| lymphoid tissue | <anatomy> Tissue that is particularly rich in lymphocytes (and accessory cells such as macrophages and reticular cells), particularly the lymph nodes, spleen, thymus, Peyer's patches, pharyngeal tonsils, adenoids and (in birds) the Bursa of Fabricius. Central lymphoid tissue: A term occasionally used as synonym for primary lymphoid tissue but should be avoided to prevent confusion between anatomical location, which is irrelevant and centrality in the system. Peripheral lymphoid tissue: Secondary lymphoid tissue, not necessarily located peripherally. Primary lymphoid tissue: Lymphoid tissues in which immune cells develop as opposed to the secondary or peripheral lymphoid tissues in which antigen independent or antigen dependent stages of maturation take place and in which responsive lymphocytes are found. Primary lymphoid tissues are foetal liver, adult bone marrow and thymus (and Bursa of Fabricius in birds). Secondary tissues are lymph nodes, spleen, tonsils and mucosa associated lymphoid tissue. (20 Mar 1998) |
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| lymphoma, mucosa-associated lymphoid tissue | Extranodal lymphoma of lymphoid tissue associated with mucosa that is in contact with exogenous antigens. Many of the sites of these lymphomas, such as the stomach, salivary gland, and thyroid, are normally devoid of lymphoid tissue. They acquire malt tissue as a result of an immunologically mediated disorder. (12 Dec 1998) |
| 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-binding site | <immunology> In immune network theory, an idiotope, an antigenic site of an antibody that is responsible for that antibody binding to an antigenic determinant (epitope). Also used of the site on a ligand molecule to which a cell surface receptor binds. (18 Nov 1997) |
| antigen-combining site | See: paratope. (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) |
| 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) |