Immunity system complexity: helps digest chitin (Introduction)

by David Turell , Wednesday, January 17, 2024, 17:27 (101 days ago) @ David Turell

Chitin is a tough fiber:

https://www.the-scientist.com/news/the-immune-system-helps-with-digestion-71595?utm_cam...

"Most dietary fibers are broken down by the microbiome because they are too complicated for digestion by the stomach and intestines alone. However, in a paper published in Science, a team at Washington University reported that the stomach uses an immune-mediated circuit to digest chitin, a ubiquitous structural fiber found in fungi, shrimp, and insects, and that this circuit also influences metabolic homeostasis. These findings could help scientists understand the relationship between digestive processes and metabolic activities.

Chitin is often found in airway allergens like dust mites and spores. It activates type two immune responses, the body’s defenses against allergens or parasites, which include type 2 innate lymphoid cells (ILC2), a group of immune cells that produce cytokines to drive allergic or parasitic responses. ILC2 also induce the production of chitinase, an enzyme that breaks down chitin in airways. However, this may not be the full story of chitin and ILC2. (my bold)

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"Chitin-eating mice had increased stomach thickening and higher numbers of chemosensory epithelial cells, called tuft cChitin is often found in airway allergens like dust mites and spores. It activates type two immune responses, the body’s defenses against allergens or parasites, which include type 2 innate lymphoid cells (ILC2), a group of immune cells that produce cytokines to drive allergic or parasitic responses. ILC2 also induce the production of chitinase, an enzyme that breaks down chitin in airways. However, this may not be thells, in their stomachs compared to cellulose-eating mice, suggesting that digesting chitin remodeled the existing tissue. Chitin also induced distention of the stomach, which caused tuft cells to produce ILC2-activating cytokines. This coincided with increased numbers of ILC2 in the stomach. Because ILC2 maintain metabolic homeostasis in adipose tissue, the team investigated ILC2 responses in this tissue and found that chitin increased the number of activated ILC2 in adipose tissue.

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"This suggested that ILC2-mediated AMCase expression is necessary for the adaptation to dietary chitin, and that disrupting this circuit leads to altered ILC2 activity in gastrointestinal and adipose tissues.

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"Surprisingly, AMCase-deficient mice with chitin in their diets gained weight at a slower rate than normal mice that also ate chitin. These animals also expended more energy and had a higher respiration rate than animals with functional AMCase. However, chitin-eating mice had better glucose and insulin tolerance than animals eating a high-fat diet with cellulose. This finding suggested that the adaptation to chitin through AMCase and ILC2 activation plays an important role in metabolic homeostasis."

Comment: if the immune system is involved in allergic reactions, it is easy to understand how it was designed to be coopted by the need for digestion.