an experiment with a CTL line from a patient (Fig. 5 A). A similar although less dramatic difference in recognition was obtained with two CTL lines obtained by in vitro immunization (Fig. 5 B and data not shown). In contrast, one of these lines recognized TAP-deficient T2 cells expressing the two epitope forms with equal, intermediate efficiency, demonstrating that more efficient sensitization by expression of the precursor form was due to TAP-mediated ER access of this epitope variant (Fig. 5 C).

Bottom Line: Antigen presentation by major histocompatibility complex (MHC) class I molecules requires peptide supply by the transporters associated with antigen processing (TAPs), which select substrates in a species- and, in the rat, allele-specific manner.Conflicts between TAPs and MHC preferences for COOH-terminal peptide residues in rodent cells strongly reduce the efficiency of MHC class I antigen presentation.Therefore, the previously reported aminopeptidase activity in the ER can also act on TAP-translocated peptides.

View Article: PubMed Central - PubMed

Affiliation: Institut National de la Santé et Recherche Medicale (INSERM) U25, Hôpital Necker, 75015 Paris, France.

ABSTRACT
Antigen presentation by major histocompatibility complex (MHC) class I molecules requires peptide supply by the transporters associated with antigen processing (TAPs), which select substrates in a species- and, in the rat, allele-specific manner. Conflicts between TAPs and MHC preferences for COOH-terminal peptide residues in rodent cells strongly reduce the efficiency of MHC class I antigen presentation. Although human TAP is relatively permissive, some peptide ligands for human histocompatibility leukocyte antigen class I molecules are known to possess very low TAP affinities; the significance of these in vitro findings for cellular antigen presentation is not known. We studied two naturally immunodominant viral epitopes presented by HLA-A2 that display very low affinities for human TAP. Low TAP affinities preclude minimal epitope access to the endoplasmic reticulum (ER) and assembly with HLA-A2 in vitro, as well as presentation by minigene-expressing cells to cytotoxic T lymphocytes. However, NH(2)-terminally but not COOH-terminally extended epitope variants with higher TAP affinities assemble in vitro and are presented to cytotoxic T lymphocytes with high efficiency. Thus, human TAP can influence epitope selection and restrict access to the ER to epitope precursors. Analysis of TAP affinities of a panel of viral epitopes suggests that TAP selection of precursors may be a common phenomenon for HLA-A2-presented epitopes. We also analyzed HLA-A2-eluted peptides from minigene-expressing cells and show that an NH(2)-terminally extended variant with low A2 binding affinity undergoes ER processing, whereas another with high affinity is presented unmodified. Therefore, the previously reported aminopeptidase activity in the ER can also act on TAP-translocated peptides.

Show MeSH
Related in: MedlinePlus