Our question this week comes from the Nature Check discord. Nature Check is a project where we use games like D&D to talk about science, and you should totally check it out!
In the food channel, we were talking about bugs as food and the concept of cross-allergies came up. When introducing any new food into the supply chain, it’s something we have to consider because choosing the wrong food could cause a lot of people to get sick.
I’ve discussed the idea of cross-allergies in relation to wasp stings, and they all kind of work the same way. Basically, there’s something you become allergic to. Sometimes, it’s a protein and sometimes it’s a sugar or something like that. If that something is similar enough between different the different kinds of plants and animals you eat as food, you could become allergic to another kind of food.
Given how important food is to my life-I’m an agricultural scientist, after all-I like to keep up on food allergies. I hadn’t heard anything about the cricket/nut allergy connection, and wasn’t able to find any literature about it. That’s not to say that it’s never happened, but I was unable to find any evidence that was a thing.
So, it’s unlikely that kind of cross-reactivity actually exists…but there is a lot of cross-reactivity between different arthropods used as food. These are called pan-allergens because if you become allergic to one critter, suddenly you’re allergic to lots of critters.
So let’s talk about the proteins which make you allergic to everything, and why they can do that.
Why can you become allergic to multiple things?
The things which cause allergies are actually pretty neat, because we know a lot about them. They cause a lot of health problems, so it’s a good idea to know exactly what their functions are in the animals so we can make predictions. From my perspective, though, it’s just kind of cool to know about the things which can affect our physiology so much without actually being a venom.
When you eat meat, you’re eating muscle tissue composed of thousands of proteins and each has a distinct function. One of those proteins is called tropomyosin, and it’s a really important part of helping your muscles move. It regulates a big chunk of the process, by telling the parts of the muscles which move when and where to bind.
Tropomyosin is a really important protein, so all invertebrate tropomyosins look pretty similar. If there’s too big of a change, the critter won’t survive to adulthood. Because of this, large parts of the molecule remain unchanged for long stretches of evolutionary history. Because large parts of it are unchanged, the portions of the molecule you become allergic to can be found in a lot of different things. This protein is why people become allergic to shrimp, mussels, and even things like mealworms and crickets all at the same time.
Besides sequence, structure is also really important. We can see this here with alpha-amylase, the enzyme which breaks down starch. This enzyme is why bread becomes sweet after awhile; it turns sugar chains into things we can use.
Alpha-amylase pretty much looks the same across all insects. We can take a picture of the protein-through the magic of X-ray crystallography-and overlay a whole bunch of pictures on the proteins…and they all line up almost perfectly. Because of this remarkably similar structure, it’s possible for antibodies to recognize everything at once.
The Bottom Line
The reason proteins make you allergic to multiple things is because these animals will have the same molecules, or their proteins either have the same sequence, or the same structure. In order for those antibodies to bind to them, they just have to be really similar.
So this is all to say that I don’t think a cricket/nut cross-allergy is a thing. The protein you find in nuts which makes people allergic to them is generally a protein called Ara (Ara H1 is the big one, but there are others). Ara proteins are storage proteins. They exist to, well, be proteins. When the peanut grows into a plant, they chew up the Ara proteins to make other things.
Ara and Tropomyosin are two very different proteins, not only in structure, but also in function. Not every tropomyosin protein causes allergies. Pigs, chickens, and even peanuts, have tropomyosin but don’t cause allergies. A lot of seeds have proteins similar to Ara, but it’s only a few different kinds of seeds which seem to cause these problems.
So in the case of the cricket/nut allergy, I think it’s more likely these folks have two allergies at once…a cricket and nut allergy which are caused by two proteins at the same time.
Barre, A., Simplicien, M., Cassan, G., Benoist, H., & Rougé, P. (2018). Food allergen families common to different arthropods (mites, insects, crustaceans), mollusks and nematods: Cross-reactivity and potential cross-allergenicity. Revue Française d’Allergologie, 58(8), 581-593.
James, J. K., Pike, D. H., Khan, I. J., & Nanda, V. (2018). Structural and dynamic properties of allergen and non-allergen forms of tropomyosin. Structure, 26(7), 997-1006.
Note from Joe:
I actually consulted about a dozen different reviews of insect allergens, but none addressed cross-kingdom cross reactivity so I chose to cite the two articles I thought were the most informative and best written. Despite this, there is a potential cross-kingdom pan-allergen called chitin. This is the crunchy substance which makes up the majority of the insect exoskeleton. It’s also a major component of the cell walls of fungi. Therefore, it’s possible for someone who’s allergic to shellfish to be allergic to mushrooms. However, tropomyosin (and a few other molecules) are considered to be more important allergens when discussing invertebrates.
Because this was specifically about crickets and nuts, I wanted to focus on that. However, at the same time, I also felt a note about chitin would be appropriate just in case someone comes here looking for this kind of thing. There’s a lot of potential allergens, and not all of them are well characterized.
As always, consult a qualified medical professional about allergies. We’re not doctors, so this isn’t medical advice, but this kind of information could help people talk to their doctors.