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Frequently Asked Questions about Allergies

What are allergies?
Allergies, also known as hypersensitivities, are excessive or inappropriate responses of the immune system to allergens.

What cells are involved in the human allergic response?
B cells- also known as B lymphocyte. A type of white cell which produces antibodies.

T cells- also known as T lymphocyte. A type of white cell that matures in the thymus and is responsible for cellular immunity (direct binding to antigen leading to destruction of the antigen) and for regulation of a variety of stages in the immune response.

Macrophages- white blood cells which phagocitize and "process" antigens. Processed antigens are displayed on the surface of the macrophage where they are "presented" to B cells which, in turn, make specific antibodies. Macrophages are desc ribed as "antigen presenting cells."

Mast cells- white cells which contain cytoplasmic granules filled with histamines and other molecules. These chemicals are released, in a process called "degranulation", during both the immune response and the inflammatory process.

What molecules are important in the allergic response?
Antibodies- proteins formed by B cells which are "specific" to a particular molecule (allergen)--that is to say that production of each antibody is induced by a single allergenic molecule or fragment of a molecule, and that each antibody is capable of binding only to the allergen that induced its production.

Allergens-"foreign" or non-self molecules that induce an allergic response.

Histamines- molecules which are released from mast cells and which play an important role in the production of allergic symptoms by causing dilation and increased "leakiness" of surrounding blood vessels.

What initiates an allergic response?
An allergic response starts with the sensitization stage, or the first exposure to an allergen such as bee venom. Specific antibodies are produced by the B cell in response the that first exposure. These antibodies then bind to mast cells, and other cells, where they remain bound for weeks or months. The allergic response occurs when there is a second exposure to the original antigen. When that happens, the antigen binds to the IgE which is already bound to the surface of the mast cells and causes degranulation and release of histamines and other molecules into the blood stream. It is the action of these chemicals which cause allergic symptoms.

What causes the symptoms of an allergic reaction?
Mast cell granules contain a variety of substances, including histamine, platelet- activating factors, and prostaglandins. These substances are released by the mast cell during degranulation, and cause both dilation and increased leakiness of the surrounding capillaries. The resulting dilated, blood filled capillaries cause redness, while plasma leaking into surrounding tissues causes swelling, itching, and discharge. Allergic symptoms can occur in a variety of locations in and on the body, because mast cells can be located in such scattered areas of the body as the respiratory tract, the skin and the digestive tract. Thus allergic mast cell degranulation can lead to such widely varying symptoms as coughing and wheezing, hives, nasal congestion, nausea and itchy watery eyes, to name but a few.

What is anaphylactic shock?
Anaphylaxis is a sudden systemic--not restricted to a single area of the body-- allergic response. Anaphylaxis, which can lead to death if it is not quickly treated, occurs when large numbers of cells degranulate in a short period of time.

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