CXCL13 and synovial sarcoma: CXCL13 directs B-cell chemotaxis and is elevated in several autoimmune diseases, including SS (35), CXCR5 is a chemokine receptor mainly expressed on B cells and a subset of T cells, called follicular B helper T cells, and binds the chemotactic ligand CXCL13 (36), while BAFF is central to the cross talk between early activation of the immune system and the stimulation of autoreactive B cells (37).