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.
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.
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
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.
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.
(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.
antibody /an·ti·body/ (Ab) (an´tĭ-bod-e) an immunoglobulin molecule that reacts with a specific antigen that induced its synthesis and with similar molecules; classified according to mode of action as agglutinin, bacteriolysin, hemolysin, opsonin, or precipitin. Antibodies are synthesized by B lymphocytes that have been activated by the binding of an antigen to a cell-surface receptor. See immunoglobulin.
anaphylactic antibody IgE antibody causing anaphylaxis.
antimitochondrial antibodies circulating antibodies directed against inner mitochondrial antigens seen in almost all patients with primary biliary cirrhosis.
antinuclear antibodies (ANA) autoantibodies directed against components of the cell nucleus, e.g., DNA, RNA, and histones.
antireceptor antibodies autoantibodies against cell-surface receptors, e.g., those directed against β2-adrenergic receptors in some patients with allergic disorders.
(ASA) any of various surface-bound antibodies found on sperm after infection, trauma to the testes, or vasectomy
; they interfere with the fertilization
process or result in nonviable zygotes
antithyroglobulin antibodies those directed against thyroglobulin, demonstrable in about one-third of patients with thyroiditis, Graves' disease, and thyroid carcinoma.
1. one (usually IgG) that reacts preferentially with an antigen, preventing it from reacting with a cytotropic antibody (IgE), and producing a hypersensitivity reaction.
complement-fixing antibody one that activates complement when reacted with antigen: IgM and IgG fix complement by the classical pathway; IgA, by the alternative pathway.
complete antibody one that reacts with the antigen in saline, producing an agglutination or precipitation reaction.
cytotoxic antibody any specific antibody directed against cellular antigens that, 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 through their Fc segments to induce the release of histamine and other vasoconstrictive amines important in immediate hypersensitivity reactions.
an IgG antibody directed against the P blood group antigen; it binds to red cells at low temperatures and induces complement-mediated lysis on warming, and is responsible for hemolysis in paroxysmal cold hemoglobinuria
Forssman antibody heterophile antibody directed against the Forssman antigen.
heteroclitic antibody antibody produced in response to immunization with one antigen but having a higher affinity for a second antigen that was not present during immunization.
heterogenetic antibody , heterophil antibody, heterophile antibody antibody directed against heterophile antigens. Heterophile sheep erythrocyte agglutinins appear in the serum of patients with infectious mononucleosis.
immune antibody one induced by immunization or by transfusion incompatibility, in contrast to natural antibodies.
1. antibody that binds to erythrocytes or bacteria but does not produce agglutination.
2. a univalent antibody fragment, e.g., Fab fragment.
indium-111 antimyosin antibody a monoclonal antibody against myosin, labeled with indium 111; it binds selectively to irreversibly damaged myocytes and is used in infarct avid scintigraphy.
monoclonal antibodies chemically and immunologically homogeneous antibodies produced by hybridomas, used as laboratory reagents in radioimmunoassays, ELISA, and immunofluorescence assays.
natural antibodies ones that react with antigens to which the individual has had no known exposure.
neutralizing antibody one which, on mixture with the homologous infectious agent, reduces the infectious titer.
OKT3 monoclonal antibody a mouse monoclonal antibody directed against T3 lymphocytes and used to prevent or treat organ rejection after transplantation.
1. the preexisting antibody against HLA antigens in the serum of a potential allograft recipient that reacts with a specific antigen in a panel of leukocytes, with a higher percentage indicating a higher risk of a positive crossmatch.
2. the percentage of such antibody in the recipient's blood.
P-K antibodies , Prausnitz-Küstner antibodies cytotropic antibodies of the immunoglobulin class IgE, responsible for cutaneous anaphylaxis.
protective antibody one responsible for immunity to an infectious agent observed in passive immunity.
antibody (ant'i-bod?e) [ anti- + body],
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
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.
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. illustration
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.
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).
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.
An antibody formed against the chemical components of nerves, found in the serum of those with Guillain-Barré syndrome.
An antibody formed against the gluten in wheat, found in the serum of people with celiac sprue.
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.
An autoantibody associated with paraneoplastic encephalomyelitis. It is also known as ANNA-1 (antineuronal nuclear antibody-1).
An autoantibody found in the plasma of patients with thyroid injury, e.g., in several forms of thyroiditis and other rheumatologic or autoimmune diseases.
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.
An autoantibody found in patients with small blood vessel vasculitides, such as Wegener granulomatosis. Synonym: diffusely cytoplasmic anti–neutrophil 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 antibodyAnti-topoisomerase I antibody.
antithyroperoxidase antibody Abbreviation: TPOAb
A serum marker of autoimmune thyroid destruction, i.e., of Grave disease or Hashimotothyroiditis.
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
An antibody that prevents an antigen from binding with a cellular receptor.
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
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.
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.
An antibody produced by immunization or as a result of transfusion of incompatible blood.
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.
; B cell
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 antibodyAntimyeloperoxidase antibody.
p504s antibody Alpha-methylacyl-CoA racemase.
An antibody that reacts with many different antigens.
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.
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 antibodyWarm autoagglutinin.illustration
specialized serum proteins produced by B lymphocytes in response to an immense number of different antigens (>107
) to which an animal may be exposed. Antibody produced by a particular antigen combines with that antigen only. The exquisite specificity of Ab for the antigen that stimulated its production is the basis for all antibody-antigen reactions both in vivo and in vitro. Antibodies are heterodimers composed of two light (L) and two heavy (H) chain polypeptide molecules. The amino termini of the L and H chains have a variable amino acid sequence VL
. The specificity of Ab for Ag is conferred by the VL
domains. There are five major classes of antibody, designated IgG, IgM, IgA, IgD and IgE. Abbreviated Ab or Ig. Called also immunoglubulin or gamma globulin. See also immunity
affinity purification of antibody anaphylactic antibody
antibody, usually IgE, formed after the first injection of certain allergens and responsible for the signs of anaphylaxis following subsequent exposures to the same allergen.
the specific combination of antigen with homologous antibody resulting in the reversible formation of antibody-antigen complexes that differ in composition according to the antibody-antigen ratio. See also antigen
antinuclear antibody (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, Sjögren's syndrome and rheumatoid arthritis.
antibodies against the antibody variable region.
those produced against an immunoglobulin, often used as reagents to study immunoglobulin molecules.
produced following entry of sperm into the bloodstream, e.g. following rupture of the epididymis as in Brucella ovis infections.
circulating antibody (usually IgG) that reacts preferentially with an antigen, preventing it from reacting with a cell-bound antibody (IgE) and blocking the induction of anaphylaxis.
clone specific antibody.
see cold agglutinin.
immunoglobulins of the IgG or IgM class which bind complement.
one that combines with an antigen other than, but structurally related to, the one that induced its production.
cytotropic antibody (below).
that which binds antigens expressed on the cell surface, which may (a) activate the complement pathway or (b) activate killer cells, resulting in cell lysis.
those that attach to tissue cells (such as IgE to mast cells and basophils) that have an Fc receptor.
antibody-dependent cell-mediated cytotoxicity (ADCC)
a cytotoxic reaction in which nonsensitized cells bearing Fc receptors recognize target cells that have antibody bound to antigen exposed in the cell membrane of the target cell.
one with greater affinity for an antigen other than the one that stimulated its formation.
has been investigated mostly as a means of controlling fertility in animals. See also contraception
one induced by immunization or by transfusion incompatibility, in contrast to natural antibodies.
an antibody which combines with antigen without producing an observable reaction such as agglutination; originally used to describe Rh antibodies.
those passively transferred from dam to fetus or neonate, transplacentally or via colostrum or yolk sac. See also passive immunity
damage to cells, especially erythrocytes, caused by the reaction of antibodies (IgG, IgM or IgA) with cell surface antigens.
ones that react with antigens to which the individual has had no known exposure. The best examples are anti a and b antibodies present in serum of humans of blood group B and A, respectively.
one that reduces, destroys or blocks infectivity of an infectious agent, particularly virus, by partial or complete destruction of the agent.
see incomplete antibody (above).
a collection of immunoglobulins that react against the same or different antigenic determinants of the one antigen molecule.
one responsible for immunity to an infectious agent.
all the antibody specificities that can be produced by an individual.
skin-sensitizing antibody univalent antibody
see incomplete antibody (above).