HIV antibody therapy. Molecular model of the interaction of the HIV surface protein gp120 (green) as it interacts with a human white blood cell surface protein (CD4, blue) and the anti-HIV antibody (17B, yellow and orange). 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.