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an immunoglobulin molecule having a specific amino acid sequence that gives each antibody the ability to adhere to and interact only with the antigen that induced its synthesis. This antigen-specific property of the antibody is the basis of the antigen-antibody reaction that is essential to an immune response. The antigen-antibody reaction begins as soon as substances interpreted as foreign invaders gain entrance into the body. See also immunity. Abbreviated Ab.

Antibodies are synthesized by the plasma cells formed when antigen-specific groups (clones) of B lymphocytes respond to the presence of antigen. The developmental process of antibody production begins when stem cells are transformed into B lymphocytes; this transformation usually is completed a few months after birth, at which time the lymphocytes migrate to lymphoid tissue primarily located in the lymph nodes, although they are also found in the spleen, gastrointestinal tract, and bone marrow.

Antibody production, its interaction with a specific antigen, and the activation of complement (C), an interrelated group of eleven proteins, are the major components of the humoral system of immunity.
Antibody-mediated immunity. From Applegate, 2000.
Fortunately, the immune response of antibody and complement can be transferred passively from one individual to another, as for example the transfer of maternal antibody across the placental barrier to the fetus, who has not yet developed a mature immune system. An antibody present in an individual without known prior exposure to the corresponding red cell antigen is termed an isoagglutinin. (Examples are the ABO antibodies anti-A, anti-B, and anti-A,B.)

Antibodies can be classified according to their mode of action as they react to and set about defending the body against foreign invaders. Some cause clumping together of bacterial cells (agglutination) and are called agglutinins. Those antibodies that cause bacterial cells to dissolve or liquefy are called bacteriolysins. This activity is assisted by complement, which interacts with the antigen-antibody complex in such a way that the cell ruptures and there is dissolution (lysis) of the cell body. Opsonins coat the outside of bacteria, making them more attractive to phagocytes. Other types of antibodies include those that neutralize the toxins of antigens (antitoxins) and those that cause precipitation of antigens in a fluid medium (precipitins).
anaphylactic antibody a substance formed as a result of the first injection of a foreign anaphylactogen and responsible for the anaphylactic symptoms following the second injection of the same anaphylactogen.
antinuclear a's (ANA) autoantibodies directed against components of the cell nucleus, e.g., DNA, RNA, and histones; they may be detected by immunofluorescence. A positive ANA test is characteristic of systemic lupus erythematosus. Antinuclear antibodies also occur in patients with rheumatoid arthritis, Sjögren's syndrome, and scleroderma.
blocking antibody any antibody that by combining with an antigen blocks another immunologic reaction with the antigen. Immunotherapy (hypersensitization) for allergic disorders induces in most treated patients IgG blocking antibodies that can bind the allergen and prevent it from binding to cell-fixed IgE and trigger immediate hypersensitivity; thus it can induce partial immunologic tolerance. Blocking antibodies can prevent agglutination in serologic tests.
complement-fixing antibody antibody (primarily IgM and the IgG subclasses 1, 2, and 3) that activates complement when reacted with antigen.
complete antibody antibody capable of agglutinating cells in physiologic saline solution.
cross-reacting antibody one that combines with an antigen other than the one that induced its production.
cytophilic antibody cytotropic antibody.
cytotoxic antibody any specific antibody directed against cellular antigens, which when bound to the antigen, activates the complement pathway or activates killer cells, resulting in cell lysis.
cytotropic antibody any of a class of antibodies that attach to tissue cells (such as mast cells and basophils) through their Fc segments to induce the release of histamine and other vasoconstrictive amines important in immediate hypersensitivity reactions. In humans this antibody, also known as reagin, is of the immunoglobulin class known as IgE. Called also cytophilic antibody.
heterophil antibody a characteristic antibody found with many cases of infectious mononucleosis; see also heterophil antibody.
immune antibody a type of isoantibody induced by immunization, either by pregnancy or by transfusion, in contrast to natural antibodies.
incomplete antibody
1. antibody that binds to erythrocytes or bacteria but does not produce agglutination; in blood banking, the nonagglutinating antibody is detectable in serum by using the antiglobulin (Coombs') test. For example, IgG anti-Rh antibodies do not agglutinate erythrocytes in physiologic saline whereas IgM antibodies do.
2. a univalent antibody fragment.
monoclonal a's (MOAB) proteins produced from a single clone of B lymphocytes; used as laboratory reagents in radioimmunoassays, ELISA assay, and immunofluorescence assays, and also as biological response modifiers fused with rapidly reproducing myeloma cells, resulting in a hybridoma capable of synthesizing a massive amount of one specific antibody; the antibody is made in response to tumor cells injected into mice and is produced from mouse serum. Monoclonal antibodies may be used alone (unconjugated) or bound (conjugated) to radioisotopes, toxins, or other biological response modifiers. When bound to radioisotopes they may also be used as a diagnostic tool to locate tumors and metastatic disease.
natural a's (naturally occurring a's) antibodies present in the serum of normal individuals in the apparent absence of any contact with the specific antigen, probably induced by exposure to cross-reacting antigens; examples are the ABO antibodies, anti-A and anti-B. Such antibodies may play a major role in resistance to infection.
neutralizing antibody one that reduces or destroys infectivity of a homologous infectious agent by partial or complete destruction of the agent.
protective antibody one responsible for immunity to an infectious agent, observed in passive immunity.
Rh a's those directed against Rh antigen(s) of human erythrocytes. Not normally present, they may be produced when Rh-negative persons receive Rh-positive blood by transfusion or when an Rh-negative person is pregnant with an Rh-positive fetus.
saline antibody complete antibody.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

an·ti·bod·y (Ab),

(an'tē-bod'ē), Avoid the jargonistic use of the plural antibodies when the reference is to a single antibody species.
An immunoglobulin molecule produced by B-lymphoid cells that combine specifically with an immunogen or antigen. Antibodies may be present naturally, their specificity is determined through gene rearrangement or somatic replacement or may be synthesized in response to 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. After binding antigen, some antibodies may fix, complement, bind to surface receptors on immune cells, and in some cases may neutralize microorganisms.
See also: immunoglobulin.
Farlex Partner Medical Dictionary © Farlex 2012


n. pl. antibod·ies
A Y-shaped protein on the surface of B cells that is secreted into the blood or lymph in response to an antigenic stimulus, such as a bacterium, virus, parasite, or transplanted organ, and that neutralizes the antigen by binding specifically to it; an immunoglobulin.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


An immunoglobulin produced by plasma cells, which has a specific amino acid sequence and specifically binds to the antigen(s) (e.g., foreign proteins, microbes or toxins) that induced its synthesis; antibodies may also bind to closely related antigens.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.


Immunology An immunoglobulin produced by plasma cells, which has a specific amino acid sequence and specifically binds to the antigen(s)–eg, foreign proteins, microbes or toxins, that induced its synthesis; antibodies may bind to closely related antigens. See Acetylcholine receptor antibody, Anticardiolipin antibody, Anticentromere antibody, Anti-double-stranded DNA antibody, Anti-epidermal antibody, Anti-extractable nuclear antibody, Antigliadin antibody, Antihistone antibody, Anti-idiotype antibody, Anti-insulin antibody, Anti-islet cell antibody, Anti-Jo-1 antibody, Anti-LANA antibody, Antimicrosomal antibody, Antimitochondrial antibody, Antimyelin antibody, Antimyeloperoxidase antibody, Antineuronal-nuclear antibody, Antineutrophil cytoplasmic antibody, Antinuclear antibody, Antiparietal cell antibody, Anti-platelet antibody, Anti-PRP antibody, Anti-Purkinje cell antibody, Anti-receptor antibody, Anti-reticulin antibody, Anti-ribosomal antibody, Anti-Ro/SSA antibody, Anti-single-stranded DNA antibody, Anti-striated muscle antibody, Anti-thyroglobulin antibody, Antithyroid antibody, Antithyroid peroxidase antibody, Anti-tumor necrosis factor- α monoclonal antibody, Autoantibody, Bexxar radiolabeled monoclonal antibody, Secondary antibody, Binding antibody, Blocking antibody, Catabolic antibody, Catalytic antibody, Chimeric antibody, Core antibody, Cross-reactive antibody, Designer antibody, Enhancing antibody, Fluorescent treponemal antibody, Functional antibody, GAD antibody, Glutamic acid decarboxylase autoantibody, HAMA antibody, Heterophile antibody, HIV antibody, HTLA antibody, Humanized antibody, Immunoglobulin, Insulin receptor antibody, Intrinsic factor antibody, Islet antibody, Isotypic control antibody, Ku antibody, LW antibody, Miniantibody, MOC-31 antibody, Monoclonal antibody, Neutralizing antibody, Parietal cell antibody, Plantibody antibody, PM-1 antibody, Polyclonal antibody, Primary antibody, Purkinje cell antibody, RANA antibody, Scleroderma antibody, Sjögren antibody, Sm antibody, Smooth muscle antibody, Sperm antibody, Thyroid stimulating hormone receptor antibody, Trichinosis antibody, Warm antibody.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


(Ab) (an'ti-bod-ē)
An immunoglobulin molecule with a specific amino acid sequence evoked in humans or other animals by an antigen and characterized by reacting specifically with the antigen in some demonstrable way, produced by B lymphocytes in response to an antigen. It is believed that antibodies also may exist naturally, without being present as a result of the stimulus provided by the introduction of an antigen.
See also: immunoglobulin
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


(ant'i-bod?e) [ anti- + body],


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ANTIBODY: Structure of one igG molecule
A substance produced by B lymphocytes in response to a unique antigen. Each Ab molecule combines with a specific antigen to destroy or control it. All antibodies, except natural antibodies (antibodies to different blood types), are made by B cells stimulated by a foreign antigen, typically a foreign protein, polysaccharide, or nucleic acid. Synonym: immunoglobulin See: illustration; antigen; autoantibody; cytokine; isoantibody

Antibodies neutralize or destroy antigens in several ways. They can initiate lysis of the antigen by activating the complement system; neutralize toxins released by bacteria, coating (opsonizing) the antigen or forming a complex to stimulate phagocytosis; promote antigen clumping (agglutination); or prevent the antigen from adhering to host cells.

An antibody molecule consists of four polypeptide chains (two light and two heavy), which are joined by disulfide bonds. The heavy chains form the complement-binding site, and the light and heavy chains form the site that binds the antigen.

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acetylcholine receptor binding antibody

Abbreviation: AChR-Ab
An autoantibody against acetylcholine receptors in the neuromuscular junction. Binding, blocking, or modulating antibodies against this receptor are found in the blood of most patients with generalized myasthenia gravis and in about half of all patients with ocular forms of the disease.

agonistic antibody

An antibody that stimulates or activates an organ. E.g., agonistic antibodies against the thyrotropin receptor in Grave disease stimulate the thyroid gland to release thyroid hormones that produce hyperthyroidism.

anticardiolipin antibody

Abbreviation: aCLa
An autoantibody against the cell membrane lipid, diphosphatidyl glycerol. It produces abnormal and sometimes life-threatening blood clotting. The antibody is found in a variety of autoimmune and infectious diseases, including in patients with the antiphospholipid antibody syndrome and syphilis.

anticyclic citrullinated peptide antibody

Abbreviation: anti-CCP
An antibody found in the serum of patients with rheumatoid arthritis but not in those with other joint or soft tissue diseases.

anti–DNase B antibody

An antibody formed during infection with group A beta-hemolytic streptococci. It is used, retrospectively, to help diagnose recent streptococcal infections.

antiendomysial antibody

An antibody that cross-reacts with smooth muscle collagen and the gluten in wheat, found in the serum of people with celiac sprue and some related autoimmune diseases.

antiendothelial cell antibody

An autoantibody present in the serum of patients with a variety of autoimmune diseases, including scleroderma (systemic sclerosis), systemic lupus erythematosus, interstitial lung diseases, and sarcoidosis. They attach to antigens on the cells that line blood vessels and injure those cells, producing blood vessel injury and inflammation (vasculitis).

antifibrillarin antibody

An autoantibody to the nucleolar protein fibrillarin, found in patients with diffuse systemic sclerosis (scleroderma), esp. those with relatively severe disease. It is identified more often in men than in women with the disease and in people of African descent as opposed to Europeans or Asians.

antiganglioside antibody

An antibody formed against the chemical components of nerves, found in the serum of those with Guillain-Barré syndrome.

antigliadin antibody

An antibody formed against the gluten in wheat, found in the serum of people with celiac sprue.

antileukocyte antibody

Any antibody found in plasma that, when donated and infused into a recipient, damages the recipient's white blood cells. Leukocyte injury after plasma exchange or infusion is the event that triggers transfusion-related acute lung injury.

anti-Hu antibody

An autoantibody associated with paraneoplastic encephalomyelitis. It is also known as ANNA-1 (antineuronal nuclear antibody-1).

antimicrosomal antibody

An autoantibody found in the plasma of patients with thyroid injury, e.g., in several forms of thyroiditis and other rheumatologic or autoimmune diseases.

anti-myeloperoxidase antibody

An antibody found in patients with several autoimmune vasculitides, such as microscopic polyangitis.
Synonym: perinuclear anti–neutrophil cytoplasmic antibody

antineuronal nuclear antibody

Abbreviation: ANNA
Any of several antibodies that bind to neuronal targets in the cerebrum and cerebellum, producing paraneoplastic neurological dysfunction. The antibodies are typically released by cancers such as small-cell carcinoma of the lung (also known as ANNA-1 and ANNA-2), testicular cancer (anti-Ta antibody), or breast cancer (ANNA-2).

antineutrophil cytoplasmic antibody

Abbreviation: ANCA
An autoantibody found in the blood of patients with certain forms of vasculitis (such as Churg-Strauss syndrome, microscopic polyangiitis, Wegener granulomatosis) esp. when it affects small blood vessels.

antinuclear antibody

Abbreviation: ANA
Any of a group of autoantibodies that react against normal components of the cell nucleus. These antibodies are present in a variety of immunologic diseases, including systemic lupus erythematosus, progressive systemic sclerosis, Sjögren syndrome, scleroderma, polymyositis, and dermatomyositis, and in some patients taking hydralazine, procainamide, or isoniazid. In addition, ANA is present in some normal people. Tests for ANAs are used in the diagnosis and management of autoimmune diseases.

antiphospholipid antibody

Abbreviation: aPLa
Any of a group of immunoglobulin autoantibodies that react with phospholipids, which are one of the primary components of the cell membrane (the other components are glycolipids and steroids). These antibodies are found in patients with a variety of connective tissue and infectious disorders, including systemic lupus erythematosus, the antiphospholipid antibody syndrome, syphilis, and malaria. They cause abnormal blood clotting, thrombocytopenia; and in women of childbearing age, repeated miscarriages. The anticardiolipin antibodies are one type of antiphospholipid antibody.

anti–proliferating cell nuclear antigen (PCNA) antibody

Abbreviation: anti-PCNA
An antibody found in the blood of patients with diseases in which cells replicate rapidly. Such conditions include autoimmune and inflammatory diseases and malignancies.

antiproteinase-3 antibody

An autoantibody found in patients with small blood vessel vasculitides, such as Wegener granulomatosis.
Synonym: diffusely cytoplasmic anti–neutrophil antibody

antireceptor antibody

An antibody that reacts with the antigen receptor on a cell rather than with an antigen itself.

antiribosomal P antibody

An autoantibody found in patients with systemic lupus erythematosus, esp. those with neurological or psychiatric manifestations of the disorder.

anti-scl-70 antibody

Anti-topoisomerase I antibody.

antithyroperoxidase antibody

Abbreviation: TPOAb
A serum marker of autoimmune thyroid destruction, i.e., of Grave disease or Hashimotothyroiditis.

antititin antibody

An antibody that reacts with striated muscle cells. It is found principally in people with myasthenia gravis who also have thymoma.

anti-topoisomerase I antibody

An autoantibody found in the serum of patients with progressive systemic sclerosis, silicosis, and systemic lupus erythematosus. Higher levels of the antibody correlate with worsening kidney, lung, and skin disease.
Synonym: anti-scl-70 antibody

blocking antibody

An antibody that prevents an antigen from binding with a cellular receptor.

catalytic antibody


cross-reacting antibody

An antibody that reacts with antigens other than its specific antigen because they contain binding sites that are structurally similar to its specific antigen.
See: antigenic determinant

cytotoxic antibody

An antibody that lyses cells by binding to a cellular antigen and activating complement or killer cells.

diffusely cytoplasmic anti-neutrophil cytoplasmic antibody

Abbreviation: C-ANCA.
Antiproteinase-3 antibody.

direct fluorescein-conjugated antibody

Abbreviation: DFA
Direct fluorescent antibody.

direct fluorescent antibody

Abbreviation: DFA
A fluorescent antibody test performed on sputum to detect microorganisms that invade the respiratory tract, e.g., Legionella, Mycoplasma, or Bacillus anthracis.
Synonym: direct fluorescein-conjugated antibody; direct immunofluorescence test

Donath-Landsteiner antibody

See: Donath-Landsteiner antibody

fluorescent antibody

Abbreviation: FA
An antibody that has been stained or marked by a fluorescent material. The fluorescent antibody technique permits rapid diagnosis of various infections.

glutamic acid decarboxylase antibody

Abbreviation: GADA
An antibody to glutamic acid decarboxylase. It is a serum marker of type 1 diabetes mellitus and is found in the blood of patients with stiff-person syndrome.

immune antibody

An antibody produced by immunization or as a result of transfusion of incompatible blood.

maternal antibody

An antibody produced by the mother and transferred to the fetus in utero or during breastfeeding.

monoclonal antibody

Abbreviation: MoAB
A type of antibody, specific to a certain antigen, created in the laboratory from hybridoma cells. Because monoclonal antibodies are derived from a single cell line and raised against a single antigen, they are highly specific. Diagnostically, they are used to identify microorganisms, white blood cells, hormones, and tumor antigens. In patient care, they are used to treat transplant rejection, certain cancers, and autoimmune diseases.

Hybridoma cells, used to produce monoclonal antibodies, are formed by the fusion of a spleen cell from a mouse immunized with an antigen and a multiple myeloma cell (a cancerous plasma B cell). The fused cells are screened to identify those that secrete antibodies against a specific antigen. A continuous supply of these antigen-specific monoclonal antibody secreting cells can then be grown in cultures.

See: antibody; B cell; hybridoma

natural antibody

An antibody present in a person without known exposure to the specific antigen, such as an anti-A antibody in a person with B blood type.

panel reactive antibody

Abbreviation: PRA
A measure of an organ transplant recipient's level of sensitization to antigens on donated organs. It is the percentage of cells taken from a broad selection of blood donors against whose antigens the organ recipient's serum reacts. The higher the panel reactive antibody, the more challenging it is to match a donor organ to the recipient.

perinuclear antineutrophil cytoplasmic antibody

Antimyeloperoxidase antibody.

p504s antibody

Alpha-methylacyl-CoA racemase.

polyclonal antibody

An antibody that reacts with many different antigens.

protective antibody

An antibody produced in response to an infectious disease. See: immunity

radionuclide-linked monoclonal antibody

A monoclonal antibody to which a radioisotope has been attached. The antibody attaches to receptors on the surface of undesired cells (e.g., cancer cells) and delivers a dose of radiation directly to those cells, leaving healthy cells and tissues relatively unaffected.

sensitizing antibody


toxin-linked monoclonal antibody

A monoclonal antibody to which a cell-killing drug has been attached. The antibody combines preferentially with receptors on undesired cells (such as cancer cells) and delivers its lethal drug to those cells but not to healthy cells and tissues. To increase their effectiveness and decrease immune responses to these cells, genes for antigen binding sites from human antibodies are added, creating humanized monoclonal antibodies.

warm antibody

Warm autoagglutinin.illustration
Medical Dictionary, © 2009 Farlex and Partners


A Y-shaped protein molecule, called an IMMUNOGLOBULIN, produced by the B group of lymphocytes in response to the presence of a ANTIGEN. An appropriate B lymphocyte is selected from the existing repertoire. This then produces a clone of PLASMA CELLS each capable of synthesizing large numbers of specific antibodies to combat the infection. The B cells also produce memory cells. Subsequent infection with the same antigen prompts the memory cells to clone plasma cells and produce the correct antibodies without further delay. This is an important way in which an infection leads to subsequent immunity. Antibodies are able to neutralize antigens or render them susceptible to destruction by PHAGOCYTES in the body. The basic structure of an antibody consists of four polypeptide chains linked by disulphide bridges, two larger structures called HEAVY CHAINS and two smaller called LIGHT CHAINS.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

antibody (Ab)

a type of protein called an IMMUNOGLOBULIN that reacts with a specific ANTIGEN, and serves as part of a vital body-defence mechanism. Various reactions can occur between antigen and antibody. If the antigen is a TOXIN (as in snake venom, or as produced by bacteria causing, for example, botulism and tetanus), neutralizing antibodies are called antitoxins. If the antigen is adhering to the surface of a cell, antibodies called agglutinins cause clumping or AGGLUTINATION of cells, while another antibody type (lysins) cause disintegration or LYSIS of the cell in conjunction with COMPLEMENT. Other antibodies (opsonins) facilitate uptake of antigens by PHAGOCYTES in the blood, while precipitins cause soluble antigens to precipitate.

Antibodies are produced in the lymphoid tissues of the body, e.g. LYMPH NODES, by a type of LYMPHOCYTE called B-CELLS. Most antibodies are produced during exposure to an antigen, such a response being termed active immunity. Specific antibodies to rare or synthetic antigens can be manufactured as easily as those to common antigens. A few antibodies are produced even without the apparent presence of the appropriate antigen. Such ‘natural’ antibodies include several involved in blood grouping, e.g. A and B antibodies in the ABO BLOOD GROUP. Young mammals have limited capacity to produce antibodies in the first few weeks of life, but can obtain some passive immunity by receiving maternal antibodies via the mother's milk. This fact has been used to encourage human mothers to breast-feed their infants rather than bottle-feed. Most antibodies circulate in the blood and other body fluids, but most if not all body secretions also contain antibodies, mainly of the IgA type; See IMMUNOGLOBULIN.

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005


A protein manufactured by a type of white blood cells called lymphocytes, in response to the presence of an antigen, or foreign protein, in the body. Because bacteria, viruses, and other organisms commonly contain many antigens, antibodies are formed against these foreign proteins to neutralize or destroy the invaders.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


Any of a large variety of proteins normally present in the body or produced in response to an antigen, which it is capable of combining with and destroying, thus producing an immune reaction. Antibodies are produced by a type of white blood cell called B cell (B lymphocyte) secreted by lymphatic tissue (e.g. bone marrow, lymph nodes) usually in response to an antigen. Some eye diseases are antibody-dependent (e.g. allergic conjunctivitis, atopic keratoconjunctivitis, vernal conjunctivitis).
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann


(Ab) (an'ti-bod-ē) Avoid the jargonistic use of the plural antibodies when the reference is to a single antibody species.
An immunoglobulin molecule produced by B-lymphoid cells that combine specifically with an immunogen or antigen. Antibodies may be present naturally; their specificity is determined through gene rearrangement or somatic replacement or may be synthesized in response to stimulus provided by the introduction of an antigen.
Medical Dictionary for the Dental Professions © Farlex 2012

Patient discussion about Antibody

Q. what is anh cardiolipin antibody

A. Cardiolipin is a protein that is very common in the body. Mostly on heart and skeletal muscles. During several illnesses, mostly autoimmune, our body creates an antibody against it that do great damage and needs to cbe controlled.

More discussions about Antibody
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