| b | 1. Symbol for boron; for aspartic acid or asparagine when it is unclear which of the two amino acids is present; for bromouridine; second substrate in a multisubstrate enzyme-catalyzed reaction. 2. As a subscript, refers to barometric pressure. 3. In chemistry, denotes the second in a series, the second carbon from a functional (e.g., carboxylic) group, or the direction of a chemical bond toward the viewer. For terms having this prefix, see the specific term. (05 Mar 2000) |
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| b and t cell count | A test that measures the respective quantities of B lymphocytes and T lymphocytes. This test is often performed in the analysis of an immune deficiency disorder. Normal values include: 68 to 75% of total lymphocytes are T lymphocytes and 10 to 20% are B lymphocytes. Increased T-cell counts can indicate infectious mononucleosis, acute lymphocytic leukaemia or multiple myeloma. Increased B lymphocytes can indicate chronic lymphocytic leukaemia, multiple myeloma, Waldenstrom's macroglobulinaemia or Di George syndrome. Decreased T-cells may indicate congenital T-cell deficiency, Wiskott-Aldrich syndrome or AIDS. Decreased B-cells may indicate acute lymphocytic leukaemia or a congenital immunoglobulin deficiency disorder. (27 Sep 1997) |
| b c1 complex | <biochemistry> A part of the mitochondrial electron transport chain that accepts electrons from ubiquinone and passes them on to cytochrome C. The b/c1 complex consists of 2 cytochromes. (18 Nov 1997) |
| B chain | A polypeptide component of insulin containing 30 amino acyl residues, beginning with a phenylalanyl residue (NH2-terminus); insulin is formed by the linkage of a B chain to an A chain by two disulfide bonds; the amino-acid composition of the B chain is a function of species. Synonym: phenylalanyl chain. (05 Mar 2000) |
| B chromosome | <genetics> Small acentric chromosome, part of the normal genome of some races and species of plants. (18 Nov 1997) |
| B fibres | Myelinated fibre's autonomic nerves, with a diameter of 2 um or less, conducting at a rate of 3 to 15 m/sec. (05 Mar 2000) |
| b galactosidase | <enzyme> An enzyme that hydrolyzes the beta galactoside linkage in lactose-producing glucose and galactose; also hydrolyzes the chromogenic substrate IPTG (isopropylthiogalactoside) and thus is used as an indicator of fused genes and gene expression. (05 Mar 2000) |
| b haemolysin | See: b haemolysis. Bacterial haemolysin, any haemolytic agent elaborated by various species of bacteria, or by certain strains within a species. (05 Mar 2000) |
| b haemolysis | Complete or "true" haemolysis observed in blood agar cultures of various bacteria, especially haemolytic streptococci and staphylococci; virtually all of the erythrocytes are destroyed in a relatively wide, regularly circumscribed, circular zone about the colony, thereby resulting in a clear "halo" of transparent agar; the zone of haemolysis is frequently much wider than the diameter of the colony; the degree of change varies with species of erythrocytes, e.g., those of sheep and rabbits are usually more easily haemolyzed than those of man, and so on; the haemolysin acts extracellularly (in the absence of the bacterial cells) and may be quantitatively estimated by means of tube-dilution tests of a bacteria-free filtrate (containing the haemolytic substance) with a suspension of erythrocytes. (05 Mar 2000) |
| B lymphocyte | <haematology, immunology> An immunologically important lymphocyte, produced by the bone marrow, that is responsible for the production of immunoglobulins, it is the precursor of the plasma cell. The surface markers can be used to detect and differentiate chronic lymphocytic leukaemia from acute lymphocytic leukaemia. (13 Nov 1997) |
| b phage | b corynebacteriophage |
| B virus | A herpesvirus, in the family Herpesviridae, affecting Old World monkeys, that is very similar morphologically to herpes simplex virus; fatal infection may occur in humans following the bite of an infected monkey, although other modes of transmission have also been documented. Synonym: monkey B virus. (05 Mar 2000) |
| B-cell | <haematology, immunology> A type of lymphocyte normally involved in the production of antibodies to combat infection. It is a precursor to a plasma cell. During infections, individual B-cell clones multiply and are transformed into plasma cells, which produce large amounts of antibodies against a particular antigen on a foreign microbe. This transformation occurs through interaction with the appropriate CD4 T-helper cells. (09 Oct 1997) |
| B-cell antigen receptors | In the primary immune response immunoglobulin D and monomeric immunoglobulin M are the B-cell antigen receptors. On memory B-cells, other immunoglobulin molecules can serve as antigen receptors. (05 Mar 2000) |
| B-cell differentiating factor | <cytokine> A soluble cytokine factor produced by activated T-lymphocytes that promotes antibody production by causing proliferation and differentiation of B-cells. Interleukin-4 induces the expression of class II major histocompatibility complex and fc receptors on B-cells. It also acts on T-lymphocytes, mast cell lines, and several other haematopoietic lineage cells including granulocyte, megakaryocyte, and erythroid precursors, as well as macrophages. Acronym: IL-4 (12 Dec 1998) |