- Any substance that, as a result of coming in contact with appropriate cells, induces a state of sensitivity and/or immune responsiveness after a latent period (days to weeks) and that reacts in a demonstrable way with antibodies and/or immune cells of the sensitized subject in vivo or in vitro. Modern usage tends to retain the broad meaning of a., employing the terms “antigenic determinant” or “determinant group” for the particular chemical group of a molecule that confers antigenic specificity. SEE ALSO: hapten. SYN: immunogen. [anti(body) + G. -gen, producing]- Aus a. SYN: Australia a..- Australia a. so-called because it was first recognized in an Australian aborigine, but now known to be subunits of the hepatitis B virus surface a.. SYN: Au a. (2), Aus a..- Bile a. SYN: Bi a..- blood group a. generic term for any inherited a. found on the surface of erythrocytes that determines a blood group ing reaction with specific antiserum; antigens of the ABO and Lewis blood group s may be found also in saliva and other body fluids; the genes controlling development of blood group antigens vary in frequency in different population and ethnic group s. See also Blood Groups appendix. SYN: blood group substance.- CA-125 a. tumor marker elevated in 85% of women with advanced ovarian cancer. SEE ALSO: cancer a. 125 test.- capsular a. that found only in the capsules of certain microorganisms; e.g., the specific polysaccharides of various types of pneumococci.- carcinoembryonic a. (CEA) a glycoprotein constituent of the glycocalyx of embryonic endodermal epithelium, which may be elevated in the serum of some patients with colon and certain other cancers and in serum of chronic tobacco smokers.- C carbohydrate a. an a. found in the cell wall of Streptococcus species and denotes different strains. See β-hemolytic streptococci, under streptococcus.- class I antigens cell-membrane–bound glycoproteins found on most nucleated cells that are coded by genes of the major histocompatibility complex.- class II antigens a cell membrane glycoprotein encoded by genes of the major histocompatibility complex. These antigens are distributed on a.-presenting cells such as macrophages, B cells, and dendritic cells.- class III antigens non–cell-membrane molecules that are encoded by the S region of the major histocompatibility complex. These antigens are not involved in determining histocompatibility and include the complement proteins as well as certain cytokine genes i.e., tumor necrosis factors α and β.- common a. cross-reacting a. (epitope); a common a. that occurs in two or more different molecules or organisms.- complete a. any a. capable of stimulating the formation of antibody with which it reacts in vivo or in vitro, as distinguished from incomplete a. (hapten).- D a. one of 6 antigens that compose the Rh locus. Antibody induced by D a. is the most frequent cause of hemolytic disease of the newborn.- Dharmendra a. a chloroform-ether extracted suspension of Mycobacterium leprae; used to produce the Fernandez reaction in a lepromin test.- epithelial membrane a. (EMA) a heavily glycosylated, 70 kd protein complex, first isolated in human milk fat globulin; this a. is present in a variety of glandular epithelia, especially in breast carcinoma cells, but may also be seen in cultured fibroblasts, lymphoid cells, and some stromal cells. Immunohistochemical staining may be used as a diagnostic aid in tissue diagnosis.- flagellar a. the heat-labile antigens associated with bacterial flagella, in contrast to somatic a.. SEE ALSO: H a..- Forssman a. a type of heterogenetic a. found in dogs, horses, sheep, cats, turtles, eggs of some fish, in certain bacteria ( e.g., some strains of enteric organisms and pneumococci), and varieties of corn; usually found in the tissues and organs (not in blood), but is present in sheep erythrocytes, though not in this animal's tissues; with the exception of guinea pig s and hamsters, Forssman a. is not found in rodents, or in frogs, hogs, and most primates; the antibody that develops in infectious mononucleosis of humans reacts specifically with the Forssman. a..- G a. an antigenic glycoprotein frequently associated with viral surfaces. [Ger. gebundenes, bound]- Gerbich a. glycophorin C. See glycophorins.- Gm antigens allotypic determinants (antigens) that are present on the heavy chain of immunoglobulin G. There are 25 different determinants present throughout the human population.- H a. 1. the a. in the flagella of motile bacteria; important in serologic classification of enteric bacteria. SEE ALSO: O a. (1). 2. the chemical precursor of antigens of the ABO blood group locus.- H-2 antigens antigens that are coded by the H-2 complex of genes in mice and are involved in self/nonself recognition.- hepatitis-associated a. (HAA) a term used for the surface a. of hepatitis B virus before its nature was established. See hepatitis B surface a..- hepatitis B core a. (HBcAb, HBcAg) the a. found in the core of the Dane particle (which is the complete virus) and also in hepatocyte nuclei in hepatitis B infections.- hepatitis B e a. (HBeAb, HBe, HBeAg) an a., or group of antigens, associated with hepatitis B infection and distinct from the surface a. (HBsAg) and the core a. (HBcAg); it is associated with the viral nucleocapsid. Its presence indicates that the virus is replicating and the individual is potentially infectious.- hepatitis B surface a. (HBsAb, HBsAg) a. of the small (20 nm) spherical and filamentous forms of hepatitis B a., and a surface a. of the larger (42 nm) Dane particle (complete infectious hepatitis B virus). SEE ALSO: hepatitis B core a., hepatitis B e a..- heterogeneic a. heterophile a..- heterogenetic a. SYN: heterophile a..- heterophil a. SYN: heterophile a..- heterophile a. 1. an a. or antigenic determinant that is found in different tissues in more than one species. 2. an a. that is possessed by a variety of different phylogenetically unrelated species; e.g., the various organ- or tissue-specific antigens, the α- and β-crystalline protein of the lens of the eye, and Forssman a.. SYN: heterogenetic a., heterophil a..- histocompatibility a. an a. on the surface of nucleated cells, particularly leucocytes and thrombocytes. SEE ALSO: H-2 antigens. SYN: transplantation a..- HL-A antigens now obsolete, this was the original designation for human leukocyte histocompatibility antigens. The HLA histocompatibility system in humans is composed of MHC classes I, II, III. See major histocompatibility complex.- homologous a. the specific a. that generates the formation of an antibody that in turn can react with that a..- Hu antigens SYN: He antigens.- human leukocyte antigens (HLA) [MIM*142560] system designation for the gene products of at least four linked loci (A, B, C, and D) and a number of subloci on the sixth human chromosome that have been shown to have a strong influence on human allotransplantation, transfusions in refractory patients, and certain disease associations; more than 50 alleles are recognized, most of which are at loci HLA-A and HLA-B; autosomal dominant inheritance.- H-Y a. an a. factor, dependent on the Y chromosome, responsible for the differentiation of the human embryo into the male phenotype by inducing the initially bipotential embryonic gonad to develop into a testis; in the absence of this a., the indifferent gonad develops into an ovary. There are at least two loci involved, an autosomal gene that generates the a. [MIM*143170] and one that makes the receptor [MIM*143150].- incomplete a. SYN: hapten.- InV group a. SYN: Km a..- Km a. allotypic antigens that are present on human kappa immunoglobulin light chains. SYN: InV group a..- Kveim a. a saline suspension of human sarcoid tissue prepared from the spleen of an individual with active sarcoidosis; used in the Kveim test. SYN: Kveim-Siltzbach a..- Kveim-Siltzbach a. SYN: Kveim a..- leukocyte common a. (loo′ko-sit) family of glycoproteins found on most leukocytes and absent from other cell types. These cell surface antigens can comprise up to 10% of the membrane proteins.- lymphocyte function associated a. (LFA) (limf′o-sit) a member of the integrin family that is expressed on all leukocytes and binds to ICAM-1 and ICAM-2 on a variety of cells.- lymphogranuloma venereum a. a sterile preparation of inactivated chlamydiae grown in the yolk sac of domestic fowl and used as an a. in the Frei test.- Lyt antigens a group of alloantigens that are present on either T or B murine lymphocytes, e.g., Lyt 2,3 is equivalent to human CD8.- M a. an a. found in the cell of Streptococcus pyogenes; associated with virulence. See β-hemolytic streptococci, under streptococcus.- Mitsuda a. an autoclaved suspension of human tissue naturally infected with Mycobacterium leprae; used to produce the Mitsuda reaction in a lepromin test.- mumps skin test a. a sterile suspension of killed mumps virus in isotonic sodium chloride solution, used to determine susceptibility to mumps or to confirm previous exposure.- O a. 1. somatic a. of enteric Gram-negative bacteria. External part of cell wall lipopolysaccharide; SEE ALSO: H a. (1). 2. see ABO blood group, Blood Groups appendix.- oncofetal antigens tumor-associated antigens present in fetal tissue and some malignant tumors but not in normal adult tissue, including α-fetoprotein.- organ-specific a. a heterogenetic a. with organ specificity; e.g., in addition to species-specific a., kidney of one species contains a. that is identical to that in kidney of other species. SYN: tissue-specific a..- partial a. SYN: hapten.- pollen a. an extract of the antigenic protein from the pollen of plants; i.e., pollen allergen, used in the diagnosis and prevention of hay fever.- proliferating cell nuclear a. a nuclear nonhistone protein with a molecular weight of 36 kd that plays a role in the initiation of cell proliferation by augmenting DNA polymerase; stains for proliferating cell nuclear a. in tumors correlate with grade and mitotic activity.- prostate-specific a. (PSA) a single-chain, 31-kDa glycoprotein with 240 amino acid residues and 4 carbohydrate side-chains; a kallikrein protease produced by prostatic epithelial cells and normally found in seminal fluid and circulating blood. Elevations of serum PSA are highly organ-specific but occur in both cancer (adenocarcinoma) and benign disease (benign prostatic hyperplasia, prostatitis). A significant number of patients with organ-confined cancer have normal PSA values. SYN: human glandular kallikrein 3.Levels of PSA below 4 ng/dL are considered normal, while levels above 10 ng/dL are strongly indicative of prostatic carcinoma. Approximately 30% of patients with PSA levels between these limits will have prostate cancer detectable by biopsy within 1 year. Measurement of both free PSA and PSA that is complexed with the protease inhibitor α-1 antichymotrypsin (PSA-ACT) enhances the sensitivity of testing for carcinoma in men with total PSA levels between 4 and 10 ng/dL. The percentage of free PSA is lower in the serum of men with prostate cancer than in patients with normal prostates or benign disease. A level of free PSA that is 25% or more of total PSA in a patient with a palpably benign gland effectively rules out the need for prostatic biopsy when total PSA is below 10 ng/dL. A free PSA of 15% or less strongly suggests carcinoma. A level of 20% or more may be seen in adenocarcinoma when the prostate is enlarged. During the 1980s the increased use of PSA screening led to an apparent shift in the incidence of prostatic carcinoma, with proportionately more diagnoses in men under 70 and fewer in men over 70, and also a higher incidence of early or prostate-confined disease. This shift peaked in 1992; incidence statistics have now nearly returned to pre–PSA-screening levels. Prostatic cancer mortality has declined substantially since 1990. Many observers attribute this decline to the ability of PSA screening to detect cancer at a curable stage. However, the use of PSA testing as well as other diagnostic maneuvers to screen asymptomatic elderly men for prostate cancer is controversial, since most men with prostate cancer do not die of it, and to many observers the consequences of aggressive treatment, which may include urinary incontinence and impotence, seem worse than the disease.- R a. β-hemolytic streptococci, under streptococcus.- Rhus toxicodendron a. an extract of fresh leaves of poison ivy, with 0.4% of procaine hydrochloride; used by intradermal injection to determine sensitiveness to the poison of Rhus toxicodendron.- Rhus venenata a. an extract of fresh leaves of poison sumac; used to determine sensitiveness to the plant or to relieve the dermatitis caused by contact with its leaves.- S a. SYN: soluble a..- sensitized a. the complex formed when a. combines with specific antibody; so called because the a., by the mediation of antibody, is rendered sensitive to the action of complement.- shock a. an a. capable of producing anaphylactic shock in an animal that has been sensitized to it.- soluble a. viral a. that remains in solution after the particles of virus have been removed by means of centrifugation; in the case of the influenza viruses, it is the internal helical structure, free of the external envelope. SYN: S a..- somatic a. an a. located in the cell wall of a bacterium in contrast to one in the flagella (flagellar a.) or in a capsule (capsular a.).- species-specific a. antigenic components in the tissues and fluids of members of a species of animal, by means of which various species may be immunologically distinguished; e.g., serum albumin of horses is immunologically different from that of man, dogs, sheep, and so on.- Streptococcus M a. the somatic a. associated with virulence and type specificity of group A streptococci. It is antiphagocytic and there are more than 80 different types. SYN: M protein (1).- T antigens tumor antigens associated wtih replication and transformation by certain DNA tumor viruses, including adenoviruses and papovaviruses. SEE ALSO: β-hemolytic streptococci, under streptococcus, tumor antigens.- Tac a. an antigenic determinant of the human interleukin 2 receptor that is identified by a murine monoclonal antibody, anti-Tac. Binding of this a. with antibodies to TAC prevents the proliferation of T cells, which is normally stimulated by binding interleukin-2.- T-dependent a. an a. that requires T helper cells in addition to appropriate B cells. Most antigens are T-dependent.- theta a. (tha′ta) a surface glycoprotein that is present on thymocytes and mature T cells of mice and rats.- thymus-independent a. an a. that does not require T helper cell activation in order for the host's B cells to be stimulated. Repeating polymers such as polysaccharides are examples of T-independent antigens.- tumor antigens 1. antigens that may be frequently associated with tumors or may be specifically found on tumor cells of the same origin (tumor specific); 2. tumor antigens may also be associated with replication and transformation by certain DNA tumor viruses, including adenoviruses and papovaviruses. SYN: neoantigens. SEE ALSO: T antigens.- tumor-associated a. antigens that are highly correlated with certain tumor cells. They are not usually found, or are found to a lesser extent, on normal cells.- tumor-specific transplantation antigens (TSTA) surface antigens of DNA tumor virus-transformed cells, which elicit an immune rejection of the virus-free cells when transplanted into an animal that has been immunized against the specific cell-transforming virus.- V a. viral a. that is intimately associated with the virus particle, is protein in nature, has multiple antigenicities, and is strain-specific; antibody to such a. is demonstrable as protective or neutralizing antibody, such as hemagglutinin projections on surface of influenza virus.- Vi a. “virulence a.,” an external capsular a. of enterobacteria formerly thought to be related to increased virulence.
* * *an·ti·gen 'ant-i-jən n any substance (as an immunogen or a hapten) foreign to the body that evokes an immune response either alone or after forming a complex with a larger molecule (as a protein) and that is capable of binding with a product (as an antibody or T cell) of the immune responsean·ti·gen·ic .ant-i-'jen-ik adjan·ti·gen·i·cal·ly -i-k(ə-)lē adv
* * *n.any substance that may be specifically bound by an antibody molecule. In order to generate antibodies specific for small molecules, the latter are attached to a larger molecule before immunization. The small molecule is called a hapten; the larger molecule is called a carrier.• antigenic adj.
* * *an·ti·gen (anґtĭ-jən) [antibody + -gen] any substance 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 the portion of the protein or polysaccharide molecule known as the antigenic determinant (q.v.) combines with antibody or a specific receptor on a lymphocyte. Abbreviated Ag.
Medical dictionary. 2011.