CD147 is expressed in epithelial cells [99], fibroblasts [123], psoriatic peripheral blood mononuclear cells [124], cytotrophoblasts [125], the normal basal epithelial layer reportedly harboring stem cells [126], ectopic endometrial tissues [127], systemic lupus erythematosus [128], synovial joint disease tissue of rheumatoid arthritis (RA) patients [115,129], plasma of lupus nephritis patients [130], peripheral monocytes and T lymphocytes of patients with ankylosing spondylitis [131]. Here, BSG is linked to rheumatoid arthritis.