IL21 and rheumatoid arthritis: In patients with Sjögren syndrome, CCR9+CD4+ T cells are expanded in PB, and CCR9: CCL25 interactions induce the migration of CCR9+CD4+ T cells, which have a greater potential to provide IL-21.[23] In another study of Sjögren syndrome, enriched CCR9 expression on mucosal-associated invariant T cells may facilitate migration to inflamed salivary glands known to overexpress CCL25.[12] In this study, the percentage of CCR9+CD4+ T cells and the MFI of CCR9 on CD4+ T cells were all elevated in SF compared to PB, which indicated that more CCR9+CD4+ T cells had migrated to the joint in RA.