P Beta Entry prefix is given as 'beta'; alternatively look for the main portion of the word.

B7 Superfamily of co-stimulatory molecules that bind to CD28 or CTLA-4 and regulate T-cell responses. They are part of the immunoglobulin superfamily and have an extracellular Ig variable-like (IgV) and constant-like (IgC) domains. B7-1 is CD80, B7-2 is CD86. Other members are ICOS-L, B7-H1, B7-DC. Several B7 homologues are expressed on cells other than professional antigen-presenting cells.

B12 Vitamin B12. See Table V1.

B220 The mouse CD45R antigen, predominantly expressed on B-cells. See Table C2.

Babes-Ernst granules Metachromatic intracellular deposits of polyphosphate found in Corynebacterium diph-theriae when the bacteria are grown on suboptimal media. Stain reddish with methylene blue or toluidine blue.

Babesia Genus of protozoa that are found as parasites within red blood cells of mammals and are transmitted by ticks.

babesiosis Piroplasmosis Disease caused by infection with protozoa of the genus Babesia.

BAC library Bacterial artificial chromosome library Library constructed in a vector with an origin of replication that allows its propagation in bacteria as an extra chromosome. Advantageous in constructing genomic libraries with relatively large DNA fragments (100-300 kb). See also bacterial artificial chromosome.

Bac7 Proline- and arginine-rich antimicrobial peptide (7 kDa) isolated from bovine neutrophils. Bac-5 is similar. The upstream region of proBac-5 and proBac-7 both have sequence homology with similar regions of other neutrophil antimicrobial peptides (CAP18 from rabbit neu-trophils and bovine indolicidin). The pro-region also has similarity to porcine cathelin. Member of the protegrin family of peptides.

Bacille Calmette-Guerin An attenuated mycobac-terium derived from Mycobacterium tuberculosis. The bacterium is used in tuberculosis vaccination. Extracts of the bacterium have remarkable powers in stimulation of lymphocytes and leucocytes and are used in adjuvants.

Bacillus Cylindrical (rod-shaped) bacterium. Bacilli are usually 0.5-1.0 jm long, 0.3-1 jm wide.

Bacillus cereus A Gram-positive, facultatively aerobic spore-forming bacterium. B. cereus food poisoning is caused by two distinct metabolites; the diarrhoeal type of illness by a large molecular weight protein, the vomiting (emetic) type of illness by a low-molecular weight, heat-stable peptide.

Bacillus megaterium A Gram-positive, spore producing, rod-shaped bacterium found in the soil. It is one of the largest Eubacteria and is extensively used in biotechnology due to its size and cloning abilities. Enzymes produced by

B. megaterium are used in production of synthetic penicillin, modification of corticosteroids and include several amino acid dehydrogenases.

Bacillus thuringiensis Soil-living bacterium that produces a delta-endotoxin that is deadly to insects. Many strains exist, each with great specificity as to target Orders of insects. In general, the mode of action involves solubi-lization at high pH within the target insect's gut, followed by proteolytic cleavage; the activated peptides form pores in the gut cell apical plasma membranes, causing lysis of the cells. The toxin has been genetically engineered into various plant species (GM plants) to confer insect resistance, although many human consumers have perceived this as being unacceptable.

bacitracin Branched cyclic peptides produced by strains of Bacillus licheniformis. Interfere with murein peptido-glycan synthesis in Gram-positive bacteria.

baclofen y-Amino-^-(p-chlorophenyl) butyric acid Skeletal muscle relaxant, a derivative of GABA, used to relieve muscle spasm in trauma, multiple sclerosis and cerebral palsy. Selectively binds GABA-B receptor and inhibits release of other neurotransmitters in the CNS.

bactenecin Highly cationic polypeptides found in lysoso-mal granules of bovine neutrophil granulocytes. They are thought to be involved in bacterial killing and occur in a third class of granules, the large granules, not found in the neutrophils of most species.

bacteraemia Bacteremia (USA) The presence of living bacteria in the circulating blood; usually implies the presence of small numbers of bacteria that are transiently present without causing clinical effects, in contrast to septicaemia.

bacteria One of the two major classes of prokaryotic organisms (the other being the Cyanobacteria). Bacteria are small (linear dimensions of around 1 | m), non-compartmentalized, with circular DNA, and ribosomes of 70S. Protein synthesis differs from that of eukaryotes, and many anti bacterial antibiotics interfere with protein synthesis, but do not affect the infected host. Recently bacteria have been subdivided into Eubacteria and Archaebacte-ria, although some would consider the Archaebacteria to be a third kingdom, distinct from both Eubacteria and Eukary-otes. The Eubacteria can be further subdivided on the basis of their staining using Gram stain. Since the difference between Gram positive and Gram negative depends upon a fundamental difference in cell wall structure, it is therefore more soundly based than classification on gross morphology alone (into cocci, bacilli, etc.).

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