Why do some people get allergies, and others don’t?

[upbeat music] So Alex, can you tell us something about how allergies work?

Yeah.

So if we go back one step, it's important to realize that it's a key job for your immune system to be able to distinguish between things that are dangerous, like bacteria, viruses, and parasites, versus things that are completely harmless, like pollen and peanuts.

And that way, your immune system can attack dangerous incomers with gusto but avoid triggering an immune response when you are simply walking in the park or eating a meal.

And most of the time, it does do a really good job of this, and harmless proteins, like the ones in peanuts and pollen, which can be allergens, are correctly identified as harmless.

And the result is that the immune system ignores them.

But in people with allergies, something goes wrong.

In an allergic reaction, the immune system flags harmless proteins as threats, and the thing is, every future encounter triggers that same alarm because, as we've covered in previous episodes, the immune system is quite good at learning.

But in terms of allergies, it's actually a different kind of immune response than the ones that we've talked about during previous episodes.

Could you tell us more, Merel?

Yes.

So the immune response that is triggered by allergens, um, immunologists call it a type two immune response.

And this type two immune response is actually the same immune response that is triggered when the body is trying to fight off parasitic worms called helminths.

So from an evolutionary perspective, there will always be a purpose for a certain immune response.

It's just that sometimes the immune system will mistakenly use the type of immune response that was meant for parasites to overreact against peanuts or pollen in the case of allergies.

How does this happen? What actually goes wrong?

So when somebody with the potential to develop allergies first encounters an allergen, for instance, pollen floating in on a warm spring breeze, their immune system picks it up.

And there are a few steps in between the immune system first noticing the allergy and a full-blown allergic reactions.

But what's important to know here is that the first pickup of that allergen can lead to a recipe being delivered to B cells, the cells that produce antibodies.

And this recipe includes instructions on how to produce a very specific type of antibody, called immunoglobulin E, or IgE for short.

So as a bit of background, there are a bunch of different types of antibodies, but one thing they all have in common is that they're very good at sticking to specific types of proteins.

When the B cells get a recipe to produce a antibody, it's always to produce an antibody that will stick to a given protein.

And in this case, in the case of a pollen allergy about to develop, the immune system of this person who doesn't have an allergy yet but soon will, well, it will start producing IgE that specifically aims to grab proteins in the pollen.

And the next step where things really go wrong is that those IgE antibodies stick around.

IgE antibodies are kind of weird ones in that they aren't only floating around your body on their own.