Objective: To examine fibroblasts grown from the synovial fluid of rheumatoid arthritis (RA) patients for TRAIL-R2 expression, and for susceptibility to apoptosis induced by an agonistic anti-TRAIL-R2 monoclonal antibody (mAb).
Methods: The expression of TRAIL-R2 (DR5) was determined by flow cytometry on fibroblasts grown from the synovial fluid of patients with RA, osteoarthritis (OA), seronegative arthritis, and unclassified monarthritis or oligoarthritis, and on fibroblasts from the synovial membrane of RA and OA patients. Susceptibility to apoptosis mediated by an agonistic anti-TRAIL-R2 mAb was determined by alamar blue bioassay, fluorescence microscopy (annexin V/propidium iodide staining), and caspase activation.
Results: Fibroblasts grew from 35 of 50 RA synovial fluid samples, of which 26 were DR5(+) (mean [+/-SD] fluorescence intensity [MFI] 18.74 +/- 2.5). Fibroblasts also grew from 15 of 30 seronegative arthritis synovial fluid samples, 28 of 40 OA synovial fluid samples, and 8 of 20 unclassified monarthritis or oligoarthritis synovial fluid samples; all of these were DR5- (MFI 0.32 +/- 0.02). All 10 of the fibroblast lines from joint replacement surgery or synovectomy specimens of RA patients were DR5(+) (MFI 20.3 +/- 3.2). All fibroblast lines from the synovium of 10 OA patients were DR5-, as were fibroblasts from the skin of 5 healthy subjects. DR5(+) fibroblast cultures underwent apoptosis when treated in vitro with an agonistic anti-DR5 antibody.
Conclusion: Fibroblasts grown from the synovial fluid and synovial membrane of RA patients express TRAIL-R2 that is functionally active. An agonistic anti-TRAIL-R2 antibody that does not induce hepatocyte toxicity may be an alternative strategy for treatment of RA.