By allergy the immune system react against a substance that it is not supposed to react against, and the reaction is often exaggerated. Objects containing substances that commonly cause allergy are domestic dust, animal hair, household chemicals, chlorine, microorganisms, pollen, nuts, citrus fruits and seafood. Also bacteria and parasites can cause inappropriately strong immune reactions.

THE MECHANISMS OF ALLERGY

The total set of reactions occurring by allergy is very complicated. Many of these are the same as by normal immune reaction, even though they occur when they should not take place, Here are listed some of these reactions:

By exposure to a new substance, cells in the immune system learn to recognize that substance (allergen), and it learns to produce anti-bodies towards the substance, and a certain amount of antibodies is produced. The type of anti-bodies called IgE is the most important by allergic reactions.

IgE will glue itself to some cells in the blood called mast-cells, and stick out from the surface of these cells. By following exposures to antigens, these will attach themselves to the IgE-ends sticking out from the mast-cells. This will trigger the mast-cells to produce histamine and other signal substances. These signal substances will then spread through the surrounding tissues.

The signal substances will then trigger the walls of small blood vessels to leak fluid into the tissues and accumulate in the tissues. This will cause tissue swelling. They also will cause blood vessels to widen and thus increase the blood stream in the tissues. The consequence of this will be swelling and redness in the affected body parts. The signal substances will also make glands in the tissue produce more mucus, making symptoms like running nose and tight throat.

The new exposures to the antigens will also provoke even more anti-body production. The antibodies will also glue allergens together to bigger complexes. These complexes can clog small blood vessels and in other ways disturb the function of the affected organ.

The allergen-antibody-complexes are then recognized by the cells and other mechanisms that the body uses to collect and eliminate garbage. Eater-cells gather and engulf the complexes.

The immune system also will make enzymes that attack the antigens to break them down. Also this production is stimulated when antigens attach themselves to anti-bodies at cell surfaces. But these enzymes are not entirely specific, and can also to some extend break down components of the body’s own tissue, causing harm and disease symptoms.

WHAT CAUSES THE IMMUNE SYSTEM TO REACT WITH ALLERGY TO A SUBSTANCE

In the beginning of the life of a person, the immune system has the potency to react against most substances in the body itself and the surroundings. However, there are mechanisms that learn the immune system to recognize normal substances found in the daily life in the early infanthood, and suppress the reactions against these. If this learning mechanism is disturbed, allergy can develop.

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