What causes a peanut allergy? A peanut allergy happens because the immune system attacks the proteins that are present in the peanuts. Peanut allergies are surprisingly common. It is estimated that roughly 2% of people have a peanut allergy. The reaction can range from mild to life-threatening, depending on the person.
Many people in the world have allergies and there are many different types of allergies. The most common allergy in the world is probably hay fever. More people have an allergy to the pollen released by trees and plants than any other substance. It seems as though more people have hay fever than ever before, and that is probably true. More people live in urban areas, which makes them less used to pollen. Also, the planet is warming and the warmer temperatures enable the plants to produce pollen for longer and in larger quantities. The extra carbon dioxide in the atmosphere also stimulates the plants to grow more and produce more pollen.
So, what happens when someone has an allergic reaction? We all have an immune system that is there to protect us from invading viruses, bacteria, or fungi. Our immune system can react to any invader, but to make it more efficient, the immune system remembers and learns about each invading organism. We have antibodies in our blood that are called immunoglobulins. When they come into contact with an invading organism, they remember the chemical makeup of that organism. If they come into contact with a new organism, it takes them a while to initiate an immune response, but if they come into contact with an organism they have already contacted, they initiate the response more quickly. There are five types of immunoglobulins: IgA, IgD, IgE, and IgM. IgE is the immunoglobulin that is responsible for allergic reactions. People can have one allergy or many allergies and in each case, the IgE is triggered by whatever the person is allergic to. If it is pollen, for example, the IgE antibody is triggered by the pollen to think the body is under attack and it initiates an immune response. The IgE antibody can be triggered by just one particular type of pollen without being triggered by any others. Why that is is a mystery.
In the case of a peanut allergy, the IgE antibody gets triggered by some of the proteins in the peanut. There are many proteins in a peanut, but only a few of them are a problem. The main problem proteins are called Ara h1, Ara h2, Ara h3, They come from a group of proteins called the Cupin superfamily and the Prolamin superfamily. These groups of proteins are used by plants to store metal ions and amino acids for when they start to germinate. They are also notorious allergy triggers and they are contained in many different foods that we eat, such as grains. When someone with an allergy eats a peanut, their IgE antibodies come into contact with one or more of the proteins and they remember it. The body then produces more of the IgE antibodies that are coded to recognize the protein from a peanut. When that person eats another peanut later on, the IgE antibodies recognize the protein as an invader and start the immune response. This is where the allergic reaction comes from.
When the IgE antibodies detect a peanut protein, they bind to it and signal white blood cells. The white blood cells start to produce various chemicals, one of which is histamine. The job of histamine is to dilate blood vessels and to make them more permeable. That allows more blood to flow through the blood vessels and more fluid to pass out of the blood vessels into the surrounding tissue, which makes it swell. The IgE antibody has a pure motive. It wants your flesh to swell so that it can isolate the invader, make more space for white blood cells to get in, and make it easier to get rid of the invader. The problem is that there is no invader and so you swell up for no real reason. Most of the time, this is just annoying and will go away after a few hours. The problem comes when places like your throat swell up and you can no longer breathe.
In some severe cases, people can go into anaphylactic shock. This is caused because the histamine makes the throat swell up to the point where breathing becomes difficult. It also causes blood pressure to drop because too many blood vessels expand at the same time increasing the overall space the blood has to flow in. These two things together can be fatal if they are not stopped. The only way to stop them quickly is with an injection of epinephrine, which is often from an EpiPen. The drug is very fast-acting and it counteracts the histamine by making the blood vessels contract, raising blood pressure, and reducing the swelling. Sometimes two pens are needed, but the EpiPen will give someone enough time to get to the hospital and receive proper care. And this is what I learned today.
Sources
https://en.wikipedia.org/wiki/Antibody
https://en.wikipedia.org/wiki/Immunoglobulin_E
https://www.hopkinsmedicine.org/health/conditions-and-diseases/allergies-and-the-immune-system
https://www.foodallergy.org/living-food-allergies/food-allergy-essentials/common-allergens/peanut
https://www.mayoclinic.org/diseases-conditions/peanut-allergy/symptoms-causes/syc-20376175
https://pmc.ncbi.nlm.nih.gov/articles/PMC4785306
https://www.aaaai.org/tools-for-the-public/conditions-library/allergies/peanut-allergy
https://en.wikipedia.org/wiki/Cupin_superfamily
https://en.wikipedia.org/wiki/Prolamin
https://www.atlantaallergy.com/articles/view/533-what-is-an-epipen-and-who-needs-it
https://en.wikipedia.org/wiki/Anaphylaxis
Photo by shattha pilabut: https://www.pexels.com/photo/close-up-photo-of-peanuts-135755/