Anti-DR5 mAb inhibits proliferation of human fibroblast-like synovial cells and reduces their cytokine secretion in vitro

BACKGROUND We have previously reported that anti-death receptor 5 (DR5) monoclonal antibody (mAb) is therapeutically effective in the treatment of rheumatoid arthritis (RA) in a collagen-induced arthritis rat model. However, the molecular mechanism and the effect of anti-DR5 mAb on proapoptotic genes and cytokine secretion in the human fibroblast-like synovial cells (FLS) requires further clarification. This study may provide new evidence for the application of anti-DR5 mAb as a treatment for RA. METHODS Human FLS were isolated from patients with RA and were treated with anti-DR5 mAb. An MTT assay and flow cytometry were used to detect the induction of apoptosis in vitro. Cytokine secretion by the FLS was detected using the enzyme-linked immunosorbent assay. The mRNA expression was assessed by reverse transcription polymerase chain reaction, and the protein expression was analyzed by Western blot. The apoptotic pathway was investigated further using a caspase inhibition assay. RESULTS Anti-DR5 mAb-induced apoptosis in human RA FLS in vitro. The protein expressions of caspase-8, -3, and -9 were decreased in human anti-DR5 mAb-treated FLS in a dose-dependent manner through exposure to a caspase inhibitor, indicating that anti-DR5 mAb induction of apoptosis is through the caspase pathway. Decreased levels of tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) were detected after treatment with anti-DR5 mAb in vitro. CONCLUSION Anti-DR5 mAb may induce apoptosis in human FLS through the caspase pathway and through decreased secretions of TNF-α and IFN-γ.