antigen-presenting cells

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an·ti·gen-·pre·sent·ing cells (APC),

cells that process protein antigens into peptides and present them on their surface in a form that can be recognized by lymphocytes. APCs include Langerhans cells, dendritic cells, macrophages, B cells, and, in humans, activated T cells.
Synonym(s): accessory cell

an·ti·gen-pre·sent·ing cells

(APC) (an'ti-jen-prĕ-zent'ing selz)
Cells that process protein antigens into peptides and present them on their surface in a form that can be recognized by lymphocytes. APCs include Langerhans cells, dendritic cells, macrophages, B cells, and in humans, activated T cells.
Synonym(s): accessory cell.


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 ?
Krummel calls the cells antigen-presenting CD103+ dendritic cells, and they make up fewer than 1 percent of all antigen-presenting cells, he said.
Ley said antigen-presenting cells take up infectious organisms, foreign materials and self-proteins (in the case of autoimmune diseases) and "chop them into little pieces called epitopes" and then display the pieces on the surface of the cell.
Chakraborty, a chemical engineer and biochemist by training, became interested in immunology after hearing about a paper on the immunological synapse, a crucial communications point for T cells and antigen-presenting cells.
TCI taps into the unique benefits of a major group of antigen-presenting cells found in the outer layers of the skin (Langerhans cells) to generate an enhanced immune response.
We have evidence that ethylmercury and thimerosal alter the signaling properties of antigen-presenting cells, known as dendritic cells, at nanomolar levels.
The vaccine is an autologous cellular product composed of antigen-presenting cells enriched from peripheral blood mononuclear cells obtained via leukapheresis.
The Ii protein normally blocks the antigenic peptide binding site of MHC Class II molecules at time of synthesis in the endoplasmic reticulum of antigen-presenting cells.
Targeted antigen delivery to antigen-presenting cells including dendritic cells by engineered Fas-mediated apoptosis.
To make sure that foreign antigens are identified, some B cells serve as antigen-presenting cells (or APCs), scooping up these fragments all over the body, and sailing around offering them on stick-like projections to the cells they pass.
But that has been because the peptides or viral particles used in the vaccines to provoke a response, when simply released into circulation, have not been taken up properly by antigen-presenting cells of the immune system.
But a more effective approach may be to block the recipient's antigen-presenting cells (APC), scavenger cells that actually trigger the T-lymphocyte attack.
16, will be based on the company's Vaccibody DNA vaccine platform, which targets antigen-presenting cells.