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Researchers have discovered a previously unknown mechanism that immune cells use to protect themselves from a friendly fire. 

Immune system includes natural killer cells (NK cells) which recognize and eliminate tumor or virus infected cells. NK cells therefore combat the body's own stressed cells so that they don't become a potential hazard. However, this leads to another risk. Other immune cells, i.e, specific killer cells also exhibit stress symptoms and thereby potentially end up on the NK cells' hit list.

Researchers in their study discovered what keeps NK cells from killing off their "colleagues from the other department" of the immune system: healthy CD8+ cells are able to detect the immune messenger substance type 1 interferon, which binds to specific receptors on the surface of these immune cells and thereby conceals their stress, researchers explained in the press release.

In other words, it acts as a camouflage cloak that helps them render as invisible to the NK cells. Researchers added that if the T cells lack the docking site for type 1 interferon, they would be hunted down by the NK cells and exterminated. 

"So far, it is unclear whether the same mechanism also exists in humans. However, the basic processes that the human immune system uses to protect its T cells against an attack from natural killer cells might well be comparable. On the one hand, the researchers now understand which mechanisms the stressed T cells need to protect themselves against NK cells. On the other hand, this insight enables new hypotheses to be formulated," the press release added.

The study has been published in the journal Immunity.