AQP5 and synovial sarcoma: Subsequent immunofluorescence analysis indicated that P2X7R expression in SS salivary gland biopsies co-localized with the acinar epithelial cell marker aquaporin 5, rather than immune cell markers, suggesting that P2X7Rs on salivary gland epithelium contribute to SS pathogenesis through a process termed autoimmune epithelitis (Mitsias et al., 2006; Baldini et al., 2017).