HIV particle, illustration. HIV (human immunodeficiency virus) causes AIDS (acquired immune deficiency syndrome). The virus consists of an RNA (ribonucleic acid) genome (not seen), surrounded by a protein capsid (red, orange and pink). The whole virus is enclosed in an envelope (white) derived from the host cell's plasma membrane. The envelope has viral proteins integrated into it, including glycoprotein spikes (GP120, blue) that aid its attachment to host cells. HIV infects the immune system's T-lymphocytes, ultimately killing them, leading to a very weak immune system.