OSCAR and rheumatoid arthritis: In particular, both circulating pre-osteoclasts, synovial pre-osteoclasts, and peri-resorption sites’ mature osteoclasts in RA show an abundance of OSCAR expression [45,66], somehow suggesting that RA bone damage may be partly due to the OSCAR-mediated differentiation of imprinted osteoclasts’ precursors and excessive activation of pathologic mature osteoclasts [67].