Evidence that rheumatoid arthritis synovial T cells are similar to cytokine-activated T cells: Involvement of phosphatidylinositol 3-kinase and nuclear factor ?B pathways in tumor necrosis factor ? production in rheumatoid arthritis

Abstract

Objective To investigate the mechanism that leads to the spontaneous production of tumor necrosis factor α (TNFα) in rheumatoid arthritis (RA) synovial tissue. Methods Normal blood monocytes were cocultured either with fixed activated T cells generated from normal blood or RA synovial T cells purified from synovium. TNFα production was measured in supernatants from these cocultures following blockade of the transcription factor nuclear factor κB (NF‐κB) using adenoviral transfer of the inhibitor of NF‐κB kinase α into the responding monocytes, or blockade of phosphatidylinositol 3‐kinase (PI 3‐kinase) using the inhibitory drugs wortmannin or LY294002. TNFα production was measured by enzyme‐linked immunosorbent assay. Results TNFα production in synovial tissue from patients with RA but not osteoarthritis was found to be T cell dependent. The RA synovial joint T cells resembled normal T cells that had been activated for 8 days using a cocktail of cytokines. These T cells, designated Tck (cytokine‐activated T cells), and RA synovial T cells both induced TNFα production in resting monocytes in a cell‐contact‐dependent manner, which was abrogated by blockage of the transcription factor NF‐κB but augmented if PI 3‐kinase was inhibited. Normal blood T cells activated conventionally via the T cell receptor with crosslinked anti‐CD3 antibody resulted in TNFα production from monocytes; this was unaffected by NF‐κB blockade, but was inhibited in the presence of PI 3‐kinase‐blocking drugs. Conclusion These data provide strong evidence for the importance of T cells in inducing TNFα in chronic inflammatory rheumatoid tissue, and give insight into the mechanism whereby these T cells are activated in vivo. Furthermore, they indicate that production of TNFα in pathologic tissue is regulated differently from physiologic antigen‐dependent TNFα production, which raises the possibility that selective inhibitors of TNFα in disease may be developed.