Synovial fluid monocytes or polymorphonuclear neutrophils (PMNs) were layered onto fibroblast-like synoviocyte (FLS) monolayers in the presence or absence of a transwell membrane (pore size 0.45 μm). After 24 hours of incubation, the supernatants were collected from the cocultures and from the FLS monolayer (FLS-sup) and leukocyte suspension (monocyte-sup or PMN-sup) sides of the transwell membrane, and assayed using enzyme-linked immunosorbent assay. Values represent the mean (pg/ml) ± SEM of three independent experiments, which were performed using two different rheumatoid arthritis fibroblasts and three different rheumatoid arthritis synovial fluid leukocytes. Percentage inhibition was calculated by subtracting the IFN-γ inducible protein-10 (IP-10) contents obtained with either FLS-sup or monocyte-sup/PMN-sup from those with cocultures and dividing by the IP-10 contents obtained with cocultures (as 100%). ** P < 0.01, versus the respective coculture. ND, not done.