字幕表 動画を再生する 英語字幕をプリント For some people, a simple peanut or a bite of a shrimp can cause the body's immune system to wildly overreact. In some cases, the results can be deadly. But what exactly is happening in the body for it to confuse nuts or shellfish with a true threat? By definition, a reaction to a food is only considered an actual allergy if the immune system is involved. And if the response is caused by immune cells called IgE antibodies, which we'll get more into later. But it's important to distinguish an allergy from a sensitivity or an intolerance, which involve uncomfortable symptoms as a reaction to food, but don't cause an immune response. So if you're lactose intolerant, you're not allergic to milk. Hi. My name is Tina Sindher. I'm a Clinical Assistant Professor in allergy and immunology at Stanford University. And I see patients in my clinic with, eczema, with asthma, food allergies, with environmental allergies. And my main focus lies in food allergy research. In order to understand food allergies, we need to know how the body evaluates food in the first place. In a typical immune system, your body is constantly evaluating different antigens to deem them either benign or dangerous, in this case, the proteins on the food particles. When they eat a peanut for the first time, their body kind of tells your immune system, like, look at this, this is a peanut, do not fight this in the future. So that every time they eat a peanut, their immune system does not react to it at all. The immune system is basically building up a tolerance for the next time peanuts are around. But in the allergy afflicted, by the time they eat something like a peanut, their body is already primed for an immune response. Our immune system is kind of like a seesaw, it needs balance. So, on one side of the seesaw is your T regulatory cells. And they are kind of your brakes. They're the cells that tell your immune system, calm down, slow down, do not fight this. And then the Th2 is your allergic cells. And they are ready to go, and revved up. And they will bring in all other inflammatory cells to fight what they perceive as danger. In most people, the T regulatory cells hold more weight in determining what's problematic and what's harmless. But in people with a more Th2-skewed system, their cells sound the alarm much more easily and have a high sensitivity to the harmless proteins on foods, most commonly milk, eggs, wheat, soy, peanuts, tree nuts, fish, or shellfish. But having a skewed immune system isn't enough, there has to be a trigger point to developing a specific allergy, and that's still not completely known. One of the proposed thoughts on how allergy begins has to do with the allergen entering the body the wrong way, through the skin. Minuscule food particles floating in the air can enter the body through the skin if there is dysfunction in the skin barrier due to something like eczema. We're talking about nanoparticles of peanuts. So it can be in your bedding, it can be in the air. You might be getting exposed to it without any knowledge of it. It's that it's entering our, it's interacting with our immune system in a way that it's not meant to. We're not supposed to get food allergens to come in through our skin. Or environmental. So really the initial process is the barrier breakdown that we're seeing. So, in some people, when immune cells in the skin encounter these antigens, they recognize that they are foreign and in the wrong place. This ultimately signals the immune system to produce antibodies called immunoglobin E or IgEs to fight against the food proteins. Now, when this same food is finally ingested the right way through the mouth, the body's IgE's will recognize it as a threat and respond in full force, leading to an allergic reaction. And the way this looks is basically, when your mast cells and basophils open up, they contain histamine and tryptase, and a bunch of other inflammatory mediators. And those are what drives the reaction. This inflammatory response mirrors the body's reaction to a parasitic infection. But, skin exposure is not dangerous for those with food allergy already. Our body shouldn't be responding like that, right, to food, and that's what we're hoping to figure out, and that's what we're hoping to prevent. We know that our immune system has developed this kind of response, but we don't know the why. There is a genetic component to who has allergies and who doesn't. Children whose parents have allergies are more likely to have allergies themselves. But there are other environmental factors at play that mess with the balance of the seesaw of an individual's immune system. So it's not one thing, it's multifactorial. And it's our diet, it's our lifestyle, it's modern conveniences that may push us kind of over the edge for some, not all, but some. The thing is, we might just be too clean. This is what's known as the hygiene hypothesis which says that a lack of exposure to germs early in life can trigger the immune system to mistake a food protein as an invading germ. So for fewer allergies, maybe... Get a dog, roll around in dirt, don't wash your clothes, and play in the sun.