XCL1 and rheumatoid arthritis: In phorbol myristate acetate/ionomycin-stimulated PBMCs, activation-induced, T cell-derived, and chemokine-related cytokine (ATAC)/lymphotactin (Lptn) is detected in CD8+ T cells and is upregulated in CD4+CD28− T cells from patients with RA as compared with their levels in healthy controls (38).