CXCL9, a member of the alpha subfamily of chemokines that lack the ELR domain, was initially identified as a lymphokine-activated gene in mouse macrophages. Human CXCL9 was subsequently cloned using mouse MIG cDNA as a probe. The human CXCL9 cDNA encodes a 125 amino acid residue precursor protein with a 22 amino acid residue signal peptide that is cleaved to yield a 103 amino acid residue mature protein.The carboxyterminal residues of CXCL9 are prone to proteolytic cleavage resulting in size heterogeneity of natural and recombinant CXCL9.The CXCL9 gene is induced in macrophages and in primary glial cells of the central nervous system specifically in response to IFN-gamma. CXCL9 has been shown to be a chemoattractant for activated Tlymphocytes and TIL. And it elicits their chemotactic functions by interacting with the chemokine receptor CXCR3.