BMP4 and juvenile idiopathic arthritis: To demonstrate that the inhibition of BMP4 is necessary to cause JIA FLS to dedifferentiate away from a hypertrophic chondrocyte-like phenotype, using ELISA, we measured chondrocyte marker expression in JIA FLS treated with either noggin or chordin, two prominent BMP4 inhibitors that act by binding directly to BMP4 ligand.