Mar 10 2008

The Homeopathy-Allergy Shot Analogy

Homeopathy is a pre-scientific healing belief system that is based on several invented “laws” that turn out to be no more than magical thinking. The “law of similars” holds that a substance that causes a symptom will actually treat that symptom when given in small doses. The “law of infinitesimals” holds that the smaller the dose the more potent the homeopathic remedy. Such homeopathic notions have no basis in reality, and modern scientific investigations of homeopathic remedies, when taken together, show that they have no clinical effect – they are no different than placebo. This is not surprising given that a typical homeopathic remedy is diluted far past the point where even a single molecule of active ingredient remains.

One argument often used by defenders of homeopathy is that they are analogous to allergy shots, which involve giving a small dose of a substance in order to cure an allergy to that same substance. During one of my lectures this argument was made to me by a fellow physician who is a believer in homeopathy. Allergy shots therefore seem to follow the laws of similars and infinitesimals. Superficially this analogy may seem compelling, but a closer look reveals that it is not legitimate.

The principle behind allergy shots has to do with the various types of antibodies that our immune systems produce. Antibodies are proteins that have a binding region with highly variable shape at one end, and receptors for immune cells at the other. The job of antibodies is to bind to foreign invaders (like infecting bacteria) and then target the immune system against them. We naturally make antibodies with a great deal of variability so that by chance some antibodies will have affinity for any possible invader. During an infection or challenge by a foreign object those B-cells (the immune cells that make antibodies) that make the antibodies that have affinity for the invader are stimulated to reproduce and make more antibodies, and also hone their affinity. This creates a large number of circulating antibodies with high affinity for the particular invader, and also results in the creation of memory B-cells – these wait for any future exposure when they will immediately release a large number of specific antibodies. Memory B-cells are the chief mechanism of immunity.

There are also different kinds of antibodies that serve different purposes. IgM are antibodies that are made during an acute infection, but they do not last long. IgG antibodies are the primary antibodies of immunity. They are produced slightly later than IgM but will last years instead of just weeks. IgA are adapted for mucous membranes, so they provide first-line immunity in our mouths, our GI tract, and in our lungs. IgE are the type of antibodies that are involved with allergies. They are also produced rapidly after exposure to a foreign molecule (anything that can trigger such a reaction is called an allergen). IgE then activates other immune cells that produce inflammation, sneezing, bronchoconstriction, coughing, itching, tearing and sometimes nausea and vomiting. The current thinking is that IgE and the reactions it produces evolved as a rapid response reaction to quickly expel invaders from the body.

An allergy occurs when someone has a reaction to a specific allergen that is too vigorous, or to an allergen that is not a threat to the body, like to a specific protein found in peanuts or to certain kinds of pollen. Allergic reactions can be life threatening if they are severe enough – a reaction called anaphylactic shock. The primary danger of this reaction is bronchoconstriction, causing asphyxiation.

Allergy shots work in a similar fashion to vaccines – they introduce a small and hopefully harmless amount of the offending allergen in order to produce an immune response, but of IgG rather than IgE. The goal is to give a small enough dose that there will be little or no allergic reaction, but large enough to stimulate an immune response and produce circulating IgG antibodies as well as their memory B-cells. IgG antibodies do not provoke an allergic reaction, but they do bind with the allergen and block it from binding with IgE. Such IgG are therefore called blocking antibodies. A series of allergy shots are given with increasing dose, so that each step of the way increasing numbers of blocking IgG are created, and therefore the recipient can tolerate the larger and larger doses of the substance that they are allergic to. This is a very clever treatment, exploiting our knowledge of the immune system, and it works very well.

It should now also be clear that allergy shots have absolutely nothing in common with the principles of homeopathy. Homeopathic remedies are not given exclusively for allergic reactions and they do not produce blocking antibodies or otherwise activate the immune system. Also, allergy shots are given in initially small doses but then in increasing doses until a sizable dose is given. Homeopathic ingredients are not given in small doses – they are given in nonexistent doses. There is a very real and important difference between a small dose and no dose at all.

Homeopathic preparation uses serial dilutions that often do not leave a single molecule behind. Modern homeopaths have had to resort to the argument that water has “memory” and can store the information of what was previously diluted in it. However, no one has been able to demonstrate this water memory, or provide a chemical model for how it could possibly work. Water is a liquid and any structure in water molecules is extremely transient. Invoking “water memory” is just using magical thinking to explain other magical thinking.

The allergy shot analogy to homeopathy is therefore a false analogy, a conclusion that is revealed by a basic knowledge of immunology. Anyone who invokes this argument in the defense of homeopathy is demonstrating pseudoscientific sloppy thinking.

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