Background In osteoarthritis (OA), synovial inflammation may contribute disease progression. Moreover, monocytes and Toll-like receptors 2 (TLR2) or 4 (TLR4) may play a role in promoting inflammation of OA. However, inflammatory cells in osteoarthritis synovial fluid (OASF) have been rarely studied.

Objectives In order to reveal the inflammatory cells in OASF, we investigated cell markers of mononuclear cells in OA synovial fluid and TLR2 or TLR4 expression in the subtypes of monocyte.

Methods Mononuclear cells were purified by Ficoll density gradient methods from OASFs. Mononuclear cells were stained using anti-CD3, anti-CD4, anti-CD14, anti-CD16, anti-CD64, anti-CD90, anti-TLR4, or anti-TLR2 and analyzed using FACS Canto II.

Results In OASF, there are many CD14+CD16- cells (10.9±10.0%) or CD14+CD16+ cells (21.2±21.8%), CD3+CD4+ cells (16.7±12.9%), CD3+CD4- cells (20.7±12.8%) but rare CD90+ cells (1.7±1.3%). In the majority of CD14+ cells, CD64 and low level CD4 was expressed (CD64, 84.6±1.1%; CD4, 71.0±20.5%). TLR4 expression was higher in CD14+CD16+ cells than in CD14+CD16- cells or CD14-CD16+ cells (mean fluorescence intensity [MFI], CD14+CD16-: 159±128, CD14+CD16+: 307±272, CD14-CD16+: 57±92, p<0.005). TLR2 expression also more increased in CD14+CD16+ cells compared to other subsets (MFI, CD14+CD16-: 117±89, CD14+CD16+: 216±193, CD14-CD16+: -3±34, p<0.005).

Conclusions In OASF, CD3+ T cells and CD14+ monocytes were abundant and majority of CD14+ cells showed CD64 and CD4. Monocyte subtypes are mainly CD14+CD16+ or CD14+CD16- and those subtypes expressed TLR4 and TLR2.

Disclosure of Interest None declared

DOI 10.1136/annrheumdis-2014-eular.3425