Crucial Immune Protein IL-17 more Versatile and Important than Thought, not just in the Mucosa

Researchers at ETH Zurich have demonstrated the importance of the immune protein interleukin 17 (IL-17) and what are known as NK cells in fighting infections in the body. Until now, IL-17 has been known mostly for its role in the immune response in the mucosa.

NK cells are an important part of the body's innate immune system (micrograph of such a cell). (Photo: Science Photo Library / Keystone)

Researchers at ETH Zurich have discovered that one particularly important chemical messenger protein in the immune system plays a much greater and broader role than previously thought. Interleukin 17 (IL-17) is one of several dozen messenger proteins used by various cells to communicate with each other in the immune system. It has been known before that IL-17 is produced mainly by immune cells in the mucosa and in the skin - for example, in the oral mucosa or gastrointestinal tract. There, it protects the tissue against infectious diseases - particularly fungal infections - by triggering the appropriate immune response.

Under the direction of Salomé LeibundGut, professor at the Institute of Microbiology, researchers recently discovered that IL-17 also plays a crucial role for entirely different defence mechanisms inside the body. Namely, it helps to fight off pathogens in the blood vessels and internal organs.

In mouse experiments, the ETH Zurich researchers showed how the effect of the messenger protein inside the body is closely related to a specific type of white blood cell: NK cells. Mice unable to produce or detect IL-17 did not generate functional NK cells and were therefore unable to fight off fungal infections in the bloodstream. In further experiments, researchers were able to show that NK cells do not directly kill the pathogens but instead activate phagocytes, which then eliminate the pathogens.

"The effect of IL-17 within the body has a broader scope than in the mucous membranes," says LeibundGut. The NK cells that rely on IL-17 in the body defend against pathogenic fungi as well as viruses, for example. Scientists also know that these cells inhibit the development and growth of tumours.

Reference:

Bär E, Whitney PG, Moor K, Reis e Sousa C, LeibundGut-Landmann S: IL-17 Regulates Systemic Fungal Immunity by Controlling the Functional Competence of NK Cells, Immunity, 2014, 40: 1-11, doi: 10.1016/j.immuni.2013.12.002