| macrophage activation | The process of altering the morphology and functional activity of macrophages so that they become avidly phagocytic. It is initiated by lymphokines, such as the macrophage activation factor (maf) and the macrophage migration-inhibitory factor (mmif), immune complexes, c3b, and various peptides, polysaccharides, and immunologic adjuvants. (12 Dec 1998) |
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| gene activation | The process of activation of a gene so that it is expressed at a particular time. This process is crucial in growth and development. (05 Mar 2000) |
| Gibbs energy of activation | The Gibbs energy that must be added to that already possessed by a molecule or molecules in order to initiate a reaction. (05 Mar 2000) |
| virus activation | The mechanism by which latent viruses, such as genetically transmitted tumour viruses or prophages of lysogenic bacteria, are induced to replicate and are released as infectious viruses. It may be effected by various endogenous and exogenous stimuli, including B-cell lipopolysaccharides, glucocorticoid hormones, halogenated pyrimidines, ionizing radiation, ultraviolet light, and superinfecting viruses. (12 Dec 1998) |
| cis activation | <molecular biology> Activation of a gene by an activator located on the same chromosome i.e. Not by a diffusible product. (18 Nov 1997) |
| complement activation | The sequential activation of serum components c1 through c9, initiated by an erythrocyte-antibody complex or by microbial polysaccharides and properdin, and producing an inflammatory response. (12 Dec 1998) |
| platelet activation | A series of progressive, overlapping events triggered by exposure of the platelets to subendothelial tissue. These events include shape change, adhesiveness, aggregation, and release reactions. When carried through to completion, these events lead to the formation of a stable haemostatic plug. (12 Dec 1998) |
| neutron activation analysis | Activation analysis in which the specimen is bombarded with neutrons. Identification is made by measuring the resulting radioisotopes. (12 Dec 1998) |
| neutrophil activation | The process in which the neutrophil is stimulated by diverse substances, resulting in degranulation and/or generation of reactive oxygen products, and culminating in the destruction of invading pathogens. The stimulatory substances, including opsonised particles, immune complexes, and chemotactic factors, bind to specific cell-surface receptors on the neutrophil. (12 Dec 1998) |
| EEG activation | The low voltage, fast pattern of attentive wakefulness. (05 Mar 2000) |
| trans-activation (genetics) | Increased rate of gene expression directed by either viral or cellular proteins. These regulatory factors (diffusible gene products) act in trans -- that is, act on homologous or heterologous molecules of DNA. (cis-acting factors act only on homologous molecules.) (12 Dec 1998) |
| energy of activation | Energy that must be added to that already possessed by a molecule or molecules in order to initiate a reaction; usually expressed in the Arrhenius equation relating a rate constant to absolute temperature. (05 Mar 2000) |
| enzyme activation | Conversion of an inactive form of an enzyme to one possessing metabolic activity. It includes 1) activation by ions (activators); 2) activation by cofactors (coenzymes); and 3) conversion of an enzyme precursor (proenzyme or zymogen) to an active enzyme. (12 Dec 1998) |
| juxtacrine activation | Activation of target cells by membrane anchored growth factors, also used for activation of leucocytes by PAF bound to endothelial cell surface. (18 Nov 1997) |
| feedback activation | The activation of an enzyme by an end product of a biochemical pathway in which that enzyme plays a part. For example, the activation of factors VIII and V by thrombin during blood clotting. (05 Mar 2000) |