Ligation of TLR7 by rheumatoid arthritis synovial fluid single strand RNA induces transcription of TNFα in monocytes
- Nathan D Chamberlain1,
- Seung-jae Kim1,
- Olga M Vila1,
- Michael V Volin2,
- Suncica Volkov1,
- Richard M Pope3,
- Shiva Arami1,
- Arthur M Mandelin II3,
- Shiva Shahrara1
- 1Department of Medicine, Division of Rheumatology, University of Illinois at Chicago, Chicago, Illinois, USA
- 2Department of Microbiology & Immunology, Midwestern University, Chicago College of Osteopathic Medicine, Downers Grove, Illinois, USA
- 3Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
- Correspondence to Dr Shiva Shahrara, Department of Medicine, Division of Rheumatology, University of Illinois at Chicago, 835 S Wolcott Ave., E807-E809 MSB, Chicago, Illinois 60612, USA;
- Received 15 December 2011
- Accepted 20 May 2012
- Published Online First 23 June 2012
Objective The aim of the study was to characterise the expression, regulation and pathogenic role of toll-like receptor 7 (TLR7) and TLR8 in rheumatoid arthritis (RA).
Methods Expression of TLR7 and TLR8 was demonstrated in RA, osteoarthritis (OA) and normal (NL) synovial tissues (STs) employing immunohistochemistry. The authors next examined the mechanism by which TLR7 and TLR8 ligation mediates proinflammatory response by Western blot analysis and ELISA. Expression of TLR7 and TLR8 in RA monocytes was correlated to disease activity score (DAS28) and tumour necrosis factor α (TNFα) levels. Further, the effect of TLR7 ligation in RA monocytes was determined on synovial fluid (SF)-mediated TNFα transcription.
Results TLR7/8 are predominately expressed in RA ST lining and sublining macrophages. The authors show that NF-κB and/or PI3K pathways are essential for TLR7/8 induction of proinflammatory factors in RA peripheral blood (PB)-differentiated macrophages. Expression of TLR7 in RA monocytes shows a strong correlation with DAS28 and TNFα levels. By contrast, expression of TLR8 in these cells does not correlate with DAS28, TLR7 or TNFα levels. The authors further demonstrate that RNA from RA SF, but not RA or NL plasma, could modulate TNFα transcription from RA monocytes that can be downregulated by antagonising TLR7 ligation or degradation of single stand (ss) RNA. Thus, ssRNA present in RA SF may function as a potential endogenous ligand for TLR7.
Conclusions These results suggest that expression of TLR7, but not TLR8, may be a predictor for RA disease activity and anti-TNFα responsiveness, and targeting TLR7 may suppress chronic progression of RA.