| trophoblastic tumour, placental site | A tumour that arises from the trophoblast of the placental bed and is composed mainly of cytotrophoblastic cells. It encompasses lesions of low- and high-grade malignancy. (holland et al., cancer medicine, 3d ed, p1691) (12 Dec 1998) |
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| expression site | The location in the genome of the gene for the variable surface glycoprotein that is currently being expressed (an expression-linked copy) by the trypanosome (a parasitic protozoan which causes the disease African sleeping sickness). most of these sites are near the ends, or telomeres, of a chromosome. (09 Oct 1997) |
| upstream activation site | A DNA sequence that regulates transcription like an enhancer but does notwork if its located downstream from a promoter. (09 Oct 1997) |
| fragile site | Places on chromosomes that tend to break more often than other places. These places also tend to be where chromosomal translocations (a type of chromosomal mutation) occur. (09 Oct 1997) |
| ligand binding site | The site on a protein's surface that binds a ligand; equivalent to the active site if the ligand is the substrate of an enzyme. (05 Mar 2000) |
| acetone-insoluble antigen | A diphosphatidyl glycerol that is found in the membrane of Treponema pallidum and is the antigen detected by the Wasserman test for syphilis. (18 Nov 1997) |
| allogeneic antigen | Genetic variations of the same antigens within a given species. (05 Mar 2000) |
| antigen | Virus coded cell surface antigens that appear soon after the infection of a cell by virus, but before virus replication has begun. See: early gene. (18 Nov 1997) |
| antigen-antibody complex | The complex formed by the binding of antigen and antibody molecules. The deposition of large antigen-antibody complexes leading to tissue damage causes immune complex diseases. If the antigen is polyvalent the complex may be insoluble. Immune complexes activate complement through the classical pathway. See: glomerulonephritis, Arthus reaction, type III hypersensitivity. (12 Dec 1998) |
| antigen-antibody reaction | The phenomenon, occurring in vitro or in vivo, of antibody combining with antigen of the type that stimulated the formation of the antibody, thereby resulting in agglutination, precipitation, complement fixation, greater susceptibility to ingestion and destruction by phagocytes, or neutralization of exotoxin. See: skin test. (05 Mar 2000) |
| antigen excess | In a precipitation test, the presence of uncombined antigen above that required to combine with all of the antibody; precipitation may be inhibited because the presence of excess antigen gives rise to soluble antigen-antibody complexes, in vivo the resultant antigen-antibody interaction in such an antigen excess may give rise to immune complexes, which have a potential to induce cellular damage; such injury underlies the pathologic changes seen in certain immune complex diseases. (05 Mar 2000) |
| antigen interferon | <cytokine> Interferon elaborated by T lymphocytes in response to either specific antigen or mitogenic stimulation. This type II interferon can be produced by recombinant DNA technology and is similar to the interferon secreted by lymphocytes and has antiviral and antineoplastic activity. Synonym: antigen interferon, immune interferon. Pharmacological action: antineoplastic agent, antiviral agents. (20 Sep 2002) |
| antigen p150,95 | A major adhesion-associated heterodimer molecule expressed by human monocytes, granulocytes, nk cells, and some lymphocytes. The alpha subunit is the CD11c antigen (also called leu-m5), a surface antigen expressed on some myeloid cells. The beta subunit is the CD18 antigen (antigens, CD18). The p150,95 antigen has been shown to play an important role in cell-cell and cell-substrate adhesive interactions. (12 Dec 1998) |
| antigen presentation | A cell that carries on its surface antigen bound to MCH Class I or Class II molecules and presents the antigen in this context to T-cells. Includes macrophages, endothelium, dendritic cells and Langerhans cells of the skin. See: MHC restriction, histocompatibility antigens. (18 Nov 1997) |
| antigen presenting cell | A cell that carries on its surface antigen bound to MCH Class I or Class II molecules and presents the antigen in this context to T-cells. Includes macrophages, endothelium, dendritic cells and Langerhans cells of the skin. See: MHC restriction, histocompatibility antigens. (18 Nov 1997) |