CXCL13 and juvenile idiopathic arthritis: Although there are reports that some human Th17 clones (34) or synovial Treg cells of juvenile idiopathic arthritis (35), in addition to Tfh cells, express CXCL13, single-cell RNA sequencing (scRNA-seq) of the entire RA synovial tissue shows that Tph cells are the main source of CXCL13 (36).