"不干不净,吃了没病?"

 Allergies of today

Adnan Custovic,MD,DM,PhD
Professor of Allergy
North West Lung Centre
University of Manchester,UK

 A remarkable increase in the prevalence of allergic diseas appears to parallel the psot-industrial lifestyle changes in westernized societies. Insufficient microbial exposure during infancy and early childhood is one of the proposed explanations for the increase in prevalence of atopic sensitisation and associated clinical phenotypes (asthma, allergic rhinitis, eczema).One of the inadvertent consequences of the fight against infectious diseases and our obsession with cleanliness might have been the interference with the immune system development. The changing pattern of microbial exposure, with the decline in some infectious diseases, may lead to a slower maturation of the immune system,with a delayed development of the optimally alanced immune responses. This notion forms the immunological basis of the hygiene hypothesis. However,the hygiene hypothesis originatied from epidemiological studies.

Searching for the cause of allergy: the link between epidemiology and immunology

Family size: The pioneering proposal that a decrease in family size reduced the possibility of cross-infections, facilitating the clinical expression of allergic rhinitis had lead to intense interest in this area.

Helminths: Children in developing countries infested with helminths are less likey to develop atopy and allergic diseas. Furthermore, long-term treatment of intestinal helminthes in infested children increases specific sensitisation to dust mite. In addition, there appears to be an inverse dose-response relationship between the burden of infestation by helminthes and expression fo allergic disease. However, helminths may only be a marker of environmental exposure to other microbial agents and/or endotoxin.The fascinating question which needs addressing is whether allergic disease can be treated, or even prevented by exposure to helminths or their products.

intestinal microbiota: Recently, a number of studies have suggested that non-pathogenic intestinal microbiota may have potent immuno-modulatory effect on the development of immune system. Composition of gut microbiota may influence the development of allergic disease, but the effect may differ depending on the geographical region, diet and hygiene prctices. There has been a special interest in probiotic supplementation as  a potential therapeutical of preventative modality for allergic diseases.

Farming and anthroposophic lifestyle: Evidence suggesting that farming lifestyle is  protective against allergic disease is consistent, and has been reproduced in a number of studies from different countries. Growing up on farms is associated with exposure to endotoxin, helminths, lactobacilli and saprohytic mycobacteria, whilst anthroposophic lifestyle is related to less interference with common childhood infections due to reduced antibiotic use and vaccination, and consumption of naturally fermented vegetable.

Environmental exposures, genetic predispostion and development of allergic disease - from whole population to individuals at risk

It is important to emphasise that the potential protective effect of any of the above mentioned exposures is not going to be applicable to every individual in the population, but only to those with a particular genetic susceptibility. Consequently, broadly speaking, exposure to "dirt" may be beneficial for some, have no effect on the others, and there may be individuals within population in whom these exposures may be detrimental.

We need to move away from the concept of "one size fits all" assessment of risk and the consequent blanket advice on what may be beneficial aimed at everybody, to the tailor-made assessments of individual susceptibilities coupled with therapeutic or preventive measures which are specific to individuals at risk. (End)

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