Budding HIV. Computer artwork of an HIV (human immunodeficiency virus) particle exiting a T-lymphocyte (a type of white blood cell). HIV causes AIDS (acquired immune deficiency syndrome). The virus consists of an RNA (ribonucleic acid) genome, surrounded by an icosahedral (20-sided) protein nucleocapsid (coat). The whole virus is enclosed in an envelope derived from the host cell's plasma membrane. The envelope has viral proteins integrated into it, including glycoprotein spikes that aid its attachment to host cells. When the virus particles leave the host cell they kill it, leading to a very weak immune system.