Description: The 12G5 monoclonal antibody reacts with human CXCR4 (CD184), also termed Fusin, LESTR, or HUMSTR. Fusin is a member of the G-protein-coupled chemokine receptor family with seven membrane-spanning domains, and functions as a coreceptor for X4 HIV-1 entry into CD+ cells. CXCR4 is expressed predominantly on naïve T cell subsets of peripheral blood and is rapidly upregulated by PHA and IL-2 stimulation. 12G5 shows partial inhibition of chemotaxis and calcium influx induced by SDF-1 (the natural ligand of CXCR4), blocks CD4-independent HIV-2 infection, and blocks CD4-dependent infection by some T-tropic HIV-1 isolates.