Foreign body giant cells and osteoclasts are TRAP positive, have podosome-belts and both require OC-STAMP for cell fusion.

Macrophages have the ability to fuse and form multinucleated giant cells such as Osteoclast (OCs) and FBGCs. Osteoclast stimulatory transmembrane protein (OC-STAMP) is an important cell surface protein involved in the formation of OCs. This study sought to determine if OC-STAMP also regulates formation of FBGCs using expression analysis and subsequent inhibition studies. qPCR and Western blot analysis showed that OC-STAMP expression is significantly higher in FBGCs compared to control monocytes (P < 0.05). Four days following cell culture, OCs were positive for TRAP and F-actin ring formation, but FBGCs were not. In contrast, FBGCs were positive for TRAP and showed podosome belts comprised of F-actin on Day 8. FBGCs were subsequently plated onto dentine, but despite presenting some morphologic features of OCs (OC-STAMP expression, TRAP reactivity, and podosome belts) they failed to resorb bone. To evaluate a role for OC-STAMP in FBGCs, we inhibited this cell surface protein with anti-OC-STAMP antibody and observed that cell fusion and podosome belt formation was inhibited in both OCs and FBGCs. Our data support the hypothesis that OC-STAMP is a regulatory molecule for FBGCs; and that they are functionally distinct from OCs, despite similarities in gene expression profile, podosome belt formation, and TRAP expression.