Biomedical subjects

S Schnell

Publications and source records attributed to S Schnell.

At least 19 recordsLinked to original sources

PubMed2001

Lentivirus-transduced human monocyte-derived dendritic cells efficiently stimulate antigen-specific cytotoxic T lymphocytes.

Dendritic cells (DCs) are professional antigen-presenting cells that are highly effective adjuvants for immunizing against pathogens and tumor antigens. The potential merit of genetic approaches to loading DCs with antigens is to express high and sustained levels of proteins that can be subsequently processed and presented to T lymphocytes. Replication-defective oncoretroviruses are able to efficiently transduce CD34(+) progenitor-derived DCs but not monocyte-derived DCs. Here, it is shown that efficient gene transfer is obtained using a human immunodeficiency virus-1-derived lentiviral vector deleted of all structural and accessory genes. Infection of immature DCs with the lentiviral vector at a multiplicity of infection of 20 resulted in stable gene expression in 30% to 40% of the matured DCs. Proviral DNA was detectable by Alu polymerase chain reaction for the lentiviral but not the oncoretroviral vector. Most importantly, it is demonstrated that lentivirus-transduced DCs were fully functional and effectively activated autologous HLA A2.1(+) peripheral blood cytotoxic T lymphocytes (CTLs). DCs expressing lentiviral vector-encoded Flu peptide were at least as efficient as DCs pulsed with the same peptide in stimulating specific CTLs. The efficacy of the lentivirus-transduced DCs was further demonstrated by their ability to directly activate freshly harvested peripheral blood Flu-specific CTLs in the absence of CD4(+) T-cell help and exogenous cytokines. The availability of a stable gene delivery system based on a multiply attenuated lentivirus that does not encode any viral protein and that allows sustained antigen presentation by DCs derived from blood monocytes will be very useful for the biologic investigation of DCs and the improvement of immunotherapeutic strategies involving DCs.

CD4-Positive T-Lymphocytes↗

PubMed2001

A fast method to estimate kinetic constants for enzyme inhibitors.

We present a method to determine the reaction type and kinetic constants for enzyme inhibitors that decreases the number of experimental assays by at least a factor of five. It is based on a new theoretical formalism in terms of concentrations that dismisses the requirement of estimating initial velocities. Expressions for the time evolution of the concentrations of all the reactants are also given.

Algorithms↗

PubMed2001

Nitrate-dependent iron(II) oxidation in paddy soil.

Iron(III) profiles of flooded paddy soil incubated in the greenhouse indicated oxidation of iron(II) in the upper 6 mm soil layer. Measurement of oxygen with a Clark-type microelectrode showed that oxygen was only responsible for the oxidation of iron(II) in the upper 3 mm. In the soil beneath, nitrate could be used as electron acceptor instead of oxygen for the oxidation of the iron(II). Nitrate was still available 3 mm below the soil surface, and denitrifying activity was indicated by higher concentrations of nitrite between 3 and 6 mm soil depth. Nitrate was generated by nitrification from ammonium. Ammonium concentrations increased beneath 6 mm soil depth, indicating ammonium release and diffusion from deeper soil layers. High concentrations of ammonium were also found at the surface, probably resulting from N2 fixation by cyanobacteria. Experimental adjustment of the nitrate concentration in the flooding water to 200 microM stimulated nitrate-dependent iron(II) oxidation, which was indicated by significantly lower iron(II) concentrations in soil layers in which nitrate-dependent iron(II) oxidation was proposed. Soil incubated in the dark showed high iron(III) concentrations only in the layer where oxygen was still available. In this soil, the nitrogen pool was depleted because of the lack of N2 fixation by cyanobacteria. In contrast, soil incubated in the dark with 500 microM nitrate in the flooding water showed significantly higher iron(II) and significantly lower iron(II) concentrations in the anoxic soil layers, indicating nitrate-dependent iron(II) oxidation. Anoxic incubations of soil with nitrate in the flooding water also showed high concentrations of iron(II) and low concentrations of iron(II) in the upper 3 mm. As oxygen was excluded in anoxic incubations, the high iron(III) concentrations are a sign of the activity of nitrate-dependent iron(II) oxidizers. The presence of these bacteria in non-amended soil was also indicated by the most probable number (MPN) counts of nitrate-dependent iron(II) oxidizers in the layer of 3-4 mm soil depth, which revealed 1.6 x 10(6) bacteria g(-1) dry weight.

Anaerobiosis↗

PubMed2000

A cell cycle model for somitogenesis: mathematical formulation and numerical simulation.

After many years of research, the mechanisms that generate a periodic pattern of repeated elements (somites) along the length of the embryonic body axis is still one of the major unresolved problems in developmental biology. Here we present a mathematical formulation of the cell cycle model for somitogenesis proposed in Development105 (1989), 119-130. Somite precursor cells in the node are asynchronous, and therefore, as a population, generate continuously pre-somite cells which enter the segmental plate. The model makes the hypothesis that there exists a time window within the cell cycle, making up one-seventh of the cycle, which gates the pre-somite cells so that they make somites discretely, seven per cycle. We show that the model can indeed account for the spatiotemporal patterning of somite formation during normal development as well as the periodic abnormalities produced by heat shock treatment. We also relate the model to recent molecular data on the process of somite formation.

Animals↗

PubMed2000

Retrovirally transduced mouse dendritic cells require CD4+ T cell help to elicit antitumor immunity: implications for the clinical use of dendritic cells.

Presentation of MHC class I-restricted peptides by dendritic cells (DCs) can elicit vigorous antigen-specific CTL responses in vivo. It is well established, however, that T cell help can augment CTL function, raising the question of how best to present tumor-associated MHC class I epitopes to induce effective tumor immunity. To this end, we have examined the role of MHC class II peptide-complexes present on the immunizing DCs in a murine melanoma model. To present MHC class I- and II-restricted Ags reliably on the same cell, we retrovirally transduced bone marrow-derived DCs with the model Ag OVA encoding well-defined class I- and II-restricted epitopes. The importance of CD4+ T cells activated by the immunizing DCs in this model is demonstrated by the following findings: 1) transduced DCs presenting class I and class II epitopes are more efficient than class I peptide-pulsed DCs; 2) MHC class II-deficient DCs fail to induce tumor protection; 3) CD4+ T cell depletion abolishes induction of tumor protection; and 4) DCs presenting bovine serum Ags are more effective in establishing tumor immunity than DCs cultured in syngeneic serum. When MHC class II-deficient DCs were directly activated via their CD40 receptor, we indeed observed a moderate elevation of OVA-specific CTL activity. However, this increase in CTL activity was not sufficient to induce in vivo tumor rejection. Thus, our results demonstrate the potency of genetically modified DCs that express both MHC class I and II epitopes, but caution against the use of DCs presenting only the former.

Animals↗

PubMed2000

Clock and induction model for somitogenesis.

After many years of research, somitogenesis is still one of the major unresolved problems in developmental biology. Recent experimental findings show a novel type of pattern formation in which a signal sweeps along the presomitic mesoderm and narrows simultaneously as a new somite is formed. The signal then residues in the posterior half of the new somite, and another wave begins to sweep up from the caudal end. This behaviour is not easily explained by the existing theoretical models. We present a new model for somitogenesis that can account for this behaviour and is consistent with previous experimental observations.

Animals↗

PubMed2000

Time-dependent closed form solutions for fully competitive enzyme reactions.

An analytic formalism developed earlier to describe the time evolution of the basic enzyme reaction is extended to fully competitive systems. Time-dependent closed form solutions are derived for the three nominal cases of competition: even, slow and fast inhibitors, allowing for the first time the complete characterization of the reactions. In agreement with previous work, the time-independent Michaelis-Menten approach is shown to be inaccurate when a fast inhibitor is present. The validity of the quasi-steady-state approximation on which the present framework is based is also revised.

Enzyme Inhibitors↗

PubMed2000

Enzyme kinetics at high enzyme concentration.

We re-visit previous analyses of the classical Michaelis-Menten substrate-enzyme reaction and, with the aid of the reverse quasi-steady-state assumption, we challenge the approximation d[C]/dt approximately 0 for the basic enzyme reaction at high enzyme concentration. For the first time, an approximate solution for the concentrations of the reactants uniformly valid in time is reported. Numerical simulations are presented to verify this solution. We show that an analytical approximation can be found for the reactants for each initial condition using the appropriate quasi-steady-state assumption. An advantage of the present formalism is that it provides a new procedure for fitting experimental data to determine reaction constants. Finally, a new necessary criterion is found that ensures the validity of the reverse quasi-steady-state assumption. This is verified numerically.

Enzymes↗

PubMed2000

Microbiology of flooded rice paddies.

Flooded rice paddies are one of the major biogenic sources of atmospheric methane. Apart from this contribution to the 'greenhouse' effect, rice paddy soil represents a suitable model system to study fundamental aspects of microbial ecology, such as diversity, structure, and dynamics of microbial communities as well as structure-function relationships between microbial groups. Flooded rice paddy soil can be considered as a system with three compartments (oxic surface soil, anoxic bulk soil, and rhizosphere) characterized by different physio-chemical conditions. After flooding, oxygen is rapidly depleted in the bulk soil. Anaerobic microorganisms, such as fermentative bacteria and methanogenic archaea, predominate within the microbial community, and thus methane is the final product of anaerobic degradation of organic matter. In the surface soil and the rhizosphere well-defined microscale chemical gradients can be measured. The oxygen profile seems to govern gradients of other electron acceptors (e.g., nitrate, iron(III), and sulfate) and reduced compounds (e.g., ammonium, iron(II), and sulfide). These gradients provide information about the activity and spatial distribution of functional groups of microorganisms. This review presents the current knowledge about the highly complex microbiology of flooded rice paddies. In Section 2 we describe the predominant microbial groups and their function with particular regard to bacterial populations utilizing polysaccharides and simple sugars, and to the methanogenic archaea. Section 3 describes the spatial and temporal development of microscale chemical gradients measured in experimentally defined model systems, including gradients of oxygen and dissolved and solid-phase iron(III) and iron(II). In Section 4, the results of measurements of microscale gradients of oxygen, pH, nitrate-nitrite, and methane in natural rice fields and natural rice soil cores taken to the laboratory will be presented. Finally, perspectives of future research are discussed (Section 5).

Archaea↗

PubMed2000

Molecular analyses of novel methanotrophic communities in forest soil that oxidize atmospheric methane.

Forest and other upland soils are important sinks for atmospheric CH(4), consuming 20 to 60 Tg of CH(4) per year. Consumption of atmospheric CH(4) by soil is a microbiological process. However, little is known about the methanotrophic bacterial community in forest soils. We measured vertical profiles of atmospheric CH(4) oxidation rates in a German forest soil and characterized the methanotrophic populations by PCR and denaturing gradient gel electrophoresis (DGGE) with primer sets targeting the pmoA gene, coding for the alpha subunit of the particulate methane monooxygenase, and the small-subunit rRNA gene (SSU rDNA) of all life. The forest soil was a sink for atmospheric CH(4) in situ and in vitro at all times. In winter, atmospheric CH(4) was oxidized in a well-defined subsurface soil layer (6 to 14 cm deep), whereas in summer, the complete soil core was active (0 cm to 26 cm deep). The content of total extractable DNA was about 10-fold higher in summer than in winter. It decreased with soil depth (0 to 28 cm deep) from about 40 to 1 microg DNA per g (dry weight) of soil. The PCR product concentration of SSU rDNA of all life was constant both in winter and in summer. However, the PCR product concentration of pmoA changed with depth and season. pmoA was detected only in soil layers with active CH(4) oxidation, i.e., 6 to 16 cm deep in winter and throughout the soil core in summer. The same methanotrophic populations were present in winter and summer. Layers with high CH(4) consumption rates also exhibited more bands of pmoA in DGGE, indicating that high CH(4) oxidation activity was positively correlated with the number of methanotrophic populations present. The pmoA sequences derived from excised DGGE bands were only distantly related to those of known methanotrophs, indicating the existence of unknown methanotrophs involved in atmospheric CH(4) consumption.

Bacteria↗

PubMed1998

Anatomy of the central nervous system.

OBJECTIVES: To provide an overview of central nervous system anatomy. DATA SOURCES: Published books and articles. CONCLUSIONS: Classification of tumors, location of primary and metastatic tumors, and initial and progressive symptoms are best understood within a solid knowledge base of neuroanatomy. IMPLICATIONS FOR NURSING PRACTICE: It is essential for nurses caring for neuro-oncology patients to be familiar with normal central nervous system anatomy. This knowledge will enable them to anticipate symptoms, response to treatment, and prognosis for recovery. Understanding of the effects of central nervous system tumors on the function of the central nervous system will help nurses provide holistic care to both patients and significant others.

Central Nervous System↗

PubMed1998

Tumors of the spine and spinal cord.

OBJECTIVES: To provide an overview of spinal cord neoplasms with a focus on location, histology, pathophysiology, diagnosis, treatment and nursing assessment and management. DATA SOURCES: Published books and peer-reviewed articles. CONCLUSIONS: Tumors of the spine and spinal cord are rare, and they can have grave implications for the patient. The key in the management of spinal cord tumors is their timely diagnosis and treatment to preserve function. IMPLICATIONS FOR NURSING PRACTICE: A thorough nursing assessment and timely intervention can have a positive impact on the outcome of patients with tumors of the spine and spinal cord.

Humans↗

PubMed1997

Theoretical description of the polymerase chain reaction.

Taking into account expressions for the efficiency of the polymerase chain reaction (PCR) recently deduced from enzymological considerations, and making use of a continuous model based on the law of mass action, closed form solutions are derived that enable a complete description of the standard and quantitative competitive PCR methods. The resulting behaviour is in reasonable agreement with that from a previous, empirical, discrete approach; but the latter is nonetheless shown to overestimate the amplification yield by as much as 30% due to the weak assumption of a constant efficiency during the cycle duration. The present formalism will facilitate the implementation of accurate fitting procedures of experimental data to manage quantification.

Animals↗

PubMed1997

Enzymological considerations for a theoretical description of the quantitative competitive polymerase chain reaction (QC-PCR).

The enzymological principles of the polymerase chain reaction (PCR) and of the quantitative competitive PCR (QC-PCR) are developed, proposing a theoretical framework that will facilitate quantification in experimental methodologies. It is demonstrated that the specificity of the QC-PCR, i.e. the ratio of the target initial velocity to that of the competitor template, remains constant not only during a particular amplification but also for increasing initial competitor concentrations. Linear fitting procedures are thus recommended that will enable a quantitative estimate of the initial target concentration. Finally, expressions for the efficiency of the PCR and QC-PCR are derived that are in agreement with previous experimental inferences.

Animals↗

PubMed1996

Complete assimilation of cysteine by a newly isolated non-sulfur purple bacterium resembling Rhodovulum sulfidophilum (Rhodobacter sulfidophilus).

A rod-shaped, motile, phototrophic bacterium, strain SiCys, was enriched and isolated from a marine microbial mat, with cysteine as sole substrate. During phototrophic anaerobic growth with cysteine, sulfide was produced as an intermediate, which was subsequently oxidized to sulfate. The molar growth yield with cysteine was 103 g mol-1, in accordance with complete assimilation of electrons from the carbon and the sulfur moiety into cell material. Growth yields with alanine and serine were proportionally lower. Thiosulfate, sulfide, hydrogen, and several organic compounds were used as electron donors in the light, whereas cystine, sulfite, or elemental sulfur did not support phototrophic anaerobic growth. Aerobic growth in the dark was possible with fructose as substrate. Cultures of strain SiCys were yellowish-brown in color and contained bacteriochlorophyll a, spheroidene, spheroidenone, and OH-spheroidene as major photosynthetic pigments. Taking the morphology, photosynthetic pigments, aerobic growth in the dark, and utilization of sulfide for phototrophic growth into account, strain SiCys was assigned to the genus Rhodovulum (formerly Rhodobacter) and tentatively classified as a strain of R. sulfidophilum. In cell-free extracts in the presence of pyridoxal phosphate, cysteine was converted to pyruvate and sulfide, which is characteristic for cysteine desulfhydrase activity (l-cystathionine gamma-lyase, EC 4.4. 1.1).

Cystathionine gamma-Lyase↗

PubMed1996

Comparison of fluorescence in situ hybridization, cytogenetic analysis, and DNA index analysis to detect chromosomes 4 and 10 aneuploidy in pediatric acute lymphoblastic leukemia: a Pediatric Oncology Group study.

PURPOSE: Chromosome abnormalities are an important prognostic factor in childhood acute lymphoblastic leukemia (ALL). Recently, a subset of patients with hyperdiploid ALL and trisomy of chromosomes 4 and 10 has been reported to have a very favorable event-free survival. Rapid and accurate detection of these patients will allow them to be treated with highly effective and relatively nontoxic antimetabolite therapy. Because of inherent problems associated with conventional cancer cytogenetics, we examined the efficacy of fluorescence in situ hybridization (FISH) to identify this ALL subgroup. PATIENTS AND METHODS: Fifty uncultured bone marrow specimens from children with newly diagnosed ALL were examined for chromosomes 4 and 10 aneuploidy with FISH. These results were compared with routine cytogenetics and DNA Index (DI). RESULTS: Interphase FISH cytogenetics identified the abnormal cell line(s) in all cases in which cytogenetics showed aneuploidy of chromosomes 4 and 10. In cases in which cytogenetics was not informative, FISH identified the presence of an aneuploid chromosome 4 and/or 10 cell line in concordance with the DI. CONCLUSIONS: FISH interphase cytogenetics can accurately detect chromosome 4 and 10 aneuploidy in leukemic cells. It is a rapid and clinically applicable technique that can reliably identify childhood ALL cases who have trisomy of chromosomes 4 and 10 and who have very favorable event-free survival.

Aneuploidy↗

PubMed1995

Identification of male epithelial cells in routine postcoital cervicovaginal smears using fluorescence in situ hybridization. Application in sexual assault and molestation.

In a prospective blinded controlled study, the efficacy of fluorescence in situ hybridization (FISH) to detect non-sperm male cells verifying sexual contact was examined. Cervicovaginal smears (CVS) from 40 women with reported post-coital intervals were examined for sperm by cytology and for sperm and non-sperm male cells by FISH using X and Y chromosome specific DNA probes. Fluorescence in situ hybridization identified sperm and/or non-sperm male cells in all specimens from women with positive coital histories, including when the partner had a vasectomy. Male cells were also detectable by FISH in CVS up to 3 weeks after coitus. In comparison, cytology identified sperm in 41% of the positive coital history cases, and none beyond 2 weeks. Fluorescence in situ hybridization is highly sensitive and specific in detecting male cells, and can be performed rapidly on routine CVS. Application of this technique can provide new and additional evidence of sexual contact when current tests are inconclusive.

Coitus↗

PubMed1995

Function and stationary-phase induction of periplasmic copper-zinc superoxide dismutase and catalase/peroxidase in Caulobacter crescentus.

Although cytosolic superoxide dismutases (SODs) are widely distributed among bacteria, only a small number of species contain a periplasmic SOD. One of these is Caulobacter crescentus, which has a copper-zinc SOD (CuZnSOD) in the periplasm and an iron SOD (FeSOD) in the cytosol. The function of periplasmic CuZnSOD was studied by characterizing a mutant of C. crescentus with an insertionally inactivated CuZnSOD gene. Wild-type and mutant strains showed identical tolerance to intracellular superoxide. However, in response to extracellular superoxide, the presence of periplasmic CuZnSOD increased survival by as much as 20-fold. This is the first demonstration that periplasmic SOD defends against external superoxide of environmental origin. This result has implications for those bacterial pathogens that contain a CuZnSOD. C. crescentus was shown to contain a single catalase/peroxidase which, like Escherichia coli KatG catalase/peroxidase, is present in both the periplasmic and cytoplasmic fractions. The growth stage dependence of C. crescentus catalase/peroxidase and SOD activity was studied. Although FeSOD activity was identical in exponential- and stationary-phase cultures, CuZnSOD was induced nearly 4-fold in stationary phase and the catalase/peroxidase was induced nearly 100-fold. Induction of antioxidant enzymes in the periplasm of C. crescentus appears to be an important attribute of the stationary-phase response and may be a useful tool for studying its regulation.

Catalase↗