High-level antigen exposure during the first few months of life Is suspected of predisposing Individuals to allergic sensltlsatlon and, therefore, various atopic Probiotics 955
conditions such as skin reactions and even systemic or respiratory manifestations.
Intestinal inflammation seems to be a predisposing factor in increased sensitisation of a subject (Holt 1994), which in turn promotes further inflammation when antigen exposure occurs.
Considering that the gut microflora is an important factor in regulating both the intestinal and systemic immune system, probiotics are used to promote endogenous barrier mechanisms, reduce gut permeability and alleviate intestinal inflammation in patients with atopic dermatitis and food allergy (Majamaa & Isolauri 1997). A 1 -month study of 10 breastfed infants who had atopic eczema and cow's milk allergy found that L GG reduced certain faecal inflammatory markers.
Clinical note — The hygiene hypothesis
The intestinal tract is the largest immune organ of the body. It produces more antibodies than any other part of the body and contains 80% of all antibody-producing cells. The intestinal mucosa functions as a barrier against infections, but it also provides communication between the different mucosal surfaces of the body (Ouwehand et al 2002).
At birth, the gastrointestinal tract is sterile. Normal gut flora develops gradually over time and is influenced by factors such as composition of the maternal gut microflora, diet, degree of hygiene, use of antibiotics or other medication, the environment and possibly genetic aspects. Studies in germ-free mice have shown that without these bacteria, the systemic immune system will not function normally (Vanderhoof & Young 2002).
In the absence of microbes, a mammal develops fewer Peyer's patches (part of the gut-associated lymphoid tissue) and less than 10% of the number of IgA-producing B cells compared with normal. However, on exposure to a normal microflora, previously germ-free animals develop their immune system very much like other animals. This indicates that the intestinal microflora is instrumental in the proper development of the immune system (Ouwehand et al 2002) and has led to the emergence of the 'hygiene theory of immune disorders'.
More specifically, the hygiene hypothesis suggests that improved hygienic conditions and vaccinations, which reduce early-life exposure to microbes, are associated with a heightened risk of allergic disease and other immune disorders. This is because reduced exposure may result in reduced stimulation of the immune system. As a result, lymphocytes that would normally differentiate to become Th1 type, differentiate to Th2-type cells and produce inflammatory cytokines in the allergic response in much greater quantities. As such, very early stimulation of the immune system is important in dampening the Th2 dominance and reducing the development of IgE-mediated food reactions as well as other allergic reactions. In a © 2007 Elsevier Australia
closely observed cohort of 329 Finnish children it was shown that the earlier an acute respiratory infection occurred, the greater the protective effect was against atopic eczema (Vanderhoof &Young 2003).
The obvious solution for increasing microbial exposure without increasing the health risk is the use of prebiotics and probiotics. Supplementation with probiotics has been shown to both reduce the risk and treat the symptoms of childhood eczema (see later).
Modulating the intestinal microflora with probiotics and prebiotics (fibre) may be an effective and safe therapy for the natural development of a balanced immune defence in infants and children. In adults and the elderly, prebiotics and probiotics may be used to improve the general functioning of the immune system.
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