Acute serum amyloid A is an endogenous TLR2 ligand that mediates inflammatory and angiogenic mechanisms.
Acute-phase serum amyloid A (A-SAA) has cytokine-like properties and is expressed at sites of inflammation. We examined whether A-SAA-induced pro-inflammatory mechanisms are mediated through Toll-like receptor 2 (TLR2) in rheumatoid arthritis (RA).



The effect of A-SAA on human embryonic kidney (HEK), TLR2 or TLR4 cells was quantified by nuclear factor (NF)-κB luciferase reporter assays. A-SAA-induced RASFC and dHMVEC function were performed in the presence of a specific neutralising anti-TLR2 mAb (OPN301) (1 μg/mL) and matched IgG isotype control Ab (1 μg/mL). Cell surface expression of intracellular adhesion molecule (ICAM)-1, chemokine expression, cell migration, invasion and angiogenesis were assessed by flow cytometry, ELISA, Matrigel invasion chambers and tube formation assays. MyD88 expression was assessed by real-time PCR and western blot.



A-SAA induced TLR2 activation through induction of NF-κB (p<0.05), but failed to induce NF-κB in HEK-TLR4 cells, confirming specificity for TLR2. A-SAA-induced proliferation, invasion and migration were significantly inhibited in the presence of anti-TLR2 (all p<0.05), with no significant effect observed for tumour necrosis factor-α-induced events. Additionally, A-SAA-induced ICAM-1, interleukin-8, monocyte chemoattractant protein-1, RANTES and GRO-α expression were significantly reduced in the presence of anti-TLR2 (all p<0.05), as was A-SAA induced angiogenesis (p<0.05). Finally, A-SAA induced MyD88 signalling in RASFC and dHMVEC (p<0.05).



A-SAA is an endogenous ligand for TLR2, inducing pro-inflammatory effects in RA. Blocking the A-SAA/TLR2 interaction may be a potential therapeutic intervention in RA.
Centre for Arthritis and Rheumatic Diseases, Dublin Academic Medical Centre and Conway Institute of Biomolecular and Biomedical Research, Dublin 4, Ireland.
Mary
M
Connolly
Centre for Arthritis and Rheumatic Diseases, Dublin Academic Medical Centre and Conway Institute of Biomolecular and Biomedical Research, Dublin 4, Ireland.
Peter R
PR
Rooney
Centre for Arthritis and Rheumatic Diseases, Dublin Academic Medical Centre and Conway Institute of Biomolecular and Biomedical Research, Dublin 4, Ireland.
Trudy
T
McGarry
Department of Biology, Institute of Immunology, National University of Ireland Maynooth, Maynooth, County Kildare, Ireland.
Ashwini X
AX
Maratha
Centre for Arthritis and Rheumatic Diseases, Dublin Academic Medical Centre and Conway Institute of Biomolecular and Biomedical Research, Dublin 4, Ireland.
Jennifer
J
McCormick
Department of Biology, Institute of Immunology, National University of Ireland Maynooth, Maynooth, County Kildare, Ireland.
Sinead M
SM
Miggin
Centre for Arthritis and Rheumatic Diseases, Dublin Academic Medical Centre and Conway Institute of Biomolecular and Biomedical Research, Dublin 4, Ireland.
Douglas J
DJ
Veale
Centre for Arthritis and Rheumatic Diseases, Dublin Academic Medical Centre and Conway Institute of Biomolecular and Biomedical Research, Dublin 4, Ireland.
Ursula
U
Fearon
D000208:Acute Disease; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000473:pathology; D002465:Cell Movement; D016207:Cytokines / Q000097:blood; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D008024:Ligands; D016328:NF-kappa B / Q000378:metabolism; D009389:Neovascularization, Pathologic; D000685:Serum Amyloid A Protein / Q000378:metabolism*; D051195:Toll-Like Receptor 2 / Q000097:blood*
D016207:Cytokines; D008024:Ligands; D016328:NF-kappa B; D000685:Serum Amyloid A Protein; D051195:Toll-Like Receptor 2; D018799:Intercellular Adhesion Molecule-1
Fibroblasts; Inflammation; Rheumatoid Arthritis