Bacterial peptidoglycans but not CpG oligodeoxynucleotides activate synovial fibroblasts by toll-like receptor signaling

Arthritis Rheum. 2003 Mar;48(3):642-50. doi: 10.1002/art.10848.


Objective: To test the hypothesis that bacterial products acting as adjuvants, such as CpG oligodeoxynucleotides (ODNs) and peptidoglycans (PGs), are able to activate synoviocytes, and to determine the involvement of Toll-like receptors (TLRs) in this activation process.

Methods: Cultured synovial fibroblasts obtained from patients with rheumatoid arthritis (RA) or osteoarthritis (OA) were stimulated with CpG ODNs or PGs. The expression of various integrins was determined by fluorescence-activated cell sorting. TLR and matrix metalloproteinase (MMP) messenger RNA (mRNA) was measured by real-time polymerase chain reaction. Additionally, levels of interleukin-6 (IL-6) and IL-8 in the culture supernatants were assessed by enzyme-linked immunosorbent assay. Blocking experiments were performed by adding anti-TLR-2 and anti-TLR-4 monoclonal antibodies to cultures stimulated with bacterial PGs.

Results: Incubation of synovial fibroblasts with CpG ODNs resulted in neither up-regulation of the expression of integrins on the cell surface, up-regulation of MMP mRNA expression, nor IL-6 and IL-8 production. However, incubation of RA synovial fibroblasts as well as OA synovial fibroblasts with staphylococcal PGs led to an up-regulation of CD54 (ICAM-1) surface expression and to increased expression of MMP-1, MMP-3, and MMP-13 mRNA. Furthermore, production of the proinflammatory cytokines IL-6 and IL-8 was increased by treatment with PGs. We demonstrated that cultured synovial fibroblasts express low levels of TLR-2 and TLR-9 mRNA. TLR-2 was up-regulated after stimulation with PGs, whereas TLR-9 mRNA remained at baseline levels after stimulation with CpG ODNs. Anti-TLR-2 monoclonal antibodies significantly inhibited production of IL-6 and IL-8 induced by stimulation with PGs.

Conclusion: We demonstrate that bacterial PGs activate synovial fibroblasts, at least partially via TLR-2, to express integrins, MMPs, and proinflammatory cytokines. Inhibition of TLR signaling pathways might therefore have a beneficial effect on both joint inflammation and joint destruction.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arthritis, Rheumatoid / metabolism
  • Arthritis, Rheumatoid / pathology
  • Cells, Cultured
  • CpG Islands*
  • DNA, Bacterial
  • Dose-Response Relationship, Drug
  • Drosophila Proteins*
  • Escherichia coli
  • Fibroblasts / drug effects
  • Fibroblasts / metabolism*
  • Fibroblasts / pathology
  • Flow Cytometry
  • Humans
  • Intercellular Adhesion Molecule-1 / biosynthesis
  • Intercellular Adhesion Molecule-1 / genetics
  • Interleukins / biosynthesis
  • Membrane Glycoproteins / genetics
  • Membrane Glycoproteins / immunology
  • Membrane Glycoproteins / metabolism*
  • Metalloendopeptidases / biosynthesis
  • Metalloendopeptidases / genetics
  • Oligodeoxyribonucleotides / metabolism
  • Oligodeoxyribonucleotides / pharmacology*
  • Osteoarthritis / metabolism
  • Osteoarthritis / pathology
  • Peptidoglycan / isolation & purification
  • Peptidoglycan / pharmacology*
  • RNA, Messenger / metabolism
  • Receptors, Cell Surface / genetics
  • Receptors, Cell Surface / immunology
  • Receptors, Cell Surface / metabolism*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction
  • Staphylococcus aureus* / chemistry
  • Synovial Membrane / drug effects
  • Synovial Membrane / metabolism*
  • Synovial Membrane / pathology
  • Toll-Like Receptor 2
  • Toll-Like Receptor 9
  • Toll-Like Receptors


  • CPG-oligonucleotide
  • DNA, Bacterial
  • Drosophila Proteins
  • Interleukins
  • Membrane Glycoproteins
  • Oligodeoxyribonucleotides
  • Peptidoglycan
  • RNA, Messenger
  • Receptors, Cell Surface
  • TLR2 protein, human
  • TLR9 protein, human
  • Toll-Like Receptor 2
  • Toll-Like Receptor 9
  • Toll-Like Receptors
  • Intercellular Adhesion Molecule-1
  • Metalloendopeptidases