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hypersensitivity, heightened response in a body tissue to an antigen or foreign substance. The body normally responds to an antigen by producing specific antibodies against it. The antibodies impart immunity for any later exposure to that antigen. When exposure takes place under certain physiological conditions, or in allergic individuals with abnormal immune systems, a heightened immune response results that causes cell damage. Histamines, substances released from damaged cells, cause dilation of small blood vessels, tissue inflammation, and constriction of the bronchi of the lungs. Anaphylaxis is the immediate, sometimes fatal hypersensitivity reaction to drugs or serum to which an individual has been previously sensitized. Serum sickness is a similar but milder hypersensitivity to serum proteins or drugs that occurs several weeks after injection of foreign material. Delayed reaction allergies occur when cells of the immune system, the lymphocytes, that have previously been sensitized react to antigenic substance. The lymphocytes slowly infiltrate an area, such as skin exposed to poison ivy toxin and cause tissue damage. Anaphylaxis, serum sickness, and delayed sensitivity may occur in otherwise normal, nonallergic individuals as well as allergics, as a response to substances that are highly sensitizing. Individuals with allergic, or atopic, hypersensitivity form special weak types of antibodies, that cause local tissue damage and such symptoms as hives, hay fever, and asthma. Antihistamines are drugs that prevent histamine from acting on blood vessels, bronchioles, and other organs. Acute reactions, such as anaphylaxis, are treated by giving epinephrine and other sympathomimetic drugs. Steroids such as cortisone are also given to suppress inflammation and depress the immune system. In some cases, hypersensitized individuals receive injections of gradually increasing quantities of the antigenic material to which they are sensitive, in order to avoid or lessen their hypersensitivity to that particular substance.
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Heightened reactivity to antigens (molecules capable of stimulating an immune response). Many different examples of hypersensitivity have been recognized in animals and humans. These are often referred to collectively as allergies, and clinically may take such forms as asthma, hives, hay fever, anaphylactic reactions to certain foods or insect venoms, some forms of eczema and kidney diseases, and skin reactions to poison ivy antigens and many other substances. See Antigen

Because molecules foreign to the body are often antigenic, the various forms of hypersensitivity are most commonly induced either by exposure to foreign antigens derived from microorganisms during infections, or by contact with certain noninfectious agents (some plant pollens, some drugs, and certain simple chemicals such as components of poison ivy). However, under certain circumstances, molecules of the body itself can induce an immune response. In these cases, hypersensitivity reactions can be directed against antigens of the body's own organs or tissues. Whether foreign or derived from the body itself, antigenic substances often produce little or no tissue reaction in unsensitized individuals. But once hypersensitivity develops, additional exposure to antigen can give rise to clinically obvious symptoms (hives, sneezing, runny nose), tissue damage, or even (in certain extreme cases) death. See Autoimmunity

The development of hypersensitivity in animals or humans may be divided into two phases. During the first phase, induction of hypersensitivity, exposure of the organism to antigen results in (1) recognition of the antigen by cells of the immune system; (2) proliferation (multiplication) of the types of immune cells that recognize and respond to that antigen; and (3) long-term storage of the information required to recognize and respond to the antigen in immune “memory” cells. Although a variety of cell types assist in these processes, all of the three functions are primarily dependent on various types of lymphocytes.

Once the state of hypersensitivity has been induced, reexposure of the organism to the antigen that induced the response usually leads to the second phase, expression of a hypersensitivity reaction. Hypersensitivity reactions historically have been classified according to two characteristics: the delay between the exposure of a previously sensitized (hypersensitive) individual to antigen and the development of a clinically recognizable reaction; and the types of cells and humoral substances thought to be responsible for the induction and expression of the reaction. According to this scheme, classical delayed hypersensitivity reactions differ from other forms of hypersensitivity in first becoming clinically prominent in sensitized individuals approximately 1 day after exposure to the specific antigen against which the individual expresses hypersensitivity; and depending for their expression on the activity of certain lymphocytes (thymic-dependent lymphocytes, or T cells) rather than soluble antibodies. By contrast, immediate hypersensitivity reactions may develop within seconds or minutes of exposure to specific antigen, and require the participation of antibodies. See Antibody

In addition to its association with certain infections, delayed hypersensitivity has been implicated in a variety of noninfectious disease processes. These include the annoying reactions induced in some individuals by contact with certain plants (for example, poison ivy), detergents, or drugs, as well as certain of the immune responses resulting in the rejection of transplanted tissues such as skin, kidneys, and hearts. In many of these processes, the immunological reactions are thought largely to reflect the activity of T lymphocytes (as in classical delayed hypersensitivity), whereas in others soluble antibodies may also have a role. See Cellular immunology, Transplantation biology

Immediate hypersensitivity reactions, collectively known as allergies, occur usually within minutes or up to a few hours after inhalation, ingestion, or injection of an antigen. Such reactions may be severe, even life-threatening, such as anaphylactic shock and asthma, or relatively minor but uncomfortable, such as hay fever or urticaria (hives). They may be of short duration—hours for anaphylaxis—or prolonged for several days or even weeks, as in immune complex-induced vasculitis. See Allergy

Hypersensitivities have been classified into four main types with different mechanisms: type I, anaphylaxis or atopy; type II, cytotoxic or cytolytic; type III, immune complex or Arthus reaction; and type IV, delayed or cellular-immune; the last type has been described above.

In type I the antigen is recognized immunologically upon first exposure and initiates antibody formation, usually of immunoglobulin E (IgE) or IgG class. IgE-mediated allergy, known as atopy, has a strong hereditary component, and occurs commonly in humans and dogs, while IgG-mediated anaphylaxis can occur in most vertebrates. The antibodies (IgE or IgG) attach or fix to target cells, such as tissue mast cells and blood basophils. Upon subsequent exposure to the antigen, the target cell–fixed antibodies react with antigen to cause degranulation and release of chemical mediators, such as histamine. See Histamine, Immunoglobulin

In cytotoxic or cytolytic (type II) reactions, the antigen may be certain altered body cells themselves; they may be altered physically or by chemicals and drugs attached to the cells. These are usually circulating cells, such as red blood cells coated with penicillin, platelets coated with a drug, or white blood cells coated with sulfonamides. Altered cells are recognized by the body's immune system as foreign or altered self, and IgG or IgM antibodies are formed which react with the altered cells and activate the serum complement enzymatic cascade that culminates in the lysis of the altered cells. Thus, cytotoxic hypersensitivity leads to anemia, bleeding due to low platelet levels, and increased infections from loss of white blood cells (agranulocytosis).

In immune complex or Arthus (Type III) reaction, neither antibody nor antigen is fixed to cells. Rather, they combine in various ratios in blood and tissues. If they are in the proper ratio, they form microprecipitates, or immune complexes, in capillaries and venules. The immune complexes activate complement to form chemoattractants for neutrophils and monocytes. Microprecipitates and phagocytosing neutrophils block the small vessels, resulting in a typical Arthus reaction—lack of blood to the tissue and subsequent tissue necrosis and death.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


The state of being abnormally sensitive, especially to allergens; responsible for allergic reactions.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

electromagnetic hypersensitivity

A negative reaction to wireless signals. Also called "gadget allergies," symptoms can be headaches, nausea, ringing in the ear (tinnitus), fatigue, irritability, fainting and pain throughout the body. In order to feel improvement, some people have moved into remote areas; however, it is difficult to avoid wireless signals no matter where one lives on the planet.

A Very Controversial Subject
Although studies relating to cellphones were inconclusive in the past, most of them were conducted by the cellular industry, and independent researchers have claimed foul play. However, people are increasingly speaking out because they are being affected. It is not unreasonable to think that the molecules of the human brain and body can be disturbed by the thousands of signals passing through them every second from AM, FM and HD Radio, satellites (TV, radio, GPS), cellular voice and data, cordless phones, radar, smart electric meters, Bluetooth (headphones, speakers, keyboards, mice) and especially the myriad applications of Wi-Fi.

When people around the world swear they feel better after moving from the city to a rural location or when shutting down their Wi-Fi, it is reasonable to think that electromagnetic hypersensitivity (EHS) is very real. We humans have genetic differences that can result in different reactions to the environment. Some may be very sensitive to radiation, while others are not. However, this is the first generation raised from infancy that is bombarded with wireless in such profusion, which has increased exponentially since the turn of the century. The higher frequencies of upcoming 5G cellular networks are also causing a lot of apprehension (see 5G radiation).

Duration and Constant Frequencies
Duration is one of two major reasons why radiation can be so harmful. People are bombarded 24/7 with manmade signals that emanate outside the home, and household members stream TV and premium channels via Wi-Fi for hours on end inside the home. The second reason is that manmade signals transmit as uniform frequencies in contrast to atmospheric radiation that is more random. The randomness is less harmful to human cells.

As a precaution when telephoning, many people turn the speaker on and hold the phone away from their head, or they use a wired headset. Even better are headsets with less wire (see air tube headset). Rather than stream video via Wi-Fi, households have switched from wireless to wired, running Ethernet cables from their router to their home theater equipment.

The constant beaconing in the Wi-Fi access point, which advertises the name of the Wi-Fi network all day long, can be easily turned off (see SSID broadcast). In addition, Wi-Fi routers and access points can be turned off at night with a timer while people sleep (see wireless router and PoE injector). In 2014, France took a major step by banning Wi-Fi entirely in nursery schools and turning Wi-Fi off in elementary schools when not specifically used for teaching. See SAR.

An Electromagnetic Field (EMF) Meter
Walking around the house with this meter can be very disturbing. When placed next to a Wi-Fi access point, the meter reaches the top 6.00 level and switches from yellow to red. Its audio output clicks faster as the radiation increases.

Wireless Wake-up Call
Working in Silicon Valley with a masters degree in engineering, Jeromy Johnson is an expert on EMF radiation. His 2016 TEDx Talk on the subject entitled a Wireless Wake-up Call is alarming but also informative, outlining ways people can prevent harmful exposure. For more information, visit www.emfanalysis.com.

Very Educational
Radiation Nation contains a lot of worthwhile information about electromagnetic hypersensitivity, including tips on how to diminish exposure to EMF radiation. The author started DefenderShield, a company that makes products that minimize radiation (www.defendershield.com)

electromagnetic hypersensitivity syndrome

A negative reaction to wireless signals. Also called "gadget allergies," symptoms can be headaches, nausea, fainting and pain throughout the body. In order to feel improvement, people have moved into remote areas; however, it is increasingly difficult to avoid wireless signals in any developed country.

A Lot of Controversy
This is a very controversial subject, and studies, mostly relating to cellphones pressed against the head, have been inconclusive. However, it is not unreasonable to think that the molecules of the human brain may be disturbed in some manner by the thousands of signals passing through it every second from AM, FM, TV, HD radio, satellite data, satellite radio, satellite video, 2G, 3G and 4G cellular voice and data, Wi-Fi, WiMAX, Bluetooth and other wireless networks.

When people around the world swear they can sense radiation and then feel better in a different location, it is reasonable to think that electromagnetic hypersensitivity syndrome (EHS) is not entirely bunk. Humans are genetically different from each other. Some may be very sensitive, while the majority may not be, and this is the first generation raised from infancy that is bombarded with wireless in such profusion. Time will tell. In the meantime, citing health reasons, a lot of people use earphones with wires to their cellphones.

The Pong iPhone Case
This iPhone case directs most of the radiation from the phone away from the brain. Inside the case, a ladder configuration causes the signal to move up and out. (Image courtesy of Pong Research LLC, www.pongresearch.com)
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References in periodicals archive ?
Delayed type hypersensitivity assay: There was change in skin thickness observed in all groups at 24, 48 and 72 hours following application of DNCB (Dinitro chloro benzene).Groups II, III and IV received colchicine 40ug/kg, 80ug/kg and 160ug/kg body weight respectively.
Delayed type hypersensitivity and contact sensitivity was used in understanding the basis of some dermatological diseases and the clinical spectrum seen in leprosy.
Nine Sprague-Dawley rats that have been exposed to 10 grams of ethanol per kilogram body weight per day with varying degrees of calorie deprivation were subjected to Delayed Type Hypersensitivity skin tests with sheep erythrocytes serving as the immunogen.
In order to investigate the type of immunological adjuvant activity of GA against the SM in mice, IgG isotype, cytokine profiles, and delayed type hypersensitivity of the mice immunized with the formula were determined.
Th-1 cells are responsible for cell-mediated inflammatory reactions, delayed type hypersensitivity and tissue injury in infections and autoimmune diseases and secrete interferon-gamma (IFN-[gamma]), interleukin-2 (IL-2) and tumour necrosis factor-beta (TNF-[beta])).
The biopsy showed extensive spongiosis and edema of the dermis with a deep lymphohistiocytic infiltrate, consistent with polymorphous light eruption--an idiopathic, delayed type hypersensitivity to UVA and UVB light.
An intact gram-negative flora is a prerequisite for the induction of delayed type hypersensitivity (DHT) responses.
The immunomodulatory activity of flurbiprofen was evaluated in this work by using immunological experimental models like cyclophosphamide induced neutropenia assay, delayed type hypersensitivity assay, haemagglutination assay and mice lethality test.
Key words: Ivermectin, Immunomodulatory, Macrophage engulfment assay, Delayed type hypersensitivity, Macrophages, Broilers.