antibody

An immunoglobulin molecule produced by B lymphoid cells with a specific amino acid sequence evoked in humans or other animals by an antigen (immunogen). These molecules are characterized by reacting specifically with the antigen in some demonstrable way, a. and antigen each being defined in terms of the other. Antibodies may also exist naturally, without being present as a result of the stimulus provided by the introduction of an antigen; antibodies are found in the blood and body fluids, although the basic structure of the molecule consists of two light and two heavy chains, antibodies may also be found as dimers, trimers, or pentamers. SEE ALSO: immunoglobulin. SYN: immune protein, protective protein, sensitizer (2).

- affinity a. the strength of binding between an a. and an antigen. This interaction is reversible.

- agglutinating a. SYN: agglutinin (1).

- anaphylactic a. SYN: cytotropic a..

- anti–basement membrane a. autoantibodies to renal glomerular basement membrane antigens.

- anticardiolipin antibodies antibodies directed against cardiolipid, a phosphorylated polysaccharide ester of fatty acid s found in cell membranes. Associated with immune-mediated illnesses, syphilis, and strokes; thought to be from a hypercoagulable state.

- antiidiotype a. an antiantibody, the activity of which is directed specifically against the antigenic determinants (idiotope) of a particular immunoglobulin (a.) molecule. SYN: idiotypic a..

- anti-MAG a. a specific a. against myelin-associated glycoprotein; the most important of the specific antibodies against myelin so far identified, present in the majority of patients with IgM-associated polyneuropathies.

- antineutrophil cytoplasmic a. an autoantibody to cytoplasmic constituents of monocytes and neutrophils found in patients with vasculitis.

- antineutrophil cytoplasmic antibodies (ANCA) autoantibodies found in some autoimmune diseases, recognized by their reactivity with cytoplasmic antigens in neutrophils; two groups are recognized: c-ANCA, reacting with proteinase 3, is found in polyangiitis and Churg-Strauss syndrome; p-ANCA, reacting with myeloperoxidase is found in Wegener granulomatosis.

- antinuclear a. (ANA) an a. showing an affinity for nuclear antigens including DNA and found in the serum of a high proportion of patients with systemic lupus erythematosus, rheumatoid arthritis, and certain collagen diseases, in some of their healthy relatives; also in about 1% of normal individuals.

- antiphospholipid antibodies antibodies directed against phosphorylated polysaccharide esters of fatty acid s, includes lupus anticoagulant, VDRL, and anticardiolipin antibodies. Associated with immune-mediated illnesses, syphilis, and stroke; thought to be from a hypercoagulable disorder.

- antithyroglobulin a. a. to thyroglobulin.

- avidity a. the sum total of the functional binding strength between a polyvalent and its a. antigen. The total binding strength represents the sum strength of all the affinity bonds.

- bivalent a. a. that causes a visible reaction with specific antigen as in agglutination, precipitation, and so on; so-called because according to the “lattice theory” aggregation occurs when the a. molecule has two or more binding sites that can crosslink one antigen particle to another; probably a characteristic of the class of immunoglobulin.

- blocking a. 1. a. which, in certain concentrations, does not cause precipitation after combining with specific antigen, and which, in this combined state, “blocks” activity of additional a. added to increase the concentration to a level at which precipitation would ordinarily occur; 2. the IgG class of immunoglobulin which combines specifically with an atopic allergen but does not elicit a type I allergic reaction, the combined IgG a. “blocking” available IgE class (reaginic) a. activity.

- blood group antibodies see Blood Groups appendix.

- catalytic a. an a. that has been altered to give it a catalytic activity. SYN: abzyme.

- cell-bound a. a term used for a. on the surface of cells that may be bound either through antigen combining sites or other sites such as the Fc region.

- CF a. SYN: complement-fixing a..

- chimeric antibodies antibodies that may have the FAB fragment from one species fused with FC fragment from another species.

- cold a. cold agglutinin.

- cold-reactive a. cold agglutinin.

- complement-fixing a. a. that combines with antigen leading to the binding and activation of complement, which may result in cell lysis. SYN: CF a..

- complete a. SYN: saline agglutinin.

- cross-reacting a. 1. a. specific for an epitope shared by members of a group, i.e., those with identical functional epitopes; 2. a. for antigens that have functional groups of similar, but not identical, chemical structure.

- cytophilic a. SYN: cytotropic a..

- cytotropic a. a. that has an affinity for certain kinds of cells, in addition to and unrelated to its specific affinity for the antigen that induced it, because of the properties of the Fc portion of the heavy chain. SEE ALSO: heterocytotropic a., homocytotropic a., cytotropic a. test. SYN: anaphylactic a., cytophilic a..

- fluorescent a. an immunoglobulin (a.) to which a fluorescent dye has been attached.

- Forssman a. a heterogenetic a. specific for the Forssman group of heterogenetic antigens. SYN: heterophil a., heterophile a..

- heterocytotropic a. a cytotropic a. (chiefly of the IgG class) similar in activity to homocytotropic a., but having an affinity for cells of a different species rather than for cells of the same or a closely related species.

- heterogenetic a. an a. that reacts to a heterogenetic antigen.

- heterophil a. SYN: Forssman a..

- heterophile a. SYN: Forssman a..

- homocytotropic a. a. usually of the IgE class that has an affinity for tissues (notably mast cells) of the same or a closely related species and that, upon combining with specific antigen, triggers the release of pharmacologic mediators of anaphylaxis from the cells to which it is attached; the tropism seems to be dependent upon the Fc portion of the a. molecule; in anaphylaxis in the guinea pig, the homocytotropic a. involved is of the γG class. SYN: reagin (4), reaginic a..

- human antimouse a. (HAMA) a. produced after exposure to mouse proteins.

- idiotypic a. an a. that binds to an idiotope of another a.. SYN: antiidiotype a..

- immobilizing a. SYN: treponema-immobilizing a..

- incomplete a. 1. SYN: univalent a.. 2. nonagglutinating.

- inhibiting a. SYN: univalent a..

- lymphocytotoxic antibodies antibodies specific for antigens of lymphocytes and which, upon combining with the antigens, induce cellular damage or death.

- monoclonal a. (MAB, MoAb) an a. produced by a clone or genetically homogeneous population of fused hybrid cells, i.e., hybridoma; hybrid cells are cloned to establish cell lines producing a specific a. that is chemically and immunologically homogeneous.The technique for producing monoclonal antibodies, invented in 1975 by molecular biologists Cesar Milstein and Georges Kohler, has become a mainstay of immunologic research and medical diagnosis. MoAbs serve as experimental probes in cell biology, biochemistry, and parasitology, and are used in purification of biologic substances and certain drugs ( e.g., interferons). Because of their high specificity in binding to target antigens, they provide far more accurate assays than conventional antiserum. Tagged with radionuclides, they have been employed to deliver radiation doses directly to cancerous tissues.

- natural a. SYN: normal a..

- neutralizing a. a form of a. that reacts with an infectious agent (usually a virus) and destroys or inhibits its infectivity and virulence; may be demonstrated by means of mixing serum with the suspension of infectious agent, and then injecting the mixture into animals or cell cultures that are susceptible to the agent in question.

- nonprecipitable a. SYN: nonprecipitating a..

- nonprecipitating a. a. that, under conditions normally employed in precipitin tests, is refractory to precipitation by specific a., demonstrable when antigen is added serially in small amounts; nonprecipitating a. will precipitate under special conditions such as addition of complement. SYN: nonprecipitable a..

- normal a. a. demonstrable in the serum or plasma of various persons or animals not known to have been stimulated by specific antigen, either artificially or as the result of naturally occurring contact. SYN: natural a..

- P-K antibodies igE antibodies involved in the Prausnitz-Kustner reaction.

- polyclonal a. (pol-e-klo′nal) a. that is derived from different clones of plasma cells but reacts with different epitopes of a particular antigen.

- Prausnitz-Küstner a. one of the IgE class of antibodies first demonstrated by Prausnitz and Küstner by passive transfer to the skin. See homocytotropic a.. SYN: atopic reagin.

- precipitating a. SYN: precipitin.

- reaginic a. SYN: homocytotropic a..

- ricin-blocked a. a. to which ricin has been attached.

- treponema-immobilizing a. a., evoked during syphilitic infections, possessing specific affinity for Treponema pallidum, and which in the presence of complement immobilizes the organism. SYN: immobilizing a., treponemal a..

- treponemal a. SYN: treponema-immobilizing a..

- univalent a. an “incomplete” form of a. that has a single binding site; in the case of Rh+ erythrocytes, such an anti-Rh a. may coat the cells but not cause them to agglutinate in saline; however, agglutination does occur when such coated cells are suspended in serum or other protein media, such as albumin, therefore called serum agglutinin. SYN: incomplete a. (1), inhibiting a..

- Vi a. a form of a. that agglutinates highly virulent strains of Salmonella typhi, i.e., cells with Vi antigen; such bacteria are not agglutinable with O antiserum until the Vi antigen is destroyed. See Vi antigen.

- Wassermann a. a nonspecific a., evoked during syphilitic infections, that combines with cardiolipin in the presence of lecithin and cholesterol; it is distinct from the treponema-immobilizing a..

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an·ti·body 'ant-i-.bäd-ē n, pl -bod·ies any of a large number of proteins of high molecular weight that are produced normally by specialized B cells after stimulation by an antigen and act specifically against the antigen in an immune response, that are produced abnormally by some cancer cells, and that typically consist of four subunits including two heavy chains and two light chains called also immunoglobulin

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n.

a special kind of blood protein that is synthesized in lymphoid tissue in response to the presence of a particular antigen and circulates in the plasma to attack the antigen and render it harmless. The production of specific antibodies against antigens as diverse as invading bacteria, inhaled pollen grains, and foreign red blood cells is the basis of both immunity and allergy. Chemically, antibodies are proteins of the globulin type; they are classified according to their structure and function (see immunoglobulin).

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an·ti·body (anґtĭ-bod″e) an immunoglobulin molecule that has a specific amino acid sequence by virtue of which it interacts only with the antigen that induced its synthesis in cells of the lymphoid series (especially plasma cells), or with antigen closely related to it. Antibodies are classified in groups named according to their mode of action, such as agglutinins, bacteriolysins, hemolysins, opsonins, precipitins, and others. See immunoglobulin.