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S Schmitz

Publications and source records attributed to S Schmitz.

84 records · Page 5Linked to original sources
PubMed1990

Migration of stem cells and progenitors between marrow and spleen following thiamphenicol treatment of mice.

Recovery of hemopoiesis was studied after a 3-day treatment with the antibiotic thiamphenicol (TAP). A contrasting behavior of the spleen colony-forming units (CFU-S), granulocyte-macrophage colony-forming units (CFU-GM), erythroid burst-forming units (BFU-E), and erythroid colony-forming units (CFU-E) numbers in the bone marrow versus those in the spleen was found. Whereas the cell numbers reached nadirs in the marrow, they peaked 30 to 100-fold above control values in the spleen on day 4. Simultaneously the number of CFU-S, BFU-E, and CFU-GM, but not of CFU-E, increased drastically in the peripheral blood. The tritiated thymidine kill of the splenic CFU-S was too small to explain the endogenous splenic production of these cells. A quantitative analysis further revealed that an effective erythropoiesis was established in the spleen. As a consequence, the first part of a reticulocytosis was mainly due to the splenic contribution, whereas the second part predominantly originated from a delayed marrow erythropoiesis. In contrast, the CFU-GM of the spleen did not effectively differentiate into granuloid precursors. The bulk of the granuloid production occurred in the marrow. The best explanation for these results is a net migration of CFU-S, BFU-E, and CFU-GM from the marrow to the spleen during early recovery, and a back-migration of CFU-GM to the marrow later in the recovery phase. These observations indicate a link between migration of hemopoietic cells and their differentiation at the two hemopoietic sites.

Animals↗
PubMed1989

Hemopoiesis during thiamphenicol treatment. I. Stimulation of stem cells during eradication of intermediate cell stages.

Continuous treatment of C57bl/6 mice for 4 days with the cytostatic antibiotic thiamphenicol revealed a dual response of hemopoietic cells. On one hand, morphologically recognizable erythroid precursors and late progenitors (erythroid colony-forming units; CFU-E) and, to a lesser extent, granuloid precursors were found substantially reduced. On the other hand, early granuloid (granulocyte-macrophage colony-forming units; CFU-GM) and erythroid (erythroid burst-forming units; BFU-E) progenitors increased on day 3 to 220%-240% and 120%-130% of the control value, respectively. This was accompanied by a decline of the initial spleen colony-forming units (CFU-S) (day 8) pool size to approximately 60%. These patterns were similar in the bone marrow and the spleen. In addition, the tritiated thymidine kill of femoral and splenic CFU-S rose significantly (p less than 0.05) from 16% +/- 3% to 38% +/- 2% and from 3% +/- 1% to 17% +/- 2%, respectively. A sudden decline of peripheral reticulocytes between days 2 and 3 from 2.8% +/- 0.3% to 0.6% +/- 0.2% was observed, whereas the hematocrit gradually decreased from day 1 to day 4 from 45.2% +/- 0.1% to 39.3% +/- 0.3%. The white blood cells were not affected. From these results we conclude that stem cells were stimulated as a consequence of the suppression of the intermediate cell stages. As analyzed in the accompanying paper, this confirms a prediction stated by a quantitative theoretical concept of in vivo stem cell regulation.

Animals↗
PubMed1989

Hemopoiesis during thiamphenicol treatment. II. A theoretical analysis shows consistency of new data with a previously hypothesized model of stem cell regulation.

In a recent theoretical model of stem cell regulation, specific quantitative assumptions were made about an in vivo feedback process from erythroid and granuloid precursor cell stages to the spleen colony-forming units (CFU-S), erythroid burst-forming units (BFU-E), and granulocyte-macrophage colony-forming units (CFU-GM). Utilizing specific effects of the antibiotic thiamphenicol (TAP), new experiments have been performed to challenge this model. Here these data are treated in an analysis that implies three steps. First, model assumptions about TAP toxicity are justified. The toxic TAP effects on erythroid and granuloid precursors are quantified as a continuous reduction of the normal amplification coefficient for CFU-E (down to 1/250), proerythroblasts, basophilic erythroblasts, and proliferating granuloid precursors (down to 1/4). Second, the original model predictions for the behavior of CFU-S, CFU-GM, and BFU-E are compared with the corresponding data. Third, discrepancies are discussed and it is demonstrated that adjustment of one single parameter resolves most of them. Thus one can quantitatively explain the experimental results for CFU-S, BFU-E, and CFU-GM by an activation of the regulatory process postulated: the decline in erythroid (and granuloid) cell numbers enhances the cycling of CFU-S while their self-renewal probability is reduced; consequently CFU-S numbers decline; as more cells differentiate towards BFU-E and CFU-GM per unit time the cell numbers of these cell stages increase. Thus the new data on stem cell behavior during TAP treatment support the hypothesis of a feedback from erythroid and granuloid precursors to the stem cells.

Animals↗
PubMed1988

A concept of hemopoietic regulation and its biomathematical realization.

Although the amount of experimental data on the behavior of the hemopoietic system after various perturbations is considerable, a conclusive understanding of hemopoietic regulation is still absent. In the last years, we have examined murine erythropoiesis, thrombopoiesis, granulopoiesis, and stem cell hemopoiesis by means of mathematical modeling in order to identify some of the underlying principles. Our results can be summarized in four hypotheses. 1) The regulation of hemopoiesis is governed by three interrelated control loops: autoregulation of stem cells, feedback from progenitors and precursors to the stem cells, and feedback from mature cells to progenitor and precursor cells. 2) The feedback from mature cells to the progenitor and precursor cells predominantly varies the number of cell divisions taking place during hemopoietic maturation. 3) Two distinct properties of the stem cells are regulated: their cyclic activity and their self-renewal. Both are under the control of stem cell autoregulation and the feedback from progenitors and precursors. 4) A large variance in the maturation time from the stem cells to the mature cells stabilizes the hemopoietic control. The mathematical formulation of these assumptions allows us to understand a broad range of experimental observations including recovery from stem cell damage, hypoproliferative and hyperproliferative situations, and interactions between different cell lines.

Animals↗
PubMed1986

Monoclonal antibodies against the nonhemagglutinating fimbrial antigen 1C (pseudotype 1) of Escherichia coli.

Hybridoma-derived monoclonal antibodies were produced with fimbrial preparations from Escherichia coli 20025 (04:K12:H-) with fimbrial (F) antigens 1C, 13, one related to 12, and one preliminarily termed y and from E. coli 2980 (018ac:K5:H-) with F antigens 1C and 8. Two clones of subclonal hybrid cells were studied which produced monoclonal antibodies (mc-20025-F2b, immunoglobulin G2b [IgG2b]; mc-2980-F2, IgG1) that were reactive with E. coli 20025, 2980, and a number of additional strains which exhibited the F1C antigen. Results of enzyme-linked immunosorbent assay and Western blot analysis indicated that the antibodies had F1C specificity, and competitive enzyme-linked immunosorbent assay with 125I-labeled antibodies showed that they recognized different epitopes on the fimbrial subunit. Neither of the antibodies agglutinated F1C-fimbriated E. coli but bound to the bacteria. There was no binding to E. coli without F1C fimbriae.

Adhesiveness↗
PubMedDate not supplied

Troubles in Smurftown: youth gangs and moral visions on Guam.

An explosive youth gang problem in U.S. Guam may derive from the changes in island traditionalism wrought by modern society. Island youths sense the erosion of the traditional culture's moral visions, but find modern Western individualism unpalatable as an alternative. Gang membership offers a third option, bestowing on youths a sense of honor, bravery, and solidarity lost from traditional society. Gang members must be viewed not as social deviants but as members of a culture that proposes moral visions and prescribes group behaviors for its membership.

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