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B W Hess

Publications and source records attributed to B W Hess.

40 records · Page 3Linked to original sources
PubMed1993

Increased viral titer through concentration of viral harvests from retroviral packaging lines.

Dependent on the viral vector and the specific assay used, viral titers produced from commonly used retroviral packaging cell lines have an upper limit in the range of 10(5) to 10(7) infectious units/ml. We have developed a generally applicable method, using hollow-fiber filtration technology, which allows for the concentration of infectious virus derived from packaging lines. This method resulted in a reproducible 10- to 30-fold increase in viral titer and can readily be scaled to accommodate larger input volumes. Over 80% of the input virus is recovered in an infectious form in the concentrate. Concentrated virus containing media was seen to produce higher infection frequencies in Jurkat T cells as compared to unconcentrated virus containing media; however, this was not proportional to the differences in viral titer observed by limiting dilution analysis on NIH-3T3 cells. These results are discussed in relation to the importance of factors other than viral titer in determining transduction frequencies.

3T3 Cells↗
PubMed1993

Influence of supplementation on behavior of grazing cattle.

Dormant grasses are usually deficient in nutrients needed to meet cattle requirements. Research results indicate that grazing activities are sensitive to some environmental variables and vegetative (sward) characteristics; however, minimal information is available on the influence of supplementation regimens on cattle grazing activities. Supplementation studies reviewed had forage N levels that ranged from .9 to 1.2% and forage intakes that ranged from 12.3 to 31.0 g of OM/kg of BW. Protein supplementation affected (P < .05) time spent grazing: unsupplemented (NS) cattle grazed approximately 1.5 h/d more than did supplemented (S) cattle. Type of supplemental protein and time of daily feeding did not affect (P > .10) this response. Different types and timing of starch-based supplements produced variable results; however, increasing the level of supplemental starch decreased (P < .05) daily grazing time. Protein supplementation increased (P < .05) harvesting efficiency (HE; grams of forage intake.kilogram of BW-1.minute spent grazing-1); however, high-starch supplements either did not alter (P > .10) or decreased (P < .05) HE compared with NS. Progressive defoliation can influence grazing behavior in both sheep and cattle grazing actively growing forage; however, evaluation of vegetative characteristics of dormant forage and the corresponding effect on grazing behavior are not known. The effects of various grazing management strategies on cattle behavior are inconclusive and deserve additional attention. Methods and (or) management practices that modify behaviors to control feed intake, improve efficiency, or reduce stress could be major contributions to the livestock industry.

Animal Feed↗
PubMed1991

Efficient gene transfer and expression in primary B lymphocytes.

In this study we have used a panel of vectors expressing the chloramphenicol acetyltransferase (CAT) reporter gene under the control of different regulatory elements to optimize gene transfer and expression in primary B lymphocytes. The Moloney murine leukemia virus long terminal repeat (MoMLV LTR) and the SV40 early region promoters, while functional in transfected plasmacytoma cell lines, did not give rise to detectable CAT activity following transfection into primary activated mouse or human B lymphocytes. In contrast, the human cytomegalovirus immediate-early (HCMV-IE) enhancer/promoter functioned in both established and primary B cells. The highest expression levels in the primary cells were obtained with vectors containing the Adenovirus 2 major late promoter or the HCMV-IE enhancer/promoter in combination with the Adenovirus 2 tripartite leader and VA genes. These latter expression cassettes were placed in a retroviral vector with the aim of combining their capacity for high-level gene expression with the efficient stable gene transfer afforded by retroviral infection. Several retroviral constructs were made, some of which were able to generate high virus titers. However all of these underwent deletions during the process of retroviral infection, as judged by Southern analysis of infected cells, indicating that they were not optimal gene transfer vectors. The HCMV enhancer/promoter, which was the most active of the other expression cassettes tested in the primary B cells, was inserted into a retroviral vector which also expressed the hph gene under the transcriptional control of the retroviral LTR. This vector did not undergo rearrangement during the process of retroviral infection, as judged by Southern analysis. The CAT gene was inserted downstream of the HCMV promoter in this vector, and a high-titer retroviral stock was generated. Primary B lymphocytes infected with this vector gave high levels of CAT activity, under conditions in which parallel experiments with the hph drug resistance marker showed that one in 20 of the cells were infected. These experiments demonstrate efficient gene transfer and expression in primary B lymphocytes in vitro.

Animals↗