FAP and rheumatoid arthritis: CD34, CD44, CD55, CD90 (also called THY1), cadherin 11, VCAM1 (CD34), CD248, fibroblast activation protein (FAP), and podoplanin (PDPN) are highly expressed on fibroblasts in inflammatory conditions, [19–28], and have all been used to distinguish different fibroblast subsets in rheumatoid arthritis (RA).