Secretion of IFN-γ inducible protein-10 (IP-10) mediated by the interaction of fibroblast-like synoviocytes (FLSs) and leukocytes. (a) Monocytes (mono; 5 × 105/0.5 ml per well) or (b) polymorhonuclear neutrophils (PMNs; 2.5 × 106/0.5 ml per well) obtained from either synovial fluid (SF) or peripheral blood (PB) were layered onto unstimulated semiconfluent rheumatoid arthritis (RA) FLS monolayers in 48-well plates, after which monoclonal antibodies (10 μg/ml) against IFN-γ or tumor necrosis factor (TNF)-α, and control mouse IgG (10 μg/ml) were added. Supernatants were collected at 24 hours after coculture, and then IP-10 was measured using enzyme-linked immunosorbent assay. Data represent the mean (pg/ml) ± SEM of seven independent experiments that were performed using three different RA fibroblasts and seven different RA SF leukocytes or normal PB leukocytes. *P < 0.05, versus cocultures with PB leukocytes.