CD antigen

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

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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 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).

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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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 by their cluster of differentiation, as in CD1, CD2, etc.

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CD²

cluster of differentiation or cell differentiation glycoproteins.

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CD antigen

a group of cell surface molecules which act as markers on T lymphocytes.

CD3

found on T helper (Th) and T cytotoxic (Tc) lymphocytes; associated with signal transduction.

CD4

found on T helper lymphocytes; an adhesion molecule that binds to class II MHC molecules.

CD8

found on T cytotoxic and variably on NK lymphocytes; an adhesion molecule that binds to class I MHC molecules.