CCL21 and synovial sarcoma: In the pathogenesis of SS, the interaction of lymphocyte homing receptors and addressins such as L-selectin/PNAD, α4β7/MAdCAM-1, VLA-4/VCAM-1, LFA-1/ICAM-1, and chemokines and their receptors such as CXCL13/CXCR5, CXCL12/CXCR4, CCL21/CCR7, CCL25/CCR9, CX3CL1/CX3CR1 regulate lymphocyte migration to the corresponding tissues and organs.