T cell

noun

: any of several lymphocytes (such as a helper T cell) that differentiate in the thymus, possess highly specific cell-surface antigen receptors, and include some that control the initiation or suppression of cell-mediated and humoral immunity (as by the regulation of T and B cell maturation and proliferation) and others that lyse antigen-bearing cells : t lymphocyte

The immature lymphoid cell, in turn, can be processed into a B cell, which makes infection-fighting antibodies, or a T cell, which recognizes foreign tissue and virally infected cells and directs the activities of the rest of the immune system.

—Gina Kolata

T cells recognize antigen only in association with cell surface molecules encoded by the major histocompatibility complex …

—Miranda Robertson

see helper t cell, killer t cell compare b cell

Examples of T cell in a Sentence

Recent Examples on the Web

At the same time, there was a 1.7-fold increase in melanocyte-protecting regulatory T cells. —Ben Coxworth, New Atlas, 9 Feb. 2025

On the other hand, immunity against severe disease is through cellular mechanisms, such as memory T cells, which appear unaffected by the pandemic shift, the researchers write. —Ars Technica, 6 Feb. 2025

Still, Bryan was impressed an early dose of CAR T cells worked quickly in two dogs, back to back, as were the owners. —Dan Perry, Newsweek, 31 Jan. 2025

Reina-Campos leads research into how the body’s T cells might be used to fight tumors. —Noah Lyons, San Diego Union-Tribune, 28 Jan. 2025

Word History

Etymology

thymus-derived cell

First Known Use

1970, in the meaning defined above

Kids Definition

T cell

noun

: any of the lymphocytes (as a helper T cell) that usually mature in the thymus and take an active part in immune responses compare b cell

Medical Definition

T cell

noun

: any of several lymphocytes (as a helper T cell) that differentiate in the thymus, possess highly specific cell-surface antigen receptors, and include some that control the initiation or suppression of cell-mediated and humoral immunity (as by the regulation of T and B cell maturation and proliferation) and others that lyse antigen-bearing cells

called also T lymphocyte

see cytotoxic t cell, helper t cell, suppressor t cell, t4 cell