Dec

16

I'm looking for some clarity about the issues of immunity, allergies, etc. Possibly this question will reach a reader with expertise.

In my college biology class, about 26 years ago, the professor explained that we've all got antibodies to "everything", but the antibodies only multiply themselves to large numbers when the body is attacked by an invader. At the time I asked the professor, "what's everything?", and the professor answered only "everything". I wanted to follow up and ask if "everything" included anti-neutrinos? Buicks? But there were >100 other students in the lecture, and anyway I don't think the professor really knew the answer. (Maybe the answer is "proteins"?)

What about foods? There has been much recent publicity about allergies to gluten, protein(s) found in wheat. Presumably gluten in included in "everything", and so everyone should have antibodies to it. Why then do some people react to gluten, multiplying the gluten antibodies up to big numbers, while others don't?

More broadly, since "everyone" has antibodies to "everything", why is that in only some people an allergen is treated as an invader?

Mr. Justa Guy replies:

JanewayYour professor was indeed correct, we all do have antibodies against virtually everything, or at least everything proteinacious. That is because of (i) continual recombination, and (ii) ongoing mutation.

Antibodies are made up of two heavy chains, and two light chains. Each heavy chain and each light chain have a unique specificity for a particular target (aka antigen). There are three genes which contribute to the specificity of each heavy chain, or light chain, called the variable (v), diversity(d) and joining (j) regions. There are multiple (ie dozens) of different V regions, dozens of different D regions and a few different j regions. This number is constantly increasing because of somatic hypermutation. One heavy chain made up of a specific combination of V, D and J chains, and one light chain made up of a different combination of V and D chains are made by one particular B cell. Mathmatically this diversity allows for tens of thousands of different antibody specificities. The presence of somatic hypermutation where one amino acid (there are 26 amino acids) is mutated with each round of cell division allows for a virtually infinite total number of antibody combinations, which in principal will include antibodies specific for every possible antigen (except perhaps Buicks).

Lets take the case scenario of a B cell that makes an antibody against influenza. In the case of the flu, a naive B cell which is specific for flu, is activated when it encounters flu antigen (either vaccine or flu virus). This causes the B cell to proliferate and make different kinds of antibodies, starting with IgM and IgD, and then maturing into either IgA, IgG, or IgE which help with either defense at mucosal surfaces, in the blood, or in causing allergy. Ultimately the activated B cell makes daughter cells of memory B cells, or plasma cells whose job it is to produce large amounts of antibody.

That is a short version of how it works.

There are many excellent intro level immunology texts, one of my favorite is by Janeway. They can provide a much more detailed explanation.

Jeff Sasmor writes:

Recently there has been much publicity about allergies to gluten, protein(s) found in wheat. Presumably gluten in included in "everything", and so everyone should have antibodies to it. Why then do some people react to gluten, multiplying the gluten antibodies up to big numbers, while others don't?

But Gluten Intolerance, also known as Celiac Disease isn't an allergy — it's an autoimmune disease; gluten sensitive enteropathy.

My older daughter has it… so I learned more about it than I ever wanted to know.

Justa Guy adds:

That is where it get more complex.

In order for B cells to maximally proliferate, they require "help" from another cell, the CD4 T cell. The CD4 T cell that helps a given B cell is specific to that same antigen. When CD4 T cells recognise antigens, it is done in concert with recognising another class of molecules called MHC class II, which is what defines self. So If a CD4 cell recognises an antigen but does not see MHCII, it is non self, and the CD4 cell helps coordinate the immune sytem to attack the non self antigen. If the CD4 cell recognises antigen, but also sees MHC II, then it is self and the CD4 cell is prevented from proliferating, and so it does not supply the necissary "help" to the B cell so that the B cell cannot proliferate to produce antibody.

Celiac Sprue is felt to be a food intolerance, where antibodies are produced that also react with self antigens expressed in the small bowel. In essence the antibodies are reacting against self, and so Sprue ( and many other diseases - eg lupus, rheumatoid arthritis etc) are circumstances where the process of tolerance ( breifly outlined above) to self antigens fails.

Riz Din responds:

As Justa Guy says, it's all about finding one's optimum dose. Unfortunately this is very difficult to do with vitamin D, as official lines are quite wishy-washy.

In order to get to where you want you first have to know where you are, and having a vitamin D blood serum test has to be the best first step in this direction. After spending a long summer outdoors I had my blood taken and my level came in a rather pitiful 63 nmol/L. It isn't woefully inadequate, though it does fall in the 'insufficient' zone. I shudder to think what my winter reading would have been. My doctor simply recommended a multi-vitamin tablet of all things as a solution, which is not wise as many of the other vitamins can be toxic at much lower multiples of the RDA. I'll eventually get retested to make sure I'm not at an risk of toxicity from vitamin D supplementation (currently taking 1000IU a day), but I think this is close to impossible on the existing dose.

From (a rather wobbly) memory, I understand the benefits for many conditions (bone fracture risk, etc) really kick it at the slightly higher doses of 800IU upwards, and also that the negative effects are very rare and tend to occur at extremely high doses, except for people who display a particular sensitivity. For my mother, who is also taking supplements, vitamin d has bought significant improvements. For me however, I haven't experienced anything beyond stronger nail growth, but I guess that's the point.

My 'vitamin d' bookmarks folder is on another machine, so I've put together a few interesting links for people who want to dig a little deeper (see below).

Here are the links:

- Dr Holick is a significant figure in the field of vitamin D research and he is also the most recent winner of the Linus Pauling Award. His UV Advantage website contains links to articles, videos, interviews, etc . I know the site looks a bit cheesy, but this guy is pretty well respected.

- On the issue of life extension, a recent study of lymphoma patients found that 'Patients with deficient vitamin D levels had a 1.5-fold greater risk of disease progression and a twofold greater risk of dying, compared to patients with optimal vitamin D levels after accounting for other patient factors associated with worse outcomes.' Pretty impressive stuff.

- The Institute of Medicine is reviewing the daily reference intake recommendation for vitamin D. Their work is ongoing but if you follow the link and click on 'presentations' in the 'other resources' section on the right, you can download presentations from people who attended the workshops (Holick is among the names).

- An AJCN Editorial from 2007 states: 'The balance of the evidence leads to the conclusion that the public health is best served by a recommendation of higher daily intakes of vitamin D (3). Relatively simple and low-cost changes, such as increased food fortification or increasing the amount of vitamin D in vitamin supplement products, may very well bring about rapid and important reductions in the morbidity associated with low vitamin D status.'

- An older AJCN review article looked at toxicity levels and reported 'Throughout my preparation of this review, I was amazed at the lack of evidence supporting statements about the toxicity of moderate doses of vitamin D. Consistently, literature citations to support them have been either inappropriate or without substance.'

The author presents this insightful graph and comments that 'The serum 25(OH)D concentration is maintained within a narrow range (Figure 2Go), {approx}75–220 nmol/L across vitamin D supplies from 20 µg (800 IU) to the physiologic limit of 250–500 µg (10000–20000 IU)/d. The most reasonable explanation for this kind of relation is that there are homeostatic control systems to regulate serum 25(OH)D and to buffer against variability in vitamin D supply. … Beyond the vitamin D supply limit, which is comparable with that attainable with sunshine, there is a classic rise in the dose-response curve. The sharp rise reflects the introduction of vitamin D and 25(OH)D at rates that exceed the capabilities of the various mechanisms to regulate 25(OH)D.'


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