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Small-Scale Question Sunday for January 8, 2023

Do you have a dumb question that you're kind of embarrassed to ask in the main thread? Is there something you're just not sure about?

This is your opportunity to ask questions. No question too simple or too silly.

Culture war topics are accepted, and proposals for a better intro post are appreciated.

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Potentially a stupid question based on misunderstanding, but it's really confusing to me now.

So, as far as I know, allergies are caused by immune system reacting to some substance, usually harmless to most people. One of the ways to treat allergies is to introduce small quantities of the allergen and try to get the immune system to stop treating it as a threat.

Then, the main function of the immune system is fighting infections - e.g. viruses or bacteria or whatever. Unfortunately, sometimes viruses and bacteria do their business so quickly that they overwhelm the system and it can not fight them off. To prevent that, we have vaccinations - where we introduce the small quantities of the antigen to the system and try to get the immune system to recognize it and fight them better when they come next time.

What is confusing to me is why in these two instances the same system is behaving in two opposite ways? In the first instance, if you introduce something it then makes the immune system to ignore it eventually, but in the second instance, if you introduce something, the immune system starts to react stronger to it? What am I missing?

Also, does this mean that if somebody didn't have a certain allergy, and I were their evil nemesis and wanted to give them one, I could do it by concocting a specific "vaccine" that would stimulate their immune system to react on the specific substance - just as regular vaccines do? Or somehow it works with one class of substances and not with the others, and if so - why?

I understand the full answer might be "get PhD in immunology and it'll all be clear to you" but maybe there's a shorter answer to this?

Vaccines are intentionally designed to produce a strong immune response even in minuscule quantities. That goes as far as adding adjuvants to increase the antigenicity of a base antigen. Not to mention that they're usually given parenterally, meaning that the immune system is exposed to a higher concentration than is typical for normal allergens that are inhaled or contact spread.

So, does it mean if I injected somebody (non-allergic) with peanut butter extract mixed with an adjuvant (provided I find a safe way to do it without causing them harm) they'd get a peanut allergy?

Conversely, if somebody were vaccinated, e.g. against flu, and subjected constantly to low doses of flu virus - would they lose the immunity eventually? If not, again, why does it work with allergens and not with the flu virus?

In the first case, unless they already had a genetic predisposition to peanut allergies, it's unlikely that they'd develop an allergy at all. They might develop a local hypersensitivity reaction at the time of injection, but I don't believe that it'll go as far as making normal peanut butter eaten later an allergen.

In the second case, I'm unsure myself.