CD274 and synovial sarcoma: Their results suggest, for the first time, a concerted increase in ETS1 and LEF1 expression in salivary gland epithelial cells of pSS patients that may contribute as an effector mechanism of salivary gland destruction in pSS.18 Peripheral blood programmed cell death protein 1 (PD-1) and its ligand (PD-L1) expressed on the surface of T cells, B cells may also participate in the pathogenesis and development of SS through interactions.