Effect of synovial fluid from patients with oligoarticular form of juvenile idiopathic arthritis (oJIA) and polyarticular form of JIA (pJIA) on the differentiation of osteoblasts from normal human bone marrow (BM) progenitors. Osteoblastogenesis was induced by ascorbic acid and β-glycerophosphate. Synovial fluid from patients with oJIA or pJIA was added to osteoblastogenic culture with each medium exchange. Osteoblastogenesis was assessed by AP activity and expression of Runx2 gene by real time PCR. (A) AP activity measured at day 7 and 17 in control cultures (hBM) and cultures supplemented with 10% synovial fluid from children with oJIA (hBM + oJIA SF) and pJIA (hBM + oJIA SF, * P < 0.05 vs. control group, Mann-Whitney test). (B) Expression of Runx2 gene in control cultures (hBM) and cultures supplemented with synovial fluid from children with oJIA (hBM + oJIA SF) and pJIA (hBM + pJIA SF). mRNA expression was calculated according to the standard curve for each gene expression in the calibrator sample (cDNA from osteoblastogenic cultures) and normalized to the mRNA quantity for glyceraldehyde 3-phosphate dehydrogenase (GAPDH) (endogenous control). Results are expressed as median and interquartile range (IQR) for each group; lines represent minimum and maximum values. AP, alkaline phosphatase; hBM, human bone marrow.