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M Nahm

Publications and source records attributed to M Nahm.

15 recordsLinked to original sources
PubMed2006

Physiological performance of beech (Fagus sylvatica L.) at its southeastern distribution limit in Europe: seasonal changes in nitrogen, carbon and water balance.

To assess the physiological performance of drought-sensitive European beech ( Fagus sylvatica L.) under the dry Mediterranean climate prevailing at its southeastern distribution limit in Europe, we analyzed seasonal changes in carbon, nitrogen and water balance of naturally grown adult trees. We determined the foliar C and N contents, delta13C and delta18O signatures, total soluble non-protein nitrogen compounds (TSNN) in xylem, leaves, and phloem, as well as leaf water potential and photosynthetic quantum yield in northern Greece during 2003. Tissue sampling was performed in May, July, and September, while field measurements were conducted regularly. Climatic conditions for the 2003 growing season fall within the typical range of the studied area. The N- and C-related parameters displayed distinct seasonal courses. TSNN was highest in May in all tissues, and asparagine (Asn) was then the most abundant compound. Thereafter, TSNN decreased significantly in all tissues and both its concentration and composition remained constant in July and September. In both months, glutamate (Glu) prevailed in leaves, gamma-aminobutyric acid (GABA) in phloem exudates from twigs and trunks, and arginine (Arg) in the xylem sap, where loading with amino acids was rather low during that period, amounting to only 0.8 micromol N ml-1 in September. Highest total foliar N and C contents were detected in May, and the elevated abundance of nutrients as well as an increased foliar delta13C signature at the beginning of the growing season is attributed to remobilization processes. The signatures of delta18O, quantum yield and leaf water potentials varied only slightly throughout the growing season. Although summer precipitation at the study site was considerably lower compared to what is usual for typical central European beech forests, no intensive drought responses of the physiological apparatus were detected in the studied beech trees. This suggests efficient internal regulation mechanisms, constantly ensuring a favourable physiological status under the relatively dry Mediterranean climate.

Carbon↗
PubMed2004

Water shortage affects the water and nitrogen balance in Central European beech forests.

Whilst forest policy promotes cultivation and regeneration of beech dominated forest ecosystems, beech itself is a highly drought sensitive tree species likely to suffer from the climatic conditions prognosticated for the current century. Taking advantage of model ecosystems with cool-moist and warm-dry local climate, the latter assumed to be representative for future climatic conditions, the effects of climate and silvicultural treatment (different thinning regimes) on water status, nitrogen balance and growth parameters of adult beech trees and beech regeneration in the understorey were assessed. In addition, validation experiments with beech seedlings were carried out under controlled conditions, mainly in order to assess the effect of drought on the competitive abilities of beech. As measures of water availability xylem flow, shoot water potential, stomatal conductance as well as delta (13)C and delta (18)O in different tissues (leaves, phloem, wood) were analysed. For the assessment of nitrogen balance we determined the uptake of inorganic nitrogen by the roots as well as total N content and soluble N compounds in different tissues of adult and young trees. Retrospective and current analysis of delta (13)C, growth and meteorological parameters revealed that beech growing under warm-dry climatic conditions were impaired in growth and water balance during periods with low rain-fall. Thinning affected water, N balance and growth mostly of young beech, but in a different way under different local climatic conditions. Under cool, moist conditions, representative for the current climatic and edaphic conditions in beech forests of Central Europe, thinning improves nutrient and water status consistent to published literature and long-term experience of forest practitioners. However, beech regeneration was impaired as a result of thinning at higher temperatures and under reduced water availability, as expected in future climate.

Carbon Isotopes↗
PubMed2001

Comparison of a classical phagocytosis assay and a flow cytometry assay for assessment of the phagocytic capacity of sera from adults vaccinated with a pneumococcal conjugate vaccine.

Antibody- and complement-mediated phagocytosis is the main defense mechanism against Streptococcus pneumoniae. A standardized, easy to perform phagocytosis assay for pneumococci would be a great asset for the evaluation of the potential efficacy of (experimental) pneumococcal vaccines. Such an assay could replace the laborious phagocytosis assay of viable pneumococci (classical killing assay). Therefore, a newly developed phagocytosis assay based on flow cytometry (flow assay) was compared with the conventional killing assay and enzyme-linked immunosorbent assay (ELISA), using sera obtained from adults pre- and postvaccination with either a bivalent conjugate, a tetravalent conjugate, or the 23-valent polysaccharide vaccine. Highly significant correlations were observed between flow assay phagocytosis titers, killing assay phagocytosis titers, and ELISA antibody titers for serotype 6B and 23F as well. For serotype 19F, strong correlations were only observed between killing assay and ELISA titers. A potential drawback of the flow assay might be the low sensitivity compared with that of the killing assay. The choice of what assay to use, however, will depend on the objectives of the assay. When speed, easy performance, sample throughput, improved worker safety, absence of influence of antibiotics, and absence of false positives are the major criteria, the flow assay is the method of choice. When higher sensitivity is the major requirement, the classical killing assay should be used.

Adult↗
PubMed1991

BCL2 protein is topographically restricted in tissues characterized by apoptotic cell death.

The BCL2 protooncogene encodes an inner mitochondrial membrane protein that blocks programmed cell death. BCL2 was isolated from the chromosomal breakpoint of follicular B-cell lymphoma. Transgenic mice that overexpress BCL2 display extended survival of resting B cells. In this study we use a monospecific anti-human BCL2 antibody to define the distribution of BCL2 protein within organized tissues. BCL2 is restricted within germinal centers to the follicular mantle and to portions of the light zone implicated in the selection and maintenance of plasma cells and memory B cells. BCL2 is present in the surviving T cells in the thymic medulla. All hematopoietic lineages that derive from a renewing stem cell also display BCL2. A limited number of nonlymphoid tissues demonstrate BCL2 and can be grouped as (i) glandular epithelium in which hormones or growth factors regulate hyperplasia and involution, (ii) complex differentiating epithelium such as skin and intestine characterized by long-lived stem cells, and (iii) long-lived postmitotic cells such as neurons. Within these tissues that demonstrate apoptotic cell turnover, BCL2 is often topographically restricted to long-lived or proliferating cell zones. BCL2's function as an antidote to apoptosis may confer longevity to progenitor and effector cells in these tissues.

Adult↗
PubMed1991

Human rib bone marrow mononuclear cells spontaneously synthesize and secrete IgE in vitro.

We have examined spontaneous secretion of IgE by human rib bone marrow mononuclear cells (MNC). Bone marrow MNC from nine out of 12 rib specimens synthesized and secreted substantial amounts of IgE during 14 days of in vitro culture. The 14-day supernatants from these bone marrow MNC contained a mean of 2589 pg/ml of IgE (n = 12) with a maximum production of 15,408 pg/ml of IgE compared with small amounts of IgE (80-200 pg/ml) produced by similarly cultured normal and inflammatory bowel disease intestinal lamina propria MNC. Using two rib specimens, time-course studies revealed spontaneous secretion of IgE to be minimal during the first 2 days of culture (152 pg/ml), followed by a steady increase between days 4 (517 pg/ml) and 14 (3588 pg/ml). The addition of pokeweed mitogen resulted in 72% suppression of spontaneous IgE production by bone marrow MNC. The bone marrow MNC isolated from the ribs consisted of 22% Leu12+ (B) cells of which 3.2% were surface IgE positive. Staining for cytoplasmic immunoglobulin revealed 1% of the bone marrow MNC to be cytoplasmic IgE+. The presence of IgE-bearing and IgE-secreting MNC in human bone marrow is consistent with the observation that allergen-specific IgE-mediated hypersensitivity is adoptively transferred by human bone marrow transplantation and demonstrates the usefulness of human bone marrow MNC for examination of IgE secretory and regulatory events.

Adult↗
PubMed1987

Naturally occurring antibodies to phosphocholine as a potential index of antibody responsiveness to polysaccharides.

Naturally occurring antibodies reactive with the phosphocholine (PC) determinant of pneumococcal teichoic acids may be useful for evaluating the potential of patients to make antibodies to polysaccharides. Antibodies to PC are present in most adults under the age of 60 years, are absent in very young children, and are present at low levels in Wiscott-Aldrich patients and in IgG2-deficient adults. These last three groups respond very poorly to polysaccharide antigens. Antibodies to PC are also found at low levels in the elderly, a group that has previously been shown to have low levels of antibody to blood groups A and B carbohydrates. The levels of antibody to PC over time were constant in most individuals and, in adults, seemed to show slightly less variation than did titers of antibody to blood group B. Our findings suggest that titers of antibody to PC may be superior to titers of antibody to blood group A or B for monitoring responsiveness to carbohydrate antigens.

ABO Blood-Group System↗
PubMed1986

Human IgG subclass assays using a novel assay method.

To facilitate assays for human IgG subclasses, we have adapted a novel assay method (particle concentration fluorescence immunoassay) (Jolley et al., 1984; MacCrindle et al., 1985) using one polyclonal and several monoclonal antibodies for human IgG subclasses. The advantages of this new assay over previously described methods are sensitivity (0.3-3 micrograms/ml), and automated measurement of multiple samples in a short time (2 h). We found that a monkey antibody for IgG2 and monoclonal antibodies for IgG1, IgG4b epitope, and IgG3 can be adapted to this method. We evaluated 7 different antibodies to IgG4 without finding a suitable monoclonal antibody for this assay method. Several of these IgG4 hybridoma antibodies, however, could be used in a competitive radioimmunoassay using polyvinyl microtiter plates. The usefulness of a monoclonal antibody to the IgG4b epitope was evaluated because no suitable monoclonal antibodies for IgG2 are available. Because IgG4 levels are usually much smaller than IgG2 levels, and the IgG4b epitope is expressed on all IgG2 alleles and only some IgG4 alleles (Kunkel et al., 1970), the antibody for IgG4b is potentially useful to screen a large number of samples for IgG2 deficiency. However, when the monoclonal antibody for IgG4b was compared with an IgG2 specific antibody produced in a monkey, the IgG4b antibody could identify only about half of the patients with known IgG2 deficiency.

Antibodies, Monoclonal↗
PubMed1984

Multiple VH gene segments encode murine antistreptococcal antibodies.

Most mouse strains are able to mount a diverse antibody response against group A streptococcal carbohydrate (GAC). We have previously reported that murine anti-GAC antibodies are for the most part restricted to IgM and IgG3 subclasses. In addition, despite extensive heterogeneity in their isoelectric focusing patterns, greater than 50% of A/J anti-GAC antibodies share a common light chain defined by spectrotypic and idiotypic (VK1GAC) criteria. We have used protein and DNA sequencing strategies to examine the genetic basis of diversity in murine anti-GAC antibodies. In particular, we report that, (a) multiple, closely homologous VH gene segments contribute to the generation of anti-GAC antibodies, (b) a common framework sequence, related to the VK27 subgroup, probably defines VK1GAC, and (c) the A/J anti-GAC VH regions and BALB/c anti-inulin VH sequences are 95% homologous at the protein level and are likely encoded by overlapping VH gene families. Lastly, we discuss the genetic mechanisms that might permit the evolution of multiple, closely homologous germline VH gene segments in the context of highly divergent flanking region sequences.

Alleles↗
PubMed1982

Streptococcal group A carbohydrate has properties of both a thymus-independent (TI-2) and a thymus-dependent antigen.

Streptococcal group A carbohydrate, which elicits mouse antibody of primarily the IgM and IgG3 isotypes, is relatively nonimmunogenic in nu/nu or xid mice, and thus appears to be a type of TD-2 antigen. The TD-2 antigens described previously have been proteins that elicit IgG antibody primarily of the IgG1 and IgG2 isotypes. Our findings indicate that TD-2 properties may also be a characteristic of at least some carbohydrate antigens that can elicit IgG antibody predominantly of the IgG3 class.

Animals↗
PubMed1981

Antiphosphocholine antibodies found in normal mouse serum are protective against intravenous infection with type 3 streptococcus pneumoniae.

The antiphosphocholine (PC) antibody in normal mouse sera (NMS) provides protection against intravenous infection with encapsulated strain WU2 of type 3 Streptococcus pneumoniae. Mice unable to make anti-PC antibody, as a result of suppression with anti-T-15 idiotype or inheritance of the xid gene of CAB/N mice, are highly susceptible to infection with strain WU2. Mice inheriting the xid gene can be protected with NMS from immunologically normal mice or with IgM hybridoma anti-PC antibody. The protective effect of NMS can be removed with PC-containing immunoabsorbents.

Animals↗
PubMed1980

Subclass restriction of murine antibodies. II. The IgG plaque-forming cell response to thymus-independent type 1 and type 2 antigens in normal mice and mice expressing an X-linked immunodeficiency.

Antigens have been classified previously into three categories, thymus-dependent (TD), thymus-independent type (TI) 1, and TI-2, based upon thymic dependence and ability to stimulate an immunodeficient strain of mouse, CBA/N. Here we demonstrate that the different antigen classes elicit IgG antibodies of different subclasses. TD antigens stimulate predominantly IgG1 antibodies, with smaller amounts of IgG2 and IgG3 being expressed. TI-1 antigens stimulate almost no IgG1 antibodies and equal amounts of IgG2 and IgG3. TI-2 antigens elicit predominantly IgG3 antibodies. Mice expressing the CBA/N phenotype are known to be nonresponsive to TI-2 antigens. This was confirmed in this study. In addition, we demonstrate that the IgG3 component of the response to TI-1 antigens is virtually absent in mice expressing the CBA/N phenotype, which supports our previous finding that the CBA/N defect may be restricted to a B-lymphocyte subpopulation containing most of the precursors of IgG3-secreting cells.

Animals↗
PubMed1979

Immunoglobulin subclass-specific immunodeficiency in mice with an X-linked B-lymphocyte defect.

CBA/N mice express an X-linked deficiency in their antibody response to many bacterial carbohydrates; we have shown recently that these antigens normally elicit antibody responses predominantly of the IgM and IgG3 isotypes. Here we demonstrate that mice, with the CBA/N phenotype have perferential deficiencies of IgM and IgG3 immunoglobulin expression, both when measured in serum and in cells secreting these isotypes, and that this deficiency is only partially corrected by polyclonal activation of B cells. This suggests that CBA/N mice may lack a subpopulation of B cells that contain most of the IgG3 precursors.

Animals↗
PubMedDate not supplied

Flavopiridol induces apoptosis and caspase-3 activation of a newly characterized Burkitt's lymphoma cell line containing mutant p53 genes.

Burkitt's lymphoma cell lines have been important in vitro models for studying the pathogenesis of Burkitt's lymphoma (BL) and for exploring new treatment strategies. A new EBV(-) Burkitt's lymphoma cell line (GA-10) was established from a patient with a clinically aggressive, chemorefractory BL and characterized. Although functional p-glycoprotein could not be demonstrated by dye-efflux assays, both p53 genes were mutated in the GA-10 cells, perhaps contributing to the resistant phenotype of the original neoplasm. Two properties of BL cells which may be useful targets for novel cytotoxic therapeutics are their surface expression of CD77, the receptor for Shiga toxin (Stx), and their high rate of proliferation. Expression of CD77 on the GA-10 cells was heterogeneous in that certain subclones expressed high levels of CD77 and correspondingly exhibited strong growth inhibition by Stx while others showed low levels of CD77 expression and weak Stx-induced growth inhibition. Flavopiridol, a potent inhibitor of cell cycle progression through G1 and G2, induced cytotoxicity of the GA-10 cells with an LC(50) of approximately 40 nM vs 70 nM for HL-60 cells (P < 0.05). The concentrations of flavopiridol at which only 10% of the cells were viable (LC(10)) were approximately 280 nM for the GA-10 cells and 520 nM for the HL-60 cells (P < 0.05). Dose-related induction of apoptosis in response to flavopiridol was demonstrated in the GA-10 cells by morphology, TUNEL assay, and activation of caspase-3. Flavopiridol was also cytotoxic to seven other BL cell lines tested. These data suggest that flavopiridol may have therapeutic value in the treatment of Burkitt's lymphoma.

ATP Binding Cassette Transporter, Subfamily B, Mem↗