Food allergy

A food allergy is a medical condition where there’s an abnormal immune reaction to some food.

Now, a variety of food proteins can cause food allergies, but the most common are known as the big eight, these include proteins within milk, eggs, peanuts, tree nuts, seafood, shellfish, soy, and wheat.

Food is essential to life, and normally food doesn’t cause an allergic reaction - in fact, the process that allows for that is called oral tolerance.

Let’s see how that works. Normally, when food travels through the stomach and intestines, the proteins within them are broken down by gastric acid and proteases into tiny fragments, called oligopeptides - small strings of amino acids.

These oligopeptides reach the Peyer’s patches which are bits of tissue along the intestinal wall where M-cells live.

M-cells are antigen-presenting cells in the gut that grab protein fragments from the intestines and then present them on their cell surface to a nearby helper T cell.

The protein fragments are presented by the M-cell using an MHC class II molecule, which is basically a serving platter for the helper T cells.

The helper T cell is key because it largely controls the immune response.

Now here’s the catch, even if a helper T cell binds to that oligopeptide, another type of T cell called a regulatory T cell can release cytokines so that the helper T cell undergoes anergy.

Anergy is a bit like turning off that helper T cell so that it doesn’t induce an immune response.

In other words, regulatory T cells release cytokines in the lining of the intestines to help prevent the helper T cells from ever getting stimulated by food.

Now, in food allergy, this process doesn’t work properly.

An allergic reaction towards food happens in two steps, a first exposure, or sensitization, and then a subsequent exposure, which usually gets a lot more serious.

So, let’s say a person eats shrimp for the first time, and for some reason the helper T cell is able to generate an immune response towards the proteins within shrimp.