hypersensitivity reaction

reaction /re·ac·tion/ (-ak´shun)

1. opposite action, or counterreaction; the response to stimuli.

2. a phenomenon caused by the action of chemical agents; a chemical process in which one substance is transformed into another substance or other substances.

3. the mental and/or emotional state that develops in any particular situation.

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acrosome reaction  structural changes and liberation of acrosomal enzymes occurring in spermatozoa in the vicinity of an oocyte, facilitating entry into the oocyte.

alarm reaction  the physiologic effects (increase in blood pressure, cardiac output, blood flow to skeletal muscles, rate of glycolysis, and blood glucose concentration; decrease in blood flow to viscera) mediated by sympathetic nervous system discharge and release of adrenal medullary hormones in response to stress, fright, or rage.

allergic reaction  hypersensitivity r., sometimes specifically a type I hypersensitivity reaction.

anaphylactic reaction  anaphylaxis.

anaphylactoid reaction  one resembling generalized anaphylaxis but not caused by IgE-mediated allergic reaction.

antibody-mediated hypersensitivity reaction 

1. type II hypersensitivity r.; see Gell and Coombs classification, under classification.

2. occasionally, any hypersensitivity reaction in which antibodies are the primary mediators, i.e., types I–III.

antigen-antibody reaction  the reversible binding of antigen to homologous antibody by the formation of weak bonds between antigenic determinants on antigen molecules and antigen binding sites on immunoglobulin molecules.

anxiety reaction  a reaction characterized by abnormal apprehension or uneasiness; see also anxiety disorders, under disorder.

Arias-Stella reaction  nuclear and cellular hypertrophy of the endometrial epithelium, associated with ectopic pregnancy.

cell-mediated hypersensitivity reaction  type IV hypersensitivity r.; see Gell and Coombs classification, under classification.

conversion reaction  see under disorder.

cross reaction  the interaction of an antigen with an antibody formed against a different antigen with which the first antigen shares identical or closely related antigenic determinants.

cytotoxic hypersensitivity reaction  type II hypersensitivity r.; see Gell and Coombs classification, under classification.

defense reaction  see under mechanism.

delayed hypersensitivity reaction , delayed-type hypersensitivity reaction that taking 24 to 72 hours to develop and mediated by T lymphocytes rather than by antibodies; usually denoting the subset of type IV hypersensitivity reactions involving cytokine release and macrophage activation, as opposed to direct cytolysis, but sometimes used more broadly, even as a synonym for type IV hypersensitivity r. (see Gell and Coombs classification, under classification ).

reaction of degeneration  the reaction to electrical stimulation of muscles whose nerves have degenerated, consisting of loss of response to a faradic stimulation in a muscle, and to galvanic and faradic stimulation in the nerve.

foreign body reaction  a granulomatous inflammatory reaction evoked by the presence of exogenous material in the tissues, characterized by the formation of foreign body giant cells.

hemiopic pupillary reaction  in certain cases of hemianopia, light thrown upon one side of the retina causes the iris to contract, while light thrown upon the other side arouses no response.

Herxheimer's reaction  Jarisch-Herxheimer r.

hypersensitivity reaction  one in which the body mounts an exaggerated or inappropriate immune response to a substance perceived as foreign, resulting in local or general tissue damage. Such reactions are usually classified as types I–IV on the basis of the Gell and Coombs classification (q.v.).

id reaction  a secondary skin eruption occurring in sensitized patients as a result of circulation of allergenic products from a primary site of infection.

immediate hypersensitivity reaction 

1. type I hypersensitivity r.; see Gell and Coombs classification, under classification.

2. occasionally, any hypersensitivity reaction mediated by antibodies and developing rapidly, generally in minutes to hours (i.e., types I–III ), as distinguished from those mediated by T lymphocytes and macrophages and requiring days to develop (type IV, or delayed hypersensitivity r. ).

immune reaction  see under response.

immune complex–mediated hypersensitivity reaction  type III hypersensitivity r.; see Gell and Coombs classification, under classification.

Jarisch-Herxheimer reaction  a transient immunologic reaction following antibiotic treatment of early and later stages of syphilis and certain other diseases, marked by fever, chills, headache, myalgia, and exacerbation of cutaneous lesions; due to release of toxic or antigenic substances by the infecting microorganisms.

Jones-Mote reaction  a mild skin reaction of the delayed (type IV) hypersensitivity type occurring after challenge with protein antigens.

late phase reaction  an IgE-mediated immune reaction occurring 5 to 8 hours after exposure to antigen, after the wheal and flare reactions of immediate hypersensitivity have diminished, with inflammation peaking around 24 hours, and then subsiding.

lengthening reaction  reflex elongation of the extensor muscles which permits flexion of a limb.

leukemoid reaction  a peripheral blood picture resembling that of leukemia or indistinguishable from it on the basis of morphologic appearance alone; seen in certain infectious diseases, inflammatory conditions, and intoxications.

Neufeld's reaction  swelling of the capsules of pneumococci, seen under the microscope, on mixture with specific immune serum, owing to the binding of antibody with the capsular polysaccharide.

oxidation-reduction reaction  redox r.

Pirquet reaction  appearance of a papule with a red areola 24 to 48 hours after introduction of two small drops of Old tuberculin by slight scarification of the skin; a positive test indicates previous infection.

polymerase chain reaction  (PCR) a rapid technique for in vitro amplification of specific DNA or RNA sequences, allowing small quantities of short sequences to be analyzed without cloning.

precipitin reaction  the formation of an insoluble precipitate by reaction of antigen and antibody.

redox reaction  a reaction oxidizing one substrate while reducing another.

Schultz-Charlton reaction  disappearance of scarlet fever rash around the site of an injection of scarlet fever antitoxin.

serum reaction  seroreaction.

startle reaction  the various psychophysiological phenomena, including involuntary motor and autonomic reactions, evidenced by an individual in reaction to a sudden, unexpected stimulus, as a loud noise.

stress reaction  any physiological or psychological reaction to physical, mental, or emotional stress that disturbs the organism's homeostasis.

T cell–mediated hypersensitivity reaction  type IV hypersensitivity r.; see Gell and Coombs classification, under classification.

Weil-Felix reaction  agglutination by blood serum of typhus patients of a bacillus of the proteus group from the urine and feces.

Wernicke's reaction  hemiopic pupillary r.

wheal and erythema reaction , wheal and flare reaction a cutaneous sensitivity reaction to skin injury or administration of antigen, due to histamine production and marked by edematous elevation and erythematous flare.

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hypersensitivity reaction,

an inappropriate and excessive response of the immune system to a sensitizing antigen, called an allergen. Several factors determine the degree of the response: the person's genetic predisposition for an exaggerated response, the amount of allergen, the kind of allergen, its route of entrance into the body, the timing of the exposures to the allergen, and the site of the allergen-immune mediator reaction. Hypersensitivity reactions are classified into four types according to the components of the immune system involved in their mediation. A type I or immediate hypersensitivity reaction occurs rapidly, within several minutes, on reexposure to an antigen, and is the result of interaction of immunoglobulin E and the antigen; anaphylaxis is a particularly severe type I hypersensitivity reaction. A type II or cytotoxic hypersensitivity reaction is one of tissue or cell damage resulting from antibody-antigen interactions on cell surfaces. A type III or immune complex-mediated hypersensitivity reaction is a local or general inflammatory response caused by formation of circulating antigen-antibody complexes and their disposition in tissues. A type IV hypersensitivity reaction (also called cell-mediated or T-cell-mediated hypersensitivity reaction) is one initiated by antigen-specific T lymphocytes. Unlike hypersensitivity reactions mediated by antibodies, this type takes one or more days to develop, and the hypersensitivity can be transferred by lymphocytes but not by serum. The term is often equated with delayed hypersensitivity reactions that are cytokine-mediated (as contrasted with direct cytolysis).

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Patient discussion about hypersensitivity reaction.

Q. what is the most common allergy? is it dust allergy?

A. thanks, I've heard of a new allergy treatment and trying to learn some more about the different kinds...

Q. What is Gluten and what is gluten allergy? My nephew is coming to stay with me for a few days and his mother told me that since he is allergic to gluten that I shouldn't give him to eat any. What is gluten?

A. Gluten is a protein that is found in wheat (and similar proteins of the tribe Triticeae which includes other cultivars such as barley and rye). When someone is allergic to gluten the only effective treatment is a lifelong gluten-free diet.
Here is a link to a website with ideas for cooking without gluten:
http://www.celiac.com/categories/Gluten%252dFree-Cooking/

Q. What happens when you get an allergy test? My doctor told me that I should have an allergy test done. I have had a friend have an allergy test done and she had a bunch of bumps on her arm. My doctor said it was just a simple blood test. Has the test changed? What should I expect? Is it painful?

A. Today, you can check allergy also with a blood test. What you check is the antibodies that your body manufactures. They extract antibodies from the blood and react it to all sort of allergens and see what happens. Here is a more elaborated explanation about it :
http://www.labtestsonline.org/understanding/analytes/allergy/sample.html