Model for population distributions of lymphocyte-target cell conjugates

A quantitative model for the population distributions of the different types of conjugates formed between cytotoxic T lymphocytes and target cells has been developed. The comparison of the theoretical predictions with data of the literature reveals that the transit populations among the different types of conjugates depends on the lymphocyte-to-target ratio, R, and two constants, k and k1. These constants (where k greater than k1) govern, respectively, the transit populations among conjugates of the type LTi (LTn----LTn-1----...LT), and among LjT conjugates (LT----L2T----...----LmT). We have found that high ratios are necessary to obtain conjugates where multiple T lymphocytes are bound to one target cell, and that under these conditions the predominant conjugate, LjT, varies according to j = 1 + k1R. Conversely, for low values of R the predominant population is of the type LTi, where i also shows a linear dependence on R. Our model explains also why the conjugate LT is normally the predominant population under the experimental conditions reported in the literature. A discussion of the influence exerted by the population distributions of lymphocyte-target cell conjugates on the kinetic of the lytic process for these kinds of effector-target systems has also been made.     

Intracellular amorphous Ca-carbonate and magnetite biomineralization by a magnetotactic bacterium affiliated to the Alphaproteobacteria

Bacteria synthesize a wide range of intracellular submicrometer-sized inorganic precipitates of diverse chemical compositions and structures, called biominerals. Their occurrences, functions and ultrastructures are not yet fully described despite great advances in our knowledge of microbial diversity. Here, we report bacteria inhabiting the sediments and water column of the permanently stratified ferruginous Lake Pavin, that have the peculiarity to biomineralize both intracellular magnetic particles and calcium carbonate granules. Based on an ultrastructural characterization using transmission electron microscopy (TEM) and synchrotron-based scanning transmission X-ray microscopy (STXM), we showed that the calcium carbonate granules are amorphous and contained within membrane-delimited vesicles. Single-cell sorting, correlative fluorescent in situ hybridization (FISH), scanning electron microscopy (SEM) and molecular typing of populations inhabiting sediments affiliated these bacteria to a new genus of the Alphaproteobacteria. The partially assembled genome sequence of a representative isolate revealed an atypical structure of the magnetosome gene cluster while geochemical analyses indicate that calcium carbonate production is an active process that costs energy to the cell to maintain an environment suitable for their formation. This discovery further expands the diversity of organisms capable of intracellular Ca-carbonate biomineralization. If the role of such biomineralization is still unclear, cell behaviour suggests that it may participate to cell motility in aquatic habitats as magnetite biomineralization does.Subject terms: Phylogenetics, Biodiversity, Biogeochemistry, Water microbiology     

Identification and mapping of Lm-1, an Igh-linked locus for a murine alloantigen

Analyzing Igh congenic, Igh recombinant, and recombinant inbred mouse strains with a cytotoxic T-cell assay, we have identified and mapped an Igh-linked locus (Lm-1) that codes for a cell-surface alloantigen (Lm-1). Lm-1 maps 5 units telomeric to Pre-1 and is genetically distinct from previously described Igh-linked loci. The importance of Lm-1 and its possible relationship to other Igh-linked alloantigens is discussed.Abbreviations used in this paper CTL cytotoxic T lymphocytes - LPS lipopolysaccharide - HBSS Hanks' balanced salt solution - CFA complete Freund's adjuvant - E : T effector-to-target ratio - %SL percent specific lysis     

Entwicklung und Polyploidie in der Veronica-Gruppe Agrestis

Ohne ZusammenfassungMit 18 Textabbildungen.     

Regulatory mutations that allow the growth ofEscherichia coli on butanol as carbon source

Summary Starting withadhC mutants ofEscherichia coli in which alcohol dehydrogenase (ADH) and acetaldehyde CoA dehydrogenase (ACDH) are expressed constitutively at high levels, we selected mutants with still higher levels of both enzymes. Selection for growth on ethanol in the presence of inhibitors of ADH gave several mutants that had from 2- to 10-fold increases in the levels of both enzymes. These mutations were found to map far from theadhC locus at around 90 min. SuchadhR mutants were unable to grow on acetate or ethanol in certain media unless supplemented with extramanganese. This growth disability was suppressed by secondary mutations, one of which,aceX, increased sensitivity to several toxic metals and may perhaps derepress Mn transport. When theadhR mutation expressing the highest ADH and ACDH levels was present together withfadR andatoC mutations (allowing efficient catabolism of acetoacetyl-CoA) and with anaceX mutation, the resulting strains became capable of usingn-butanol as sole carbon and energy source. The use of butanol byE. coli illustrates the artificial evolution of a new catabolic pathway, in this case by the selection of four successive regulatory mutations (fadR, adhC, atoC, andadhR) together with the poorly definedaceX mutation. Each stage in the acquisition of this nove pathway confers the ability to use a new growth substrate: decanoic acid (fadR), ethanol (adhC), butyric acid (atoC), and butanol (adhR, when present withaceX).     

Inhibition of sulfation of phenols in vivo by 2,6-dichloro-4-nitrophenol: selectivity of its action in relation to other conjugations in the rat in vivo

The effect of 2,6-dichloro-4-nitrophenol, an inhibitor of the sulfation of the phenolic compound harmol in vivo, on the sulfation of other phenolic substances and on various conjugation reactions has been studied in the rat in vivo. Compounds chemically related to 2,6-dichloro-4-nitrophenol were also tested as sulfation inhibitors. 2,6-Dichloro-4-nitrophenol inhibited the sulfation of phenol while it had no effect on biliary excretion of dibromosulphthalein, glucuronidation of phenolphthalein, acetylation of procainamide ethobromide or glutathione conjugation of ethacrynic acid. It is concluded that of these conjugation reactions sulfation is inhibited selectively at the dose level used. Some phenols with chloro- or nitro-substituents effectively inhibited the sulfation of harmol but to a lesser extent than 2,6-dichloro-4-nitrophenol. Many other phenols did not affect the conjugation of harmol, which is both glucuronidated and sulfated.