HIV antibody therapy. Molecular model of the interaction of the HIV surface protein gp120 (green, lower right) as it interacts with a human white blood cell surface protein (CD4, blue, upper right) and the anti-HIV antibody (17B, yellow, red and orange, upper left). Overlapping foreground and background models show the helices and arrowed sheets representing the protein shapes (secondary structures, foreground) and the 8322 atoms (tubes, background) of the molecular structure. HIV (the human immunodeficiency virus) causes AIDS (acquired immune deficiency syndrome). The antibody neutralises the effect of gp120, helping to prevent the onset of AIDS, and is being studied for use in HIV antibody therapy. This is the HXBc2 strain of the HIV-1 form of HIV.