The chemokine family constitutes a group of specialized cytokines, the primary function of which is to regulate the trafficking of leucocytes. All family members are small secreted heparin-binding proteins that can be distinguished from classical chemoattractant molecules such as bacterial-derived N-formyl peptides, complement fragment peptides C3a and C5a, and lipid molecules such as leukotriene B4 and platelet-activating factor) on the basis of shared structural similarities. Chemokines have four conserved cysteine residues that form disulphide bonds which are critical for the tertiary structures of the proteins. The chemokine family is organized into four subclasses according to the position of the first two cysteines. The two major subclasses include the CC chemokines, where the cysteines are adjacent, and the CXC chemokines, where the cysteines are separated by one amino acid. Two other subclasses have been identified with, to date, one member in each. The C class has only two cysteines instead of four and has lymphotactin as its member, while the CX3C subclass has three amino acids between the first two cysteines and a mucin stalk at the N-terminal end, and incorporates fractalkine. Chemokines have a short N-terminal domain preceding the first cysteine, a backbone made of b-strands with the connecting loops found between the second and fourth cysteines, and a C-terminal a-helix of 20ą30 amino acids.

The chemokine superfamily has rapidly expanded as a result of the availability of large databases of expressed sequence tags ESTs) and bioinformatics. 1 Indeed, the distinct motifs contained within chemokine structures have made identifying new family members within these EST databases relatively easy. To date, 23 human CC chemokines, 14 human CXC chemokines and one member of both the CX3C and C subclasses have been described. This rapid expansion of the chemokine/receptor family has led to problems when several research groups have described a single chemokine that has become known by multiple names. To counteract this confusion a new