A simplified diagram of the human chemokine superfamily, arranged by the receptors they bind to. Chemokines are represented by only their ligand number, and the receptor name also indicates whether each ligand is a CC or CXC; for example, the '6' adjacent to 'CXCR1' represents CXC6. The colors represent the chromosomal location of the ligands: the genes encoding the ligands shown in the same color are at the same chromosomal location. It can be seen that ligands whose genes are located in the same chromosomal location tend to bind to the same receptor. The extra lines attached to CXCL16 and CX3CL1 mean that these proteins exist as transmembrane proteins.