Immunity system complexity: innate & adaptive actions (Introduction)

by David Turell , Friday, June 06, 2025, 19:28 (5 days ago) @ David Turell

Performed by different cell types:

https://www.the-scientist.com/the-innate-immune-system-s-secret-weapon-73061

"When a pathogen enters the body and begins multiplying, the immune system has to respond with haste. However, adaptive immune cells—so-named because they can recognize, respond to, and remember specific microbes—require four to seven days to mount a tailor-made defensive.1 Meanwhile, innate immune cells, which recognize general signs of a threat, such as common bacterial lipids, strike immediately and buy time for the adaptive immune system to prepare its attack. Immunologists have long accepted the “innate-first, adaptive-second” model of the immune response, but following an odd discovery 15 years ago, the line separating the innate and adaptive axes began to blur.2 Scientists uncovered a new group of immune cells called innate lymphoid cells that elicit similar responses to the adaptive arm’s T cells, mainly by triggering inflammation through the secretion of chemical signals called cytokines. However, like other innate cells, they are unable to recognize specific antigens.

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"These novel cells didn’t possess any antigen-specific receptors, indicating that they belonged to the innate immune system...Today, scientists call them type-2 innate lymphoid cells (ILC2s).

"In the years that followed, other groups identified more types of innate lymphoid cells and noticed a peculiar pattern: For every class of T cell, an ILC counterpart exists that resembles it. For example, both type-1 helper T cells (Th1s) and ILC1s mount a similar immune response against viruses and other intracellular parasites by secreting a signature set of cytokines.

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"Despite their many similarities to T cells, ILCs lack a key feature that make T cells adaptive. They cannot recognize specific antigens, which means they lack the marksmanship to attack diseased cells while leaving healthy bystanders unharmed.7 They also make their appearance during the immediate, innate phase of the immune response rather than during the delayed, adaptive phase.

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"Even after T cells are activated, ILCs continue to play an important role in the immune response by recruiting T cells to threats, and producing cytokines that keep them active.

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"...Jefferies’s team found that the cytokine IL-33 plays an important role in helping T cells to fight solid lung tumors. “We were interested in what IL-33 actually regulates,” Jefferies said. Other researchers had previously shown that this cytokine activates ILC2s, so Jefferies transferred a small number of these cells into mice with lung cancer.16 They found that these innate immune fighters significantly shrank the tumors by recruiting T cells to the cancer, narrowing the focus of the T cells to the tumor.

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"The innate-then-adaptive model of immunity implies that each axis employs distinct tactics depending on whether they indiscriminately target whole tissues or pinpoint strikes on diseased cells. ILCs obscure the distinction by eliciting a general, imprecise reaction using functions typically associated with the antigen-specific adaptive response. Beyond serving as a potential therapeutic against cancers, these elusive cells force immunologists to question the tidy separation between innate and adaptive immunity."

Comment: the concluding paragraph Tells us where new current research is needed. The interplay between innate and adaptive cells is fascinating and suggests a designer at work creating a very flexible response to all challenges. dhw will be pleased at the automatic intelligent interplay between the cell types.