Thus, PDPN+FAPα+THY1+ cells play the role of an immune effector in the development of rheumatoid arthritis, capable of maintaining inflammation through the secretion of a different repertoire of chemokines and cytokines, as PDPN+FAPα+THY1− cells are capable of regulating osteoclast behavior [76,155]. This evidence concerns the gene FAP and rheumatoid arthritis.