Chemokines are a large family of small secreted proteins that regulate migration of white blood cells. Based on the arrangement of the first two of the four conserved cysteine residues, chemokines are classified into four subfamilies, CXC, CC, C and recently identified CX3C . The CC chemokines, in which the first 2 cysteines are adjacent, usually act on monocytes, T lymphocytes, and, in some cases, eosinophils, basophils, or mast cells. The CC subfamily proteins are 70 to 100 amino acids long, have 25 to 75% identity with each other, and include novel member of the CC chemokine subfamily, designated ABCD1 （SCYA22）. The SCYA22 protein shares 28 to 34% identity with other CC chemokines and contains the characteristic 4-cysteine motif and 9 other highly conserved residues .
The activated T cell-attracting CC chemokine CCL22 is expressed by stimulated B cells and mature dendritic cells （DC）. Both identical and distinct proteins contribute to expression of CCL22 in DC and B cells .