Distinct uptake mechanisms but similar intracellular processing of two different toll-like receptor ligand-peptide conjugates in dendritic cells

J Biol Chem. 2007 Jul 20;282(29):21145-59. doi: 10.1074/jbc.M701705200. Epub 2007 Apr 26.

Abstract

Covalent conjugation of Toll-like receptor ligands (TLR-L) to synthetic antigenic peptides strongly improves antigen presentation in vitro and T lymphocyte priming in vivo. These molecularly well defined TLR-L-peptide conjugates, constitute an attractive vaccination modality, sharing the peptide antigen and a defined adjuvant in one single molecule. We have analyzed the intracellular trafficking and processing of two TLR-L conjugates in dendritic cells (DCs). Long synthetic peptides containing an ovalbumin cytotoxic T-cell epitope were chemically conjugated to two different TLR-Ls the TLR2 ligand, Pam(3)CysSK(4) (Pam) or the TLR9 ligand CpG. Rapid and enhanced uptake of both types of TLR-L-conjugated peptide occurred in DCs. Moreover, TLR-L conjugation greatly enhanced antigen presentation, a process that was dependent on endosomal acidification, proteasomal cleavage, and TAP translocation. The uptake of the CpG approximately conjugate was independent of endosomally-expressed TLR9 as reported previously. Unexpectedly, we found that Pam approximately conjugated peptides were likewise internalized independently of the expression of cell surface-expressed TLR2. Further characterization of the uptake mechanisms revealed that TLR2-L employed a different uptake route than TLR9-L. Inhibition of clathrin- or caveolin-dependent endocytosis greatly reduced uptake and antigen presentation of the Pam-conjugate. In contrast, internalization and antigen presentation of CpG approximately conjugates was independent of clathrin-coated pits but partly dependent on caveolae formation. Importantly, in contrast to the TLR-independent uptake of the conjugates, TLR expression and downstream TLR signaling was required for dendritic cell maturation and for priming of naïve CD8(+) T-cells. Together, our data show that targeting to two distinct TLRs requires distinct uptake mechanism but follows similar trafficking and intracellular processing pathways leading to optimal antigen presentation and T-cell priming.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • CD8-Positive T-Lymphocytes / metabolism
  • Caveolins / metabolism
  • Clathrin / metabolism
  • CpG Islands
  • Dendritic Cells / cytology
  • Dendritic Cells / metabolism*
  • Endocytosis
  • HLA Antigens / chemistry
  • Ligands*
  • Mice
  • Mice, Inbred C57BL
  • Models, Biological
  • Peptides / chemistry
  • T-Lymphocytes / metabolism
  • Toll-Like Receptors / metabolism*

Substances

  • Caveolins
  • Clathrin
  • HLA Antigens
  • Ligands
  • Peptides
  • Toll-Like Receptors