The Science of Anaphylaxis – An Allergic Storm

May 11, 2015

By Sarah Boudreau-Romano, MD

As we kick off Food Allergy Awareness Week, I thought it would be helpful to teach you what happens in the body during an allergic reaction and how an allergic reaction can quickly become anaphylaxis (a severe life-threatening allergic reaction). I hope that after reading this you will have a better understanding of your child’s food allergy and feel more confident recognizing and treating anaphylaxis. Or, if you don’t have a child who has food allergy, that you will have a greater empathy for those millions of individuals who live with this disease. Here we go…

A Tale of Two Cells

There are two main allergic cells in your body, the mast cell and the basophil. These cells contain pockets (or granules, seen in red in the image below) filled with chemicals that mediate allergic disease. Mast cells are found in tissues whereas basophils are floating around in the blood. Both of these types of cells have receptors on their surface. Some of these receptors have IgE (immunoglobulin type E) antibodies attached to them. Think of the IgE antibody as a hand that projects out from the cell (seen in dark blue, shaped like a “Y” in the image below). Each of the hands will only grab onto specific food proteins. They have a favorite food, so to speak.

Normal Cell
A normal cell.

When an individual eats a food to which he or she is allergic – let’s say it’s a peanut, but it could be virtually any food – it enters the gastrointestinal (GI) tract. The peanut protein then finds its way to the blood stream and tissues. This is where the peanut protein finds the mast cells and basophils. Now, there are those “Y”-shaped IgE antibodies (the hands) on these mast cells and basophils, remember? The hands on some of the cells of a peanut-allergic person are looking for peanut protein. When these hands make contact with the peanut protein, they grab onto it and in turn, the cell becomes “excited.”

The IgE antibodies “grab” the peanut protein
The IgE antibodies “grab” the peanut protein.

The pockets of chemicals (granules) found within the cells quickly move to the edge of the cell and pour their chemical contents out into the bloodstream or tissues (degranulation). The chemicals spilling from these cells (seen in red in image below) include histamine and tryptase, among others. This process can occur very rapidly, and it happens in cells all over the body. It’s important to remember that this process occurs even if there was only a tiny amount of peanut protein that originally started the reaction, even if the blood test showed a low number for peanut, even if all of the past reactions were minor.

Pockets of chemicals (red), including histamine and tryptase, spill from the cells.
Pockets of chemicals (red), including histamine and tryptase, spill from the cells.

These chemicals are now swirling in the blood and the tissues, and they start to cause immediate symptoms.

Histamine causes many changes in the body — some more considerable than others. For instance, it causes smooth muscles to contract, which leads to abdominal pain, cramping, nausea, vomiting and diarrhea. It can lead to wheezing (like asthma) from airway constriction that can ultimately lead to respiratory distress, respiratory arrest and death. Histamine also causes vasodilatation. This is when blood vessels get bigger and have less ability to contract to get blood back to the heart. This can cause a decrease in blood pressure that can lead to dizziness,feeling faint, shock and death. Histamine also induces microvascular leakage. This means that both cells and fluid that are supposed to stay in the blood vessels are able to leak out of the blood vessels. This can lead to hives, itching, and swelling of the throat, leading to suffocation. If enough fluid leaks out of the blood vessels, there can be a decrease in blood pressure that causes shock and death.

A young patient shows signs of anaphylaxis
A young patient shows signs of anaphylaxis

 

Onset of Anaphylaxis

Now we are in the midst of anaphylaxis, WE MUST STOP IT. YOU MUST — USE INJECTABLE EPINEPHRINE. How does epinephrine work to stop an allergic reaction? You need to know this. You need to understand WHY those with food allergy must carry this medication everywhere they go. You need to know WHY you must use this medication when your son or daughter, parent, grandchild, student or friend is having a serious allergic reaction. I told you how fast these reactions occur (and many of you have seen the speed of a reaction first hand) so there is no time to waste. If someone is experiencing anaphylaxis, injectable epinephrine must be given immediately. Be a hero. Save a life. Don’t be afraid.

What Does Epinephrine Do?

Epinephrine can help to stop anaphylaxis from progressing to death if given early and appropriately. It is the only thing that can. Antihistamines can relieve some of the skin symptoms (hives, itch) but they do not have the ability to save a life from anaphylaxis.

Epinephrine constricts blood vessels. This is important because it curbs that microvascular leaking that leads to decreased blood volume and plummeting blood pressure, potentially leading to shock and death.

Epinephrine relaxes airways. So while histamine is trying to make the airways tight, epinephrine tries to relax them in order to allow air to pass more easily.

Epinephrine helps to decrease swelling in the upper airway so that air is not obstructed from getting to the lungs. It decreases cramping of the GI tract. It helps to block the hives and itching that accompany an allergic reaction.

That is anaphylaxis in a nutshell, so to speak. This is why it can be deadly and this is why epinephrine can save a life. Please share this post with your friends, families, teachers, administrators, school nurses, physicians and anyone else you can think of. The more we can educate about the seriousness of food allergy, the safer the world will be for those who live with it.

 

Dr. Sarah Boudreau-RomanoDr. Sarah M. Boudreau-Romano is an attending physician in the Division of Allergy and Immunology at Ann & Robert H. Lurie Children’s Hospital of Chicago. She became a board-certified allergist following her fellowship at Children’s Memorial Hospital and Northwestern Memorial Hospital. Sarah has four children, three of whom have life-threatening food allergies. She spent the past several years learning first-hand how families with children who have multiple food allergies live and how they can live well. She also shares her stories in a blog called The Allergist Mom.

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