killer T cell
Meaning of killer T cell: The immune system's targeted assassin, destroying one marked cell at a time while leaving its healthy neighbors untouched.
Definition of killer T cell
A killer T cell is a white blood cell that destroys the body's own cells once they have been taken over by a virus or have turned cancerous. It inspects the protein fragments each cell displays on its surface, and when it finds one it was trained to recognize, it opens channels in that cell and switches on the cell's own self destruction program.
How does it find its target?
Every cell with a nucleus displays samples of the proteins made inside it. A killer T cell carries a receptor tuned to one specific fragment, moves from cell to cell testing displays, and ignores everything that does not fit. A second confirming signal is needed before it acts, which limits damage to healthy tissue. These cells belong to the lymphocyte family and mature in the thymus, where clones reacting to the body's own normal proteins are weeded out before release.
How does it kill?
The killer T cell presses against its target and empties granules into the narrow gap between them. One protein drills a channel through the target membrane, and enzymes pass through it to trigger the target's suicide program. The cell shrinks, breaks into sealed packets and is cleared by scavenging cells, which contains any virus inside instead of spilling it. A surface signal can set off the same program without granules. The killer T cell itself survives and moves on.
How does it differ from a natural killer cell?
| Killer T cell | Natural killer cell | |
|---|---|---|
| Recognizes | One specific displayed fragment | Cells with missing or abnormal surface display |
| Needs priming first | Yes | No, it acts straight away |
| Memory afterwards | Long lived memory cells remain | Limited |
A tumor that hides by shedding its surface display escapes the killer T cell but becomes conspicuous to the natural killer cell, so the two systems cover each other's blind spots.
Why do they matter in treatment?
Several cancer treatments work by releasing the brakes that tumors apply to these cells, or by growing them outside the body and returning them. Cells collected from a patient can be expanded in the laboratory, or fitted with an engineered receptor aimed at a tumor protein, then infused back. Rejection of a transplanted organ is driven by the same machinery pointed at the graft. Laboratory reports and older textbooks use the names cytotoxic T cell and CD8 T cell for exactly the same cell.
Also known as
Used in a sentence
Flow cytometry was used to count circulating killer T cells before and after the infusion.
Good to know
Killer T cells act only on cells displaying a fragment they were primed against, so tumors that reduce that display evade them while remaining visible to natural killer cells.
Word origin
Where “killer T cell” comes from
The T marks the thymus, the chest gland where these cells mature, from the Greek thymos.