|MadSci Network: Immunology|
This is a very interesting question. What seems to be the case is that while specific allergies (eg against shellfish, or peanuts, or ragweed) are not inherited, the propensity (likelihood) of developing allergies is. This propensity to develop allergies is known as "atopy" and atopy does run in families. Many of the genes thought to contribute to atopy / allergies (and asthma, for that matter) are part of the immune system, coding for cytokines and cytokine receptors. This likely reflects the fact that allergies and asthma are merely "inappropriate" immune responses, where the body overreacts to something that is not dangerous to the body, such as peanuts or ragweed pollen. Therefore, it is not surprising that genes associated with atopy would also be associated with the immune response, and that it could be possible to inherit a hair- triggered immune system. This, then, is reflected in the fact that there are a high incidence in allergies in the British population, while relatively lower incidence in Portuguese populations. A really good website examining the genetics of atopy is http://www2.qimr.edu.au /davidD/asthma6.html, which comprehensively reviews the scientific literature, but is a little technical.
Although there is certainly a genetic component to allergies, there are also environmental components. It has been noted that there has been an "epidemic" of asthma in the United States over the past few decades. Some people have hypothesized that this increase in allergies is due to overcleanliness - that the immune system doesn't have enough to work on, so it starts attacking harmless things, like pollen. An example of this viewpoint can be found at this website. This viewpoint is known as the "hygiene hypothesis." In fact, some people have proposed feeding people allergens or even intestinal parasites in order to cure allergies. Some people also took this viewpoint to mean that children should not be vaccinated. Recent research, however, has shown that there is no link between vaccination and increased risk of developing allergies or asthma (see this article for a summary). Overall, a link between raising a child in an overly clean environment and development of allergies is controversial (see this more recent article).
Hope this helps!
1) Curr Opin Allergy Clin Immunol. 2001 Oct;1(5):387-92. Genes for atopy and asthma. Heinzmann A, Deichmann KA.
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