A recent review article suggests that the bacteria symbiotically found in the intestines play a key role in allergy. The author describes the “intestinal immune system” as the largest component of our total immune system. It has the unique property of distinguishing beneficial bacteria from pathogenic ones. Intestinal infections by viruses, protozoa, and helminthic worms, as well as bacteria, are common. In addition, food contains many potential allergens. When everything works perfectly, the lining of the intestines mounts an inflammatory response against the pathogenic invaders but not the many non-self proteins that it encounters every day.
Lactobacillus and Bifisobacterium species are widely sold as probiotic dietary supplements. Many other types of bacteria can be isolated from the intestines of healthy people. It is still not established how many different species should “normally” be present. I have seen dietary supplements with several dozen species listed, including some that do not sound healthy, such as streptococcus.
The hygiene theory, introduced in 1989, suggests that children who have too few infections are more likely to develop allergies such as hay fever. Our immune systems have evolved to fight numerous infections, and according to the British researcher D. P. Strachan, we need a certain amount of exposure to pathogens in early childhood in order to develop a healthy and well regulated immune response. This idea has been expanded by many researchers.
The Japanese researcher K. Takahashi examined the role of IgE receptors in allergic reactions. He reported numerous anti-allergy effects of probiotics, including a correlation between atopic eczema (skin rash) and intestinal bacteria in children. He concluded that “control of the interaction between the intestinal immune system and intestinal commensal bacteria is a key factor in regulating allergy.”
Other researchers are expanding the definition of “probiotic” to include helminthic worms for the treatment of autoimmune disease.