CXCR3, also known as GPR9, is a member of the CXC chemokine receptor subfamily. Similar to other chemokine receptors, it is a G protein-coupled receptor (GPCR). In humans, two alternatively spliced CXCR3 isoforms, CXCR3 and CXCR3B, have been identified and have different chemokine binding affinities. Human CXCR3 is 368 amino acids (aa) in length with a predicted molecular weight of 41 kDa. CXCR3B contains an additional N-terminal sequence and is 415 aa in length with a predicted molecular weight of 46 kDa. Mouse and rat CXCR3 share 86% aa sequence identity with human CXCR3. CXCR3 is expressed on leukocytes and is upregulated following T cell activation. It binds multiple CXC chemokines and is known to mediate leukocyte trafficking. CXCR3 has been implicated in neuroinflammatory and autoimmune diseases.