HIV

Human immunodeficiency virus (HIV) infects and progressively damages immune cells, especially CD4 T cells. Without effective treatment, advanced HIV infection can lead to AIDS.

CD4: A cell-surface protein that serves as a receptor for HIV and is found on helper T cells and other immune cells. HIV uses CD4 as its primary attachment point when entering susceptible cells.
Antiretroviral therapy: A combination of medicines that suppresses HIV replication and supports immune recovery. Consistent therapy can reduce viral load to undetectable levels and prevent disease progression.
AIDS: The most advanced stage of HIV infection, defined by severe immune damage or certain opportunistic illnesses. Untreated HIV can progress to AIDS as CD4 T-cell levels fall or defining illnesses occur.
Simian immunodeficiency virus: A group of related viruses that naturally infects various nonhuman primates. HIV arose through cross-species transmission of simian viruses into humans.
Hepatitis B: A viral infection of the liver caused by hepatitis B virus, which can become chronic. Like HIV, hepatitis B can be sexually and blood transmitted, but it infects different cells and has a vaccine.
CCR5: A chemokine receptor on some immune cells that serves as a coreceptor for many HIV strains. Many transmitted HIV strains need CCR5, making it a target for entry-blocking drugs.
Pre-exposure prophylaxis: Antiretroviral medication taken by HIV-negative people to reduce the risk of acquiring HIV. PrEP prevents infection by blocking HIV before it establishes itself in the body.
CD4 T cell: A helper lymphocyte that coordinates immune responses and is a principal target of HIV. Loss of these cells weakens defenses against infections and some cancers.
HIV-1: The HIV type responsible for the vast majority of HIV infections worldwide. Its pandemic lineage originated from a chimpanzee simian virus lineage.
Human T-lymphotropic virus: A group of retroviruses that infect T lymphocytes and can cause leukemia or neurological disease. HTLV is another human retrovirus, but it is distinct from HIV and causes different diseases.

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