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Allergies are an excessive response of the body to substances in the environment. Any substance that triggers an allergic reaction is known as an allergen. Allergens trigger the release of chemicals called histamineshistamines
Chemicals released from cells which set up an inflammatory response.
from the mast cellsmast cells
Cells that release histamines as part of the inflammatory response.
of the immune systemimmune system
The body's natural defence mechanism against infectious diseases.
.
Allergic responses are based around a type of antibodyantibody
A protein in the blood which is produced in response to a specific antigen. Antibodies attach to antigens to remove them from the body.
found in the blood plasma known as immunoglobulin E (IgE). IgE appears to have a role in protection against gut parasiteparasite
Organism that feeds off another living host and causes it some damage. An example of a parasite is a tapeworm that lives in the digestive system of a host organism.
s, but scientists are not completely clear about what it does. What they do know is that in susceptible people, IgE antibodies bind to the antigenantigen
A protein, nucleic acid, or other molecule, which can stimulate a response from the immune system.
s on the surface of common environmental factors such as dust mites, cat skin flakes and pollen grains. Once the antibody is bound to the allergen, it also binds to a mast cell.
Cats and pollen from grasses and trees are well known for triggering allergic reactions (Photo credits: Anthony Short, Dartmouth Electron Microscope Facility)
The allergic reaction of the skin can be very dramatic
(Photo credit: James Heilman, MD)
Mast cellsmast cells
Cells that release histamines as part of the inflammatory response.
are produced in the bone marrowbone marrow
Found in the centre of bones, it contains adult stem cells which divide and differentiate to produce red and white blood cells.
and are carried all around the body. Each mast cell contains granules full of a chemical called histamine. When the mast cell binds to an allergen through IgE, the histamine is released.
Histamine brings about a number of different responses in the cells around it.
Antihistamines are effective at treating many localised allergic responses
There are a number of medicines that can be used to treat allergies.
Antihistamines are the best known drugs used to treat allergic reactions affecting the skin and the nose. There are antihistamines that are applied topically to the skin in response to stings and bites, and there are antihistamines that are taken orally and are carried through the body systems in the blood.
Antihistamines work by targeting the histamine receptorsreceptors
Protein molecules attached to cells that only bind to specific molecules with a particular structure.
on cells. By blocking the receptors, they block the response to the histamines. This damps down, and gets rid of, the allergic response.
Beta 2 agonistagonist
Drugs that bind to receptors on or in a cell and stimulate a response.
s are drugs that act very like adrenalin. They bind to β2-adrenergic receptorsreceptors
Protein molecules attached to cells that only bind to specific molecules with a particular structure.
in the smooth muscle of the bronchial tubes and the blood vesselsblood vessels
The tubes through which blood is carried around the body, e.g., arteries, veins and capillaries.
. They are often delivered by an inhalerinhaler
A medical device which delivers medicines to the lungs.
to get them directly into the lungs, and they have the immediate effect of relaxing the smooth muscles and so dilating the airways, making breathing easier.
Reliever inhalers contain β2-agonists that relax the smooth muscle of the bronchioles almost immediately
Corticosteroids are used to reduce the sensitivity of the cells to allergens and make an allergic response less likely. Scientists think they are involved in switching off the genes that produce the hypersensitive immune response, reducing the likelihood of future attacks. There is also evidence that they switch on genes that produce anti-inflammatory chemicals.
Gene switching as a result of corticosteroid medication may both switch off genes associated with the inflammatory response
and switch on genes that produce anti-inflammatory proteins