| antigen shift | Abrupt change in antigens expressed by a species or variety of organisms. Usually seen in microorganisms where the change may allow escape from immune recognition. Antigenic drift is a more gradual change. See: antigenic variation. (18 Nov 1997) |
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| antigen unit | The smallest amount of antigen that, in the presence of specific antiserum, will fix 1 complement unit. (05 Mar 2000) |
| aspergillus antigen skin test | <investigation> An antigen, prepared from aspergillus, is injected into the skin. In 48 to 72 hours the site is read as positive or negative. A positive skin test (inflammation at the test site) indicates prior exposure to aspergillus and therefore a risk for developing aspergillosis. (27 Sep 1997) |
| Au antigen | Auberger blood group |
| Aus antigen | <virology> An envelope antigen now known as HBsAg of Hepatitis B virus. Appearance of the antigen in serum is associated with a phase of high infectivity. (18 Nov 1997) |
| Australia antigen | <virology> An envelope antigen now known as HBsAg of Hepatitis B virus. Appearance of the antigen in serum is associated with a phase of high infectivity. (18 Nov 1997) |
| B-cell antigen receptors | In the primary immune response immunoglobulin D and monomeric immunoglobulin M are the B-cell antigen receptors. On memory B-cells, other immunoglobulin molecules can serve as antigen receptors. (05 Mar 2000) |
| becker antigen | bea antigen |
| blood group antigen | <haematology, immunology> The set of cell surface antigens found chiefly, but not solely, on blood cells. More than fifteen different blood group systems are recognised in humans. There may be naturally occurring antibodies without immunisation, especially in the case of the ABO system and matching blood groups is important for safe transfusion. In most cases the antigenic determinant resides in the carbohydrate chains of membrane glycoproteins or glycolipids. See: Rhesus, Duffy, Kell, Lewis and MN. (25 Jun 1999) |
| cancer antigen 125 test | Test for cell-surface antigen found on derivatives of coelomic epithelium. Elevated levels of this antigen are associated with ovarian malignancy and benign pelvic disease such as endometriosis. (05 Mar 2000) |
| capsular antigen | That found only in the capsules of certain microorganisms; e.g., the specific polysaccharides of various types of pneumococci. (05 Mar 2000) |
| carcinoembryonic antigen | <tumour marker> Antigen found in blood of patients suffering from cancer of colon and some other diseases, that is otherwise normally found in foetal gut tissue. (19 Jan 1998) |
| macrophage-1 antigen | An adhesion-promoting leukocyte surface membrane heterodimer. The alpha subunit consists of the CD11b antigen and the beta subunit of the CD18 antigen (antigens, CD18). The antigen, which is an integrin, functions both as a receptor for complement 3 and in cell-cell and cell-substrate adhesive interactions. (12 Dec 1998) |
| V antigen | Viral antigen that is intimately associated with the virus particle, is protein in nature, has multiple antigenicities, and is strain-specific; antibody to such antigen is demonstrable as protective or neutralizing antibody. (05 Mar 2000) |
| variable antigen | <immunology> Term usually applied to the surface antigens of those parasitic or pathogenic organisms that can alter their antigenic character to evade host immune responses. (See antigenic variation). (18 Nov 1997) |