| 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) |
|---|---|
| antigenaemia | Persistence of antigen in circulating blood; e.g., HBs-antigenaemia (presence of hepatitis B virus surface antigen in blood serum). Origin: antigen + G. Haima, blood (05 Mar 2000) |
| antigenic | Having the properties of an antigen (allergen). Synonym: allergenic, immunogenic. (05 Mar 2000) |
| antigenic competition | Competition that occurs when two different antigens, each of which can evoke an immunological response when inoculated alone, are mixed in equal quantities and inoculated together; the response may be to only one, that to the other being largely or entirely suppressed. (05 Mar 2000) |
| antigenic complex | A composite of different antigenic structures, such as a cell or a bacterium, or, by extension, a molecule containing two or more determinant groups of different antigenic specificities. (05 Mar 2000) |
| antigenic determinant | That part of an antigenic molecule against which a particular immune response is directed. For instance a tetra to penta peptide sequence in a protein, a tri to penta glycoside sequence in a polysaccharide. In the animal most antigens will present several or even many antigenic determinants simultaneously. See: hapten. (18 Nov 1997) |
| antigenic drift | <immunology> A change that occurs on the molecular level to effect a change in the antigenicity of a bacteria or virus. Antigenic drift occurs naturally and more rapidly in certain viruses (for example HIV). It is antigenic drift which complicates the development of an effective HIV (AIDS) vaccine. (27 Sep 1997) |
| antigenic modulation | Loss of detectable antigen from the surface of a cell after incubation with antibodies. This is one method in which some tumours escape detection by the immune system. Antigenic modulation of target antigens also reduces the therapeutic effectiveness of treatment by monoclonal antibodies. (12 Dec 1998) |
| antigenic shift | Mutation, i.e., sudden change in molecular structure of RNA/DNA in microorganisms, especially viruses, which produces new strains of the microorganism; hosts previously exposed to other strains have little or no acquired immunity to the new strain; antigenic shift is believed to be the explanation for the occurrence of strains of microorganisms, such as the influenza virus, associated with large scale epidemics. (05 Mar 2000) |
| antigenic switching | <immunology> The process by which a pathogenic microbe's genetic structure is altered tochange its surface antigens inorder to avoid being detected by the host's immune system. (09 Oct 1997) |
| antigenic variation | The phenomenon of changes in surface antigens in parasitic populations of Trypanosoma and Plasmodium (and some other parasitic protozoa) in order to escape immunological defense mechanisms. at least 100 different surface proteins have been found to appear and disappear during antigenic variation in a clone of trypanosomes. Each antigen is encoded in a separate gene. Antigenic variation is also known to occur in free living Protozoa and certain bacteria. (18 Nov 1997) |
| antigenicity | <immunology> The ability of a substance to trigger an immune response in a particularorganism. (09 Oct 1997) |
| antigens | Substances which are capable, under appropriate conditions, of inducing a specific immune response and of reacting with the products of that response, that is, with specific antibodies or specifically sensitised T-lymphocytes, or both. Antigens may be soluble substances, such as toxins and foreign proteins, or particulates, such as bacteria and tissue cells; however, only the portion of the protein or polysaccharide molecule known as the antigenic determinant (epitopes) combines with antibody or a specific receptor on a lymphocyte. (12 Dec 1998) |
| antigens, archaeal | Substances of archaeal origin that have antigenic activity. (12 Dec 1998) |
| antigens, bacterial | Substances elaborated by bacteria that have antigenic activity. (12 Dec 1998) |
| G antigen | An antigenic glycoprotein frequently associated with viral surfaces. Origin: Ger. Gebundenes, bound (05 Mar 2000) |
|---|---|
| major histocompatibility antigen | <immunology> A set of plasmalemmal glycoprotein antigens involved in rapid (e.g. 7 days in the mouse) graft rejection and other immune phenomena. The minor histocompatibility antigens are involved in much slower rejection phenomena. The major antigens show remarkable polymorphism and occur as Class I and Class II types in mammals, birds may have a Class III molecule as well. See: histocompatibility antigens, MHC restriction. (18 Nov 1997) |
| P antigen | <haematology, immunology> Antigenic determinant on the surface of human red blood cells to which the Donath Landsteiner antibody reacts. This antibody binds in the cold (a cold IgG), but elutes from red cells at 37쵣, is particularly associated with tertiary syphylis and its binding causes paroxysmal nocturnal haemoglobinuria. (18 Nov 1997) |
| R antigen | Those that produce active haemolysins (O and S) which cause a zone of clear haemolysis on the blood agar medium in the area of the colony; beta-haemolytic streptococci are divided into groups (A to O) on the basis of cell wall C carbohydrate (see Lancefield classification); Group A (in the strains pathogenic for man) comprises more than 50 types (designated by Arabic numerals) determined by cell wall M protein, which seems to be associated closely with virulence and is produced chiefly by strains with matt or mucoid colonies, in contrast to nonvirulent, glossy colony-producing strains; other surface protein antigens such as R and T (T substance), and the nucleoprotein fraction (P substance) seem to be of less importance. The more than 20 extracellular substances elaborated by strains of beta-haemolytic streptococci include erythrogenic toxin (elaborated only by lysogenic strains), deoxyribonuclease (streptodornase), haemolysins (streptolysins O and S), hyaluronidase, and streptokinase. Synonym: haemolytic streptococci. (05 Mar 2000) |
| gene rearrangement, alpha-chain T-cell antigen receptor | Ordered rearrangement of T-cell variable gene regions coding for the alpha-chain of antigen receptors. (12 Dec 1998) |
| gene rearrangement, beta-chain T-cell antigen receptor | Ordered rearrangement of T-cell variable gene regions coding for the beta-chain of antigen receptors. (12 Dec 1998) |
| gene rearrangement, delta-chain T-cell antigen receptor | Ordered rearrangement of T-cell variable gene regions coding for the delta-chain of antigen receptors. (12 Dec 1998) |
| gene rearrangement, gamma-chain T-cell antigen receptor | Ordered rearrangement of T-cell variable gene regions coding for the gamma-chain of antigen receptors. (12 Dec 1998) |
| M antigen | An antigen found in the cell of Streptococcus pyogenes; associated with virulence. See: beta-haemolytic streptococci. (05 Mar 2000) |
| receptor-CD3 complex, antigen, T-cell | Molecule composed of the non-covalent association of the T-cell antigen receptor (receptors, antigen, T-cell) with the CD3 complex (antigens, CD3). This association is required for the surface expression and function of both components. The molecule consists of up to seven chains: either the alpha/beta or gamma/delta chains of the T-cell receptor, and four or five chains in the CD3 complex. (12 Dec 1998) |
| receptors, antigen | Molecules on the surface of b- and T-lymphocytes that recognise and combine with specific antigens. (12 Dec 1998) |
| receptors, antigen, B-cell | Immunoglobulin molecules on the surface of B-lymphocytes that recognise and bind antigen. (12 Dec 1998) |
| receptors, antigen, T-cell | Molecules on the surface of T-lymphocytes that recognise and combine with antigens. The receptors are non-covalently associated with a complex of several polypeptides collectively called CD3 antigens (antigens, CD3). Recognition of foreign antigen and the major histocompatibility complex is accomplished by a single heterodimeric antigen-receptor structure, composed of either alpha-beta (receptors, antigen, T-cell, alpha-beta) or gamma-delta (receptors, antigen, T-cell, gamma-delta) chains. (12 Dec 1998) |
| receptors, antigen, T-cell, alpha-beta | T-cell receptors composed of CD3-associated alpha and beta polypeptide chains and expressed primarily in CD4+ or CD8+ T-cells. Unlike immunoglobulins, the alpha-beta T-cell receptors recognise antigens only when presented in association with major histocompatibility (MHC) molecules. (12 Dec 1998) |
| receptors, antigen, T-cell, gamma-delta | T-cell receptors composed of CD3-associated gamma and delta polypeptide chains and expressed primarily in CD4-/CD8- T-cells. The receptors appear to be preferentially located in epithelial sites and probably play a role in the recognition of bacterial antigens. The T-cell receptor gamma/delta chains are separate and not related to the gamma and delta chains which are subunits of CD3 (see antigens, CD3). (12 Dec 1998) |