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In this article we will discuss about Hypersensitivity in human body:- 1. Meaning of Hypersensitivity 2. Forms of Hypersensitivity 3. Skin Tests.
Meaning of Hypersensitivity:
Von Pirquet coined originally the term allergy (grallos, altered, changed; ergon, action) to describe the altered reactivity of an animal after exposure to a foreign antigen. The allergy included both immunity and hypersensitivity. It is now restricted to refer only to hypersensitivity.
There are two forms of hypersensitivity reactions:
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(1) Immediate allergy; and
(2) Delayed allergy
1. The immediate form appears rapidly after exposure of a sensitized person to further dose of antigen and usually depends upon the liberation of histamine—pharmacologically active mediator substance which is formed under the influence of antigen-antibody combination.
2. The delayed form appears more slowly (usually after 24 hours) and depends upon the immunologically activated lymphoid cells.
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Various classifications of hypersensitivity reactions have been proposed, but the most widely accepted one is that of Coombs and Gell. The classification of Coombs and Cell recognises four types of hypersensitivity reactions, three of which come under the heading of immediate reaction:
Type I, Anaphylactic reactions;
Type II, Cytotoxic or cytolytic reactions; Type II reactions are intermediate, between hypersensitivity and autoimmunity. Combination with antibody, may cause stimulation instead of damage. Such antibody mediated cell stimulation has also been called Type V hypersensitivity.
Type III, Toxic-complex syndrome;
Type IV, Cell-mediated delayed hypersensitivity form of reaction.
Forms of Hypersensitivity:
Whether immediate or delayed allergy, the basic explanation of allergic manifestation is that a reaction between antigen and its specific antibody has occurred in the body. If this reaction occurs in the blood, it will not cause allergic response and is the normal defensive process. If antigen-antibody combination occurs in or on the tissue cells, there is allergy.
There are two types of allergy:
1. Immediate Allergy:
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It is due to precipitin reaction occurring in or on certain tissue cells. It is characterised by the painful itching wheals known as “hives.”
This type of allergy may occur after eating certain foods or after injections of therapeutic serum; other manifestations are: intense gastroenteritis appearing within few minutes after consuming certain foods to which the victim is allergic and asthma after contact with pollen or with certain animals.
Shock Tissue:
The signs, symptoms and appearance of immediate allergic reactions depend upon the tissue cells which suffer precipitin reaction. The tissues that suffer are known as “shock tissues.” If the tissues are smooth muscle fibres, the muscle contracts.
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If the muscle fibres of gastrointestinal tract contract, diarrhoea and cramps may result; if the gravid uterine muscle contracts, there is abortion; asthma may occur, if the bronchioles contract. Besides smooth muscle contraction, oedema and inflammation of mucosa are manifested in the allergy. 0.5 to 1 ml. of 1: 1,000 epinephrine quickly reduces the swellings.
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Anaphylaxis is one of the most dramatic manifestations of the immediate type of allergy.
2. Delayed Allergy:
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In delayed allergy the tissue responses appears after 24 hours.
The tuberculin reaction is a best example of delayed allergy.
Histamine in Allergy:
In immediate allergy, an initial substance called histamine is released by tissue cells. The histamine causes many of the symptoms seen in hay fever, bee stings, serum reactions, antibiotic reactions and common colds. These discomforts can be relieved by antihistaminic which cause contractions of blood vessels.
Skin Tests for Hypersensitiveness:
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When a very small dose of sensitizing dose is injected or scratched into the skin of a person or animal hypersensitive to that particular antigen, a wheal (a large, red, swollen area) will develop after an interval of time. This allergic reaction persists for an hour or more. Hypersensitiveness to horse serum is tested in this way by injecting a very small quantity of the serum to be used therapeutically.
Similarly, for testing food or pollen allergy, alcoholic or aqueous extracts of various foods or pollens, likely to be involved, are introduced into (not under) the skin either by scarification or injection and the results are noted.
Application to Nursing:
The intelligent professional nurse, who acquired a sound knowledge about allergy during her training, will be able to understand and handle the untoward reactions encountered when certain sensitized individuals come into contact with that particular antigenic (allergic) substances – sera, antibiotics, some drug, vaccines, some foods.
A severe allergic reaction may ensue following the injection of an antigenic substance. This reaction can be prevented and the patient’s life can be saved by the perceptive nurse.
For example, since the patient is under constant observation of the nurse on duty, the patient may narrate that he is allergic to eggs (foreign protein); if the physician, unaware of this allergic reaction, prescribes a viral vaccine prepared from chick embryo, the nurse should inform immediately the physician about the allergy of the patient to the egg, so that a severe—possibly fatal— allergic reaction can be averted.
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If the patient who had a previous injection of horse serum, receives again a dose of antitoxic serum prepared in horse, he may have a severe and even fatal reaction to the serum, which, although given to provide the patient with immediate protection against a specific disease, becomes a very highly fatal dose to the patient, since the patient is allergic to horse serum.
It is quite essential to understand that the patient reaction to the antitoxic serum is not due to antibodies present in it; but due to animal (horse) proteins in the serum. Thus, the proteins may react to any horse serum irrespective of presence of antibodies.
The well- informed and trained nurse should keep in readiness epinephrine and antihistaminic to avoid such a fatal allergy which may occur due to the parenteral administration of horse serum for passive immunity and she should always be careful about immediate and delayed allergy to an allergenic substance and advise the patient to avoid in future the injections of this particular allergic substance.
