WHAT IS ALLERGY?
The human body reacts to foreign substances that are inhaled, ingested or come into contact with the skin. If the response to the foreign body or irritant is other than "normal" it is referred to as allergy. Allergy may be either immediate or delayed. The immediate type allergy comes on sometimes within seconds or minutes and is often seen in acute food allergy (e.g., peanuts, egg) to beestings or contact with animals. Such reactions can be extremely dangerous. If Adrenaline is available this is the drug treatment of choice followed by an antihistamine and possibly also by a cortisone injection. In contrast delayed allergic reactions to foods and chemicals respond poorly to Adrenaline and antihistamines and require cortisone. The new Leukotriene receptor blockers offers new hope in the management of delayed type allergic reactions.
The word "ALLERGY" was originally coined by Dr Clement von Pirquet to describe the altered reactions to the bacteria causing tuberculosis. The word being derived from the Greek words "allos" meaning "other" and "ergos" meaning "work"
He used the words:-
"anergy" to describe absence of reactivity
"hypergy" to describe increased reactivity
"hypogy" to describe reduced reactivity.
Now the word "allergy" is synonymous with "hypergy".
An "antigen" is a substance capable of inducing an immune response.
The word "allergen" is used to describe an antigen capable of inducing an "allergic response".
There are several different mechanisms to induce an allergic response. These have been classified variously, but the first was by Gell & Coombs who defined Types I, II, III & IV. This original classification has been extended.
The term "reagin" was originally used to describe an allergen capable of inducing TypeI allergy; this has also been referred to as "Immediate Type Allergy" and "IgE mediated Allergy".
"IgE" is "immunoglobulin E", as distinct from IgA, IgD, IgG & IgM. (The "Immunoglobulins" are the antibodies produced in response to the introduction of an antigen.)IgE occurs in the blood in such low concentrations that it was only discovered several years after the other immunoglobulins had been defined and intensively studied; little wonder the study of allergy was neglected!
Confusing? It gets worse! Particularly as the word allergy is even used in everyday language when someone says that he is "allergic to work"
The words "atopy" and "atopic" are often used (wrongly!) in relation allergy. This word literally means "a" = "out of place" and "topy" = "place".
The "Atopic Diseases" were considered to be Flexural Eczema, Asthma and Seasonal Hayfever. The original descriptions in the allergy literature referred to those allergic diseases which it has now been shown to be associated with "Type 1" or "Immediate Type Allergy".
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