The chemokine receptor CXCR4,a 7-transmembrane protein on cell surface,acts with the CD4 protein to support HIV entry into cells. CXCR4 is highly expressed in brain and heart,white blood cells,vascular endothelial cells,and umbilical cord endothelial cells. Several CXCR4 isoforms have been identified with molecular weights of 47,50,62 and 98kDa. The 62-64kDa CXCR4 is predominantly ubiquitinated and is preferentially associated with CD4. This antibody recognizes the 62kd CXCR4.