Human Immunodeficiency Virus (Hiv)

Topics: Immune system, HIV, AIDS Pages: 2 (522 words) Published: February 21, 2013
Human immunodeficiency virus (HIV) is a lentivirus (slowly-replicating retrovirus) that causes acquired immunodeficiency syndrome (AIDS),[1] an infectious disease in which progressive failure of the human immune system leads to life-threatening opportunistic infections and/or cancer. HIV infects vital cells in the human immune system such as helper T cells (specifically CD4+ T cells), macrophages, and dendritic cells. HIV infection leads to low levels of CD4+ T cells through three main mechanisms: First, direct viral killing of infected cells; second, increased rates of apoptosis in infected cells; and third, killing of infected CD4+ T cells by CD8 cytotoxic lymphocytes that recognize infected cells. When CD4+ T cell numbers decline below a critical level, cell-mediated immunity is lost, and the body becomes progressively more susceptible to opportunistic infections HIV is different in structure from other retroviruses. It is roughly spherical[10] with a diameter of about 120 nm, around 60 times smaller than a red blood cell, yet large for a virus.[11] It is composed of two copies of positive single-stranded RNA that codes for the virus's nine genes enclosed by a conical capsid composed of 2,000 copies of the viral protein p24.[12] The single-stranded RNA is tightly bound to nucleocapsid proteins, p7, and enzymes needed for the development of the virion such as reverse transcriptase, proteases, ribonuclease and integrase. A matrix composed of the viral protein p17 surrounds the capsid ensuring the integrity of the virion particle.[12] This is, in turn, surrounded by the viral envelope that is composed of two layers of fatty molecules called phospholipids taken from the membrane of a human cell when a newly formed virus particle buds from the cell. Embedded in the viral envelope are proteins from the host cell and about 70 copies of a complex HIV protein that protrudes through the surface of the virus particle.[12] This protein, known as Env, consists of a cap...
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