At least part of the adaptive immune system is implemented in the thymus. As an infant, the thymus makes examples of nearly every type of cell in the body and uses it as negative labelled examples to tune the false positive detector so it doesn't identify self as threat. From an information theory perspective, that's pretty extraordinary (you don't normally expect differentiated cells in an organ to act like cells from another organ).
Another part of the adaptive immune system randomly shuffles different regions of genes together to produce enormous diversity (searching for a rare example of something that "works"), then picks the proteins from those genes that work best and distributes them throughout the body.
Yes, it's really fascinating stuff. Just to add to that, cells must present a continuous sample of their proteasome on the cell surface in the form of a short peptide 9-12 amino acids long. T cells will recognise when the cell is producing protein it shouldn't be (i.e. because it became cancerous or infected with a virus), even if only one amino acid is incorrect.
It learns this in the thymus, which has a bizarre gene called AIRE which switches on genes from all over the body, essentially creating a representation of the entire body in the thymus gland as a sort of sandbox before they are let out.
However, we don't have enough T cells to recognise every possible sequence of 11 amino acids (which would weigh around 1.5 tons), so T cells must be so-called 'cross-reactive'[1]. And therefore other factors must go into how T cells respond to abnormalities.
yep, i was referring to AIRE without naming it. I saw a talk about it years ago and it blew my mind. In retrospect, it seems to just sort of fall out from the way you'd expect adaptive immunity to evolve, though.
On information theory [unrelated to the discussion]: both digital information (stored in DNA --4-letters)
and analog information (epigenome) can be manipulated for various effects e.g., "Lifespan: Why We Age—and Why We Don't Have To" by Sinclair
https://www.amazon.com/dp/B07N4C6LGR/
Another part of the adaptive immune system randomly shuffles different regions of genes together to produce enormous diversity (searching for a rare example of something that "works"), then picks the proteins from those genes that work best and distributes them throughout the body.
Pretty amazing stuff.