Reverse transcription (RT)-PCR analysis of IFN-γ inducible protein-10 (IP-10) mRNA expression induced by the interaction of synovial fluid (SF) leukocytes and rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLSs). SF monocytes (mono) or PMNs were layered onto RA FLS monolayers. Total RNA was isolated 12 hours later, after which RT-PCR was performed. (a) Representative expression of IP-10 mRNA; expression of β-actin mRNA served as an internal control. Lane M contains molecular weight markers (100 base pair [bp] ladder). (b) IP-10 mRNA expression was quantified and normalized to β-actin as the IP-10/β-actin ratio. Data are expressed as means ± SEM for three independent experiments that were performed using three different RA fibroblasts and three different RA SF leukocytes.