"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.
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.
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.
I thought the general rule is you should feed a child lots of different foods at appropriate (and EARLY) stages of life, even if you or the child don't like that food. They need the exposure so their body can build defenses to any negative reaction. The difference between a fussy eater and an allergic eater are profound.
"withholding something (e.g. peanuts) from an infant could reduce the likelihood of a serious allergic reaction later"
This seems to be the opposite of the "too clean" hypothesis. I'm not sure what that paragraph is trying to say. Did you mean increase rather than reduce?
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!
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.