Objective: To identify and quantitate stem cell factor (SCF; kit ligand) in the serum and synovial fluid (SF) of patients with rheumatoid arthritis (RA) and to compare these values with those measured in normal serum, RA serum, SF of patients with other rheumatic diseases, and conditioned medium from cultured synoviocytes.
Methods: SCF was measured in serum, SF, and conditioned synovial cell culture medium by a sensitive ELISA. Results were correlated with hematologic variables including white blood cell count, hemoglobin, platelet count, erythrocyte sedimentation rate, and rheumatoid factor.
Results: SCF levels in RA SF exceeded those measured in RA serum, osteoarthritis SF, and SF from patients with other inflammatory arthropathies. SCF was detectable in conditioned medium from cultured synoviocytes.
Conclusion: High levels of SCF are present in RA serum and SF. Local production of SF may influence expansion of myeloid progenitor cells and mast cell function in RA.