Okay, so Immunology is crazy complicated and there are many things that we don’t know yet, but let me explain why this question actually make sense.
In my opinion, what most people think when we talk about allergies is that the body is reacting for no reason to external substances, like pollen, dust or some food elements. And by no reason, I mean because, generally, these substances are innocuous.
Let me guide through my line of thoughts. It is true that the body is trained to recognize and develop weapons to block and destroy corpses not coming from himself (non-self). After all, the immune system is based on the fact that knowing what is ours allows us to distinguish what is not. In this way we can kill bacteria, viruses and parasites in an elegant and intuitive way.
After all, that’s the basic reason on why we are so afraid of transplant rejections. Organs from other animals or people intrinsically bare different proteins on the surface that can be recognized for destruction by our immune system.
But wait, if we recognize everything that doesn’t belong to our body as an enemy and as such, it should be destroyed; why are we not allergic to everything? I mean, why are we not allergic to everything we eat for example? It makes sense right? We swallow meat, vegetables, medicines and desserts that have nothing to do with what our body had been training to recognize, so we should react destroying those things.
Let’s first discard medicines, artificial compounds and everything that broadly is not protein based; in fact, almost everything that our antibodies are trained to recognize is protein structures, so everything that is not is in principle invisible to our immune system.
But still, if we eat that pork or chicken that we like so much, why don’t we react every time we eat them? Trust me, there are a lot of proteins there, and a lot of them are not really human-like. The answer is not yet clear, but I can try to make out an explanation based on what we know is going on.
First, the antibodies that are along our digestive system are mostly IgA, a special kind of antibodies that are not particularly good to activate our immune system response but they are there just to simply block the access, let’s say. In fact, we need another kind of Ig to activate a proper response, if this other kind never come in contact with these external bodies there is no problem.
Second. It seems that most allergies due to pollen and dust, for example, are not “random”, but they are in fact a collateral effect of our trained response for killing parasites through our antibodies IgE (another kind). These are waay better in activating the immune response and are very useful to protect us from internal parasites. IgE are also very good in activating mastocytes, specific cells dedicated to the production of histamine. Heard of it before? Yep, that’s why, when you are allergic you take antihistaminics. Too bad that in doing so they end up recognizing some innocent structures like pollen. On the other hand, as long it’s not something they are trained to recognize we should be fine.
Third. Despite these first two points, we can safely say that we are always in a continuous state of inflammation. I mean it. In one way or another, we are always attacked by bacteria, viruses and other bad stuff. Imagine how many bacterial cells you swallow when you eat your good sandwich for lunch. So it’s technically true that we “react” to everything, we have to. Almost in every moment, we are under some allergic reaction or another in a broad sense. The fact that we don’t realize it and we are still healthy, is just because our immune system does a damn good job at it. And also the response is not all-or-nothing, but it is highly regulated by other elements. For example, Regulatory (or suppressor) T-cells are special cells that go around the body blocking an exaggerated allergic response most of the time.
To summarize, we don’t die every day because: we just “eat” the food, and that food doesn’t get in other places but our digestive system (so that anything but IgAs can bind to it); although we are in a constant state of risk, regulative cells and systems are there to protect us and take care that the system doesn’t misfire; most molecules can’t be recognized because either they are not protein or because they are no similar to anything that we have seen before.
Since we don’t really know why some molecules activate allergies more strongly than others, why some people are allergic and other aren’t, and why allergies can come and go, we are clearly lacking some knowledge on the topic. But for now, be happy with what we have.
Interesting huh? Keep thinking about that whenever you will eat next. It is true that you might be allergic to peanuts but you are pretty lucky for not being allergic to everything right? Let me tell you another story..