Immunity system complexity: role of tuft cells (Introduction)

by David Turell , Friday, November 15, 2019, 20:47 (1622 days ago) @ David Turell

They can taste trouble and elicit responses:

https://www.quantamagazine.org/tuft-cells-that-taste-danger-set-off-immune-responses-20...

"Researchers around the world are tracing the ancient evolutionary roots that olfactory and taste receptors (collectively called chemosensory receptors or nutrient receptors) share with the immune system. A flurry of work in recent years shows that their paths cross far more often than anyone anticipated, and that this chemosensory-immunological network plays a role not just in infection, but in cancer and at least a handful of other diseases.

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"These studies and a torrent of others from labs around the world drove home the message that these seemingly misplaced olfactory and taste receptors serve important and often vital functions. And a theme common to many of those functions was that the chemosensory receptors often seemed to be alerting tissues to the presence and condition of microbes in the body. In hindsight, that application for the receptors made a lot of sense. For example, as Herbert notes, being able to “taste” and “smell” minute traces of pathogens gives the body more chances to respond to infections before microbes overwhelm the host’s defenses.

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"Locksley had discovered a group of cells called group 2 innate lymphoid cells (ILC2s) that secrete these cytokines. ILC2s, he found, release cytokines after receiving a signal from a chemical called IL-25. Locksley and von Moltke used a fluorescent tag to mark intestinal cells that produced IL-25. The only cells that gave off a red glow in their experiments were tuft cells. Locksley had barely even heard of them.

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"these studies provided the first explanation for what tuft cells do: They recognize parasites by means of a small molecule called succinate, an end product of parasite metabolism. Once succinate binds to a tuft cell, it triggers the release of IL-25, which alerts the immune system to the problem. As part of the defensive cascade, the IL-25 also helps to initiate the production of mucus by nearby goblet cells and triggers muscle contractions to remove the parasites from the gut.

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"In many cases, tuft cells appeared to be intimately involved with the part of the immune response known as inflammation. Vaughan was studying how tissue deep in the lungs repairs itself after inflammation caused by the flu virus. After reading about some of the new findings, Vaughan began to wonder whether tuft cells might be involved in the lungs’ recovery from influenza. He and Herbert infected mice with the influenza virus and searched the lungs of those with severe symptoms for signs of tuft cells.

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"The researchers don’t yet know what the tuft cells are doing in the lungs or what they are sensing, but Herbert believes that their ability to continually “taste” the environment for different compounds provides a key opportunity for the body to respond to even minute threats.

"The tuft cell, Herbert said, is constantly sensing the metabolic products present in microenvironments within the body. “Once some of those metabolic products go out of whack … bam! Tuft cells can recognize it and make a response if something is wrong.”

"Newly discovered connections between tuft cells and the immune and nervous systems provide further evidence that chemosensory receptors are multipurpose tools like Swiss Army knives, with evolved functions beyond taste and smell. It isn’t clear which function evolved first, though, or whether they all evolved in tandem, Howitt says. Just because scientists became aware of “taste” receptors on the tongue first, “that doesn’t mean that’s the order in which it evolved.”

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"Whatever their history, scientists now say that a major role of these receptors is to monitor the molecules in our body, tasting and smelling them for any sign that they might be from a pathogen. Then, with help from tuft cells and other parts of the immune system, the body can fight off the invaders before they’ve gotten a foothold. But Vaughan cautioned that the sudden emergence of tuft cells in tissues like the lungs, where they are not always present, might also cause its own pathologies."

Comment: An amazing group of tasting cells has been added to the obviously very complex designed immunity system. That these receptors appeared early in evolution is shown by the findings that "even single-celled bacteria such as Escherichia coli carry a type of this receptor." (A part of this article I have placed here)