Autoantibodies to glucose-6-phosphate isomerase are elevated in the synovial fluid of rheumatoid arthritis patients

Objective: This study investigated whether anti-glucose-6-phosphate isomerase (GPI) antibody in the synovial fluid is specifically related to human rheumatoid arthritis (RA). Methods: Synovial fluid was collected from patients with RA, osteoarthritis (OA), gout, Behcet's disease, or ankylosing spondylitis. GPI-binding activity was measured in the synovial fluid using a surface plasmon resonance (SPR) biosensor. Results: The mean level of anti-GPI signal in the synovial fluid of RA patients was significantly elevated compared with that of OA patients (2.84 +/- 1.41 AU versus 1.19 +/- 0.42 AU, respectively; p < 0.0001). Anti-GPI signals in the synovial fluids of patients with non-rheumatoid arthritis, such as gout, Behcet's disease, or ankylosing spondylitis were significantly lower than in the synovial fluid of RA patients (p < 0.005), and were similar to those of OA patients. Conclusion: Our study indicates that anti-GPI antibody in the synovial fluid is specifically related to RA, and suggests that GPI and its autoantibody might be important in the pathogenesis of human RA.