polymerase chain 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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polymerase chain reaction

n. Abbr. PCR

A technique for amplifying DNA sequences in vitro by separating the DNA into two strands and incubating it with oligonucleotide primers and DNA polymerase. A specific sequence of DNA can be amplified by as many as one billion times.

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Polymerase chain reaction (PCR)

A test performed to evaluate false-negative results to the ELISA and Western blot tests. In PCR testing, numerous copies of a gene are made by separating the two strands of DNA containing the gene segment, marking its location, using DNA polymerase to make a copy, and then continuously replicating the copies. The amplification of gene sequences that are associated with HIV allows for detection of the virus by this method.

Mentioned in: AIDS Tests

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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. The process can be used to make prenatal diagnoses of genetic diseases and to identify an individual by analysis of a single tissue cell.

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polymerase chain reaction (PCR),

n a process whereby a strand of deoxyribonucleic acid can be cloned millions of times within a few hours. The process can be used to make prenatal diagnoses of genetic diseases and to identify an individual by analysis of a single tissue cell.

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polymerase

an enzyme that catalyzes polymerization, particularly of nucleic acids.

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polymerase chain reaction

see pcr1.

RNA polymerase

1. an enzyme that synthesizes an RNA copy of the sequence in a limited region of DNA in a process known as DNA transcription. Called also DNA-dependent RNA polymerase.

2. a viral enzyme that synthesizes RNA from an RNA template during viral replication. Called also RNA-dependent RNA polymerase.

RNA-dependent RNA polymerase

see RNA polymerase (above).

Taq polymerase

a DNA polymerase that functions at high temperature; derived from the bacterium Thermus aquaticus and used in the polymerase chain reaction.

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polymerase chain reaction

Molecular biology A molecular technique that uses DNA polymerases from high-temperature bacteria–known as extremophiles to rapidly amplify–ie, ↑ the number of copies of–a sequence of DNA in a sample; starting from minimal amounts–<< 1 µg–as little as one copy of a sequence of DNA, PCR exponentially amplifies a target DNA sequence, which has been inserted between 2 oligonucleotide primers through multiple amplification cycles Application Prenatal Dx of hereditary disease–sickle cell anemia, PKU, cystic fibrosis; ID gene rearrangements in lymphoproliferative disorders, determine fetal sex, Lyme disease, TB, Chlamydia trachomatis, ID viruses–HIV, CMV, HPV, HBV, delineate viral link to cancer–HTLV-1, HPV, bacteria, parasites, pathogenic mechanisms–DM, pemphigus vulgaris, myasthenia gravis, oncogene-induced cancer Sensitivity In detecting leukemia in BM–Bx has a 65-75% sensitivity, Southern blot analysis of gene rearrangement, 98-99% sensitivity, PCR, 99.999%. See Allele-specific PCR, AP-PCR, DNA amplification, Fluorophore-enhanced repetitive sequence-based-PCR, Inverse PCR, Jumping PCR, Multiplex PCR, Nested PCR, Reverse-transcriptase PCR, Semi-nested PCR, Touchdown PCR. Cf Ligase chain reaction.