Several observations indicate that RA patients have a dysregulated redox balance, e.g. increased levels of antioxidants, limited access to oxygen within the joints, and granulocytes with impaired ability to produce ROS: RA patients have increased glutathione reductase activity in synovial fluid (SF), compared to SF from reactive arthritis and osteoarthritis patients48, and the antioxidant thioredoxin has been reported to be increased 5-fold in SF from RA patients compared to SF from patients with osteoarthritis.49 Here, GSR is linked to reactive arthritis.