Molecular mechanisms of TLR2-mediated antigen cross-presentation in dendritic cells

J Immunol. 2014 May 1;192(9):4233-41. doi: 10.4049/jimmunol.1302850. Epub 2014 Mar 28.

Abstract

Cross-presentation is a key function of dendritic cells (DCs), which present exogenous Ags on MHC class I molecules to prime CTL responses. The effects of TLR triggering on the cross-presentation of exogenous Ags by DCs remain unclear. In this study, we used synthetic dipalmitoylated peptides and TLR2 agonist-conjugated peptides as models to elucidate the mechanisms of TLR2-mediated cross-presentation. We observed that the internalization of dipalmitoylated peptides by bone marrow-derived DCs was facilitated by TLR2 via clathrin-mediated endocytosis. The administration of these dipalmitoylated peptide-pulsed bone marrow-derived DCs eliminated established tumors through TLR2 signaling. We further demonstrated that the induction of Ag-specific CTL responses and tumor regression by dipalmitoylated peptides was TAP independent. In addition, presentation of dipalmitoylated peptides by MHC class I molecules was blocked in the presence of an endosomal acidification inhibitor (chloroquine) or a lysosomal degradation inhibitor (Z-FL-COCHO). The endocytosed dipalmitoylated peptide also passed rapidly from early endosome Ag-1-positive endosomes to RAS-related GTP-binding protein 7 (Rab7)-associated late endosomes compared with their nonlipidated counterparts. Furthermore, we found that dipalmitoylated peptide-upregulated Rab7 expression correlated with Ag presentation via the TLR2/MyD88 pathway. Both JNK and ERK signaling pathways are required for upregulation of Rab7. In summary, our data suggest that TLR2-mediated cross-presentation occurs through the upregulation of Rab7 and a TAP-independent pathway that prime CTL responses.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • Cross-Priming / immunology*
  • Cytotoxicity, Immunologic / immunology*
  • Dendritic Cells / immunology*
  • Mice
  • Mice, Inbred C57BL
  • Microscopy, Confocal
  • Neoplasms, Experimental / immunology
  • Signal Transduction / immunology*
  • T-Lymphocytes, Cytotoxic / immunology
  • Toll-Like Receptor 2 / immunology*
  • rab GTP-Binding Proteins / immunology
  • rab7 GTP-Binding Proteins

Substances

  • Tlr2 protein, mouse
  • Toll-Like Receptor 2
  • rab7 GTP-Binding Proteins
  • rab7 GTP-binding proteins, mouse
  • rab GTP-Binding Proteins