Breakdown of an Allergic Reaction
What exactly is happening in the body during an allergic reaction?
Antibodies and IgE
Antibodies are defense proteins produced by the immune system to counter a specific antigen that it detects as a threat. There are different types that each have their unique role, but the main contributor to allergies is the IgE antibody. When produced, the claws of antibodies take shape to best catch the antigen they were designed to counter, in this case, allergens.
Let's say you were trying to catch a football, basketball, or baseball. You would have to form a different hand shape to best catch each type of ball. For example, to catch a football, you would make a diamond; for a basketball, you would form a W shape; and for a baseball, you would form a claw shape.
Antibodies leverage this approach to target specific allergens selectively. This is why you are allergic to certain things and not others. You won't react against allergens that don't bind with your antibodies.
So how does an allergen binding to an antibody make someone feel miserable?
Mast Cell and Basophil Activation
Antibodies don't directly cause your symptoms, but they act as supports for other types of cells, and in the case of IgE, mast cells and basophils. IgE antibodies connect to these cells with their tail and act as sensors. When the antibody detects its antigen by binding to it, it signals the cell to activate.
Mast cells and basophils can also be activated directly, without the need for IgE binding.1
When activated, these cells release pro-inflammatory molecules such as histamine, and vasoactive molecules that promote the dilation of blood vessels, which results in allergic symptoms.
The rapid systemic degranulation of mast cells and basophils can result in a life-threatening reaction called anaphylaxis, which can involve multiple organ systems; namely the respiratory, cutaneous, cardiovascular, or gastrointestinal systems.2
Structure of Allergens
What do these allergens, that antibodies so happily bind to, look like?
Here is an example of a common peanut allergen:
Peanut Allergen Ara h 6 - View Protein Structure
This is a protein, which is the building block of life. Foods and the environment are made up of many different proteins that give life its function. The grass grows and has structure because of proteins, the same with peanuts. The proteins that compose something give it unique qualities, and since grass and peanuts are made up of different proteins, they are distinct.
Some proteins are heat-labile, losing their structure when exposed to high temperatures, while others are not. This is why someone allergic to heat-labile allergens reacts to raw food but has no reaction when it is cooked. The cooking process destroys the allergens, which prevents antibody binding and cell activation.
Allergen Similarity
Let's look at a unique interaction with specific allergens.
Some people with a Latex allergy experience "Latex-Food Syndrome." Why is that? Why would someone allergic to rubber also be allergic to certain foods? This has to do with protein similarity; the allergen these people are allergic to is similar to proteins in foods.
Comparing other proteins to a Latex allergen Hev b 11, we find that avocado and kiwi, common allergic foods involved in "Latex-Food Syndrome", have a nearly 70% protein similarity.
Avocado Allergen Pers a 1:
Kiwi Allergen Act c Chitinase_I:
Knowing which proteins are similar to your allergens can help you avoid sneaky allergic reactions to foods or the environment.