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| Allergy and Its Mechanisms |
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| Normal airway with relaxed muscles. |
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| Constricted airway in allergic reaction, with muscles around the airway contracting. |
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What is Allergy - Amplifying the Immune System through Allergic Reactions |
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Allergy is a specific immunological reaction to a normally harmless substance, one that does not bother most people. An allergic reaction produces inflammation, a basic response of the body to injury. It is often characterized by redness of the skin, warmth, swelling, and pain. Inflammation results from a complex series of events involving cells and chemicals that are intended to protect the body against invading foreign substances. |
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The symptoms of allergies to airborne substances include: |
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Sneezing, often accompanied by a runny or clogged nose |
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Coughing and postnasal drip |
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Itching eyes, nose and throat |
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Allergic shiners (dark circles under the eyes caused by increase blood flow near the sinuses) |
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The “allergic salute” (in a child, persistent upward rubbing of the nose that causes a crease mark on the nose) |
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Watering eyes |
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Conjunctivitis (an inflammation of the membrane that lines the eyelids, causing red-rimmed, swollen eyes and crusting of the eyelids) |
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Allergic people are often sensitive to more than one substance. Types of allergens that cause allergic reactions include dust particles, mold spores, pollen, food, medicine, insect venom, man-made or natural chemicals. |
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| Who Gets Allergy |
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| In many developed countries, around 1 out of 5 people in the population suffer from allergic diseases; and around 10% of office visits to the doctor is for an allergic disease. |
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| Inheritance has a major influence on allergy. If one parent has allergies, then there are 1 in 3 chances that the children will have allergies. If both parents have allergies, then all the children will probably have allergies. Aside from inheritance, it is not known why some people get allergies while others do not. |
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| A person has to be exposed to an allergen, a foreign protein that causes allergy, for allergic reactions to take place. Worldwide, the major allergen is the feces of dust mites, which live in mattress, carpet and upholstery. Other major allergens include mould, grass and tree pollens, and animal dander. |
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| Mechanism of Developing Allergies |
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| When an allergic person first come into contact with an allergen, his / her immune system treat the allergen as an invader and mobilize to attack. The immune system does this by generating large amounts of a type of antibody (a disease-fighting protein) called immunoglobulin E (IgE). Only small amounts of IgE are produced in non-allergic people. Each IgE is specific for one particular allergy-producing substance. |
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| These IgE molecules attach themselves to the body’s mast cells, which are tissue cells, and to basophils, which are blood cells. When the allergen next encounters the IgE, it attaches to the antibody like a key fitting into a lock, signaling the cell to which the IgE is attached to release powerful inflammatory chemicals like histamine, prostaglandins, and leukotrienes. These chemicals move to various parts of the body, such as the respiratory system, and cause the symptoms of allergy. |
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| Four Types of Allergic Reactions (classified according to mechanisms) |
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Name |
Medical Mechanism |
Examples |
Type I |
Immediate hyper-sensitivity or anaphylactic
(Immediate onset) |
Immunoglobulin E (IgE) antibody on mast cell reacts with antigen resulting in release of mediators |
Hay fever, some asthma and hives, some food and drug reactions, insect-sting reactions, anaphylactic shock etc. |
Type II |
Cytotoxic
(Immediate onset) |
IgE antibody reacts with cell membranes or antigen associated with cell membrane |
Transfusion of incompatible blood types |
Type III |
Arthus
(Sickness occurs several hours or even days after exposure to antigen.) |
Antigen and antibody bind together to form immune complexes which deposit in walls of blood vessels or kidneys |
Serum sickness (injection of an animal serum), some drug reactions |
Type IV |
Cell-mediated / delayed hypersensitivity
(Sickness reaches its peak 2 or 3 days after exposure.) |
T cells interact directly with antigen |
Poison ivy, graft rejection |
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