The changing face of the Czech rural landscape

Land use and landscape structure changes were investigated using the example of an agricultural landscape in central Bohemia. Attention was paid particularly to the great changes which occurred during the 40 years of socialist collectivism. The analysis of landscape development shows that statistics about land use can give only general information about landscape macrostructure and cannot provide a perfect idea of the actual spatial composition of landscape elements. Landscape microstructure expressed in spatial arrangements, shape, size, quality and connectivity of patches, lines and small interactive elements plays the main role in landscape dynamics and is the principal influence in landscape stability.     

The cytoplasmic and the transmembrane domains are not sufficient for class I MHC signal transduction

Class I MHC molecules deliver activation signals to T cells. To analyze the role of the cytoplasmic and the transmembrane (TM) domains of class I MHC molecules in T cell activation, Jurkat cells were transfected with genes for truncated class I MHC molecules which had only four intracytoplasmic amino acids and no potential phosphorylation sites or native molecules or both. Cross-linking either the native or the truncated molecules induced IL-2 production even under limiting stimulation conditions of low engagement of the stimulating mAb. Moreover, direct comparison of transfected truncated and native class I MHC molecules expressed on the same cell revealed significant stimulation induced by cross-linking the truncated molecules, despite low expression. In addition, truncated class I MHC molecules were as able to synergize with CD3, CD2, or CD28 initiated IL-2 production as native molecules. In further experiments, hybrid constructs made of the extracellular portion of the murine CD8 alpha chain and of the TM and the intracytoplasmic domains of H-2Kk class I MHC molecule were transfected into Jurkat T cells. The expression of the transfected hybrid molecules was comparable to that of the native HLA-B7 molecules. Cross-linking the intact monomorphic HLA-A,B,C epitope or the polymorphic HLA-B7 epitope induced IL-2 production upon costimulation with PMA. In contrast, cross-linking the hybrid molecules generated neither an increase in intracellular calcium concentration ([Ca2+]i) nor stimulated IL-2 production. By contrast, cross-linking intact murine class I MHC molecules induced [Ca2+]i, signal and IL-2 production in transfected Jurkat cells. The data therefore indicate that unlike many other signaling molecules, signaling via class I MHC molecules does not involve the cytoplasmic and the TM portions of the molecule, but rather class I MHC signal transduction is likely to be mediated by the extracellular domain of the molecule.     

Nectar Minerals as Regulators of Flower Visitation in Stingless Bees and Nectar Hoarding Wasps

Various nectar components have a repellent effect on flower visitors, and their adaptive advantages for the plant are not well understood. Persea americana (avocado) is an example of a plant that secretes nectar with repellent components. It was demonstrated that the mineral constituents of this nectar, mainly potassium and phosphate, are concentrated enough to repel honey bees, Apis mellifera, a pollinator often used for commercial avocado pollination. Honey bees, however, are not the natural pollinator of P. americana, a plant native to Central America. In order to understand the role of nectar minerals in plant—pollinator relationships, it is important to focus on the plant’s interactions with its natural pollinators. Two species of stingless bees and one species of social wasp, all native to the Yucatan Peninsula, Mexico, part of the natural range of P. americana, were tested for their sensitivity to sugar solutions enriched with potassium and phosphate, and compared with the sensitivity of honey bees. In choice tests between control and mineral-enriched solutions, all three native species were indifferent for mineral concentrations lower than those naturally occurring in P. americana nectar. Repellence was expressed at concentrations near or exceeding natural concentrations. The threshold point at which native pollinators showed repellence to increasing levels of minerals was higher than that detected for honey bees. The results do not support the hypothesis that high mineral content is attractive for native Hymenopteran pollinators; nevertheless, nectar mineral composition may still have a role in regulating flower visitors through different levels of repellency.     

Human memory T cell differentiation into Th2-like effector cells is dependent on IL-4 and CD28 stimulation and inhibited by TCR ligation

Freshly isolated memory T cells primarily produced IL-2 and small amounts of IL-4 and IFN-gamma after stimulation in vitro. Priming for 5 days in vitro with anti-CD28 monoclonal antibodies (mAb) alone markedly increased production of IL-4. In comparison to fresh cells, the increase in the amount of IL-4 secreted reflected a marked increase in the number of IL-4-producing cells. Stimulation with immobilized anti-CD3 mAb during priming limited subsequent IL-4 production. By contrast, IFN-gamma production from in vitro primed memory T cells was directly correlated to the concentration of priming anti-CD3 mAb. IL-2 production by all restimulated cells was decreased. The differentiation of IL-4-producing cells could be blocked by antibody to IL-4 and enhanced by the addition of recombinant IL-4 as well as antibody to IFN-gamma. Of note, the IL-4-producing effector cells induced from in vitro priming derived from the early CD27pos memory T cell subset, whereas the small CD27neg differentiated memory subset produced IL-4 without in vitro priming. The results indicate that memory T cells can be directed to differentiate into IL-4-producing effector cells by stimulation via CD28 and IL-4, whereas increasing engagement of the TCR limits Th2 memory cell differentiation.     

Cyclooxygenase in biology and disease

Cyclooxygenase (COX), the key enzyme required for the conversion of arachidonic acid to prostaglandins was first identified over 20 years ago. Drugs, like aspirin, that inhibit cyclooxygenase activity have been available to the public for about 100 years. In the past decade, however, more progress has been made in understanding the role of cyclooxygenase enzymes in biology and disease than at any other time in history. Two cyclooxygenase isoforms have been identified and are referred to as COX-1 and COX-2. Under many circumstances the COX-1 enzyme is produced constitutively (i.e., gastric mucosa) whereas COX-2 is inducible (i.e., sites of inflammation). Here, we summarize the current understanding of the role of cyclooxygenase-1 and -2 in different physiological situations and disease processes ranging from inflammation to cancer. We have attempted to include all of the most relevant material in the field, but due to the rapid progress in this area of research we apologize that certain recent findings may have been left out.     

Interleukin 15 is produced by endothelial cells and increases the transendothelial migration of T cells In vitro and in the SCID mouse-human rheumatoid arthritis model In vivo

The capacity of endothelial cells (EC) to produce IL-15 and the capacity of IL-15 to influence transendothelial migration of T cells was examined. Human umbilical vein endothelial cells expressed both IL-15 mRNA and protein. Moreover, endothelial-derived IL-15 enhanced transendothelial migration of T cells as evidenced by the inhibition of this process by blocking monoclonal antibodies to IL-15. IL-15 enhanced transendothelial migration of T cells by activating the binding capacity of the integrin adhesion molecule LFA-1 (CD11a/CD18) and also increased T cell motility. In addition, IL-15 induced expression of the early activation molecule CD69. The importance of IL-15 in regulating migration of T cells in vivo was documented by its capacity to enhance accumulation of adoptively transferred human T cells in rheumatoid arthritis synovial tissue engrafted into immune deficient SCID mice. These results demonstrate that EC produce IL-15 and imply that endothelial IL-15 plays a critical role in stimulation of T cells to extravasate into inflammatory tissue.     

A comparison of three switching schemes in isotropic networks withnoisy channels

Previous work on analyzing three switching schemes for isotropic networks, namely single hop and two cut-through communication schemes (with and without error checking by intermediate nodes), is extended. Each scheme is modeled by a discrete Markov chain. It is shown how the performance of the communication schemes depends on path length (n ), load on the network (λ), and the error rate (p). As expected, the cut-through schemes perform much better than the single hop when the communication load is light, but as the load increases, the cut-through schemes deteriorate more rapidly, until they are comparable. In fact, when the load approaches saturation (λ is close to 1-p), the cut-through schemes are actually worse than the single-hop schemes. The schemes with checking always outperform those without, but each node must perform more work in checking the correctness of the packets passing through. The time delay becomes infinite when the throughput approaches 1-p. The solutions are expressed as simple formulas and/or algorithms for each scheme     

Rheumatoid synovium is enriched in mature antigen-presenting dendritic cells

Monocytes and dendritic cells (DC) can be purified from fresh peripheral blood (PB) based on their expression of CD33, CD13, and CD14. Whereas DC can be identified as CD33+ CD14dim or CD13+CD14dim cells, monocytes can be identified as CD33+CD14bright or CD13+CD14bright cells. Rheumatoid synovial fluid (SF) and synovial tissue (ST) non-T cells were found to be enriched in CD33+CD14dim cells compared with PB. Whereas 4 to 14% of normal or rheumatoid PB non-T cells were CD33+ and CD14dim, in rheumatoid SF or ST these cells comprised 20 to 45% of non-T mononuclear cells. Synovial CD33+CD14dim cells assumed a typical dendritic morphology on in vitro culture. Freshly isolated CD33+CD14dim PB DC precursors express low levels of HLA-DQ, CD40, and B7, which increase after in vitro incubation. In contrast, freshly isolated SF DC constitutively expressed these markers, and increased densities of HLA-DR and MHC class I molecules. Rheumatoid SF DC showed a specifically enhanced ability to stimulate autologous PB T cells compared with PB DC, or PB or SF monocytes. PB DC or monocytes preincubated in granulocyte-macrophage-CSF, TNF-alpha, or both cytokines exhibited enhanced expression of HLA-DR. Furthermore, DC preincubated in both granulocyte-macrophage-CSF and TNF-alpha were better stimulators of the autologous MLR than DC preincubated in medium, or in either cytokine alone. The data indicate that DC are enriched in rheumatoid SF and ST, and display a more differentiated phenotype than PB DC. These results suggest that PB DC accumulate in the synovium where they undergo phenotypic and functional differentiation in situ, which may be mediated by local cytokines. DC may play an important role in the ongoing presentation of antigen to autoreactive T cells in RA synovium.