TPH1 and rheumatoid arthritis: Cells with similar transcriptomic, cytometric, and functional features to RA synovial T cells can be found in the circulation as well (37), and many studies have reported quantification circulating Tph and Tfh cells in autoimmune disease patient cohorts (38), yet identifying Tph cells in the circulation has been hampered by the difficulty in discriminating Tph cells from other activated T cell populations (38).