CCL21 is a CC chemokine highly expressed in lymph nodes. CCL21 is only 32% identical to CCL19 at the amino acid level; nevertheless, these chemokines bind to the same receptor CCR7. CCL21 has a unique extension of about 30 amino acids with two extra cysteine residues in its carboxyl terminus. CCL21 is expressed in synovial tissue in rhematoid arthritis (RA), and it has been suggested that CCL21, but not CCL19, induces human microvascular endothelial cell (HMVEC) migration and/or tube formation. In addition, it has been reported that sustained high concentrations of either soluble or immobilized CCL19 and CCL21 inhibit T cell proliferation and IL-2 secretion.