CD55 and rheumatoid arthritis: YAP was upregulated in the hyperplastic compared with quiescent lining of human RA synovium (p=0.0003, figure 1A), and this was accompanied by upregulation of the transcription factor SNAIL (p=0.0003), and the YAP and SNAIL downstream target gene connective tissue growth factor (CTGF) (p=0.0078, figure 1A), a known pathogenic effector in RA.22 YAP was expressed by CD55+ fibroblasts and not by CD68+ macrophages (figure 1B).