Immunity system complexity: specialized T cells (Introduction)

by David Turell , Wednesday, January 03, 2024, 16:35 (115 days ago) @ David Turell

T cells in hiding in deep organs:

https://mail.google.com/mail/u/0/#inbox/FMfcgzGwJcXsSGKtbVTTXHGvGpdrMSWW

"Some immune cells live inside tissues 24/7 so that they can constantly keep an eye out for pathogens. These in-house monitors, known as tissue-resident CD8+ T cells, generally lie in wait until they detect chemicals released by infected cells. Then, they quickly move to the infection site to help battle the unwanted microbes. So researchers were somewhat befuddled when they saw CD8+ T cells in salivary glands jumping into action in the absence of any apparent chemical cues. If they aren’t picking up on molecular signals, how are they deciding to move?

"According to a recent Science Immunology study, they move because they feel like it—literally. These “T cell subsets are equipped to sense and react to the physical properties of their tissue of residence,” the authors write. Specifically, as the cells become confined, they sense their nuclei being squeezed, and that triggers an “evasion reflex.” That means they can move about without picking up on the chemical cries of infected cells.

"This alternate mechanism for instigating movement may have evolved because glands are rarely exposed to microbes, and therefore their cells don’t often signal T cells to move about. If immune cells aren’t constantly patrolling, they might overlook the rare but dangerous infections that do occur in these tissues until the microbes have the upper hand."

From the paper:

https://www.science.org/doi/10.1126/sciimmunol.add5724

"The distinctive mode of exocrine gland TRM locomotion was triggered by sensing physical confinement and was closely correlated with nuclear deformation, which acts as a mechanosensor via an arachidonic acid and Ca2+ signaling pathway. By contrast, naïve CD8+ T cells or TRM surveilling microbe-exposed epithelial barriers did not show mechanosensing capacity. Inhibition of nuclear mechanosensing disrupted exocrine gland TRM scanning and impaired their ability to intercept target cells. These findings indicate that confinement is sufficient to elicit autonomous T cell surveillance in glands with restricted chemokine expression and constitutes a scanning strategy that complements chemosensing-dependent migration."

Comment: all of these activities are fully automatic reactions coded into the DNA of the T cells. This type of purposeful activity requires design, not natural evolution.