CXC chemokines comprise a subfamily of the chemokine superfamily and are defined by the arrangement of the first two of four invariant cysteine residues found in most chemokines. In CC chemokines, these two cysteines are adjacent, while in the CXC subfamily, they are separated by a single amino acid. Chemokines exhibit promiscuous binding to multiple seven-transmembrane, G-protein coupled chemokine receptors. Chemokines are typically small, secreted molecules that function in leukocyte trafficking, recruitment, and activation. They also play roles in normal and pathological processes including allergic responses, infectious and autoimmune disease, angiogenesis, inflammation, and tumor growth and metastasis.