PubMed Health⌕ Search

Biomedical subjects

S W Peters

Publications and source records attributed to S W Peters.

16 recordsLinked to original sources
PubMed2001

Comparison of remote sensing data, model results and in situ data for total suspended matter (TSM) in the southern Frisian lakes.

Suspended matter plays an important role in water quality management since it is related to total primary production and fluxes of heavy metals and micropollutants such as PCBs. Synoptic information on suspended matter at a regular frequency is difficult to obtain from the routine in situ monitoring network since suspended matter is (like chlorophyll) a spatially inhomogeneous parameter. This can be solved by the integrated use of remote sensing data, in situ data and water quality models. A methodology previously developed for integrating information from remote sensing, and models (Vos and Schuttelaar, Neth Remote Sensing Board (1995) report 95-19), was applied for the assessment of suspended matter concentrations in the southern Frisian lakes in the Netherlands. The model is a one-dimensional network model. Remote sensing data (Landsat-TM5 and SPOT-HRV) were atmospherically corrected and converted to total suspended matter maps. The algorithms are based on analytical optical modelling, using the in situ inherent optical properties. This methodology enables the development of multi-temporal algorithms for estimating seston dry weight concentration in lakes from remotely sensed data; thus satellite data can now become an independent measurement tool for water management authorities.

Algorithms↗
PubMed2001

Optimization of production and downstream processing of the almond beta-glucosidase-mediated glucosylation of glycerol.

This article describes the synthesis of glyceryl glucoside from glycerol and glucose with almond beta-glucosidase as the catalyst. A yield of 54% (0.45 mmol/g) was obtained. The influence of the enzyme stability, the water concentration, and the water activity on the glucoside yield were determined. A molar fraction-based equilibrium constant of 2.4 +/- 0.6 was found, with which the glucoside yield could be calculated for all possible combinations of initial substrate and water fractions in the reaction mixture. A model was used to optimize the glucoside yield while minimizing one of the substrate concentrations at equilibrium. This straightforward model gives a good prediction of the measured glucoside yield, according to a parity plot.

Glucose↗
PubMed2001

Spontaneous formation of a mannitol-producing variant of Leuconostoc pseudomesenteroides grown in the presence of fructose.

We report the spontaneous formation of a stable mannitol-producing variant of Leuconostoc pseudomesenteroides. The mannitol-producing variant showed mannitol dehydrogenase activity which was absent in the parental strain. It was also able to use fructose and glucose simultaneously, whereas the parental strain showed diauxic growth with these sugars. A possible explanation of these observations is discussed.

Fructose↗
PubMed1992

Intercellular adhesion molecule-1 (ICAM-1) expression by lymph node dendritic cells: comparison with epidermal Langerhans cells.

Following skin sensitization of mice, epidermal Langerhans cells (LC) are stimulated to migrate via the afferent lymphatics to the draining lymph nodes. Previous studies have demonstrated that, while in transit, LC acquire the characteristics of mature dendritic cells (DC) and develop into potent immunostimulatory cells. In the present study the expression by LC and lymph node DC of intercellular adhesion molecule-1 (ICAM-1) has been compared. Freshly-isolated LC expressed only very low levels of ICAM-1. In contrast lymph node DC, irrespective of whether they were isolated from resting lymph nodes or from activated lymph nodes draining the site of sensitization with oxazolone, exhibited significant membrane ICAM-1. As a substantial proportion of the DC found within the draining nodes of skin sensitized mice derive from epidermal LC it is apparent that, during migration from the skin, LC are induced to express increased ICAM-1. Such is compatible with the development of LC into effective antigen presenting cells.

Animals↗
PubMed1992

Langerhans cells, antigen presentation, and the diversity of responses to chemical allergens.

Respiratory and contact chemical allergens provoke differential immune responses in mice, stimulating preferentially T helper-2 (TH2) and TH1 cells, respectively. In an attempt to discover whether such differences are effected at the level of antigen handling and presentation we have examined the effect of topical exposure to trimellitic anhydride (TMA), a respiratory allergen, and 2,4-dinitrochlorobenzene (DNCB), a contact allergen, on Langerhans cell (LC) MHC class II (Ia) expression. Neither chemical caused a significant change in LC size. As measured by analytical flow cytometry, exposure to DNCB resulted in a time-dependent increase in LC Ia expression that exceeded 160% of control values within 24 h. Exposure to concentrations of TMA that caused an equivalent activation of draining lymph nodes failed to affect Ia expression by LC. Application of sodium lauryl sulfate at concentrations that caused edema also failed to influence LC Ia. These data demonstrate that TMA and DNCB exert differential effects on epidermal LC, possibly indicative of differences in antigen handling.

Allergens↗
PubMed1992

Influence of topical exposure to chemical allergens on murine Langerhans cells. Comparison of 2,4-dinitrochlorobenzene with trimellitic anhydride.

Chemical allergens differ with respect to the type of hypersensitivity reactions they preferentially elicit. Some chemicals, such as trimellitic anhydride (TMA), have the potential to induce both contact and respiratory hypersensitivity. Other chemicals cause only contact allergy. For example, 2,4-dinitrochlorobenzene (DNCB), a potent contact allergen, appears not to induce respiratory sensitization. In previous studies we have shown that topical exposure of mice to TMA and DNCB, under conditions of equivalent immunogenicity with respect to draining lymph node activation and contact sensitization, caused qualitatively different antibody responses. While the chemicals provoked IgG anti-hapten antibody responses of equivalent magnitude, only TMA induced an IgE response, and DNCB caused a significantly stronger IgG2a response. These data are consistent with the preferential activation by DNCB and TMA of Th1 and Th2 cells respectively. The purpose of the present study was to examine whether the qualitative differences in immune responses stimulated by these chemicals is reflected by variable affects on Langerhans cells (LC) in situ. Mice were exposed to concentrations of DNCB (1%) and TMA (50%) which caused equivalent levels of contact sensitization. Under these conditions topical exposure to DNCB, but not to TMA, or to vehicle alone, resulted in increased expression by LC of Ia antigen. Similar treatment with an irritant concentration (20%) of sodium dodecyl sulphate failed to influence Ia expression by LC. These data indicate that, at concentrations which induce similar levels of skin sensitization, not all contact allergens cause rapid changes in LC Ia expression, and that the qualitative differences in immune responses elicited by chemical allergens DNCB and TMA is associated with variable effects on LC.

Administration, Topical↗
PubMed1991

MHC class II expression by Langerhans' cells and lymph node dendritic cells: possible evidence for maturation of Langerhans' cells following contact sensitization.

Following exposure of mice to contact sensitizing chemicals, dendritic cells (DC) rapidly accumulate in the draining lymph nodes. A proportion, at least, of the DC which arrive in the nodes bear significant amounts of antigen and are derived from epidermal Langerhans' cells (LC). It is of interest that although LC are relatively inefficient antigen-presenting cells, the antigen-bearing DC found within draining nodes are potent accessory cells and induce immune responses both in vitro and in vivo. Previous in vitro studies have shown that during culture in the presence of granulocyte/macrophage colony-stimulating factor (GM-CSF), LC are subject to a functional and phenotypic maturation characterized by the development of effective accessory cell function and elevated membrane Ia antigen expression. We have hypothesized previously that LC may undergo a similar maturation in vivo as they move to the draining lymph nodes following receipt of the stimulus to migrate. As maturation in vitro is accompanied by increased Ia, we have examined the expression of this molecule on epidermal LC and lymph node DC during the induction phase of contact sensitization. The data reported provide evidence that peripheral lymph node DC, irrespective of whether they are derived from draining or resting nodes, and irrespective of whether or not they bear antigen, express comparable high levels of Ia antigen. In contrast, compared with DC, freshly isolated LC have considerably less (on average five times less) Ia antigen. These results indicate that during migration from the skin to lymphoid tissue LC are subject to a phenotypic maturation, comparable with that observed in vitro, and consistent with the acquisition of active antigen-presenting cell function.

Animals↗
PubMed1990

Correlation between lymphocyte proliferative responses and dendritic cell migration in regional lymph nodes following skin painting with contact-sensitizing agents.

We have investigated whether there exists a correlation between the induction of draining lymph node cell (LNC) proliferation in contact allergy and the accumulation of dendritic cells (DC) within such lymph nodes. CBA/Ca mice, which compared with mice of BALB/c strain, mount a more vigorous lymphocyte proliferative response following sensitization, also exhibited a more marked accumulation of DC in draining lymph nodes 24 h following skin painting. Moreover, studies with the skin-sensitizing fluorochromes fluorescein isothiocyanate (FITC) and rhodamine B isothiocyanate (RITC) revealed that DC-enriched fractions of draining LNC prepared from CBA/Ca mice contained a higher percentage of antigen-bearing cells than did those from BALB/c mice. A relationship between DC migration into lymph nodes and the magnitude of the induced LNC proliferative response was also indicated by experiments performed in BALB/c mice with a variety of contact allergens. It was observed that there was a direct correlation between the vigour of the proliferative response measured 3 days following exposure and the frequency of DC in draining nodes at 24 h. Collectively these data suggest that following skin sensitization the migration of DC into the draining lymph nodes influences quantitatively the primary immune response and the development of contact allergy.

Allergens↗
PubMed1990

Antigenic competition in contact sensitivity. Evidence for changes in dendritic cell migration and antigen handling.

The frequency and antigen-bearing characteristics of dendritic cells (DC) within draining lymph nodes have been examined during antigenic competition in contact sensitivity. Pre-exposure of mice to oxazolone on the flank resulted in a marked depression of subsequent fluorescein isothiocyanate (FITC)-induced lymph node cell (LNC) proliferation. Antigenic competition was associated with an increased frequency of DC in the draining lymph nodes, but also with a reduced amount of antigen per cell. Thus, at 24 hr the draining nodes of FITC-challenged mice previously exposed to oxazolone exhibited an increased number of DC compared with control animals. Flow cytometric analysis revealed, however, that the percentage of antigen-bearing DC was reduced and that the median amount of antigen borne by DC was lower. Since exposure to oxazolone caused a significant increase in the frequency of DC in distant nodes, the changes observed in antigenic competition may, at least in part, be attributable to systemic effects on DC migration following application of the first antigen. These data indicate that the reduced primary proliferative response which characterizes antigenic competition in contact sensitivity is associated with, and may result from, induced changes in dendritic cell behaviour.

Animals↗
PubMed1989

Dendritic cell accumulation in draining lymph nodes during the induction phase of contact allergy in mice.

Draining lymph node cells isolated from mice 24 h following topical exposure to a variety of contact-sensitizing chemicals, including the dinitrobenzene derivatives, 2,4-dinitrochlorobenzene and 2,4-dinitrothiocyanobenzene, contained increased numbers of dendritic cells (DCs). The increase in frequency of DCs was time-dependent and preceded significant changes in either lymph node cellularity or lymph node cell proliferative activity. The degree of DC accumulation was also influenced by the chemical used and the concentration employed for sensitization. In the context of contact allergy, the biological relevance of this phenomenon to the induction of hapten-specific responses is indicated by the fact that relatively small numbers of DC--enriched fractions of lymph node cells (comprising approximately 70% DCs), but not unfractionated or DC--depleted populations, transferred sensitization to naive animals. Moreover, using the skin-sensitizing fluorochrome, fluorescein isothiocyanate, it was observed that 24 h following exposure the majority of lymph node cells bearing high concentrations of antigen were within the DC-rich fraction.

Animals↗
PubMed1989

Effects of antioestrogens on the proliferation of MCF-7 human breast cancer cells.

Non-steroidal antioestrogens, such as tamoxifen, inhibit the growth of human breast cancer cells. The experiments described here compare and contrast the efficacy of tamoxifen and the 'pure' antioestrogen, ICI 164384, on the inhibition of proliferation of MCF-7 cells. Previous studies have shown that ICI 164384 has a greater maximal inhibitory effect than conventional antioestrogens on the growth of MCF-7 cells. Both types of compound block progression of cells through the cell cycle in the early G1 phase. These studies have been extended to measure the population distribution of antioestrogen-treated cells by the use of two-parameter flow cytometry. ICI 164384 proved to be more effective than tamoxifen in decreasing the proportion of actively growing cells in an asynchronous population. In cells grown in the complete absence of exogenous oestrogens, growth was stimulated by oestradiol, insulin, insulin-like growth factor-I (IGF-I) or transforming growth factor-alpha (TGF-alpha). The potent metabolite of tamoxifen, trans 4'-hydroxytamoxifen (4'-OHT), alone also stimulated growth, whereas ICI 164384 did not. Oestradiol and insulin added together demonstrated a clear synergistic enhancement of cell growth. Correspondingly, the stimulatory effect of 4'-OHT on growth was magnified in the presence of insulin, and a combination of ICI 164384 with insulin revealed a much weaker stimulatory action of the 'pure' antagonist. For both compounds the interaction with insulin was complex and characterized by a bell-shaped dose-response curve. However, for 4'-OHT at all concentrations in the range 1 pM-1 microM in the presence of insulin, cell numbers were greater than in cultures exposed to insulin alone. This was not the case for ICI 164384 which suggested that differences in efficacy may be due to interactions between oestrogen and growth factor-mediated mechanisms. Furthermore, ICI 164384 was more effective in inhibiting the action of IGF-I and TGF-alpha alone or in combination, although both antioestrogens produced a partial blockade of growth factor responses in the complete absence of oestradiol. It is concluded that the difference in efficacy between partial agonist and 'pure' antagonist antioestrogens to inhibit growth in vitro is consistent with the difference in the pharmacological profile of these compounds. The absence of stimulatory activity of ICI 164384 is of particular significance in reducing to a minimum the synergistic interaction between oestrogens and insulin.(ABSTRACT TRUNCATED AT 400 WORDS)

Breast Neoplasms↗
PubMed1986

The ferritin content of normoblasts and megaloblasts from human bone marrow.

Erythroblasts were enriched from human bone marrow samples and fractionated on Percoll gradients according to maturity. Heart-type and spleen-type ferritin was measured in each fraction by an immunoradiometric assay. In normal marrow, heart-type ferritin content was higher in the early erythroblast fractions and fell with maturation. Spleen-type ferritin content showed no such consistent change. Megaloblastic erythroblasts had a significantly higher ferritin content.

Bone Marrow↗
PubMed1986

DNA content and cell cycle analysis of bone marrow cells in myelodysplastic syndromes (MDS).

DNA distribution in bone marrow cells from 10 normal subjects and 34 patients with MDS (24 with refractory anaemia (RA) and 10 with excess blasts (RAEB] was determined by flow cytometry using a FACS III. DNA histograms were resolved into G0/1, S and G2/M compartments by fitting Gaussian distributions and the DNA content of G0/1 cells, expressed as DNA index (DI), was determined. In 19 MDS patients the DI was outside the normal range, those with RA tending to be hyperdiploid. Two patients with RAEB had a second G0/1 peak. In five cases of RA the number of cells in G0/1 was below the normal range and the mean value was significantly lower than normal for this group as a whole (P = 0 X 018). Eleven (RA) patients had a higher percentage of cells in G2/M than normal (P = 0 001). In RAEB patients there is a suggestion of increased numbers in G0/1 and a decrease in S phase and G2/M cells. All three of the deaths amongst RA patients and four out of the five deaths in RAEB patients since the beginning of this study were associated with an abnormal DI at the initial investigation.

Bone Marrow↗
PubMed1981

Ferritin concentration in normal and abnormal erythrocytes measured by immunoradiometric assay with antibodies to heart and spleen ferritin and Mössbauer spectroscopy.

Immunoradiometric assays using antibodies to spleen and heart ferritin were combined with Mössbauer studies on normal and pathological erythrocytes. All erythrocytes examined were found to contain greater amounts of heart type than spleen type ferritin. The ferritin concentration in erythrocytes from patients with beta thalassaemia, sickle cell disease and sideroblastic anaemia is much higher than in normal cells. When the concentration of ferritin-like iron in the pathological erythrocytes measured by Mössbauer spectroscopy is compared to the total amount of ferritin assayed by the two antibodies in the same haemolysates the iron/protein ratio ranges between 0.3 and 3.4. The iron/protein ratio in iron-filled ferritin molecules is about 0.56 and values in excess of this suggest that the iron detected in these cells is a mixture of ferritin molecules, partly denatured ferritin polymers and 'haemosiderin'. There is a possibility that erythrocytes contain an immunologically distinct type of ferritin that is not detected by existing assays, but we have no direct evidence for this.

Anemia, Sickle Cell↗