natural purification (자정 작용
| natural language processing | Computer processing of a language with rules that reflect and describe current usage rather than prescribed usage. (12 Dec 1998) |
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| natural mutation | A mutation which occurs by itself without first being affected by a mutagen, for example during the process of DNA replication. Spontaneous mutations arise at a remarkably constant rate. The rate that spontaneous mutations arise has been used as an evolutionary clock to estimate how closely related two (or more) separate species are to each other. (09 Oct 1997) |
| natural passive immunity | Immunity conferred by the mother on the foetus or newborn. (14 Nov 1997) |
| natural pigment | A naturally occurring coloured compound; absorbs light in the visible range of the electromagnetic spectrum. Compare: structural colour. Synonym: biochrome. (05 Mar 2000) |
| natural products | Naturally occurring compounds that are end products of secondary metabolism; often, they are unique compounds for particular organisms or classes of organisms. (05 Mar 2000) |
| natural selection | The hypothesis that genotype environment interactions occurring at the phenotypic level lead to differential reproductive success of individuals and hence to modification of the gene pool of a population. (18 Nov 1997) |
| immunity, natural | The capacity of a normal organism to remain unaffected by microorganisms and their toxins. It results from non-specific mechanisms such as genetic endowment, naturally occurring antiviral and bactericidal substances, phagocytosis, and constitutional factors such as body temperature, oxygen tension, and age. (12 Dec 1998) |
| killer cells, natural | Cells responsible for spontaneous cytotoxicity of a variety of tumour cells without prior immunization. These natural killer cells are found in non-immune humans and experimental animals and are thought by some to be the same as killer cells (killing by antibody-dependent cell cytotoxicity), but they can also kill in the absence of antibody. (12 Dec 1998) |
| accidental host | One that harbors an organism which usually does not infect it. (05 Mar 2000) |
| amplifier host | A host in which infectious agents multiply rapidly to high levels, providing an important source of infection for vectors in vector-borne diseases. (05 Mar 2000) |
| parasite-host ecosystem | Complex of all parasite species and individuals associated with a specific host. Synonym: parasite-host ecosystem. Origin: parasite + G. Koinos, common, together (05 Mar 2000) |
| paratenic host | An intermediate host in which no development of the parasite occurs, although its presence may be required as an essential link in the completion of the parasite's life cycle; e.g., the successive fish host's that carry the plerocercoid of Diphyllobothrium latum, the broad fish tapeworm, to larger food fish eventually eaten by man or other final host's. Synonym: transport host. (05 Mar 2000) |
| reservoir host | The host of an infection in which the infectious agent multiplies and/or develops, and upon which the agent is dependent for survival in nature; the host essential for the maintenance of the infection during times when active transmission is not occurring. (05 Mar 2000) |
| graft-versus-host disease | <haematology> A common and serious, complication of bone marrow transplantation where there is a reaction of donated bone marrow against a patient's own tissue. When donor lymphocytes or a graft containing lymphocytes that are immunologically competent are given to a patient that has low immunological competence, an incompatibility reaction can result. This is due to antibodies from the donor against antigens in the host. This is due to mismatch of MHC Class I antigens and can produce lymphocyte clones that will react by a variety of processes against the host and cause damage. The clinical condition can be fatal and is due to the donor's immune cells recognising the host cells as foreign. The clinical entity characterised by anorexia, diarrhoea, loss of hair, leukopenia, thrombocytopenia, growth retardation, and eventual death brought about by the graft-versus-host reaction. It can occur in either chronic or acute forms and is treatable by immunosuppressive drugs. Seen most commonly following bone marrow transplantation, acute disease is seen after 5-40 days and chronic disease weeks to months after transplantation, affecting, principally, the gastrointestinal tract, liver, and skin. Radiological appearances of the gastrointestinal tract include; thickened wall, mucosal folds thickened or effaced, increased secretions most likely to be rapid transit of GI tract, mass most likely to be focal oedema, fibrosis, hallmark: diffuse, uniform thickening of small bowel. Synonym: GVH disease. Acronym: GVHD (20 Sep 2002) |
| graft-versus-host reaction | <haematology> A common and serious, complication of bone marrow transplantation where there is a reaction of donated bone marrow against a patient's own tissue. When donor lymphocytes or a graft containing lymphocytes that are immunologically competent are given to a patient that has low immunological competence, an incompatibility reaction can result. This is due to antibodies from the donor against antigens in the host. This is due to mismatch of MHC Class I antigens and can produce lymphocyte clones that will react by a variety of processes against the host and cause damage. The clinical condition can be fatal and is due to the donor's immune cells recognising the host cells as foreign. The clinical entity characterised by anorexia, diarrhoea, loss of hair, leukopenia, thrombocytopenia, growth retardation, and eventual death brought about by the graft-versus-host reaction. It can occur in either chronic or acute forms and is treatable by immunosuppressive drugs. Seen most commonly following bone marrow transplantation, acute disease is seen after 5-40 days and chronic disease weeks to months after transplantation, affecting, principally, the gastrointestinal tract, liver, and skin. Radiological appearances of the gastrointestinal tract include; thickened wall, mucosal folds thickened or effaced, increased secretions most likely to be rapid transit of GI tract, mass most likely to be focal oedema, fibrosis, hallmark: diffuse, uniform thickening of small bowel. Synonym: GVH disease. Acronym: GVHD (20 Sep 2002) |