Immunity system complexity: control dangerous bugs in gut (Introduction)

by David Turell , Monday, March 13, 2023, 22:53 (753 days ago) @ David Turell

A different system:

https://medicalxpress.com/news/2023-03-exploring-immune-intestines-bacteria.html

"Yersinia bacteria cause a variety of human and animal diseases, the most notorious being the plague, caused by Yersinia pestis. A relative, Yersinia pseudotuberculosis, causes gastrointestinal illness and is less deadly, but naturally infects both mice and humans, making it a useful model for studying its interactions with the immune system.

"These two pathogens, as well as a third close cousin, Y. enterocolitica, which affects swine and can cause food-borne illness if people consume infected meat, have many traits in common, particularly their knack for interfering with the immune system's ability to respond to infection.

"The plague pathogen is blood-borne and transmitted by infected fleas. Infection with the other two depends on ingestion. Yet the focus of much of the work in the field had been on interactions of Yersinia with lymphoid tissues, rather than the intestine. A new study of Y. pseudotuberculosis, led by a team from Penn's School of Veterinary Medicine and published in Nature Microbiology demonstrates that in response to infection, the host immune system forms small, walled-off lesions in the intestines called granulomas.

"The team went on to show that monocytes, a type of immune cell, sustain these granulomas. Without them, the granulomas deteriorated, allowing the mice to be overtaken by Yersinia.

***

"A biopsy of the intestinal tissues confirmed that the lesions were a type of granuloma, known as a pyogranuloma, composed of a variety of immune cells, including monocytes and neutrophils, another type of white blood cell that is part of the body's front line in fighting bacteria and viruses.

"Granulomas form in other diseases that involve chronic infection, including tuberculosis, for which Y. pseudotuberculosis is named. Somewhat paradoxically, these granulomas—while key in controlling infection by walling off the infectious agent—also sustain a population of the pathogen within those walls.

The team wanted to understand how these granulomas were both formed and maintained, working with mice lacking monocytes as well as animals treated with an antibody that depletes monocytes. In the animals lacking monocytes "these granulomas, with their distinct architecture, wouldn't form," Brodsky says.

"Instead, a more disorganized and necrotic abscess developed, neutrophils failed to be activated, and the mice were less able to control the invading bacteria. These animals experienced higher levels of bacteria in their intestines and succumbed to their infections.

***

"The researchers believe the monocytes are responsible for recruiting neutrophils to the site of infection and thus launching the formation of the granuloma, helping to control the bacteria. This leading role for monocytes may exist beyond the intestines, the researchers believe.

"'We hypothesize that it's a general role for the monocytes in other tissues as well," Brodsky says."

Comment: the responses run to bacterial types. The immune system uses granulomas as one means of control. TB makes granulomas in the lung. The mono's are programmed to individual types and respond accordingly.