Functional competency of T cell antigen receptors in human thymus

The T cell antigen receptor is likely to play a role in both positive and negative selection in the thymus. Three populations of thymocytes can be distinguished by the level of expression of the CD3-alpha/beta-chain heterodimer of the T cell antigen receptor (CD3/Ti alpha/beta) complex. Cells which fail to express these receptors or express low levels of receptors are contained in a population of thymocytes which express low levels of the CD5 antigen and are predominantly CD4+/CD8+. Thus, these cells appear to be relatively immature phenotypically. In contrast, the cells which express high levels of CD3/Ti alpha/beta co-express high levels of CD5 and are predominantly contained in the more mature single positive cells which express either CD4 or CD8. With the calcium-sensitive dye, Indo-1, and immunofluorescence, we demonstrated that, despite the relative phenotypic immaturity of cells which express low levels of CD3/Ti alpha/beta, these antigen receptors are able to mediate transmembrane signaling when stimulated with CD3 monoclonal antibodies. Although increases in calcium were observed in these CD3/Ti alpha/beta-low expressing cells in response to anti-CD3, no proliferative response was observed, even in the presence of phorbol myristate acetate. Proliferative responses were observed in the more mature cells which express high levels of CD3/Ti alpha/beta. These results suggest that, rather than a defect in the functional capability of the antigen receptor complex to mediate transmembrane signaling events, cellular responses to signals generated by the antigen receptor may differ at various stages of thymocyte development.     

Prognostic significance of DNA ploidy and morphometric analyses of adenocarcinoma of the uterine cervix

In an effort to improve the prognostic accuracy of the histologic criteria used for cervical adenocarcinomas, the nuclear DNA ploidy levels, means and standard deviations of nuclear areas and amounts of lumen and neoplastic tissue were quantitated. Useful thresholds in discriminating recurrent disease, as identified by logistic regression analysis, included a DNA ploidy level of 3.0 N, a percent of lumen of 34.6% and nuclear area mean and standard deviation of 53.1 sq micron and 20.1 sq micron, respectively. These parameters should provide useful guidelines in the visual assessment of histologic features that have prognostic significance.     

High-Efficiency Conversion of Pyruvate to Acetoin by Lactobacillus plantarum during pH-Controlled and Fed-Batch Fermentations

The influence of pH on the type and concentration of metabolites produced from pyruvate by Lactobacillus plantarum ATCC 8014 was examined in pH-controlled fermentors at pH values of 4.5 to 6.5. Specific growth rates, cell dry weights, and diacetyl concentrations were highest at pH 5.5, with values of 0.78 h⁻¹, 190 mg/liter, and 1.2 mM, respectively. While the conversion efficiency (millimoles of acetoin formed per millimoles of pyruvate utilized) was highest (94.6%) at pH 4.5, acetoin levels were similar (20 mM) between pH 4.5 and 5.5. Feeding stationary-phase cells exogenous pyruvate increased acetoin levels to 78 mM.     

Structures and biological activities of three synaptic antagonists from orb weaver spider venom

The venom of Argiope aurantia, an orb weaver spider, contains a mixture of low molecular weight "argiotoxins", which block neuromuscular transmission in insects. Complete structure elucidation of three argiotoxins reveals common features; a hydrophilic, basic domain of arginine, a polyamine and asparagine is connected to an aromatic moiety contributed either by 4-hydroxyindole-3-acetic acid or 2,4-dihydroxyphenylacetic acid. Structural assignments of two argiotoxins are verified by chemical synthesis. The argiotoxins cause reversible paralysis when injected into insects and this is correlated with a stimulus-dependent inhibition of skeletal neuromuscular transmission at submicromolar concentrations.     

Serum lipids and lipoproteins in the atherosclerosis prone LA/N corpulent rat

The LA/N rat is one of two congenic strains bred from the original obese, hyperphagic and hypertensive rats of Koletsky. With the exception of hypertension the LA/N strain, when homozygous for the corpulent gene, is phenotypically similar to the parent Koletsky strain and prone to the development of vascular and myocardial lesions. Here we report a detailed analysis of the serum lipids, lipoproteins and apolipoproteins B, E and A-I levels in young adult homozygous corpulent (cp/cp) rats of both sexes and in lean males of the same age which were demonstrable non-carriers (+/+) of the cp gene. Both male and female cp/cp rats were hypertriglyceridemic (282-512 mg/100 ml) and moderately hypercholesterolemic (74-84 mg/100 ml). Elevations in these lipids reflected the presence of large (622 A), triacylglycerol-rich and apoprotein-poor VLDL containing both apolipoproteins Bh and B1 and increased phospholipid-rich HDL. Similar, but less pronounced, elevations in serum apolipoproteins B and E in the cp/cp rats when compared to the +/+ animals were also noted. Apolipoproteins A-I levels were 2.7-3-fold higher in cp/cp rats. The levels of VLDL were significantly higher in female cp/cp rats; however, the levels of IDL (intermediate-density lipoproteins), LDL and HDL were significantly lower than in the more atherosclerosis prone male cp/cp rats. Similarly, apolipoprotein A-I was higher and apolipoprotein B lower in the male cp/cp than in the female cp/cp rats. The LDL (d = 1.030-1.063 g/ml) in cp/cp rats, like that in normal animals, was heterogeneous and contained apolipoproteins Bh, E, A-I and C. This fraction was significantly elevated in male cp/cp rats when compared to females but still represented less than 13% of the total serum cholesterol and less than 6% of the total serum lipids in 3-month-old cp/cp animals. The ratio of cholesterol to phospholipids was significantly lower for all lipoproteins in cp/cp rats when compared to +/+ males and these ratios for female cp/cp rats were in all cases lower than those of male cp/cp animals.     

Contractility, ATP, and creatine phosphate during myocardial ischaemia and reperfusion: the effects of adenosine and inhibition of adenosine catabolism in the dog heart

Provision of AMP or adenosine to heart cells during recovery from episodes of myocardial ischaemia accelerates physiological, biochemical, and structural recovery. Inhibition of adenosine loss from the tissue during ischaemia should have a similar effect. This hypothesis was tested in dog heart by infusion of adenosine and inhibitors of adenosine catabolism prior to, during, and following ischaemia. Post-ischaemic recovery of ATP and contractile function was accelerated significantly by adenosine and by inhibitors of adenosine catabolism both singly and in combination. Contractility and ATP levels during ischaemia were also increased by these inhibitors.     

Reactive oxygen-mediated damage to murine mammary tumor cells

We have shown, in a preliminary report, that macrophages can induce strand breaks in the DNA of co-cultured tumor cells (Chong et al., 1988). The present study is designed to determine if oxygen-centered species generated by the cell-free enzyme-substrate combination of hypoxanthine and xanthine oxidase can induce similar lesions and to identify the specific mediator(s). We report that co-incubation of murine mammary tumor cell lines with hypoxanthine and xanthine oxidase leads to the induction of DNA-strand breaks as determined by fluorescence analysis of DNA unwinding (FADU) assay or alkaline elution techniques. This damage is preventable by catalase which removes hydrogen peroxide but no protection is provided by agents to remove or prevent the formation of superoxide anion (superoxide dismutase), or hydroxyl radical (mannitol or the iron chelator o-phenanthroline). Likewise, cyclooxygenase or lipoxygenase inhibitors of arachidonate metabolism (indomethacin, nordihydroguaiaretic acid, caffeic acid) or bromophenacyl bromide do not alter the degree of DNA scission. Treatment with higher doses of oxygen species leads to significant toxicity as determined by evaluation of cell growth potential or colony-forming ability. Again, toxicity is prevented only by the presence of catalase. Tumor cells are able to rejoin strand breaks at lower, less toxic doses. When comparing different tumor cell subpopulations at various stages of progression, i.e., metastatic vs. nonmetastatic, for sensitivity to hydrogen peroxide-induced strand breakage, we found that at lower concentrations (less than 5μM) metastatic populations are sensitive whereas nonmetastatic populations exhibit no significant breakage. At higher concentrations of hydrogen peroxide, all lines were sensitive, suggesting that a lower threshold of sensitivity may exist for more progressed tumour cell lines.     

Metabolism of d-xylose in Schizosaccharomyces pombe cloned with a xylose isomerase gene

Summary The Escherichia coli xylose isomerase gene was transformed into Schizosaccharomyces pombe for direct d-xylose utilization. In order to understand d-xylose metabolism and determine the limiting factors on d-xylose utilization by the transformed yeast, d-xylose transport, xylose isomerization, and xylulose phosphorylation were investigated. The results indicated that low activity of xylose isomerization in the cloned yeast was the limiting step for d-xylose fermentation. An in vitro study showed that yeast proteases decreased xylose isomerase activity. Xylitol, a by-product of d-xylose fermentation, had no effect on the activity of xylose isomerase.