Role of prostaglandin E2 in the induction of nonspecific T lymphocyte suppressor activity

Activated human monocytes and concanavalin A (Con A)-activated T lymphocytes are known to suppress T and B lymphocyte proliferation and B cell maturation into immunoglobulin-producing cells. We have now shown that monocyte suppressive activity is predominantly mediated through release of prostaglandin E2 (PGE2), which is active only in the presence of a "short-lived," radiosensitive T lymphocyte subset. PGE2, at high concentration, can activate T suppressor lymphocytes (TS), which display the same characteristics as Con A-activated TS lymphocytes. Moreover, Con A activation of TS lymphocytes was obtained only in the presence of PGE2, as specific anti-PGE2 antiserum or indomethacin prevented TS activation; this suggested a double signal as a prerequisite for activation of the nonspecific TS cell subset. We propose that TS lymphocytes modified by Con A become sensitive to small amounts of PGE2 produced by monocytes that must be present during the Con A-stimulated activation phase of suppressive cells.     

The N-terminal extension of the ADP/ATP translocator is not involved in targeting to plant mitochondria in vivo

The mitochondrial ADP/ATP translocator, also called adenine nucleotide translocase (ANT), is synthesized in plants with an N-terminal extension which is cleaved upon import into mitochondria. In contrast, the homologous proteins of mammals or fungi do not contain such a transient amino terminal presequence. To investigate whether the N-terminal extension is needed for correct intracellular sorting in vivo , translational fusions were constructed of the translocator cDNA—with and without presequence—with the β-glucuronidase ( gus ) reporter gene. The distribution of reporter enzymatic activity in the subcellular compartments of transgenic plants and transformed yeast cells was subsequently analysed. The results show that: (i) the plant translocator presequence is not necessary for the correct localization of the ANT to the mitochondria; (ii) the mitochondrial targeting information contained in the mature part of the protein is sufficient to overcome, to some extent, the presence of plastid transit peptides; and (iii) the presequence alone is not able to target a passenger protein to mitochondria in vivo .     

A model of stress and strain in the interosseous ligament of the forearm based on fiber network theory

Fiber network theory was developed to describe cloth, a thin material with strength in the fiber directions. The interosseous ligament (IOL) of the forearm is a broad, thin ligament with highly aligned fibers. The objectives of this study were to develop a model of the stress and strain distributions in the IOL, based on fiber network theory, to compare the strains from the model with the experimentally measured strains, and to evaluate the force distribution across the ligament fibers from the model. The geometries of the radius, ulna, and IOL were reconstructed from CT scans. Position and orientation of IOL insertion sites and force in the IOL were measured during a forearm compression experiment in pronation, neutral rotation, and supination. An optical image-based technique was used to directly measure strain in two regions of the IOL in neutral rotation. For the network model, the IOL was represented as a parametric ruled three-dimensional surface, with rulings along local fiber directions. Fiber strains were calculated from the deformation field, and fiber stresses were calculated from the strains using average IOL tensile properties from a previous study. The in situ strain in the IOL was assumed uniform and was calculated so that the net force predicted by the network model in neutral rotation matched the experimental result. The net force in the IOL was comparable to experimental results in supination and pronation. The model predicted higher stress and strain in fibers near the elbow in neutral rotation, and higher stresses in fibers near the wrist in supination. Strains in neutral forearm rotation followed the same trends as those measured experimentally. In this study, a model of stress and strain in the IOL utilizing fiber network theory was successfully implemented. The model illustrates variations in the stress and strain distribution in the IOL. This model can be used to show surgeons how different fibers are taut in different forearm rotation positions-this information is important for understanding the biomechanical role of the IOL and for planning an IOL reconstruction.     

Ordination of breeding birds in relation to environmental gradients in three southeastern United States floodplain forests

We used an ordination approach to identify factors important to the organization of breeding bird communities in three floodplains: Cache River, Arkansas (AR), Iatt Creek, Louisiana (LA), and the Coosawhatchie River, South Carolina (SC), USA. We used 5-min point counts to sample birds in each study area each spring from 1995 to 1998, and measured ground-surface elevations and a suite of other habitat variables to investigate bird distributions and community characteristics in relation to important environmental gradients. In both AR and SC, the average number of Neotropical migrant species detected was lowest in semipermanently flooded Nyssa aquatica Linnaeus habitats and greatest in the highest elevation floodplain zone. Melanerpes carolinus Linnaeus, Protonotaria citrea Boddaert, Quiscalus quiscula Linnaeus, and other species were more abundant in N. aquatica habitats, whereas Wilsonia citrina Boddaert, Oporornis formosus Wilson, Vireo griseus Boddaert, and others were more abundant in drier floodplain zones. In LA, there were no significant differences in community metrics or bird species abundances among forest types. Canonical correspondence analyses revealed that structural development of understory vegetation was the most important factor affecting bird distributions in all three study areas; however, potential causes of these structural gradients differed. In AR and SC, differences in habitat structure were related to the hydrologic gradient, as indexed by ground-surface elevation. In LA, structural variations were related mainly to the frequency of canopy gaps. Thus, bird communities in all three areas appeared to be organized primarily in response to repeated localized disturbance. Our results suggest that regular disturbance due to flooding plays an important role in structuring breeding bird communities in floodplains subject to prolonged inundation, whereas other agents of disturbance (e.g., canopy gaps) may be more important in headwater systems subject to only short-duration flooding. Management for avian community integrity in these systems should strive to maintain forest zonation and natural disturbance regimes.     

Production of an active recombinant thrombomodulin derivative in transgenic tobacco plants and suspension cells

Thrombomodulin is a membrane-bound protein that plays an active role in the blood coagulation system by binding thrombin and initiating the protein C anticoagulant pathway. Solulin™ is a recombinant soluble derivative of human thrombomodulin. It is used for the treatment of thrombotic disorders. To evaluate the production of this pharmaceutical protein in plants, expression vectors were generated using four different N-terminal signal peptides. Immunoblot analysis of transiently transformed tobacco leaves showed that intact Solulin™ could be detected using three of these signal peptides. Furthermore transgenic tobacco plants and BY2 cells producing Solulin™ were generated. Immunoblot experiments showed that Solulin™ accumulated to maximum levels of 115 and 27 μg g⁻¹ plant material in tobacco plants and BY2 cells, respectively. Activity tests performed on the culture supernatant of transformed BY2 cells showed that the secreted Solulin™ was functional. In contrast, thrombomodulin activity was not detected in total soluble protein extracts from BY2 cells, probably due to inhibitory effects of substances in the cell extract. N-terminal sequencing was carried out on partially purified Solulin™ from the BY2 culture supernatant. The sequence was identical to that of Solulin™ produced in Chinese hamster ovary cells, confirming correct processing of the N-terminal signal peptide. We have demonstrated that plants and plant cell cultures can be used as alternative systems for the production of an active recombinant thrombomodulin derivative.     

Production of TNF-alpha and TNF-beta by staphylococcal enterotoxin A activated human T cells

Staphylococcal enterotoxin at concentrations of less than 1 pg/ml induces significant TNF activity in human peripheral blood T cells and monocytes. Maximal TNF activity is routinely detected after 48 to 72 h of culture. IL-2 and IL-4 were both growth promoting for human T cells but only IL-2 could efficiently induce TNF production. The production of TNF-alpha and TNF-beta differed greatly in kinetics. An early intracytoplasmatic production of TNF-alpha after 6 h was detected in both monocytes and T cells whereas a late production of TNF-beta (lymphotoxin) after 48 h, occurred in the T cell population. Induction of TNF-alpha and TNF-beta production by Staphylococcal enterotoxin requires the presence of both monocytes and T cells. The CD4+45R- but not CD4+45R+ and CD8+ cells supported TNF-alpha production in monocytes. The main lytic component from Staphylococcal enterotoxin-activated mononuclear cells is TNF-beta. CD4+ and CD8+ T cells produced about equal amounts of biologically active TNF into the culture supernatants but a fourfold higher frequency of TNF-beta producing cells was demonstrated among CD4+ vs CD8+ cells. The CD4+45R- T cell subset was an efficient producer of TNF-beta and IFN-gamma whereas the CD4+45R+ T cell subset produced significant amounts of TNF-beta but only marginal amounts of IFN-gamma.     

Inhibition of protein tyrosine phosphatase activity by diamide is reversed by epidermal growth factor in fibroblasts.

Diamide (azodicarboxylic acid bis(dimethylamide] inhibits protein tyrosine phosphatase activity in fibroblasts without altering protein tyrosine kinase activity associated with the epidermal growth factor receptor. The loss of protein tyrosine phosphatase activity caused by diamide is reversed by 2-mercaptoethanol or epidermal growth factor.