Real time PCR analysis of expression of early ( Runx2 ) and late ( OPG, RANKL ) osteoblast genes in synovial fluid (SF)-derived osteoblasts. (A) Primary SF-derived osteoblastogenic cultures from children with oligoarticular form of juvenile idiopathic arthritis (oJIA, n = 12) and polyarticular form of JIA (pJIA, n = 4) at culture days 14 and 21 (median and interquartile range (IQR), * P < 0.05 vs. pJIA, Mann-Whitney test). (B) Osteoblastogenic cultures from the fourth passage (P4) of SF-derived cells from children with oJIA (n = 7) and pJIA (n = 4), at culture days 10 and 14 (median and IQR,* P < 0.05 vs. pJIA, Mann-Whitney test). mRNA expression was calculated according to the standard curve for each gene expression in the calibrator sample (cDNA from osteoblast cultures) and normalized to the mRNA quantity for glyceraldehyde 3-phosphate dehydrogenase (GAPDH) (endogenous control). OPG, osteoprotegerin; RANKL, receptor activator of NF-κB ligand; Runx2, runt-related transcription factor 2.