Allergies of the first kind—type I hypersensitivity explained in context

If you have kids you have probably been exposed to the idea that more kids have food allergies these days. Well, the data seem to bear this out. There are several hypotheses about why this is so, but not a lot of data. Rather than engage in speculation, I’d like to wade back into the dangerous waters of real science and tell you a little about allergies. Perhaps after you’ve read my grossly oversimplified explication, you’ll come up with your own science-based hypothesis to explain increased childhood food allergies.

First, let’s talk about what isn’t going on. The Huffington Post, always a target-rich environment for woo-hunters, has a writer named Sloan Barnett. She is about as well-informed about health issues as Bill O’Reilly is about anger management. Two of her recent posts address child health, and both display a stunning level of ignorance. Her fetishization of “green” bears no relation to actual research on childhood health.

An example of her ignorance?

But what really stopped me in my tracks was that children with food allergies are two to four times as likely to have related conditions such as asthma or other allergies. And guess whose very own children have nut allergies AND asthma….

Um, yeah, Sloane. That’s because food allergies, asthma, and related conditions are, er, related! Asthma, allergy, and atopy are all a type of immune dysfunction known generally as type I hypersensitivity. Its determinants are partly genetic, partly environmental.

Despite many studies, no one knows why this [increase in allergy] is happening. Here’s what I know. My third child, who was raised in a non-toxic home, eating only organic formula and food, recently tested allergy free. Look, I can’t be certain that our new lifestyle is the reason this baby is allergy free, but it sure does make you think.

Actually, one of the most popular theories in scientific circles is the “hygiene hypothesis” which roughly states that our cleaner and more sterile environment exposes our kids to allergens later. If they had been exposed earlier, their immune systems may have developed a tolerance for common allergens. This hypothesis is based on observational studies that kids raised with pets, on farms and other “dirty” places have lower rates of environmental allergies.

Still, we don’t know why we have an increase in childhood allergies, and clearly, neither does Sloane. Her evidence is based on what she’s heard and her own experiences, which is worth bubkes.

Alright, let’s get to a little actual science.

A common question from parents after seeing a child’s first allergic reaction is, “he’s had it before and it never bothered him. Why now?” When you understand how allergies work, the answer will be clearer.

An allergy is a disorder of the immune system. It involves what’s known as a “type I (immediate) hypersensitivity reaction”. This reaction looks familiar to those with allergies: hives, wheezing, runny nose. Oh, and anaphylactic shock and death. But hopefully not.

The part of the immune system that goes awry during allergic reactions appears to have evolved to fight parasites. Most of the same cells and antibody types are involved both in fighting parasitic infections and in causing allergy, and this machinery is located in areas where parasites can invade—the skin, lungs, gut, etc.

This is how it works (and for another branch of the immune system, feel free to look at this…about halfway down the page). One quick fact—the immune system has both “generalist” and “specialist” branches. Some parts of the immune system will attack anything vaguely “not you”. Other parts react only to specific invaders, and in the case of allergies, otherwise harmless substances are treated as invaders.

For an allergic reaction, you first need an allergen. Let’s take peanuts. Let’s say my kid eats some peanuts for the first time. She will not have an allergic reaction. Why not?

Because her body won’t recognize the peanuts yet. The nasty symptoms of an allergic reaction are caused by a type of cell called a “mast cell”—when a mast cell attaches to an allergen, it releases granules full of fun things like histamine, which cause swelling and leaking of blood vessels, itching, hives, and difficulty breathing. But for a mast cell to “degranulate”, it has to be coated with antibodies that recognize the allergen. And that can’t happen until your immune system learns about the allergen.

Here’s how we learn about a brand new allergen (sticking with the example of peanuts). Some of the proteins from the peanuts get picked up by an immune cell (dendritic cell) in the gut that’s hanging out looking for new, nifty invaders. This protein gets taken in and processed, then presented on the surface of this patrol cell. A T-cell comes along and happens to (randomly) be able to recognize this protein (now called an allergen). Other bits of peanut protein are picked up by B-lymphocytes, who chop them up and put the pieces up like a sign on their membranes. The T-cell gets very excited and produce a number of chemicals that tell B-cells to make lots of IgE, a type of antibody.

This IgE, which is produced specifically against this peanut allergen, attaches itself to mast cells. The B-cells that make this anti-peanut IgE are specific for the particular peanut protein. That’s all they do. They cannot recognize, say, tree pollen. The anti-peanut IgE-covered mast cells then hang out waiting for the next dose of peanuts, and when they are exposed to them again, all hell breaks loose.

The point here is that when you are exposed to peanuts for the first time (or any allergen for that matter), your mast cells don’t yet have a clue. They aren’t covered with anti-peanut IgE and you cannot mount an allergic response.

So why don’t your body’s immune cells just react to everything? Why don’t they, for instance, attack their neighbors? Well, sometimes they do, leading to auto-immune diseases such as multiple sclerosis and lupus. But early in development, when your immune system is young, it works a bit differently. If, for example, a B-cell or T-cell happens to recognize something that’s part of you, say cell in the thyroid gland, instead of gearing up for a reaction, it shuts down. Your body learns to “tolerate” itself. This is another reason that some people hold to the hygiene hypothesis. Since we isolate our kids from so many foods, molds, dirts, dusts, and other nasties, perhaps our kids never learn to tolerate them.

Or perhaps not. Either way, Sloane’s hypothesis, that our kids are exposed to all sorts of “toxins”, doesn’t seem to hold with science. In fact, isolating kids from the real, messy world may have the opposite of the intended effect.

Hey, we certainly don’t know enough yet to recommend either putting your kid in a bubble or rolling them around in dirt. But that’s the point—this is something we can study. We don’t need bad science writers spreading fear of…well, of what I’m not sure. But I’m sure if it sounds vaguely scary, the Huffington Post will make something up.