| 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) |
|---|---|
| antigen-presenting cells | Immunocompetent cells, usually ia positive, that mediate the cellular immune response by processing and presenting antigens or mitogens which stimulate T-cell activation. (12 Dec 1998) |
| antigen processing | Modification of an antigen by accessory cells. This usually involves endocytosis of the antigen and either minimal cleavage or unfolding. The processed antigen is then presented in modified form by the accessory cell. (18 Nov 1997) |
| antigen-responsive cell | A small lymphocyte that, although not itself an immunologically activated cell, responds to antigenic (immunogenic) stimulus by a process of division and differentiation that results in the production of immunologically activated cells. Synonym: antigen-responsive cell. (05 Mar 2000) |
| antigen-sensitive cell | A small lymphocyte that, although not itself an immunologically activated cell, responds to antigenic (immunogenic) stimulus by a process of division and differentiation that results in the production of immunologically activated cells. Synonym: antigen-responsive cell. (05 Mar 2000) |
| 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) |
| 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 |
| 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) |