Expression of TRAIL-R2 (DR5) on fibroblasts from synovial fluid of rheumatoid arthritis

Fibroblasts can be isolated from rheumatoid arthritis (RA) synovial fluid (Sfld), and these cells may be derived from the synovium. Although normal tissues do not express DR5 protein, most cancerous tissues express high levels of DR5. Synovial fibroblasts from RA synovium share expression of DR5 protein with transformed cells. Our objective was to characterize fibroblasts from RA Sfld using an anti-DR5 monoclonal antibody. Sfld mononuclear cells were cultured from 50 patients with RA, 20 patients with seronegative arthritis, 20 patients with osteoarthritis (OA), and 15 patients with unclassified monoarthritis or oligoarthritis. Progressive growth of spindle-shaped cells was observed in some cultures. By the third passage 100% of cells were fibroblasts (Thy-1⁺, CD45^-, CD68^-). Fibroblasts were stained with a PE-conjugated anti-DR5 antibody and examined by flow cytometry. Fibroblasts grew from 35 of 50 RA Sfld samples. Twenty-six of these 35 were DR5⁺(> 95% positive cells; MFI relative to isotype control, 13.97 ± 2.5). Fibroblasts also grew from Sfld in six out of 20 seronegative arthritis, four out of 20 OA, and five out of 15 unclassified monoarthritis or oligoarthritis patients. All these were DR5^- (MFI relative to isotype control, 1.2 ± 0.23). Ten out of 10 fibroblast lines from joint replacement surgery or synovectomy specimens of RA were DR5⁺. All fibroblast lines from the synovium of 10 OA patients were DR5^-, as were fibroblasts from the skin of five healthy subjects. DR5⁺ Sfib cultures underwent apoptosis when treated in vitro with an anti-DR5 antibody, as determined by propidium iodide and annexin V staining. These results suggest that fibroblast-like cells from Sfld of RA are of at least two different lineages. Those expressing DR5 protein share this characteristic with transformed cells and with synovial fibroblasts from RA synovial membrane, and more likely derive from the synovium. The origin of DR5^- Sfld fibroblasts remains to be determined. Because all RA patients with DR5^- Sfld fibroblasts had active disease, we do not believe that DR5^- cells are derived from 'burnt out' synovial membrane.