Representative CXCR4 interactions with several different classes of CXCR4 ligands, including SDF-1α (natural agonist), vMIP-II (natural antagonist), HIV-1 gp120 (viral ligand), AMD3100 (small synthetic organic molecule), and DV1/9 (modified peptides). Orange arrows represent disease and drug related pathways, and blue arrows indicate physiologic functions of CXCR4.