Immunity complexity: immune cells help rebuilding (Introduction)

by David Turell , Tuesday, February 11, 2020, 18:17 (1535 days ago) @ David Turell

When the body is damaged immune cells, which are generally thought of as invader destroyers, are part of the helpful inflammatory reaction repair mechanism:

https://www.quantamagazine.org/immune-cell-assassins-reveal-their-nurturing-side-20200211/

"After a heart attack, patients are increasingly often offered the option of stem cell therapy, in which stem cells from their bone marrow are injected into the heart to help it heal. Skeptics, however, point out that solid evidence of the therapy’s benefits is lacking: It’s worked modestly in some animal studies, but its effectiveness is uncertain, and scientists have only been able to guess at how it helps if it does.

"Last November, a team of cardiologists set out to provide some clarity on this controversial treatment. Instead, their work found evidence that some immune system cells play a nurturing, healing role that is far removed from their familiar calling as bloodthirsty protectors of the body.

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"The protective benefit of the treatment didn’t come from a regenerative effect of the stem cells, the researchers realized. It came instead from the inflammatory immune response, which seemed to set up what Molkentin calls “a second wave of healing.”

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"The cells that delivered the healing boost to the hearts of the mice are a subset of what are called tissue-resident macrophages.

"Unlike the macrophages that circulate in the blood and look for pathogens, these cells migrate into the heart during embryonic development and remain there for the rest of their lives. Over the past decade or so, evidence has accumulated that they perform a variety of tasks, such as aiding in the maturation of coronary vasculature and maintaining a proper heartbeat.

“'They’re doing activities that are not normally associated with immunology, such as helping tissues reshape and change in response to stresses, or repair and regenerate, or even conduct electricity,” said Kory Lavine, an assistant professor...

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"The heart is not unique. In fact, most tissues and organs in the body have their own cache of tissue-resident macrophages. They have been found to carry out key functions, as if they were a part of the organ in which they reside. In the brain, for example, they remove axons and aid in the pruning of synapses during development. Those in adipose tissue help to regulate body heat. Macrophages have even been found to aid in the recycling of iron in the spleen and liver.

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"But almost from the time of their discovery, scientists have noted that subpopulations of these NK cells [natural killer]reside full time in the liver, skin, kidney and uterus. And unlike their deadly cousins, these cells don’t kill.

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“'For a long time, people thought of the immune system as basically what’s in your blood,” Haniffa said. “Then they realized that your immune system doesn’t just exist in your blood, it exists in every tissue.” Moreover, the immune system cells embedded in tissues and even among your microbiota are in communication. The cells in the brain called microglia have traditionally not been recognized as part of the immune system, but they consume cellular debris like macrophages. They have also been shown to respond to signals from gut microbiota. “We should view the immune system as a bit like a matrix that exists in the entire body,” Haniffa said.

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"Haniffa found that a trove of immune cells was present very early in human development, which she thinks could signify that the cells have an important part to play in the development of tissues. She points out that mast cells, which are traditionally involved in allergic reactions, show up in the yolk sac during the first trimester. Why would they be there when allergy is not typically an issue for embryos? But mast cells have been also implicated in blood vessel development in cancer, so Haniffa wonders whether they might have something to do with healthy blood vessel formation too."

Comment: The immune system is much more than originally thought. It is designed to multitask, which makes sense, since after any injury the inflammatory reaction has to use all the necessary inflammation cells to help is rebuilding damage tissues.