Antigen (redirected from Inv group antigens)

antigen /an·ti·gen/ (an´ti-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

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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.

2. isoantigen.

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 ? 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).

2. tumor-specific a.

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.

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an·ti·gen (nt-jn)

n.

Any of various substances, including toxins, bacteria, and the cells of transplanted organs, that when introduced into the body stimulate the production of antibodies. Also called allergen, immunogen.

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anti·genic (-jnk) adj.

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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.

Mentioned in: AIDS, AIDS Tests, Allergic Bronchopulmonary Aspergillosis, Allergic Rhinitis, Allergies, Allergy Tests, Ataxia-Telangiectasia, Blood Typing and Crossmatching, Bone Marrow Transplantation, Botulinum Toxin Injections, Coccidioidomycosis, Coombs' Tests, Cryptococcosis, Delayed Hypersensitivity Skin Test, Elephantiasis, Erythroblastosis Fetalis, i>, Giardiasis, Goodpasture's Syndrome, Hemorrhagic Fevers, Hepatitis, Autoimmune, Hepatitis B, Histoplasmosis, Immune Complex Test, Immunoelectrophoresis, Immunosuppressant Drugs, Legionnaires' Disease, Liver Transplantation, MALT Lymphoma, Multiple Myeloma, Prostate-Specific Antigen Test, Rheumatic Fever, Sore Throat, Streptococcal Antibody Tests, Throat Culture, Tissue Typing, Transfusion, Tuberculin Skin Test, Vasculitis, Waldenström's Macroglobulinemia

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antigen,

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

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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.

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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.

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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

see tolerogen.

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.