Altered function of synovial fluid granulocytes in patients with acute inflammatory arthritis: evidence for activation of neutrophils and its mediation by a factor present in synovial fluid

Abstract

In rheumatoid arthritis (RA) a chronic inflammatory state exists in which the synovial fluid is periodically filled with large numbers of polymorphonuclear leukocytes (PMNs). Oxygen radicals produced by these cells have been implicated as mediators of tissue damage and may be directly involved in the pathogenesis of RA. We examined the production of oxygen radicals by synovial fluid PMNs (SF-PMNs) and peripheral blood PMNs (PB-PMNs) by measuring chemiluminescence (CL) as well as superoxide anion (O2-) release. Increased spontaneous CL in the presence of luminol and increased CL in response to phorbol myristate acetate (PMA) was observed in SF-PMNs when compared to PB-PMNs. When zymosan was used as the stimulus in the absence of luminol, a slightly lower CL response was observed in SF-PMNs as compared to PB-PMNs. No significant differences were observed in the generation of O2- generation with any stimulus. Preincubation of normal PB-PMNs in 10% synovial fluid enhanced the luminol-dependent spontaneous and PMA-stimulated CL as well as zymosan-stimulated CL. When O2- release from normal PB-PMNs pretreated with 10% synovial fluid was compared to untreated controls, enhancement of spontaneous O2- release was observed. PMA- and zymosan-stimulated responses did not differ significantly from controls. Increased spontaneous and PMA-stimulated release of myeloperoxidase (MPO) was also observed in normal PB-PMNs pretreated with synovial fluid. These findings may explain the increased luminol-dependent CL since this type of CL requires the presence of MPO. Our findings suggest that the enhanced chemiluminescence observed in normal PMNs treated with synovial fluids may be related to increases in spontaneous O2- generation and myeloperoxidase release. Increased MPO release may account for enhanced CL observed in SF-PMNs.