P2RX7 and synovial sarcoma: Studies of human SS samples found increased P2X7 receptor expression in the salivary glands and peripheral blood mononuclear cells of patients compared to controls [167,168], which correlated with increased NLRP3, ASC, caspase-1 and pyrin expression in the salivary glands and elevated IL-18 levels in the saliva of SS patients (Table 2).