Increased basal phosphorylation of mitogen-activated protein kinases and reduced responsiveness to inflammatory cytokines in neutrophils from patients with rheumatoid arthritis

OBJECTIVE: We studied the functions of peripheral blood (PB) and synovial fluid (SF) neutrophils from patients with rheumatoid arthritis (RA), focusing the molecular basis for the activated state and the functional responsiveness of RA neutrophils to inflammatory cytokines. METHODS: Paired samples of PB neutrophils and SF neutrophils from the inflamed knee joint were obtained from 18 RA patients (5 males and 13 females). RESULTS: RA neutrophils exhibited increased spontaneous superoxide (O2-) release and adherence, increased basal phosphorylation of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase, accelerated spontaneous apoptosis, and enhanced O2- release in response to N-formyl-methionyl-leucyl-phenylalanine as compared with healthy normal PB neutrophils. When challenged with granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF) or tumor necrosis factor alpha (TNF-alpha), RA neutrophils exhibited reduced responses to these cytokines, which included O2- release, adherence, priming for enhanced O2- release, and phosphorylation of ERK and p38. The functional alterations were greater in SF neutrophils than in PB neutrophils from RA. Reduced responsiveness to cytokines in RA neutrophils was closely associated with increased serum and SF levels of GM-CSF and TNF-alpha. RF and RAHA titers were closely correlated with increased TNF-alpha level in SF. CONCLUSION: These findings indicate that RA neutrophils are in the activated state with increased basal phosphorylation of ERK and p38, and exhibit reduced responsiveness to inflammatory cytokines (G-CSF, GM-CSF and TNF-alpha) and accelerated spontaneous apoptosis.