HIV particle, illustration. HIV (human immunodeficiency virus) causes AIDS (acquired immune deficiency syndrome). The virus consists of an RNA (ribonucleic acid) genome (red lines), surrounded by a protein capsid (red hemisphere). Within the capsid is the reverse transcriptase enzyme (yellow) that converts the viral RNA to DNA (deoxyribonucleic acid) in an infected cell. The whole virus is enclosed in an envelope (orange) derived from the host cell's plasma membrane. The envelope has viral proteins integrated into it, including glycoprotein spikes (GP120) 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.