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An allergic reaction is an inappropriate immune reaction to an otherwise harmless substance. Allergens can be environmental, chemical, or food-based. Common allergens include dust mites, pollen, animal dander, and certain foods. Allergens can be absorbed into the body through the skin, respiratory tract, or gastrointestinal tract. Allergens are proteins or low-molecular weight substances that the body identifies as antigenic. This creates an immune response known as a hypersensitive or allergic reaction. The production of chemical mediators in these allergic reactions may produce symptoms ranging from mild to life threatening.
Under normal conditions, the immune system is highly adept at recognizing and destroying the myriad of foreign substances capable of invading the body (i.e., bacteria, viruses, parasites). The complex mechanisms of immune defense usually work in tandem with the host tissues of the body, averting secondary damage and destruction. The immune system consists of several branches, each with its own protective functions. B-lymphocytes (B cells) and plasma cells produce a series of plasma proteins known as immunoglobulins. Immunoglobulins are antibodies capable of recognizing, destroying, and positioning antigens for removal from the body.
Antibodies are antigen-specific, meaning they combine with only certain antigens in a "lock and key" fashion. There are five classes of immunoglobulins: IgE, IgA, IgG, IgM, and IgD. The most significant immunoglobulin in allergic disorders is IgE. The IgE molecules bind with antigens to trigger the release of chemical mediators from mast cells. Other antibodies such as IgG and IgM are being implicated in food intolerance reactions, causing a whole different set of symptoms, which could include neuropathy, intestinal symptoms, and problems with energy production.
The production of antigen-specific IgE antibodies requires the direct interaction between macrophages, T cells and B cells. Macrophages initially bind with antigens and present them to T cells. T lymphocytes (T cells) assist in antibody production by secreting lymphokines, which direct the activity of the B cells. Once IgE antibodies are formed, they attach to the mast cells concentrated in the mucous membranes and under the skin. When circulating antigens contact IgE antibodies attached to the mast cells, it triggers the degranulation and release of inflammatory mediators that produce allergic reactions to the skin, lungs, and gastrointestinal tract. These mediators include histamine, eosinophil chemotactic factor of anaphylaxis (ECF-A), leukotrienes, kinins, platelet activating factor (PAF), bradykinin, serotonin, and prostaglandins.(1)
The etiology of allergic reactions is unclear. Some immunologists suggest that allergic reactions stem from an evolutionary response to parasitic infection.(2) This theory proposes that the human immune system has developed a high sensitivity to parasites, which increase white blood cell production, and the release of pro-inflammatory factors. In developed countries, where parasitic infestation is relatively low, allergies are more common than in less developed countries. It is thought that when the immune system is fighting parasitic infections, it does not have the resources to defend against less threatening agents. Another theory is that people with dysbiosis may have a heightened allergic response.
Genetics appear to play a significant role in allergies, as the propensity to manufacture IgE antibodies is inherited. Children whose parents both have allergies are twice as likely to develop allergies themselves.(3) The term atopy refers to the inherited tendency toward allergies, but not to one specific form (hay fever, asthma, eczema, etc.) Repeated exposure to allergens and environmental pollutants may stimulate the production of IgE antibodies.(4)
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