| histocompatibility antigens class II | Large, transmembrane, non-covalently linked glycoproteins (alpha and beta). Both chains can be polymorphic although there is more structural variation in the beta chains. The class II antigens in humans are called HLA-d antigens and are coded by a gene on chromosome 6. In mice, two genes named ia and i.e. On chromosome 17 code for the h-2 antigens. The antigens are found on B-lymphocytes, macrophages, epidermal cells, and sperm and are thought to mediate the competence of and cellular cooperation in the immune response. The term ia antigens used to refer only to the proteins encoded by the ia genes in the mouse, but is now used as a generic term for any class II histocompatibility antigen. (12 Dec 1998) |
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| social class | A stratum of people with similar position and prestige; includes social stratification. Social class is measured by criteria such as education, occupation, and income. (12 Dec 1998) |
| stream class | Classification of streams based on the present and foreseeable uses made of the water, and the potential effects of on-site changes on downstream uses. Four classes are defined (05 Dec 1998) |
| immunoglobulin class switching | Gene rearrangement of the b-lymphocyte which results in a substitution in the type of heavy-chain constant region that is expressed. This allows the effector response to change while the antigen binding specificity (variable region) remains the same. The majority of class switching occurs by a DNA recombination event but it also can take place at the level of RNA processing. (12 Dec 1998) |
| first-class | Of the best class; of the highest rank; in the first division; of the best quality; first-rate; as, a first-class telescope. First-class car or First-class railway carriage, any passenger car of the highest regular class, and intended for passengers who pay the highest regular rate; distinguished from a second-class car. Source: Websters Dictionary (01 Mar 1998) |