This entry represents the CXC chemokine domain. Chemokines are clustered based on the arrangement of the two N-terminal cysteine residues; includes a number of secreted growth factors and interferons involved in mitogenic, chemotactic, and inflammatory activity; many members contain an RCxC motif which may be a general requirement for binding to CXC chemokine receptors; those with the ELR motif are chemotatic for neutrophils and have been shown to be angiogenic, while those without the motif act on T and B cells, and are typically angiostatic; exist as monomers and dimers, but are believed to be functional as monomers; found only in vertebrates and a few viruses.Many low-molecular weight factors secreted by cells including fibroblasts, macrophages and endothelial cells, in response to a variety of stimuli such as growth factors, interferons, viral transformation and bacterial products, are structurally related. Most members of this family of proteins seem to have mitogenic, chemotactic or inflammatory activities. These small cytokines are also called intercrines or chemokines. They are cationic proteins of 70 to 100 amino acid residues that share four conserved cysteine residues involved in two disulphide bonds, as shown in the following schematic representation: +------------------------------------+ | | xxxxxxxxxxxxxxxxxxxxxxCxCxxxxxxxxxxxxxxxxxxxxxxxCxxxxxxxxxxxxCxxxxx | | +-------------------------+'C': conserved cysteine involved in a disulphide bond.Chemokines can be sorted into main groups based on the spacing of the two amino-terminal cysteines. In the first group , the two cysteines are separated by a single residue (C-x-C), while in the second group , they are adjacent (C-C).