Atopy
Atopy is the tendency to produce an exaggerated immunoglobulin E immune response to otherwise harmless substances in the environment. Allergic diseases are clinical manifestations of such inappropriate, atopic responses.
Atopy may have a hereditary component, although contact with the allergen or irritant must occur before the hypersensitivity reaction can develop. Maternal psychological trauma during pregnancy may also be a strong indicator for development of atopy.
The term atopy was coined by Arthur F. Coca and Robert Cooke in 1923 from the Greek ἀτοπία meaning "the state of being out of place", "absurdity". Many physicians and scientists use the term atopy for any reaction mediated by IgE, but many pediatricians reserve it to refer only to a genetically mediated predisposition to an excessive IgE reaction.
Signs and symptoms
Atopic sensitization is considered in the case of a person having IgE positivity or a prick test positivity to any common food- or air-borne allergen. Atopic conditions are considered: atopic dermatitis, allergic rhinitis, allergic asthma, atopic keratoconjunctivitis. The likelihood of having asthma, rhinitis and atopic dermatitis together is 10 times higher than could be expected by chance. Atopy is more common among individuals with a number of different conditions, such as eosinophilic esophagitis and non-celiac gluten sensitivity.Allergic reactions can range from sneezing and rhinorrhoea to anaphylaxis and even death.
Pathophysiology
In an allergic reaction, initial exposure to an otherwise harmless exogenous substance triggers the production of specific IgE antibodies by activated B cells. These IgE antibodies bind to the surface of mast cells via high-affinity IgE receptors, a step that is not itself associated with a clinical response. However, upon re-exposure, the allergen binds to membrane-bound IgE which activates the mast cells, releasing a variety of mediators. This type I hypersensitivity reaction is the basis of the symptoms of allergic reactions, which range from sneezing and rhinorrhoea to anaphylaxis. Allergens can be a number of different substances, for example pollen, dander, dust mites, and foods.Causes
Atopic reactions are caused by localized hypersensitivity reactions to an allergen. Atopy appears to show a strong hereditary component. One study concludes that the risk of developing atopic dermatitis or atopy in general "increases by a factor of two with each first-degree family member already suffering from atopy". As well, maternal stress and perinatal programming is increasingly understood as a root cause of atopy, finding that "...trauma may be a particularly robust potentiator of the cascade of biological events that increase vulnerability to atopy and may help explain the increased risk found in low-income urban populations."Environmental factors are also thought to play a role in the development of atopy, and the 'hygiene hypothesis' is one of the models that may explain the steep rise in the incidence of atopic diseases, though this hypothesis is incomplete and in some cases, contradictory to findings. This hypothesis proposes that excess 'cleanliness' in an infant's or child's environment can lead to a decline in the number of infectious stimuli that are necessary for the proper development of the immune system. The decrease in exposure to infectious stimuli may result in an imbalance between the infectious-response elements and the allergic-response elements within the immune system.
Some studies also suggest that the maternal diet during pregnancy may be a causal factor in atopic diseases in offspring, suggesting that consumption of antioxidants, certain lipids, and/or a Mediterranean diet may help to prevent atopic diseases.
A Swedish research study titled "Atopy In Children Of Families With An Anthroposophic Lifestyle" comparing the rate of bronchial asthma, allergies, dermatitis, and other atopic diseases among Steiner school pupils and pupils in public schools originally appeared in the May 1, 1999, edition of the British medical journal The Lancet. The findings indicated that Steiner school pupils were "at a significantly lower risk of atopy" than children attending public schools. The researchers investigated a variety of factors in the lives of the Steiner school pupils that might have contributed to this lower rate of atopy, which included breastfeeding, reduced immunization, avoidance of antibiotics and medications that reduce fevers, consumption of bio-dynamic and organic foods, and other physical aspects of the children's lives.
The multicenter PARSIFAL study in 2006, involving 6,630 children age 5 to 13 in 5 European countries, suggested that reduced use of antibiotics and antipyretics is associated with a reduced risk of allergic disease in children.