Antigen

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antigen

 [an´tĭ-jen]
any substance capable, under appropriate conditions, of inducing a specific immune response and reacting with the products of that response; that is, with specific antibody or specifically sensitized T lymphocytes, or both. Antigens may be soluble substances, such as toxins and foreign proteins, or particulates, such as bacteria and tissue cells; however, only the portion of the protein or polysaccharide molecule known as the antigenic determinant combines with antibody or a specific receptor on a lymphocyte. Abbreviated Ag. See also immunity. adj., adj antigen´ic.
allogeneic antigen one occurring in some but not all individuals of the same species, e.g., histocompatibility antigens and human blood group antigens; called also isoantigen.
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.
blood-group a's erythrocyte surface antigens whose antigenic differences determine blood groups.
cancer antigen 125 (CA 125) a glycoprotein antigen found in normal adult tissues such as the epithelium of the fallopian tubes, the endometrium, the endocervix, the pleura, and the peritoneum. Elevated levels are seen in association with epithelial ovarian carcinomas, particularly nonmucinous tumors, as well as with some other malignancies, various benign pelvic disorders, tuberculosis, and cirrhosis.
carcinoembryonic antigen (CEA) an oncofetal glycoprotein antigen originally thought to be specific for adenocarcinoma of the colon, but now known to be found in many other cancers and some nonmalignant conditions. Its primary use is in monitoring the response of patients to cancer treatment.
CD antigen any of a number of cell-surface markers expressed by leukocytes and used to distinguish cell lineages, developmental stages, and functional subsets. Such markers can be identified by specific monoclonal antibodies and are numbered CD1, CD2, CD3, etc. (for cluster designation, according to how their specificity characteristics group together when analyzed by computer).
CD4 antigen an antigen on the surface of helper T cells; the normal range of helper cells is 800 to 1200 per cubic mm of blood. The human immunodeficiency virus binds to this antigen and infects and kills T cells bearing this antigen, thus gradually destroying the body's ability to resist infection. CD4 can be administered in a soluble form to increase the amount of it in the circulation and interfere with the ability of HIV to affect CD4 antigens on the cell.
class I a's major histocompatibility antigens found on virtually every cell, human erythrocytes being the only notable exception; they are the classic histocompatibility antigens recognized during graft rejection.
class II a's major histocompatibility antigens found only on immunocompetent cells, primarily B lymphocytes and macrophages.
conjugated antigen antigen produced by coupling a hapten to a protein carrier molecule through covalent bonds; when it induces immunization, the resultant immune response is directed against both the hapten and the carrier.
cross-reacting antigen
1. one that combines with antibody produced in response to a different but related antigen, owing to similarity of antigenic determinants.
2. identical antigens in two bacterial strains, so that antibody produced against one strain will react with the other.
extractable nuclear a's ENA; protein antigens, not containing DNA, that are extractable from cell nuclei in phosphate-buffered saline; anti-ENA antibodies are a component of the antinuclear antibodies occurring in systemic lupus erythematosus and other connective tissue diseases.
flagellar antigen H antigen.
Forssman antigen a heterogenetic antigen discovered in guinea pig tissues, capable of lysing sheep erythrocytes in the presence of complement. It is found usually in animal organs but occasionally in blood, and induces formation of an antibody (Forssman antibody, a type of heterophile antibody) only when combined with protein or hog serum. Davidsohn's Differential Test was historically used to differentiate between the heterophile sheep agglutinins in human serum that were due to Forssman antigen and those due to infectious mononucleosis; this is based upon the fact that boiled guinea pig kidney will absorb heterophile sheep cell agglutinins produced by Forssman antigen, but not those produced by infectious mononucleosis.
H antigen (Ger. Hauch, film), the antigen that occurs in the flagella of motile bacteria.
hepatitis B core antigen (HBcAg) a core protein antigen of the hepatitis B virus present inside complete virions (Dane particles) and in the nuclei of infected hepatic cells, indicating the presence of reproducing hepatitis B virus. The antigen is not present in the blood of infected individuals, but antibodies against it appear during the acute infection; they do not protect against reinfection.
hepatitis B e antigen (HBeAg) an antigen of hepatitis B virus sometimes present in the blood during acute infection, usually disappearing afterward but sometimes persisting in chronic disease. Anti-HBe antibodies appear transiently during convalescence; they do not protect against reinfection.
hepatitis B surface antigen (HBsAg) one present in the serum of those infected with hepatitis B, consisting of the surface coat lipoprotein of the hepatitis B virus. Tests for serum HbsAg are used in the diagnosis of hepatitis B and in testing blood products for infectivity.
heterogeneic antigen xenogeneic antigen.
heterogenetic antigen (heterophil antigen) (heterophile antigen) one capable of stimulating the production of antibodies that react with tissues from other animals or even plants.
histocompatibility a's genetically determined isoantigens present on the cell membranes of nucleated cells of most tissues, which incite an immune response when grafted onto a genetically disparate individual and thus determine the compatibility of tissues in transplantation. Major histocompatibility antigens are those that belong to the major histocompatibility complex, which in humans contains the hla antigens. Minor histocompatibility antigens are those that can cause delayed tissue rejection.
HLA a's (human leukocyte a's) see hla antigens.
H-Y antigen a minor histocompatibility antigen present in all tissues of normal males and coded for by a structural gene on the short arm of the Y chromosome; it is thought to promote the differentiation of indifferent gonads into testes, thus determining male sex.
isogeneic antigen an antigen carried by an individual which is capable of eliciting an immune response in genetically different individuals of the same species, but not in an individual bearing it.
K antigen a bacterial capsular antigen, a surface antigen external to the cell wall.
lymphogranuloma venereum antigen a sterile suspension of Chlamydia lymphogranulomatis; used as a dermal reactivity indicator.
M antigen a type-specific antigen that appears to be located primarily in the cell wall and is associated with virulence of Streptococcus pyogenes.
mumps skin test antigen a sterile suspension of mumps virus; used as a dermal reactivity indicator.
nuclear a's the components of cell nuclei with which antinuclear antibodies react.
O antigen (Ger. ohne Hauch, without film), the antigen that occurs in the bodies of bacteria.
oncofetal antigen a gene product that is expressed during fetal development, but repressed in specialized tissues of the adult and that is also produced by certain cancers. In the neoplastic transformation, the cells dedifferentiate and these genes can be derepressed so that the embryonic antigens reappear. Examples are alpha-fetoprotein and carcinoembryonic antigen.
organ-specific antigen any antigen that occurs exclusively in a particular organ and serves to distinguish it from other organs. Two types of organ specificity have been proposed: (1) first-order or tissue specificity is attributed to the presence of an antigen characteristic of a particular organ in a single species; (2) second-order organ specificity is attributed to an antigen characteristic of the same organ in many, even unrelated, species.
partial antigen an antigen that does not produce antibody formation, but gives specific precipitation when mixed with the antibacterial immune serum.
pollen antigen the essential polypeptides of the pollen of plants extracted with a suitable menstruum, used in diagnosis, prophylaxis, and desensitization in hay fever.
antigen presentation the presentation of ingested antigens on the surface of macrophages in close proximity to histocompatibility antigens. Some populations of T lymphocytes can only be triggered by antigens that are presented in this way. Thus macrophages play a role in inducing cell-mediated immunity.
private a's antigens of the low-frequency blood groups, so called because they are found only in members of a single kindred.
prostate-specific antigen (prostatic specific antigen) an antigen that is elevated in all patients with prostatic cancer and in some with an inflamed prostate gland.
public a's antigens of the high-frequency blood groups, so called because they are found in many persons.
self antigen an autoantigen, a normal constituent of the body against which antibodies are formed in autoimmune disease.
sequestered a's the cellular constituents of tissue (e.g., the lens of the eye and the thyroid) sequestered anatomically from the lymphoreticular system during embryonic development and thus thought not to be recognized as “self.” Should such tissue be exposed to the lymphoreticular system during adult life, an autoimmune response would be elicited.
somatic a's antigens, usually cell surface antigens, of the body of a bacterial cell, in contrast to flagellar or capsular antigens.
T antigen
1. any of several antigens, coded for by the viral genome, associated with transformation of infected cells by certain DNA tumor viruses. Called also tumor antigen.
2. an antigen present on human erythrocytes that is exposed by treatment with neuraminidase or contact with certain bacteria.
see CD a.
T-dependent antigen one that requires the presence of helper T cells to stimulate antibody production by B cells; most antigens are T-dependent.
T-independent antigen an antigen that can trigger B lymphocytes to produce antibodies without the participation of T lymphocytes. See also T-dependent antigen.
tumor antigen T antigen (def. 1).
tumor-specific antigen (TSA) any cell-surface antigen of a tumor that does not occur on normal cells of the same origin.
V antigen (Vi antigen) an antigen contained in the sheath of a bacterium, as Salmonella typhosa (the typhoid bacillus), and thought to contribute to its virulence.
xenogeneic antigen an antigen common to members of one species but not to members of other species; called also heterogeneic antigen.

an·ti·gen (Ag),

(an'ti-jen),
Any substance that, as a result of coming in contact with appropriate cells, induces a state of sensitivity or immune responsiveness and that reacts in a demonstrable way with antibodies or immune cells of the sensitized subject in vivo or in vitro. Modern usage tends to retain the broad meaning of antigen, employing the terms "antigenic determinant" or "determinant group" for the particular chemical group of a molecule that confers antigenic specificity.
See also: hapten.
Synonym(s): immunogen
[anti(body) + G. -gen, producing]

antigen

/an·ti·gen/ (an´tĭ-jen) any substance capable of inducing a specific immune response and of reacting with the products of that response, i.e., with specific antibody or specifically sensitized T lymphocytes, or both. Abbreviated Ag.antigen´ic
blood-group antigens  erythrocyte surface antigens whose antigenic differences determine blood groups.
cancer antigen 125  (CA 125) a surface glycoprotein associated with müllerian epithelial tissue; elevated serum levels are often associated with epithelial ovarian carcinomas, particularly with nonmucinous tumors, but are also seen in some other malignant and various benign pelvic disorders.
capsular antigen  one found in the capsule of a microorganism.
carcinoembryonic antigen  (CEA) a cancer-specific glycoprotein antigen of colon carcinoma, also present in many adenocarcinomas of endodermal origin and in normal gastrointestinal tissues of human embryos.
CD antigen  any of a number of cell surface markers expressed by leukocytes and used to distinguish cell lineages, developmental stages, and functional subsets; such markers can be identified by monoclonal antibodies.
class I antigens  major histocompatibility antigens found on every cell except erythrocytes, recognized during graft rejection, and involved in MHC restriction.
class II antigens  major histocompatibility antigens found only on immunocompetent cells, primarily B lymphocytes and macrophages.
common acute lymphoblastic leukemia antigen  (CALLA) a tumor-associated antigen occurring on lymphoblasts in about 80 per cent of patients with acute lymphoblastic leukemia (ALL) and in 40–50 per cent of patients with blastic phase chronic myelogenous leukemia (CML).
complete antigen  one which both stimulates an immune response and reacts with the products of that response.
conjugated antigen  one produced by coupling a hapten to a protein carrier molecule through covalent bonds; when it induces immunization, the resultant immune response is directed against both the hapten and the carrier.
D antigen  a red cell antigen of the Rh blood group system, important in the development of isoimmunization in Rh-negative persons exposed to the blood of Rh-positive persons.
E antigen  a red cell antigen of the Rh blood group system.
flagellar antigen  H antigen.
Forssman antigen  a heterogenetic antigen inducing the production of antisheep hemolysin, occurring in various unrelated species, mainly in the organs but not in the erythrocytes (guinea pig, horse), but sometimes only in the erythrocytes (sheep), and occasionally in both (chicken).
H antigen 
1. a bacterial flagellar antigen important in the serological classification of enteric bacilli.
2. the precursor of the A and B blood group antigens; normal type O individuals lack the enzyme to convert it to A or B antigens.
hepatitis B core antigen  (HBcAg) an antigen of the DNA core of the hepatitis B virus, indicating the presence of replicating hepatitis B virus.
hepatitis B e antigen  (HBeAg) an antigen of hepatitis B virus sometimes present in the blood during acute infection, usually disappearing afterward but sometimes persisting in chronic disease.
hepatitis B surface antigen  (HBsAg) a surface coat lipoprotein antigen of the hepatitis B virus, peaking with the first appearance of clinical disease symptoms. Tests for serum HBsAg are used in the diagnosis of acute or chronic hepatitis B and in testing blood products for infectivity.
heterogenetic antigen  heterophile a.
heterologous antigen  an antigen that reacts with an antibody that is not the one that induced its formation.
heterophil antigen , heterophile antigen an antigen common to more than one species and whose species distribution is unrelated to its phylogenetic distribution (viz., Forssman antigen, lens protein, certain caseins, etc.).
histocompatibility antigens  genetically determined isoantigens found on the surface of nucleated cells of most tissues, which incite an immune response when grafted onto a genetically different individual and thus determine compatibility of tissues in transplantation.
HLA antigens  human leukocyte antigens.
homologous antigen 
1. the antigen inducing antibody formation.
human leukocyte antigens  histocompatibility antigens (glycoproteins) on the surface of nucleated cells (including circulating and tissue cells) determined by a region on chromosome 6 bearing several genetic loci, designated HLA-A, -B, -C, -DP, -DQ, -DR, -MB, -MT, and -Te. They are important in cross-matching procedures and are partially responsible for the rejection of transplanted tissues when donor and recipient HLA antigens do not match.
H-Y antigen  a histocompatibility antigen of the cell membrane, determined by a locus on the Y chromosome; it is a mediator of testicular organization (hence, sexual differentiation) in the male.
Ia antigens  one of the histocompatibility antigens governed by the I region of the major histocompatibility complex, located principally on B lymphocytes, macrophages, accessory cells, and granulocyte precursors.
Inv group antigens  Km a's.
isogeneic antigen  an antigen carried by an individual which is capable of eliciting an immune response in genetically different individuals of the same species, but not in an individual bearing it.
K antigen  a bacterial capsular antigen, a surface antigen external to the cell wall.
Km antigens  the three alloantigens found in the constant region of the κ light chains of immunoglobulins.
Ly antigens , Lyt antigens antigenic cell-surface markers of subpopulations of T lymphocytes, classified as Ly 1, 2, and 3; they are associated with helper and suppressor activities of T lymphocytes.
mumps skin test antigen  a sterile suspension of mumps virus; used as a dermal reactivity indicator.
O antigen  one occurring in the lipopolysaccharide layer of the wall of gram-negative bacteria.
oncofetal antigen  carcinoembryonic a.
organ-specific antigen  any antigen occurring only in a particular organ and serving to distinguish it from other organs; it may be limited to an organ of a single species or be characteristic of the same organ in many species.
partial antigen  hapten.
private antigens  antigens of the low frequency blood groups, probably differing from ordinary blood group systems only in their incidence.
prostate-specific antigen  (PSA) an endopeptidase secreted by the epithelial cells of the prostate gland; serum levels are elevated in benign prostatic hyperplasia and prostate cancer.
public antigens  antigens of the high frequency blood groups, so called because they are found in almost all persons tested.
self-antigen  autoantigen.
T antigen 
1. tumor antigen, any of several coded for by the viral genome, and associated with transformation of infected cells by certain DNA tumor viruses.
2. see CD a.
3. an antigen present on human erythrocytes that is exposed by treatment with neuraminadase or contact with certain bacteria.
T-dependent antigen  one requiring the presence of helper cells to stimulate antibody production by B cells.
T-independent antigen  one able to trigger B cells to produce antibodies without the presence of T cells.
tumor antigen 
1. T a. (1).
tumor-associated antigen  a new antigen acquired by a tumor cell line in the process of neoplastic transformation.
tumor-specific antigen  (TSA) cell-surface antigens of tumors that elicit a specific immune response in the host.
Vi antigen  a K antigen of Salmonella typhi originally thought responsible for virulence.

antigen

(ăn′tĭ-jən) also

antigene

(-jēn′)
n.
A substance that when introduced into the body stimulates the production of an antibody. Antigens include toxins, bacteria, foreign blood cells, and the cells of transplanted organs.

an′ti·gen′ic (-jĕn′ĭk) adj.
an′ti·gen′i·cal·ly adv.
an′ti·ge·nic′i·ty (-jə-nĭs′ĭ-tē) n.

antigen

[an′tijən]
Etymology: Gk, anti + genein, to produce
a substance that the immune system recognizes as foreign and mounts an immune response against. The immune response may be either production of an antibody, a cell-mediated response, or both. antigenic, adj.

antigen

A molecule that usually has a molecular weight of > 1 kD, is a protein, often foreign (i.e., non-self), and which is capable of evoking a specific immune response (antibody production).

antigen

A molecule that usually has a molecular weight of > 1 kD, is a protein, often foreign–ie, non-self, which is capable of evoking a specific immune response, antibody production. See A antigen, Acquired B antigen, Alloantigen antigen, Antigenicity, Australia antigen, Autoantigen, B antigen, Bladder tumor antigen, Cancer-associated antigen, CENP antigen, Cromer-related antigen, Early antigen, Eclipsed antigen, Epithelial membrane antigen, Epstein-Barr nuclear antigen, Epstein-Barr viral capsid antigen, Extractable nuclear antigen, GAS, H antigen, Hepatitis surface antigen, High frequency antigen, H-Y antigen, Leukocyte common antigen, Lewis Y antigen, Low-frequency antigen, Mls antigen, Myeloid antigen, O antigen, Oncofetal antigen, P antigen, p24 antigen, Platelet antigen, Private antigen, PSA-prostate-specific antigen, Proliferating cell nuclear antigen, PRP antigen, Public antigen, Rh antigen, S antigen, Self antigen, Sm antigen, Soluble antigen, Squamous cell carcinoma antigen, SS-A antigen, SS-B antigen, Superantigen, TA-90, TAG-72, Targett antigen, Tumor-associated antigen, U antigen, Vi antigen, Xga antigen. Cf Antibody, Hapten.

an·ti·gen

(Ag) (an'ti-jen)
Any substance that, as a result of coming in contact with target cells, induces a state of sensitivity or immune responsiveness after a latent period (days to weeks) and that reacts in a demonstrable way with antibodies or immune cells of the sensitized subject in vivo or in vitro. Modern usage tends to retain the broad meaning of antigen, employing the terms "antigenic determinant" or "determinant group" for the particular chemical group of a molecule that confers antigenic specificity.
See also: hapten
Synonym(s): immunogen.
[anti(body) + G. -gen, producing]

antigen

Any molecule recognized by the immune system of the body as signalling ‘foreign’, and which will provoke the production of a specific ANTIBODY. Antigens include molecules on the surfaces of infective viruses, bacteria and fungi, pollen grains and donor body tissue cells.

antigen (Ag)

a complex molecule (usually a protein or carbohydrate) that, when introduced into the body, induces an IMMUNE RESPONSE which includes the production of specific ANTIBODIES. Antigens can be toxins (as in snake venom) or molecules on cell surfaces (e.g. A/B antigens on red blood cells).

Antigen

A substance that stimulates the immune system to manufacture antibodies (immunoglobulins). The function of antibodies is to fight off intruder cells, such as bacteria or viruses, in the body. Antigens stimulate the blood to fight other blood cells that have the wrong antigens. If a person with blood type A is given a transfusion with blood type B, the A antigens will fight the foreign blood cells as though they were an infection.

antigen

any substance that induces sensitivity, so that on subsequent exposure tissues react in a predetermined and predictable manner

antigen,

n any substance regarded by the body as foreign that provokes an immune system response.

antigen 

Any substance that can stimulate an immune response in the body and can react with the products of that response, that is, with specific antibodies or specifically sensitized T lymphocytes, or both. Antigens include bacteria, foreign substance (e.g. dust mite, grass, pollen of trees), toxins and viruses. See allergic reactions; sensitization.

an·ti·gen

(an'ti-jen)
Any substance that, as a result of coming in contact with appropriate cells, induces a state of sensitivity or immune responsiveness and reacts in a demonstrable way with antibodies or immune cells of the sensitized subject in vivo or in vitro.
[anti(body) + G. -gen, producing]

antigen (an´tijen),

n a substance, usually a protein, that elicits the formation of antibodies that react with it when introduced parenterally into an individual or species to which it is foreign. See also immunogens.
antigen, human leukocyte (HLA),
n the group of genes contained within the major histocompatibility complex (MHC), these antigen-bearing proteins are encoded by multiple genetic loci on human chromosome 6 and are found on the outer regions of the cellular structure.

antigen

any substance which is capable, under appropriate conditions, of inducing a specific immune response and of reacting with the products of that response; that is, with specific antibody or specifically sensitized T lymphocytes, or both. Antigens may be soluble substances, such as toxins and foreign proteins, or particulate, such as bacteria and tissue cells; however, only a small portion of the protein or polysaccharide molecule known as the antigenic determinant or epitope is recognized by the specific receptor on a lymphocyte. Similarly the antibody or effector lymphocyte produced by the response combines only with the one antigenic determinant. A bacterial cell or large protein will have many hundreds of antigenic determinants, some of which are more important than others in protective immunity. Abbreviated Ag.
See also immunity, antigenic.

allogenic antigen
one occurring in some but not all individuals of the same species, e.g. histocompatibility antigens and blood group antigens; formerly called isoantigen.
antibody-antigen reaction
see antibody-antigen reaction.
blood group a's
present on the surface of erythrocytes which vary between individuals of the same species and are used as the basis for blood typing.
antigen bridge
a link between antigen-specific receptors of two antibodies.
capsular a's
K, L and V antigens (below).
carcinoembryonic antigen (CEA)
see oncofetal antigen (below).
common antigen
an antigenic determinant present in two or more different antigen molecules and the basis for cross-reactions among them.
complete antigen
an antigen which both stimulates the immune response and reacts with the products, e.g. antibody, of that response, cf. hapten.
conjugated antigen
see hapten.
cross-reacting antigen
1. one that combines with antibody produced in response to a different but related antigen, owing to similarity of antigenic determinants.
2. identical antigens in two bacterial strains, so that antibody produced against one strain will react with the other.
dog erythrocyte antigen (DEA)
the antigens found on dog erythrocytes and used to distinguish different blood groups in the species. See Table 7.
environmental a's
those found in pollens, fungi, house dust, foods and animal dander.
antigen epitope
see antigenic determinant.
feline oncornavirus cell membrane antigen (FOCMA)
tumor-specific antigen present on the membrane of cells in cats infected with feline leukemia virus.
flagellar antigen
H antigen (below).
flea antigen
1. some components of flea saliva, as well as whole flea extracts, are antigenic and certain individuals may become hypersensitive to flea bites; the most common hypersensitivity in dogs.
2. extracts, usually of whole fleas, but sometimes of flea saliva, are used for intradermal skin testing and desensitization procedures.
Forssman antigen
heterophil antigen occurring in various unrelated species, mainly in the organs but not in the erythrocytes (guinea pig, horse), but sometimes only in the erythrocytes (sheep), and occasionally in both (chicken). Antibody to Forssman antigen is usually recognized by agglutination of sheep red blood cells.
group specific (gs) antigen
common to a certain group of organisms, e.g. streptococci, oncornaviruses.
H antigen
[Ger.] Hauch (film) the antigen that occurs in the bacterial flagella.
heterogeneic antigen
see xenogeneic antigen (below).
heterophil antigen, heterogenetic antigen
one capable of stimulating the production of antibodies that react with tissues from other animals or even plants.
hidden antigen
one not normally exposed to circulating lymphocytes, e.g. within central nervous tissue, testicular tissue and certain intracellular components, so they do not normally evoke an immune response.
histocompatibility a's
see histocompatibility antigen.
H-Y antigen
a histocompatibility antigen of the cell membrane, determined by a locus on the Y chromosome; it is a mediator of testicular organization (hence, sexual differentiation) in the male.
Ia a's
histocompatibility antigens governed by the I region of the major histocompatibility complex (MHC), located principally on B lymphocytes, although T lymphocytes, skin and certain macrophages may also contain Ia antigens.
isogenic antigen
an antigen carried by an individual, or members of the same inbred strain, which is capable of eliciting an immune response in genetically different individuals of the same species, but not in individuals bearing it.
K a's
bacterial capsular antigens.
L antigen
a capsular antigen of Escherichia coli.
Ly a's
antigenic cell-surface markers of subpopulations of T lymphocytes, classified as Ly 1, 2 and 3; they are associated with helper and suppressor activities of T lymphocytes.
lymphocyte-defined (LD) a's
class II antigens found in lymphocytes, macrophages, epidermal cells and sperm. Important in graft rejection.
M antigen
a type-specific antigen that appears to be located primarily in the cell wall and is associated with virulence of Streptococcus pyogenes.
Marek's tumor-specific antigen (MATSA)
found on the surface of cells infected by Marek's disease herpesvirus.
Nègre antigen
an antigen prepared from dead, dried and triturated tubercle bacilli by means of acetone and methyl alcohol; used in serum tests for tuberculosis in humans.
nuclear a's
the components of cell nuclei with which antinuclear antibodies react.
O antigen
[Ger.] ohne Hauch (without film) the antigen that occurs in the cell wall of bacteria.
oncofetal antigen
a gene product that is expressed during fetal development, but repressed in specialized tissues of the adult and that is also produced by certain cancers. In the neoplastic transformation, the cells dedifferentiate and these genes can be derepressed so that the embryonic antigens reappear. Examples are alpha-fetoprotein and carcinoembryonic antigen.
organ-specific antigen
any antigen that occurs exclusively in a particular organ and serves to distinguish it from other organs. Two types of organ specificity have been proposed: (1) first-order or tissue specificity is attributed to the presence of an antigen characteristic of a particular organ in a single species; (2) second-order organ specificity is attributed to an antigen characteristic of the same organ in many, even unrelated species.
partial antigen
see hapten.
pollen antigen
the essential polypeptides of the pollen of plants extracted with a suitable menstruum, used in diagnosis, prophylaxis and desensitization in hay fever.
antigen presentation
the presentation of peptide derivatives of antigens on the surface of antigen presenting cells (APCs), which include macrophages, dendritic cells and B lymphocytes, in association with class II major histocompatibility complex (MHC) antigens as required for recognition by T lymphocytes. Also includes antigen presentation in association with MHC class I by cells that are targets for lysis by cytotoxic T lymphocytes.
antigen-presenting cells
cells (macrophages, Langerhans cells, dendritic cells, and B lymphocytes) that process and present antigen to T lymphocytes.
private a's
antigens of the low-frequency blood groups, so-called because they are found only in members of a single kindred.
recall antigen
an antigen to which an individual has previously been sensitized and which is subsequently administered as a challenging dose to elicit a hypersensitivity reaction.
antigen receptors
immunoglobulin molecules on the cell membranes of B lymphocytes and a structurally related, but quite distinct molecule on the surface of T lymphocytes which recognize particular antigenic determinants of an antigen.
antigen recognition
see recognition (2).
sequestered a's
certain antigens, e.g. the lens of the eye and thyroid proteins, that are sequestered anatomically from the immune system during embryonic development and thus thought not to be recognized as 'self'. Should such antigens be exposed to the immune system during adult life, an autoimmune response would be elicited.
serologically defined (SD) antigen
class I antigen of the major histocompatibility complex, identifiable by the use of specific antisera.
synthetic antigen
chemically synthesized or produced by recombinant DNA technology, the synthesis of polymers, based on sequences found in microbial antigens, has been used in the production of vaccines.
T-dependent antigen
the immune response of most antigens requires T helper (Th) lymphocytes; lymphokines produced by T lymphocytes determine the characteristics of antibodies produced, which may change during the immune response.
thymus-dependent antigen
an antigen that requires T lymphocyte participation before an immune response can occur. Most antigens are of this type.
thymus-independent antigen
an antigen that elicits an antibody response without the participation of T lymphocytes. Usually large carbohydrate molecules with repeating epitopes are of this type.
tolerogenic antigen
tumor-specific antigen (TSA)
antigens found only in tumor cells.
V antigen, Vi antigen
an antigen contained in the capsule of a bacterium and thought to contribute to its virulence.
xenogeneic antigen
an antigen common to members of one species but not to members of other species; called also heterogeneic antigen.
References in periodicals archive ?
We showed that an MVA-based H5 (A/Vietnam/1194/2004) vaccine can elicit cross-clade antibodies against the newly emerging HPAI (H5N8) virus that is genetically and antigenically distinct from the clade 1 H5N1 virus A/Vietnam/1194/2004.
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The various Clade 2 strains are antigenically distinct from each other, but closer to each other than to Clade 1 strains.
sonnei seems to be replacing the more antigenically diverse S.
The enhancement of the anti-tumor response afforded by anti-GITR combination therapy was shown to target specific immune responses, because these animal models were resistant to tumor re-challenge while other antigenically distinct tumors grew normally.
As with GBS, a crucial factor in Hib virulence is the production of an antigenically variable polysaccharide capsule, she noted.
HIV-1 group M is antigenically different from HIV-1 group O and HIV-2.
granulosus sensu stricto G1, which may be antigenically different from E.
3 are genetically and antigenically distinct viruses that are circulating in wild birds and poultry worldwide and continue to be associated with human illness.
When this avian influenza outbreak began in Hong Kong in 1997, we developed a vaccine from an antigenically similar but nonpathogenic virus, called A/Duck/Singapore (H5N3).
The two major human metapneumovirus genetic lineages are highly related antigenically, and the fusion (F) protein is a major contributor to this antigenic relatedness.
Bright and former colleagues were honored for publication of "Development of adenoviral-vector-based pandemic influenza vaccine against antigenically distinct human H5N1 strains in mice," published in the February 11, 2006 issue of The Lancet, which described methods for developing a vaccine to prevent avian influenza.