
Immune Cells Measure Time to Identify Foreign Proteins - Anon84
https://www.quantamagazine.org/immune-cells-measure-time-to-identify-foreign-proteins-20190603/
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rossdavidh
"This process works because the immune system undergoes a sort of training
period during its early development: Nascent T-cells are presented with all
the self molecules in the body, and cells that bind for more than five seconds
to anything get weeded out. That way, the T-cells left to make up the body’s
immune system are those that bind for a long time only with things they’ve
never seen before."

Suggests a mechanism whereby withholding something (e.g. peanuts) from an
infant could reduce the likelihood of a serious allergic reaction later. As I
recall, in 2000 the American nutritionists society formally recommended not
exposing any child to peanuts until they were several years old, and then they
had to backtrack in 2010 and revoke that recommendation because of evidence
(from cross-cultural studies of genetically similar groups in the U.K. and
Israel) that this made peanut allergies more common.

Also suggests why "too clean" in early life could result in a higher incidence
of severe allergies.

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echelon
The former quoted text is the process of positive and negative selection, the
mechanism of central tolerance.

The latter part you posit is the hygiene hypothesis.

The two are probably not the same mechanism as selection occurs in the thymus
and marrow.

You can become allergic to any epitope at any point in your life if immune
cells upregulate in response to it. Immune responses are particularly
heightened during illness, which can sometimes trigger auto-immune or allergy
development.

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rossdavidh
Well I don't doubt you know more about it than I do, but I recall research
that, for example, people who worked on farms in Bavaria as children had fewer
allergies later in life, than those who did not. So, while it is certainly
possible to get allergic to something later, it might suggest that your early-
life immune system learning of "how weird is too weird" could conceivably have
an impact.

But, it is not my field.

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echelon
Oh, I'm not disagreeing! I'm just giving you the names for these two distinct
concepts so they're not conflated:

[https://en.wikipedia.org/wiki/Central_tolerance](https://en.wikipedia.org/wiki/Central_tolerance)

[https://en.wikipedia.org/wiki/Hygiene_hypothesis](https://en.wikipedia.org/wiki/Hygiene_hypothesis)

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Virtuoso
A couple years ago, a very funny experiment was published on "Cell", that used
conjugation of DNA strands to TCR transmembrane chains to quantitate in terms
of base matches the energy required to elicit ZAP70 cascades. Pretty awesome!

