XCL1 and rheumatoid arthritis: Increased levels of XCL1 and XCR1 have been reported in joint fluid of rheumatoid arthritis patients (Wang et al., 2004), and XCL1 is also present in oral mucosal endothelial cells in oral cancer (Khurram et al., 2010, Kiaii et al., 2013), suggesting that XCL1 may be present in other cell types and is upregulated in disease conditions.