When RA tissue samples were further classified into leukocyte-poor RA and leukocyte-rich RA based on the cellular composition in synovial tissue, CXCL13, a chemokine expressed by Tph cells, was upregulated in bulk-sorted T cells from leukocyte-rich RA compared with that from osteoarthritis. Here, CXCL13 is linked to rheumatoid arthritis.