Understanding allergies

It is important to differentiate between an allergy and an intolerance or sensitivity. The classification of allergic and hypersensitivity diseases, which were defined according to the European Academy of allergy and Clinical Immunology (EAACI) and the World Allergy Organization (WAO) is essential in providing a clarified definition.

According to the WAO, the correct diagnosis of an allergy is if specific conditions are met, including: a compatible clinical history, and positivity to in vivo and/or in vitro tests (IgE blood test or skin prick test) to prove underlying mechanism and etiology, meaning to be classified as allergic to an item there is a need for a positive test result as well as symptoms.

Living with an allergy is the most common chronic disease throughout Europe. According to the EAACI, up to 20% of patients with allergies struggle daily with the fear of a possible asthma attack or anaphylactic shock. It can be life threatening for certain individuals.

There are a variety of environmental influences and genetic factors of the host body, which underlie the immunopathogenesis of food allergy and its manifestations. There have been some clinical studies, which have altered many people’s understanding of what causes a food allergy. An example of this is the functional genetic variants in the IL-12 receptor b1, and the toll-like receptor 9, as these thymic stromal lymphopoietin genes and even IL-4 gene polymorphism have been associated with the increased risk of a hypersensitivity to certain foods.

Overall, food allergies are a chronic condition and can be hereditary. However, there has been a recent rise in women developing certain food allergies and allergic rhinitis during the menopause.

Allergies explained

In order for allergy to exist, allergen sensitisation must first occur. Antigen-presenting cells, including macrophages and dendritic cells are responsible for detecting the allergen. This can occur in a variety of ways, including inhalation into the nose and lungs, as well as through the skin and the gastrointestinal tract. When cells containing an antigen interact with an allergen, there is perceived to be an invader, even though this substance is not believed to be harmful on a normal basis. Subsequently, the allergen is then absorbed into the antigen-presenting cell, processed and then displayed on the surface of the cell.

What happens next is that the cell then migrates and presents the allergen, this process stimulates the B-cell, and produces antibodies specific to the allergen. From here, these specific antibodies, (IgE) are then released and are able to attach themselves to receptors on various surfaces of other cells in the mucosal surfaces and on subsequent basophils contained within the blood.

There is a period of sensitisation, and afterwards comes a period of latency, then on subsequent re-exposure to the allergen the allergic response is triggered. In this process an allergen is able to connect with the IgE on the surfaces of the mast cell, and this causes the cell to release nasty and inflammatory cell mediators. These include histamine and other mediators, all of which act differently and cause a variety of symptoms in different organs.

In order to fully define allergy pathogenesis and develop novel therapeutic possibilities, the key may well be in further understanding the gut microbiome and advancing research into epigenetics.

Prince, B.T; Mandel, M.J; Nadeau, K; Singh, A.M. Gut Microbiome and the Development of Food Allergy and Allergic Disease. Pediatric Clinics of North America. 2015;62:1479-92 Xie, J; Lotoski L.C; Chooniedass, R; et al. Elevated antigen-driven IL-9 responses are prominent in peanut allergic humans. PLoS One. 2012;7(10):e45377 Nursing Times. (2006). The pathophysiology of allergic responses.

Sian Baker DipION mBANT mCNHC

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