Activation of the neutrophil myeloperoxidase-H2O2 system by synovial fluid isolated from patients with rheumatoid arthritis.

Synovial fluid isolated from 16 patients with rheumatoid arthritis activated luminol dependent chemiluminescence in bloodstream neutrophils, and the maximal activity stimulated varied over a 50-fold range. In contrast, these same fluids only activated a much lower range (two- to threefold) of maximal rates of lucigenin dependent chemiluminescence and cytochrome c reduction, two assays which only measure oxidant secretion which is independent of myeloperoxidase. Over 95% of the luminol dependent chemiluminescence activated by all samples was inhibited by azide (indicating its dependence upon myeloperoxidase), but anti-(myeloperoxidase) IgG (which specifically inhibits only the extracellular activity of this enzyme) only inhibited the response stimulated by some samples: those fluids which activated the highest luminol dependent chemiluminescence also stimulated the greatest activity of an extracellular myeloperoxidase-H2O2 system. A clear correlation was shown to exist between the activity of myeloperoxidase already present in the fluids (after its secretion from neutrophils in situ within the rheumatoid joint) and the ability of the fluid to activate luminol dependent chemiluminescence. It is concluded, therefore, that all synovial fluid samples tested possess almost equivalent levels of a factor(s) which activated O2-/H2O2 secretion and that the variations in the measured activity of the extracellular myeloperoxidase-H2O2 system are dependent upon the level of degranulation which had occurred within the joint.