| Abstract: | Objective To characterize the expression pattern of tumor necrosis factor–related apoptosis‐inducing ligand (TRAIL) and its cognate receptors (TRAIL R1, R2, R3, and R4) on rheumatoid arthritis (RA) synovial fluid (SF) lymphocytes and monocyte/macrophages and on cultured RA synovial fibroblasts. Methods The expression of TRAIL and TRAIL receptors on RA SF lymphocytes and monocyte/macrophages, normal macrophages, and RA synovial fibroblasts was examined by flow cytometry with previously characterized monoclonal antibodies. The ability of adenoviral‐mediated delivery of TRAIL to induce macrophage or RA synovial fibroblast apoptosis was examined by flow cytometry. Results By flow cytometry, neither TRAIL nor its cognate receptors was detectable on RA SF lymphocytes or RA synovial fibroblasts. In contrast, RA SF macrophages expressed TRAIL R3, a decoy receptor (P < 0.01 versus isotype control), but not TRAIL, or TRAIL R1, R2, or R4. Normal peripheral blood–derived monocyte‐differentiated macrophages expressed TRAIL R2 (P < 0.01), but not TRAIL or the other TRAIL receptors. Adenoviral‐mediated delivery of TRAIL had no effect on the survival of normal macrophages or RA synovial fibroblasts but readily induced apoptosis in the prostate cancer cell line (PC‐3) that expressed TRAIL R1 and R2. Conclusion TRAIL R1 and R2, which are required for signal transmission by TRAIL, were not detected on RA SF lymphocytes, macrophages, or synovial fibroblasts. These observations do not support a potential therapeutic role for TRAIL in RA. |
