The role of osteopontin in foreign body giant cell formation.

Foreign body giant cells (FBGCs) are a hallmark of the foreign body reaction caused by biomaterial implantation and are thought to contribute to biomaterial degradation and the duration of the response. Osteopontin (OPN) is a secreted, acidic matricellular protein with multiple phosphorylation sites that is highly expressed at sites of inflammation. OPN wildtype and knockout mice were implanted with poly(vinyl alcohol) sponges and explanted at 14 days. OPN knockout mice had more foreign body giant cells but fewer macrophages surrounding the implants than their wildtype counterparts. In an in vitro human FBGC assay, addition of soluble OPN was found to reduce macrophage fusion to giant cells. These are the first studies to show a direct inhibitory role of OPN in FBGC formation in response to implantation.