Hyposensitization Health Dictionary

Various conditions caused by inappropriate or exaggerated reactions of the immune system (known as hypersensitivity reactions) to a variety of substances. Many common illnesses, such as asthma and allergic rhinitis (hay fever), are caused by allergic reactions to substances that in the majority of people cause no symptoms.

Allergic reactions occur only on 2nd or subsequent exposure to the allergen, once 1st contact has sensitized the body. The function of the immune system is to recognize antigens (foreign proteins) on the surfaces of microorganisms and to form antibodies (also called immunoglobulins) and sensitized lymphocytes (white blood cells). When the immune system next encounters the same antigens, the antibodies and sensitized lymphocytes interact with them, leading to destruction of the microorganisms.

A similar immune response occurs in allergies, except that the immune system forms antibodies or sensitized lymphocytes against harmless substances because these allergens are misidentified as potentially harmful antigens.

The inappropriate or exaggerated reactions seen in allergies are termed

Allergen hypersensitivity reactions and can have any of four different mechanisms (termed Types I to hypersensitivity reactions).

Most well known allergies are caused by Type I (also known as anaphylactic or immediate) hypersensitivity in which allergens cause immediate symptoms by provoking the immune system to produce specific antibodies, belonging to a type called immunoglobulin E

(IgE), which coat cells (called mast cells or basophils). When the allergen is encountered for the second time, it binds to the IgE antibodies and causes the granules in mast cells to release various chemicals, which are responsible for the symptoms of the allergy.

Among the chemicals released is histamine, which causes widened blood vessels, leakage of fluid into tissues, and muscle spasm. Symptoms can include itching, swelling, sneezing, and wheezing. Particular conditions associated with Type I reactions include asthma, hay fever, urticaria (nettle rash), angioedema, anaphylactic shock (a severe, generalized allergic reaction), possibly atopic eczema, and many food allergies.

Types to hypersensitivity reactions are less often implicated in allergies. However, contact dermatitis, in which the skin reacts to substances such as nickel, is due to a Type hypersensitivity reaction.

It is not known why certain individuals and not others get allergies, but about 1 in 8 people seem to have an inherited predisposition to them (see atopy).

Whenever possible, the most effective treatment for allergy of any kind is avoidance of the relevant allergen.

Drug treatment for allergic reactions includes the use of antihistamine drugs, which relieve the symptoms. Some antihistamine drugs have a sedative effect, which is useful in treating itching at night due to eczema. Many antihistamines do not cause drowsiness, making them more suitable for daytime use.

Other drugs, such as sodium cromoglicate and corticosteroid drugs, can be used regularly to prevent symptoms from developing.

Hyposensitization can be valuable for a minority of people who suffer allergic reactions to specific allergens such as bee stings. Treatment involves gradually increasing doses of the allergen, but it must be carried out under close supervision because a severe allergic reaction can result.... allergy

See hyposensitization.... desensitization, allergy

Stimulation of the immune system as a treatment for cancer.

The term is also used to describe hyposensitization treatment for allergy.

One type of immunotherapy used in the treatment of cancer uses immunostimulant drugs.

More recently, monoclonal antibodies (see antibody, monoclonal) directed against tumours have been produced artificially by genetic engineering.

Interferon or chemical poisons can be linked to these antibodies to increase their ability to destroy tumour cells without damaging normal cells.... immunotherapy

Reactions produced by the sting of insects such as bees and wasps.

Venom injected by the insect contains inflammatory substances that cause local pain, redness, and swelling for about 48 hours. Any sting in the mouth or throat is dangerous because the swelling may obstruct breathing. About 1 person in 200 is allergic to insect venom, and a severe allergic reaction can occur, leading to anaphylactic shock. A procedure known as hyposensitization is sometimes recommended for such people.

If the symptoms of anaphylactic shock develop, it is essential to seek emergency medical treatment. Any person who is known to be hypersensitive to bee or wasp venom should obtain and carry an emergency kit for the self-injection of adrenaline (epinephrine).... insect stings

Inflammation of the mucous membrane lining the nose due to allergy to pollen, dust, or other airborne substances.

Also called hay fever, it causes sneezing, a runny nose, and nasal congestion.

Antihistamine drugs and topical corticosteroid drugs are used to treat mild attacks.

The drug sodium cromoglicate, inhaled regularly throughout the pollen season, may help to prevent attacks.

Long-term relief of symptoms can sometimes follow desensitization to a pollen allergen by a course of injections (see hyposensitization).... rhinitis, allergic

n. 1. (hyposensitization) a method for reducing the effects of a known allergen by injecting, over a period, gradually increasing doses of the allergen, until resistance is built up. See allergy. 2. a technique used in the *behaviour therapy of phobic states. The thing that is feared is very gradually introduced to the patient, first in imagination and then in reality. At the same time the patient is taught relaxation to inhibit the development of anxiety (see relaxation therapy). In this way he or she is able to cope with progressively closer approximations to the feared object or situation.... desensitization