Association between OP-1 and IL-6 family of chemokines. A, Effect of lack (OP-1 antisense oligo) or excess of OP-1 (treatment with recombinant protein, 100 ng/ml, 48 hours) on gene expression of IL-6, IL-8, IL-11, and LIF in chondrocytes cultured in monolayers. Graphical representation of gene array data. B, Real time PCR of in vitro verification experiments, where knee chondrocytes cultured in monolayers were treated for 48 hours with the same dose of recombinant OP-1. The graph illustrates an inhibition of LIF, IL-6, and IL-8 gene expression. C, verification experiments with metabolic study. Proteoglycan synthesis measured in chondrocytes cultured in alginate beads and treated for 48 hours with 100 ng/ml IL-6 (in the presence of 150 ng/ml soluble IL-6 receptor) or the combination of IL-6 and OP-1 (100 ng/ml). Data were normalized to the DNA content and compared to 10% FBS control. OP-1 was able to overcome an inhibitory effect of IL-6 on PG synthesis.