The body's immune system is under constant assault — from viruses, bacteria and other foreign substances that threaten our health on a daily basis. How do we fight off that steady barrage of pathogens? With cells of our own that are, scientifically speaking, cold-blooded assassins.

A fascinating video published Tuesday by U.S. and British researchers in the journal Immunity shows in detail how cytotoxic T-cells, a specialized type of white blood cells, relentlessly hunt down and destroy cancer cells in the body.

"Inside all of us lurks an army of serial killers whose primary function is to kill again and again," Gillian Griffiths, director of the Cambridge Institute for Medical Research, said in a release detailing the study. "These cells patrol our bodies, identifying and destroying virally infected and cancer cells, and they do so with remarkable precision and efficiency."

Our blood contains billions of T-cells — researchers estimate that a teaspoon of blood could have 5 million of them — and each is on an unrelenting search to find and kill virus-infected cells. T-cells first probe the surface of an offending cell to identify it as unwanted, then inject it with deadly proteins known as cytotoxins. "Its fate is sealed and we can watch as it withers and dies," Griffiths said. "The T-cell then moves on, hungry to find another victim."

Scientists have been experimenting with ways to supercharge the body's T-cells to fight certain kinds of cancer, part of a growing body of research aimed at harnessing the body's immune system to better recognize and attack tumors. In some cases, doctors are harvesting T-cells from a patient, engineering them to target certain cancer cells, growing billions of them in a lab and then infusing them back into the body to do their work.

Researchers created Tuesday's 3D video using high-resolution, time-lapse imaging to show T-cells in action. Check it out to see how T-cells, which appear as roaming orange or green blobs, ruthlessly stalk and attack cancer cells (blue) by blasting them with cytotoxins (red).

Rock on, T-cells. Keep doing your thing.

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