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Medical Sciences	60%

Selected Abstracts

Changes in vegetation types and Ellenberg indicator values after 65 years of fertilizer application in the Rengen Grassland Experiment, Germany

APPLIED VEGETATION SCIENCE, Issue 2 2009
Milan Chytrý
Abstract Question: How does semi-natural grassland diversify after 65 years of differential application of Ca, N, P, and K fertilizers? Is fertilizer application adequately reflected by the Ellenberg indicator values (EIVs)? Location: Eifel Mountains, West Germany. Methods: The Rengen Grassland Experiment (RGE) was established in an oligotrophic grassland in 1941. Six fertilizer treatments (Ca, CaN, CaNP, CaNP-KCl, CaNP-K2SO4, and unfertilized control) were applied annually in five complete randomized blocks. Species composition of experimental plots was sampled in 2006 and compared with constancy tables representing grassland types in a phytosociological monograph of a wider area. Each plot was matched to the most similar community type using the Associa method. Mean EIVs were calculated for each treatment. Results: The control plots supported oligotrophic Nardus grassland of the Polygalo-Nardetum association (Violion caninae alliance). Vegetation in the Ca and CaN treatments mostly resembled montane meadow of Geranio-Trisetetum (Polygono-Trisetion). Transitional types between Poo-Trisetetum and Arrhenatheretum (both from the Arrhenatherion alliance) developed in the CaNP treatment. In the CaNP-KCl and CaNP-K2SO4 treatments, vegetation corresponded to the mesotrophic Arrhenatheretum meadow. Major discontinuity in species composition was found between control, Ca, and CaN treatments, and all treatments with P application. EIVs for both nutrients and soil reaction were considerably higher in P treatments than in Ca and CaN treatments. Surprisingly, the control plots had the lowest EIVs for continentality and moisture, although these factors had not been manipulated in the experiment. Conclusions: Long-term fertilizer application can create different plant communities belonging to different phytosociological alliances and classes, even within a distance of a few meters. Due to their correlated nature, EIVs can erroneously indicate changes in factors that actually did not change, but co-varied with factors that did change. In P-limited ecosystems, EIVs for nutrients may indicate availability of P rather than N. [source]

Long-term maternal imprinting of the specific B cell repertoire by maternal antibodies

EUROPEAN JOURNAL OF IMMUNOLOGY, Issue 1 2008
Katja Fink
Abstract Maternal antibodies protect newborns whilst they are immunologically immature. This study shows that maternal antibodies can also shape the B cell repertoire of the offspring long after the maternal antibodies themselves become undetectable. VHDJH gene-targeted (VI10) mice expressing a heavy chain specific for vesicular stomatitis virus (VSV) produce a 20-fold increased spontaneous titer of VSV-neutralizing antibodies. When transferred from mother to offspring, these antibodies prevented accumulation of Ag-specific transitional type,2 and marginal zone B cells with an activated phenotype and favored selection to the B cell follicles. This effect was B cell-intrinsic and lasted up to adulthood. The pups nursed by mothers producing specific antibodies developed higher endogenous antibody titers of this specificity which perpetuated the effects of specific B cell selection into the mature follicular compartment, presumably by blocking auto-Ag-dependent development of transitional type,2 B cells in the spleen. This repertoire change was functional, as following infection of adult mice with VSV, those pups that had received specific maternal antibodies as neonates had increased pre-immune titers and mounted strong early IgG neutralizing antibodies. [source]

Prolactin alters the mechanisms of B cell tolerance induction

ARTHRITIS & RHEUMATISM, Issue 6 2009
Subhrajit Saha
Objective Autoimmune diseases predominantly affect women, suggesting that female sex hormones may play a role in the pathogenesis of such diseases. We have previously shown that persistent mild-to-moderate elevations in serum prolactin levels induce a break in self tolerance in mice with a BALB/c genetic background. The aim of this study was to evaluate the effects of hyperprolactinemia on the mechanisms of B cell tolerance induction. Methods Effects of prolactin on splenic B cell subsets were studied in female BALB/c mice. B cell receptor (BCR),mediated apoptosis and proliferation of transitional B cells were analyzed by flow cytometry. Expression of apoptotic genes was examined by microarrays and real-time polymerase chain reaction analysis. B cells coexpressing ,/, light chains were assessed by flow cytometry and immunohistochemistry. Activation status of transitional type 3 (T3) B cells was evaluated by BCR-induced calcium influx studies. Results BCR-mediated apoptosis of the T1 B cell subset, a major checkpoint for negative selection of autoreactive specificities, was decreased in prolactin-treated mice. Microarray studies indicated that this event may be mediated by the prolactin-induced up-regulation of the antiapoptotic gene interferon-, receptor type II and down-regulation of the proapoptotic gene Trp63. Prolactin treatment also altered the amount of receptor editing, as indicated by the increased number of transitional B cells coexpressing ,/, light chains. Additionally, hyperprolactinemia modified the level of B cell anergy by increasing the degree of BCR-induced calcium influx in the T3 B cells. Conclusion Persistently elevated serum prolactin levels interfere with B cell tolerance induction by impairing BCR-mediated clonal deletion, deregulating receptor editing, and decreasing the threshold for activation of anergic B cells, thereby promoting autoreactivity. [source]

Permafrost properties, patterns and processes in the Transantarctic Mountains region

PERMAFROST AND PERIGLACIAL PROCESSES, Issue 3 2006
Iain B. Campbell
Abstract The properties, distribution patterns and thermal processes that influence the active layer and permafrost in the Transantarctic Mountains region of Antarctica, as deduced from our soil investigations since 1964 and drilling investigations since 1990, are outlined. The active layer depth varies from around 80,cm thick in coastal areas to <5,cm in inland and upland regions, due to the effect of the adiabatic lapse rate. Saline, ice-bonded, dry permafrost and transitional types of permafrost all occur. Ice content is highest in ice-bonded permafrost of the coastal regions and lowest in inland dry permafrost where values may be <1%. At the regional scale, ice-bonded permafrost most commonly occurs at lower elevations and beneath younger land surfaces but with increasing elevation, distance inland and land surface age, dry permafrost becomes predominant. At the local scale (<1,m) there are large variations in the depth to the permafrost table due to variations in ground surface features. Permafrost properties are largely governed by solar energy receipt, but albedo, air temperature cooling and available soil moisture strongly modulate the conversion of solar energy receipt into soil heating. These factors account for the considerable broad-scale and local variability in permafrost properties that exists. Copyright © 2006 John Wiley & Sons, Ltd. [source]