Bacterial CpG-DNA and lipopolysaccharides activate Toll-like receptors at distinct cellular compartments

Eur J Immunol. 2002 Jul;32(7):1958-68. doi: 10.1002/1521-4141(200207)32:7<1958::AID-IMMU1958>3.0.CO;2-U.


Recognition by innate immune cells of the pathogen associated molecular patterns (PAMP) lipopolysaccharide (LPS) from Gram-negative bacteria and bacterial CpG-DNA depends on Toll-like receptor4 (TLR4) and TLR9, respectively. To define differences in the response to these distinct PAMP we compared a key intracellular event, namely recruitment of myeloid differentiation marker 88 (MyD88) to the respective PAMP-initiated TLR signaling. Using MyD88-GFP fusion protein expressing macrophages we demonstrate that LPS and CpG-DNA trigger signaling from two different cellular locations: theformer at the cell membrane and the latter at the lysosomal compartment. While LPS does not require endocytosis to functionally associate with the membrane expressed TLR4/MD2 complex, internalization and endosomal maturation is conditional for CpG-DNA to activate TLR9. In support of these data TLR9 is not localized at the cell surface, but intracellularily. These data stress the need to characterize individual TLR at the very beginning of signal initiation in order to understand their diverse biological functions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing
  • Adjuvants, Immunologic / pharmacology*
  • Animals
  • Antigens, Differentiation / genetics
  • Antigens, Differentiation / metabolism
  • Biological Transport
  • Cell Compartmentation
  • Cell Line
  • CpG Islands*
  • DNA, Bacterial / pharmacology*
  • DNA-Binding Proteins / metabolism*
  • Drosophila Proteins*
  • Endosomes / metabolism
  • Humans
  • Lipopolysaccharides / pharmacology*
  • Lysosomes / metabolism
  • Membrane Glycoproteins / metabolism*
  • Mice
  • Myeloid Differentiation Factor 88
  • Oligodeoxyribonucleotides / pharmacology*
  • Receptors, Cell Surface / metabolism*
  • Receptors, Immunologic / genetics
  • Receptors, Immunologic / metabolism
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Signal Transduction
  • Toll-Like Receptor 4
  • Toll-Like Receptor 9
  • Toll-Like Receptors


  • Adaptor Proteins, Signal Transducing
  • Adjuvants, Immunologic
  • Antigens, Differentiation
  • CPG-oligonucleotide
  • DNA, Bacterial
  • DNA-Binding Proteins
  • Drosophila Proteins
  • Lipopolysaccharides
  • MYD88 protein, human
  • Membrane Glycoproteins
  • Myd88 protein, mouse
  • Myeloid Differentiation Factor 88
  • Oligodeoxyribonucleotides
  • Receptors, Cell Surface
  • Receptors, Immunologic
  • Recombinant Fusion Proteins
  • TLR4 protein, human
  • TLR9 protein, human
  • Tlr9 protein, mouse
  • Toll-Like Receptor 4
  • Toll-Like Receptor 9
  • Toll-Like Receptors