Exogenous peptides delivered by ricin require processing by signal peptidase for transporter associated with antigen processing-independent MHC class I-restricted presentation

J Immunol. 2002 Jul 1;169(1):99-107. doi: 10.4049/jimmunol.169.1.99.


In this study we demonstrate that a disarmed version of the cytotoxin ricin can deliver exogenous CD8(+) T cell epitopes into the MHC class I-restricted pathway by a TAP-independent, signal peptidase-dependent pathway. Defined viral peptide epitopes genetically fused to the N terminus of an attenuated ricin A subunit (RTA) that was reassociated with its partner B subunit were able to reach the early secretory pathway of sensitive cells, including TAP-deficient cells. Successful processing and presentation by MHC class I proteins was not dependent on proteasome activity or on recycling of MHC class I proteins, but rather on a functional secretory pathway. Our results demonstrated a role for signal peptidase in the generation of peptide epitopes associated at the amino terminus of RTA. We showed, first, that potential signal peptide cleavage sites located toward the N terminus of RTA can be posttranslationally cleaved by signal peptidase and, second, that mutation of one of these sites led to a loss of peptide presentation. These results identify a novel MHC class I presentation pathway that exploits the ability of toxins to reach the lumen of the endoplasmic reticulum by retrograde transport, and suggest a role for endoplasmic reticulum signal peptidase in the processing and presentation of MHC class I peptides. Because TAP-negative cells can be sensitized for CTL killing following retrograde transport of toxin-linked peptides, application of these results has direct implications for the development of novel vaccination strategies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigen Presentation* / genetics
  • Antigens, Viral / genetics
  • Antigens, Viral / immunology
  • Antigens, Viral / metabolism
  • Cytotoxicity Tests, Immunologic
  • Dogs
  • Endoplasmic Reticulum / enzymology
  • Endoplasmic Reticulum / genetics
  • Endoplasmic Reticulum / immunology
  • Endoplasmic Reticulum / metabolism
  • Genetic Engineering / methods
  • Glycoproteins / genetics
  • Glycoproteins / immunology
  • Glycoproteins / metabolism
  • H-2 Antigens / biosynthesis
  • H-2 Antigens / immunology
  • H-2 Antigens / metabolism*
  • Histocompatibility Antigen H-2D
  • Hydrolysis
  • Membrane Proteins*
  • Mice
  • Mice, Inbred C57BL
  • Peptide Fragments / genetics
  • Peptide Fragments / immunology
  • Peptide Fragments / isolation & purification
  • Peptide Fragments / metabolism*
  • Protein Processing, Post-Translational / genetics
  • Protein Processing, Post-Translational / immunology*
  • Protein Transport / genetics
  • Protein Transport / immunology
  • Rabbits
  • Recombinant Fusion Proteins / chemical synthesis
  • Recombinant Fusion Proteins / immunology
  • Recombinant Fusion Proteins / metabolism
  • Ricin / genetics
  • Ricin / immunology
  • Ricin / metabolism*
  • Serine Endopeptidases / metabolism*
  • Tumor Cells, Cultured
  • Viral Core Proteins / genetics
  • Viral Core Proteins / immunology
  • Viral Core Proteins / metabolism
  • Viral Proteins / genetics
  • Viral Proteins / immunology
  • Viral Proteins / metabolism


  • Antigens, Viral
  • Glycoproteins
  • H-2 Antigens
  • Histocompatibility Antigen H-2D
  • Membrane Proteins
  • Peptide Fragments
  • Recombinant Fusion Proteins
  • Viral Core Proteins
  • Viral Proteins
  • glycoprotein peptide 33-41, Lymphocytic choriomeningitis virus
  • nucleoprotein (366-374), influenza virus
  • Ricin
  • Serine Endopeptidases
  • type I signal peptidase