Background Superoxide production by polymorphonuclear neutrophil (PMN) participates in the rheumatoid joint lesions and mainly depends on NADPH oxidase activation. Tumour necrosis factor (TNF), interleukin-8 (IL-8) and granulocyte/macrophage colony stimulating factor (GM-CSF) have a priming effect on NADPH oxidase, depending on the phosphorylation of p47phox, a major cytosolic component of NADPH oxidase.
Objectives We sought to determine if the status (primed/activated) of NADPH oxidase of articular PMN was correlated with rheumatic disease activity and TNF, IL-8 and GM-CSF synovial concentrations.
Methods Knee joint fluid aspiration was performed in 17 patients, 11 with RA and 6 with spondyloarthropathy (SpA). Usual clinical and biological data were recorded for each patient, allowing a DAS28 scoring. NADPH oxidase activity was analysed with cytochrome c reduction technique. Phosphorylation of p47phox was evaluated with isoelectrofocusing and immunoblotting using a specific antibody. Cytokines concentrations were measured with ELISA kits.
Results NADPH oxidase activity was increased in the majority of RA knee joints, and to a lesser extent in the SpA group. In the RA group, the NADPH oxidase activity was correlated positively with DAS28, with the PMN count in the synovial fluid, with the degree of p47phox phosphorylation, and with the synovial concentrations of TNF and IL-8. Concentrations of GM-CSF remained very low or undetectable in all patients. In the RA group only, the DAS28, the PMN count and the phosphorylation of p47phox were correlated with synovial concentrations of TNF and IL-8.
Conclusion NADPH oxidase activation, through an increased phosphorylation of p47phox, seems to be implicated in joint inflammation during RA. This phenomenon could be related to high level of TNF and IL-8.