Post written by Joe Ballenger
Does the allergy to honeybee stings carry over to other bees like the bumblebees and carpenter bees?
Allergies are very complicated, but they also effect a lot of people. So this is a topic we really should tackle. We’ve talked before about how entomologists become allergic to stinging insects, but it’s not just entomologists who have allergies to bees and the like. Allergies, especially to stinging insects, are a constant fact of life for many people. So it pays to understand them really well.
This is a short question, but the answer is complicated. To understand the answer, we’ll explore a lot of things. We need to know how allergies work, what insect venom is made of, and how it interacts with the human body.
How do allergies work?
Allergies are a really specific antibody pathway. Allergies form when the human body makes a specific type of antibody which targets a specific molecule. Often, this is a protein but it can also be a sugar group. The target tends to be specific to some sort of invader.
We’ve talked about antibodies before, in a very different context. Antibodies are proteins which the human body makes to label and neutralize infections. They act as tiny beacons to help white blood cells find their targets. When the system works, the white blood cells help clear the body from infection.
There are many types of antibodies, but the type that’s most relevant to this discussion are called IgE antibodies. These are a type of antibody that’s unique to mammals, and it isn’t found in any other vertebrate. It’s important for fighting off infections by larger parasites, like the roundworm below, and helps white blood cells find them. When the white blood cells find them, they will increase bloodflow to the tissues and cause swelling and inflammation.
When the reaction is local, this is good. If the intruder is a tick or a splinter, this brings in cells that fight infections into the area. The swelling also pushes the invader out of the skin. After the invader is gone, the increased blood flow also helps the healing process.
However, the bad stuff happens when the reaction is systemic. That is, if your body reacts in this way to something that’s not a parasite, like bee venom in this case. If your body has made large amounts of IgE antibodies to a particular substance, it may over-react to the stimulus and the immune system will cause more damage than the bee venom. In an allergic reaction-the bad kind of immune response-all your mast cells will release an enormous amount of signaling molecules, causing your body to react as if there were parasites all over your body.
A little bit of an immune response is a good thing. An overactive immune response can be lethal.
What is venom?
Venom is a substance that’s meant to hurt or kill an enemy. It’s a very complicated substance, and can contain dozens of proteins and other small molecules. These can be enzymes like proteases (which break down proteins), lipases (which break down cell walls), and hyaluronase (which makes it easier for venom to spread out inside the body), or small molecules like histamine (which causes an unpleasant irritation). Each of these ‘ingredients’ combine to make a unique cocktail, which can have different effects.
Different groups of animals are going to have venom made of different ingredients, but each of those ingredients (e.g. each enzyme) can be slightly different in important ways. Different proteases can be made up of different parts, and can ‘look’ completely different to the human body. The exact differences have to do with the sequence of the building blocks they’re made of. What ingredients the insects put into the venom can also be different depending on whether the animal is hungry, or depending on the season.
Antibodies in action: single and multiple allergy
For simplicity, it’s best to divide stinging insect allergies by insect family. We can discuss bees and wasps as two different group of insects. People can become allergic to bees, wasps, or both. Which animal people become allergic to depends on whether the antibody can find a target, and whether the proteins the animals make look similar to the body.
Single allergy: bee allergies
The most common bee allergy is to a venom component called Phospholipase A2 (PLA2 for short). This is a digestive enzyme which has been modified for defense. It has an identical function in both venom and the stomach: to break down cell walls. Breaking down of cell walls in a sting victim causes a type of chemical burn, which hurts really bad.
The body can make IgE to PLA2, and all bee PLA2 looks pretty similar. Wasps make a slightly different enzyme, PLA1. PLA1 works a different way, and looks very different, but performs a similar function. People who make antibodies only to bee PLA2 are allergic to bees, but not wasps.
Double allergy: bees and wasps
The goo between your cells is made of a molecule called hylauronic acid (HA). HA has a lot of different functions, but one is to act as a sort of molecular ‘speed bump’ to keep things from diffusing too fast. HA is broken down in the body by an enzyme called Hyaluronidase (HA-ase), which helps cells get through the goo.
Bees and wasps make HA-ase, and their HA-ase looks pretty different between the two. When the body makes antibodies to target venom HA-ase, it tends to target areas which are identical between the two. In this case, people are allergic to bees and wasps because the antibodies can bind to both types of enzymes.
The Bottom Line
You become allergic to things when you make IgE antibodies to stuff that’s found in bee stings. These antibodies bind to things, and help you recover from the sting. To what degree antibodies bind to different things is called ‘cross-reactivity’. Antibodies need to hit specific targets to work, and the body can make more than one antibody to different venom components. Antibodies can also sometimes bind to targets that look similar, even if the proteins are different.
Cross-reactions are important, and whether a person becomes allergic to specific insects depends on what the antibodies are binding to. If the proteins are found in all insects, or look similar enough between them, a person could become allergic to multiple insects. If the protein is specific to that insect, or if the antibody binds to a part of a protein unique to the venom of a specific insect, then the person will be allergic to one insect.
So you can become allergic to one insect, or multiple insects. It depends on how the allergy forms, and only a doctor can tell you what’s happening inside your body.
Bilo, B. M., Rueff, F., Mosbech, H., Bonifazi, F., & Oude‐Elberink, J. N. G. (2005). Diagnosis of Hymenoptera venom allergy. Allergy, 60(11), 1339-1349.
A note for the biochemists: I explained why I decided to use human PLA1 on Twitter before this post was published. Advice on how better to use crystal structures in blog posts is definitely welcome.
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