From the findings that homophilic CD147 binding has occurred in the context of both heterotypic and homotypic cell–cell interactions and that CD147 can be a receptor in itself to induce MMP production, not only in primary fibroblast cells but also in tumor cells themselves [34], we presume that the increased expression of CD147 on FLS and the monocyte/macrophage lineage, especially on MLS, in RA synovium could possibly induce MMP production through interaction. Here, BSG is linked to rheumatoid arthritis.