Allergen

A allergen is a substance, a particle, an organic compound (Atome, Molécule, Protéine) able to cause an allergic reaction at a subject sensitized beforehand when it is with its contact (generally by contact with the Peau, inhalation, or ingestion).

It is necessary to differentiate “ allergic reaction ” and “ orthoergic reaction ”: the allergic reaction is a pathological phenomenon, related to an over-sensitiveness with a substance usually without danger to health. Conversely, the orthoergic reaction is a normal reaction to an aggressive substance. Two symptomatologies can be close, but it is the substance responsible and the mechanism for appearance of the symptoms which is important. The teargas, pepper, the nettles, is examples of substances involving of the demonstrations close to those due to an allergen, usually without true allergy.

Dust, Pollen S, Mould S, hairs of animals are the most frequent allergens, although many other substances can become an allergen for a given subject. One becomes allergic only with at least two contacts with an allergen. The first contact does not involve any visible reaction: the cells responsible for the allergy become hypersensitive (by a badly known mechanism) with a normally inoffensive substance. With the following contacts, the allergen will involve, while binding to the caused cells, a cascade of reactions leading to an allergic demonstration (of the simple hay cold to the shock anaphylactic, while passing by the crisis of Asthme)

The allergy is generally induced by a protein carrying the allergen which meets an immunizing cell and reacts with it: to the subject allergic to this allergen, the cells responsible for the allergy (Mastocyte in particular) will react to this contact (this stage does not occur at the healthy subject) and will release from the chemical molecules responsible for the allergic symptoms: Histamine, Serotonin, PAF, Leucotriène S, Prostaglandin S, etc

Histamine involves in particular vasodilatation (dilation of the Veine S and the Artère S), bronchoconstriction (contracting of the Bronche S), Prurit (desire for scraping itself), pain: when these phenomena are diffused with the whole body, one observes a Choc anaphylactic, accompanied by a phenomenon of Angoisse (the Blood-pressure crumbles in answer to the dilation of all the vessels, the bodies are not perfusés enough any more, and death occurs except in the event of early treatment).

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