: a large glycoprotein that is found associated with a T cell receptor especially on the surface of helper T cells and that binds to a major histocompatibility complex molecule on the surface of an antigen-presenting cell to facilitate antigen recognition and T cell activation
often used before another noun
the CD4 gene
CD4 T cells [=T cells bearing CD4 on their surface]

Note: CD4 is a receptor for HIV, and cells of the immune system bearing CD4 on their surface are preferentially infected with the virus and become progressively depleted.

compare CD8

Examples of CD4 in a Sentence

Recent Examples on the Web Schoenberger said the next path of exploration is to explore ways that antigens that activate CD4 and CD8 T-cells could be linked. Paul Sisson, San Diego Union-Tribune, 6 Mar. 2024 The enveloped and the lentiviral vector displayed CD3, CD4 and CD28-targeting antibody fragments on their surface to target T cells. William A. Haseltine, Forbes, 14 Feb. 2024 There’s no shortage of follow-up questions to investigate: How exactly are all these immune cells getting activated by CD4+? Isabella Cueto, STAT, 14 July 2023 In the cases where people had few CD4 cells, mpox’s normally small skin lesions grew into large necrotizing patches and their infection sometimes spread to the lungs or caused severe secondary infections with bacteria. Bykai Kupferschmidt, science.org, 21 Feb. 2023 When the adaptive response starts taking effect, CD4+ and CD8+ T-cells are released which play an important role in coordinating a sustained immune response and killing off infected cells. William A. Haseltine, Forbes, 13 Feb. 2023 The virus infects and destroys white blood cells called CD4+ cells, which weakens the immune system. Ella Lee, USA TODAY, 13 Jan. 2022 The scientists looked for antibodies, memory B cells, CD8+ T cells, and CD4+ T cells, all fighting SARS-CoV-2. Adam Rogers, Wired, 5 Mar. 2021 The disease would later be cataloged on immunological graphs illustrating the awful decline of the infected – first the CD4+ T-cell count falls as the viral load ascends, then a marching band of viral, fungal, protozoan and bacterial infections capitalizing on the loss of CD4+ T-cells. Rebecca Kreston, Discover Magazine, 28 Sep. 2014

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'CD4.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

Etymology

cluster of differentiation

First Known Use

1984, in the meaning defined above

Time Traveler
The first known use of CD4 was in 1984

Dictionary Entries Near CD4

Cite this Entry

“CD4.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/CD4. Accessed 16 Jun. 2024.

Medical Definition

: a large glycoprotein that is found associated with a T cell receptor especially on the surface of helper T cells and that binds to a major histocompatibility complex molecule on the surface of an antigen-presenting cell to facilitate antigen recognition and T cell activation
often used before another noun
the CD4 gene
CD4 T cells [=T cells bearing CD4 on their surface]

Note: CD4 is a receptor for HIV and cells of the immune system bearing CD4 on their surface are preferentially infected with the virus and become progressively depleted.

compare cd8

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