Food Allergy – Alessandro Fiocchi, MD and Vincenzo Fierro, MD (2017 WHO)
The classification of allergic and hypersensitivity diseases was established by the European Academy of Allergy and Clinical Immunology (EAACI) and the World Allergy Organization (WAO) in 2004 (1). The definitions and concepts of allergic and hypersensitivity conditions beyond the allergy community have often created misunderstanding (2). For an optimal clarification:
- the term “atopy” is used when individuals have an IgE sensitization as documented by IgE antibodies in serum or by a positive skin prick test;
- “hypersensitivity” is defined as “conditions clinically resembling allergy that cause objectively reproducible symptoms or signs, initiated by exposure to a defined stimulus at a dose tolerated by normal subjects”, and
- “allergy” is defined “a hypersensitivity reaction initiated by proven or strongly suspected immunologic mechanisms”.
Based on these definitions, a correct diagnosis of allergic disease must adhere to the following conditions:
- a) Compatible clinical history; and
- b) Positivity to in vivo and/or in vitro tests to prove underlying mechanism and etiology.
Lewis et al., (2012) – Eliminating Immunologically-Reactive Foods from the Diet and its Effect on Body Composition and Quality of Life in Overweight Persons
In 1919 a physician observed, following a blood transfusion, a case of transient asthma caused by allergy to horse dander. This was the first indication of a factor in blood capable of mediating an allergic reaction. In 1921 Prausnitz & Küstner performed the passive transfer of this substance to artificially induce a positive skin test. The search for reagin started after that, but until the 1960’s it was thought that reaginic activity was not a single, indivisible molecular species but was present in allergic sera in the form of labile complexes. This differed radically from immune antibodies that were known at the time.
A fairly good knowledge exists about the various steps in the allergic reaction, but despite present knowledge, the prevalence of allergic diseases is still increasing. In some areas of the industrialized world up to 50% of the population is affected. More efforts must be dedicated to the understanding of allergic sensitization and how it can be prevented. The identification of the pathological role of IgE and the subsequent release of inflammatory mediators and cytokines has enabled physicians to treat allergic symptoms with regard to the underlying immunological mechanisms. New pharmacotherapy in the form of a humanized monoclonal anti-IgE antibody designed to eliminate IgE may have a valuable role in treating IgE sensitized individuals.
Quantitative IgE antibody assays in allergic diseases
During the past several years, immunoassays for specific IgE antibodies have been refined to permit reporting results in mass units. Thus quantitative immunoassays for IgE antibodies may be an adjunct to skin tests. In cases of food allergy among children with atopic dermatitis, cutoff values for IgE antibody concentrations to egg, milk, peanut, and fish have been derived to provide 95% positive and 90% negative predictive values. Food-specific IgE antibody determinations can also be used to predict which food allergies are resolving spontaneously.
Elevated egg-specific IgE antibody levels in infancy are associated with significantly increased risk for development of inhalant allergies later in childhood. In cases of inhalant allergy, specific IgE antibody levels correlate closely with results of inhalation challenge studies in cat-sensitive persons. Also, mite-specific IgE antibody levels correlate significantly with the mite allergen contents of reservoir dust in the homes of mite-sensitive persons. Immunoassays for quantitation of specific IgE antibodies may be used to document allergen sensitization over time and to evaluate the risk of reaction on allergen exposure. However, immunoassays and skin tests are not entirely interchangeable, and neither will replace the other in appropriate circumstances. (J Allergy Clin Immunol 2000;105:1077-84.)
A follow‐up study of children with food allergy. Clinical course in relation to serum IgE‐ and IgG‐antibody levels to milk, egg and fish
Eighty‐two children with food sensitivity were followed‐up for 2‐5 years. Most children showed a decreasing sensitivity and the clinical course of food allergy seemed to reflect the course of the humoral immune responses to the offending foods. The occurrence of IgE‐ and IgG‐antibodies parallelled in most cases. However, an early, high IgG/IgE food antibody ratio seemed to be a good prognostic sign, indicating a possible blocking capacity of IgG‐antibodies.