Comment by pazimzadeh | Hacker News Reader

Comment by pazimzadeh | Hacker News Reader

Except that almost every cell is somehow related to immunity. Almost every cell in the body has MHC Class I which constantly presents a subset/signature of its proteome to the immune system in case it gets infected by a virus, etc. Cells that don't do this are deleted by Natural Killer cells.

Also, many immune factors that people thought were restricted to particular compartments or cell types have been found in "non-immune" cells. For example, complement protein was thought to be a blood factor that is only made in the liver, but it turns out that it is also made locally by stromal cells of the intestine:

https://www.biorxiv.org/content/10.1101/2023.02.02.523770v1....

Not to mention the burgeoning field of neuroimmunology - there are neurons in the spleen which are in direct contact with macrophages and we don't know why (or at least didn't know why a few years ago when I learned about it). But avoiding people with disease symptoms could be considered part of the 'immune system.'

I can follow what you are saying because of what I learned in the book Immune by Philipp Dettmer, which I highly recommend for a popular-level introduction to the complexities of the immune system. The whole bit about the "presentation windows" that cells use to communicate if they are infected, and how some viruses try to fight that by not presenting anything, and how the immune system tries to fight _that_ by deleting cells that don't present anything... fascinating stuff!

Thanks for the book recommendation.

Another example of how almost any cell contributes to immunity is that depending on the way a cell dies (apoptosis vs pyroptosis vs necroptosis), it can release its contents, including nuclear proteins, and other "Damage-associated molecular patterns" which act as an inflammatory recruiter of other immune cells.

https://en.wikipedia.org/wiki/Damage-associated_molecular_pa...

For pyroptosis this includes endothelial cells, epithelial cells, neurons, heart muscle cells, liver cells, fibroblasts, and pancreatic β-cells.

On top of this, there are several ways that "non-immune" cells are constantly doing internal immune tasks, or performing 'citizens arrests' if you will, including: restriction factors, cellular stress response, autophagy, and viral RNA/DNA detection. For example, many "non-immune" cells express Toll-like receptors which are used to detect "Pathogen-associated molecular patterns".

https://en.wikipedia.org/wiki/Pathogen-associated_molecular_...

+10 for Philipp Dettmer's excellent Immune book.

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