These include CD248 [15, 16], a synovial sublining glycoprotein marker expressed in perivascular and cancer stromal cells and in the RA synovium; fibroblast activation protein (FAP) [17–19], a cell surface protein that is highly expressed in established RA synovium with ectoenzyme activity and an important role in epithelial cancers; and podoplanin (gp38) [20–22], an intimal lining layer glycoprotein marker with roles in lymph node stromal networks and epithelial to mesenchymal transition. Here, PDPN is linked to rheumatoid arthritis.