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S Bischof

Publications and source records attributed to S Bischof.

7 recordsLinked to original sources
PubMed2001

Determination of retinol and retinyl esters in human plasma by high-performance liquid chromatography with automated column switching and ultraviolet detection.

A HPLC method with automated column switching and UV detection is described for the simultaneous determination of retinol and major retinyl esters (retinyl palmitate, retinyl stearate, retinyl oleate and retinyl linoleate) in human plasma. Plasma (0.2 ml) was deproteinized by adding ethanol (1.5 ml) containing the internal standard retinyl propionate. Following centrifugation the supernatant was directly injected onto the pre-column packed with LiChrospher 100 RP-18 using 1.2% ammonium acetate-acetic acid-ethanol (80:1:20, v/v) as mobile phase. The elution strength of the ethanol containing sample solution was reduced by on-line supply of 1% ammonium acetate-acetic acid-ethanol (100:2:4, v/v). The retained retinol and retinyl esters were then transferred to the analytical column (Superspher 100 RP-18, endcapped) in the backflush mode and chromatographed under isocratic conditions using acetonitrile-methanol-ethanol-2-propanol (1:1:1:1, v/v) as mobile phase. Compounds of interest were detected at 325 nm. The method was linear in the range 2.5-2000 ng/ml with a limit of quantification for retinol and retinyl esters of 2.5 ng/ml. Mean recoveries from plasma were 93.4-96.5% for retinol (range 100-1000 ng/ml) and 92.7-96.0% for retinyl palmitate (range 5-1000 ng/ml). Inter-assay precision was < or =5.1% and < or =6.3% for retinol and retinyl palmitate, respectively. The method was successfully applied to more than 2000 human plasma samples from clinical studies. Endogenous levels of retinol and retinyl esters determined in female volunteers were in good accordance with published data.

Automation↗
PubMed2000

Deficiency in the transcription factor interferon regulatory factor (IRF)-2 leads to severely compromised development of natural killer and T helper type 1 cells.

Interferon (IFN) regulatory factor (IRF)-2 was originally described as an antagonist of IRF-1-mediated transcriptional regulation of IFN-inducible genes. IRF-1(-/)- mice exhibit defective T helper type 1 (Th1) cell differentiation. We have used experimental leishmaniasis to show that, like IRF-1(-/)- mice, IRF-2(-/)- mice are susceptible to Leishmania major infection due to a defect in Th1 differentiation. Natural killer (NK) cell development is compromised in both IRF-1(-/)- and IRF-2(-/)- mice, but the underlying mechanism differs. NK (but not NK(+) T) cell numbers are decreased in IRF-2(-/)- mice, and the NK cells that are present are immature in phenotype. Therefore, like IRF-1, IRF-2 is required for normal generation of Th1 responses and for NK cell development in vivo. In this particular circumstance the absence of IRF-2 cannot be compensated for by the presence of IRF-1 alone. Mechanistically, IRF-2 may act as a functional agonist rather than antagonist of IRF-1 for some, but not all, IFN-stimulated regulatory element (ISRE)-responsive genes.

Animals↗
PubMed1997

Interferon regulatory factor-1 is required for a T helper 1 immune response in vivo.

The transcription factor interferon regulatory factor-1 (IRF-1) mediates the effects of IFN. No information exists on its role in lymphokine production. Protection against the intracellular pathogen Leishmania major depends on a Th1 response. Here, we show that CD4+ T cells from Leishmania-infected mice lacking one (+/-) or both (-/-) alleles of the IRF-1 gene developed a profound, gene dose-dependent decrease in IFNgamma production. IRF-1(-/-) mice showed dramatically exacerbated Leishmaniasis. They produced increased Leishmania-specific IgG1 and IgE, and their CD4+ T cells produced increased IL-4, characteristics of the non-protective Th2 response. In cell transfer experiments, IRF-1(-/-) CD4+ T cells mounted normal Th1 responses. However, the ability of IRF-1(-/-) mice to produce IL-12 was severely compromised. Thus, IRF-1 is a determining factor for Th1 responses.

Animals↗
PubMed1996

Effects of umbilical arterial catheterization on mesenteric hemodynamics.

Impairment of mesenteric blood flow due to the use of umbilical artery catheters (UAC) may increase the risk of necrotizing enterocolitis (NEC) in newborn infants. We used Duplex Doppler sonography to investigate the degree of vessel obstruction due to UAC and their effect on visceral hemodynamics in 12 newborn infants. Ultrasonography was performed before and immediately after removal of the UAC, which was positioned above the ostia of the celiac and superior mesenteric arteries (SMA). Vessel diameter, peak systolic blood flow velocity (PSFV), end diastolic blood flow velocity (EDFV), and Pourcelot's resistance index (RI) were measured in the celiac trunk and the SMA within 1 cm of their origins. Removal of the UAC led to a significant increase in mean PSFV (celiac trunk: 50 cm/s +/- 15 vs 62 cm/s +/- 0.22, P < 0.05; SMA: 52 cm/s +/- 0.17 vs 72 cm/s +/- 0.21, P < 0.05). RI increased from 0.7 +/- 0.14 to 0.74 +/- 0.13 and from 0.73 +/- 0.1 to 0.76 +/- 0.13 for the celiac trunk and SMA, respectively. The EDFV and vessel diameters did not change significantly after UAC removal. Our results suggest that UAC cause a decrease in mesenteric blood flow. Therefore, their use in hemodynamically unstable neonates or in those with gastrointestinal disease should be very carefully considered.

Blood Flow Velocity↗
PubMed1994

Demonstration of organic anion transport in T lymphocytes. L-lactate and fluo-3 are target molecules.

In this paper, we describe for the first time the existence of organic anion transport in T lymphocytes, exemplified by the transmembrane transport of the anions L-lactate and the Ca2+ indicator fluo-3. The transport of either anion was found to be inhibitable by probenecid, a common blocker of organic anion transport. Transport of L-lactate was observed in long-term cultured T cell lines, as well as in freshly ex vivo isolated T cells, and occurred via a saturable, pH-dependent, and stereospecific process. L-Lactate uptake was dependent on the activation state of the T cells, because activation of T cells by Con A strongly enhanced accumulation of L-lactate from the medium. Because L-lactate may be transported bidirectionally through the T cell membrane in vivo, different physiologic roles of L-lactate transport are discussed. L-Lactate uptake may serve as an alternative source of energy in an inflamed, glucose-deficient tissue or may represent a prerequisite for the earlier-published immunoregulatory function of this molecule on T cells. On the other hand, release of L-lactate emerging from glycolysis could be necessary to avoid acidification of the cell. The fact that the Ca2+ indicator fluo-3 is also transported through the cellular membranes of long-term cultured T cells via organic anion transport has important implications for the determination of Ca2+ influx into T cells. Even though the transport of both molecules, L-lactate and fluo-3, represents organic anion transport, evidence is presented that confirms that the respective transport systems are different.

Aniline Compounds↗
PubMed1983

Effects of radiation on murine T-cell leukemogenesis induced by butylnitrosourea.

BDF1 mice were exposed to butylnitrosourea for 12 weeks (BNU, 0.02% in the drinking water) and died of thymic lymphomas with median latency periods of 12-20 weeks. In addition to BNU, groups of mice received weekly radiation doses of 0.0625-1.0 Gy; 12 X 0.25 Gy enhanced leukemogenesis, 12 X 0.75 Gy delayed it and 12 X 0.50 Gy had no effect. Lower doses had marginal enhancing effects. After a dose of 12 X 1.0 Gy, the mice died earlier than after treatment with BNU alone and, as with 12 X 0.75 Gy, some extrathymic lymphomas were observed. The numbers of CFU-S in the femur and the spleen showed a dose-dependent depression, in addition to the effect of BNU alone. In lymphocyte stimulation assays with Con A und LPS and also in the mixed lymphocyte reaction, a reduced proliferation was found, again dependent on the radiation dose. Therefore, there was no correlation of leukemogenesis and the degree of stem-cell reduction or depression of these immune parameters. The delay of leukemogenesis by 12 X 0.75 Gy in addition to BNU may be caused by an enhanced target cell kill.

Animals↗