hEALTH

ALLERGY

Controversial hypotheses

Clean home, dirt, and allergies - the hygiene hypothesis

An old theory receives new support: Dirt trains the immune system. Dust of 812 mattresses from 6-13 old children were investigated for bacterial endotoxin. Children living on a farm had about the 2-fold of endotoxins in their beds than children from non-farming families. At the same time, the farm children had less problems with allergic rhinitis (4.1 % vs. 10.5 %) and atopic asthma (3.1 % vs. 5.9 %). Blood tests confirm these data. These data suggest that the permanent contact with dirt (e.g. bacteria) trains the immune system to react more tolerant against harmless allergens. “A subject’s environmental exposure to endotoxin may have a crucial role in the development of tolerance to ubiquitous allergens found in natural environments”.
Further evidence is given by research work with nonobese diabetic (NOD) mice: their T cells die faster than normal resulting in a T cell deficiency. To compensate for the missing T cells, the surviving T cells are activated to divide and proliferate (compensatory homeostatic expansion). However, not all of the T cells are able to divide; therefore a reduced number and a shift in the T cell population is observed. A part of these newly generated T cells seems to be responsible for the autoimmune process (resulting in diabetes). In contrast, the number of T cells stays stable when stimulated by a bacterial infection.
The hypothesis explains why childhood bacterial infections decrease the risk for developing autoimmune diseases and explains why autoimmunity has been rising in the last half century in populations with decreased exposure to pathogens.

Homeostatic Expansion of T Cells during Immune Insufficiency Generates Autoimmunity.
King C, Ilic A, Koelsch K, Sarvetnick N.
Cell 117: 265-77 (2004).

Eat dirt - the hygiene hypothesis and allergic diseases.
Weiss ST.
N Engl J Med 19: 930-1 (2002).

Please also notice the comment of G. Watts, Science Editor of British Medical Journal.

Allergy or not?

Allergies may be potentially more often misdiagnosed than generally assumed. Sheryl Szeinbach of Ohio State University presented a study at the 2001 Annual Meeting of the American College of Osteopathic Family Physicians. 246 patients with allergic syndromes were tested on their immunoglobulin E (IgE) reaction towards specific allergens. 65 percent of the patients were negative, and only 35 percent showed a real allergic reaction. This may be due to the commonly used skin tests. The accuracy of these tests could be variable and ranges from 30-63 percent.

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