A systematic chemokine nomenclature, based on protein structure and a previous nomenclature for chemokine gene loci, was developed by A. Zlotnik and O. Yoshie to deal with the proliferation of synonyms that has attended chemokine discovery and was proposed at the Keystone Symposium on Chemokines and Chemokine Receptors, Keystone, CO, 1999. At present, the systematic names refer only to human chemokines, in part because of uncertainties regarding the identity of mouse orthologs. Nevertheless, the table also includes accession numbers and common names for putative mouse orthologs. In cases such as CCL6, CCL9, and CCL12, where a mouse chemokine lacks a known human ortholog, the standard name is reserved for the potential human counterpart, although it may not exist due to lineage-specific gene duplication. In many cases, the same common name applies to human and mouse counterparts. In others, species-specific names are preferentially used to convey substantially different properties, such as a major difference in sequence (e.g., human I-309 versus mouse TCA-3) or length (e.g., mouse JE versus MCP-1). The number in the systematic name for each chemokine matches that in an alias for the corresponding human gene name, and the roots for gene names correspond to protein roots as follows: SCYA = CCL, SCYB = CXCL, SCYC = XCL, and SCYD = CX3CL, where SCY denotes small cytokine; A, B, C, and D denote the chemokine classes in the gene locus; and L denotes “ligand” in the root of the protein name. Thus, for example, SCYB1 is a gene alias for the human chemokine CXCL1. Accession numbers are from the SwissProt database, when available; N.A. indicates not available in any database. A discussion of tissue and cell sources and regulation for the chemokines is beyond the scope of this article but can be found in Oppenheim et al. (2000).

• ↵2-a KC and MIP-2 are mouse proteins with similar sequence relatedness to each of the three human Gro proteins.

• ↵2-b Sequential N-terminal truncation of PBP produces the chemokines shown. Only NAP-2 has leukocyte chemoattractant activity, specifically for neutrophils.

• ↵2-c β-R1 (accession number U59286) is 87% identical in amino acid sequence to I-TAC. The genomic relationship of the two is not yet defined.

• ↵2-d SDF-1α and SDF-1β are splice variants of the same human gene but appear to be functionally equivalent.

• ↵2-e LD78α and LD78β are products of two closely related human genes that arose by duplication after the human-rodent split. Thus, only a single related gene product, known as MIP-1α, has been found in mouse.

N.D., not determined; N.A., not available. Two splice variants affecting the ORF have been identified for each of the following receptors: CXCR4, CXCR5, CCR2, and CCR9; however, biological or pharmacological significance has not been determined. Other HIV coreceptors include US28 (Pleskoff et al., 1997), the leukotriene B₄ receptor (Owman et al., 1998), and the orphans Apj (Choe et al., 1998), BOB/GPR15 (Deng et al., 1997; Farzan et al., 1997), STRL33/Bonzo/TYMSTR (Deng et al., 1997; Liao et al., 1997; Loetscher et al., 1997), GPR1 (Farzan et al., 1997), ROC1 (Shimizu et al., 2000); and ChemR23 (Samson et al., 1998).

Note that leukocyte distribution is based mainly on in vitro studies, which have in some cases conflicted. See text for details and references.