CD4

noun

ˌsē-(ˌ)dē-ˈfȯr 

: 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

Normally, as an HIV infection progresses, the virus infiltrates key immune cells, known as CD4 T cells, hijacking their internal machinery to make more copies of itself, and killing the host cells in the process. — Diana Kwon, Vox, 11 Nov. 2026

Wadhams says, while the GOP still has a double-digit advantage in voter registrations in both districts, unaffiliated voters account for about half the electorate in CD4 and CD5. — Shaun Boyd, CBS News, 28 Oct. 2026

Eating a vegan diet for one month may decrease pro-inflammatory white blood cells and increase CD4+ T cells, which help regulate immune responses. — Mira Miller, Verywell Health, 28 Aug. 2026

In a paper published Wednesday in Science Translational Medicine, the team reported that HIV can drive gene expression changes in T cells, turning off their CD4 proteins and turning on a protein called CD8. — Theresa Gaffney, STAT, 4 June 2026

Word History

Etymology

cluster of differentiation

First Known Use

1984, in the meaning defined above

Medical Definition

CD4

noun

-ˈfōr, -ˈfȯr 

: 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