Probable cell surface receptor that plays a role in cellular fusion and cell differentiation. Cooperates with DCSTAMP in modulating cell-cell fusion in both osteoclasts and foreign body giant cells (FBGCs). Involved in osteoclast bone resorption. Promotes osteoclast differentiation and may play a role in the multinucleated osteoclast maturation. Expressed in osteoclast (at protein level). Ubiquitous. Highly expressed in multi-nuclear osteoclast cells compared to mono-nuclear macrophages. Expressed in foreign body giant cells (FBGCs). Up-regulated during osteoclast and foreign body giant cells (FBGCs) differentiation by TNFSF11 and cytokines. Down-regulated by estrogen. Mice show a lack of multi-nuclear osteoclast and foreign body giant cell formation and a bone-resorbing efficiency reduction.