I’m trying to explain the difference between coeliac disease and wheat intolerance to a coworker and while I understand the complexities of coeliac disease and how it can effect different people to different levels, I struggled when he asked me to explain the key differences between the disorder and an allergy.
In: Biology
I’m going to be doing a few podcast episodes on this stuff, so I’ve been reading up on it a lot.
Allergy is a certain kind of immune overreaction to a harmless external substance. Allergies typically have a kind of antibody response (IgE) and commonly involves certain immune cells (mast, eosinophils, basophils). The substance being “harmless” is an important part of the idea — not everyone reacts in to that substance and the substance doesn’t cause you damage outside of your immune overreaction. The substance being from outside your body is also important and is a major distinguishing factor between allergy and autoimmune.
An autoimmune issue is also an immune overreaction/mistake. In this case, though, your immune system is overreacting to a normal thing inside your body. Antibody responses are around, but you see more types of antibody (IgE, IgG, IgM). You also see a lot of different immune cells involved, like heavy involvement of T cells. A major point here is the thing your immune system is going after is something your own body makes.
An interesting cross-over point here is that one way your immune system can make the “autoimmune mistake” is if it is launching an immune response to something else, but then getting that other thing mixed up with something in your body. This is called “molecular mimicry”, and at least in some cases this is how autoimmune problems get started — so your immune system could start getting mad at gluten, but then confuse gluten for transglutaminase 2 (TG2). Then your immune system gets all mad about TG2 and starts attacking cells with it, namely cells in your intestinal lining.
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