Demonstration of mast cell chemotactic activity in synovial fluid from rheumatoid patients

OBJECTIVES—The significance of the mast cell in the pathogenesis of rheumatic diseases has become more evident. Although mast cell hyperplasia is a feature of rheumatoid arthritis, the nature of mast cell chemoattractants involved in the recruitment of mast cells in joint diseases has not been studied in any detail. In this study the presence of mast cell chemotactic activity in synovial fluids was examined. METHODS—Synovial fluids from seven rheumatoid patients were tested in a modified Boyden chamber, where a human mast cell line was used as responder. The presence of stem cell factor (SCF) and transforming growth factor β (TGFβ) was measured by enzyme linked immunosorbent assay (ELISA). RESULTS—Six of the seven synovial fluids tested exhibited mast cell chemotactic activity. Two characterised human mast cell chemotaxins, SCF and TGFβ, were highly expressed in the synovium. Soluble SCF could be detected in all fluids analysed. Blocking antibodies against SCF or TGFβ almost completely blocked the activity in one fluid, partially blocked the activity in three, and did not affect the activity in two. Treatment of the responder cells with pertussis toxin reduced the migratory response against seven fluids, indicating the presence of chemoattractants mediating their effect through Gi coupled receptors. CONCLUSION—These data demonstrate the presence of multiple factors in synovial fluid acting as mast cell chemoattractants, two of which are SCF and TGFβ that contribute to the effect. These findings may be of importance for developing new strategies to inhibit mast cell accumulation in rheumatic diseases.