Chemokines are a large superfamily of mostly small, secreted chemotactic cytokines that function in leukocyte trafficking, recruitment and activation. They also play a critical role in many normal and pathophysiological processes such as allergic responses, infectious and autoimmune diseases, angiogenesis, inflammation, tumor growth and metastasis, and hematopoietic development. Chemokines are divided into subfamilies based on conserved amino acid (aa) sequence motifs. Most family members have at least four conserved cysteine residues that form two intramolecular disulfide bonds. The subfamilies are defined by the position of the first two cysteine residues.