Definition for View source for Acquired immune deficiency syndrome (AIDS)

1. A disease caused by the human immunodeficiency virus (HIV) that leads to a defect in the immune system of infected individuals.

2. Acquired immunodeficiency syndrome (AIDS) is not a disease but a syndrome—a complex of signs, symptoms, and diseases with a common cause. AIDS is the presence of certain infections in association with antibodies to the human immunodeficiency virus (HIV), and a CD4 white blood cell count below 200 cells/microliter of blood. This virus replicates in humans and destroys the immune system. There are two types: HIV-1 and HIV-2. HIV has an envelope with two antigenic glycoproteins, gp120 and gp41, which impede immune clearance of HIV by aiding attachment, antigenic variability, and cell fusion. Human immunodeficiency viruses likely arose from simian immunodeficiency virus (SIV) in the 1930s. 

HIV infects four kinds of cells: helper T cells, cells of the macrophage lineage, smooth muscle cells, and dendritic cells (antigen-presenting cells). Attachment of HIV and entry into T cells and macrophages involves binding of the envelope proteins with CD4 and chemokine receptors on the leukocyte membrane. The gp41 protein also promotes the formation of a syncytium, a giant multinucleate cell, between infected and uninfected cells. Dendritic cell infection involves different receptors. The dsDNA created by reverse transcriptase is known as a provirus, which enters the nucleus and is inserted into a chromosome by the enzyme integrase. The virus is latent and may remain dormant for years, or it may be activated immediately. After HIV virions bud from the cytoplasmic membrane, the enzyme protease releases reverse transcriptase and capsomeres to make HIV virulent. The course of the syndrome is directly related to the destruction of helper T cells and leads to the collapse of immune function and development of overwhelming infections. 

HIV is primarily spread by contact with infected secretions or blood through sexual contact or IV drug use. Diagnosis involves ELISA, agglutination, or western blot testing to detect antibodies, and polymerase chain reaction to detect viral genomes. Long-term nonprogressors are people who have been infected but have not yet developed AIDS and may have unusually well-developed immune systems or lack a necessary receptor. Treatment involves highly active antiretroviral therapy, a “cocktail” of antiviral drugs, including nucleoside analogs, protease inhibitors, and reverse transcriptase inhibitors to reduce viral replication. Individual diseases must be managed and treated on a case-by-case basis. Many factors make development of a vaccine difficult. Preventive measures involve safe sex behaviors, hygienic practices for drug injections, reducing vertical transmission, and screening blood and organs.