Investigation of immunosuppressive properties of inactivated human immunodeficiency virus and possible neutralization of this effect by some patient sera

Retroviral infections are accompanied by immunosuppression in a variety of species. For feline leukemia virus, the immunosuppression has been ascribed to the transmembrane envelope protein, p15E, which suppresses the proliferative responses of cat, mouse, and human lymphocytes. A similar suppressive effect has been shown for a lysate of human immunodeficiency virus (HIV), strain HTLV-IIIB. Here we determined that detergent-disrupted HTLV-IIIB lystate exerted a strong suppressive effect on PHA-stimulated lymphocytes. Preparations of whole virions, a lysate of a local HIV isolate grown on MP-6 cells, and a commercially obtained UV and psoralene-inactivated lysate were examined and demonstrated to have a similar suppressive effect. The HIV lysate was not directly cytotoxic to lymphocytes and did not contain tumor necrosis factor or lymphotoxin. The HIV lysate specifically suppressed the proliferation of a range of hemopoietic cell lines from man and mouse including three EBV transformed CD4- and IL-2 receptor-negative B-cell lines. The lysate also suppressed the formation of human bone marrow colonies, whereas the lysate had only a slight or no effect on fibroblasts. The suppression of lymphocyte proliferation was not abrogated by addition of IL-2 or IL-1 and the HIV lysate inhibited the expression of IL-2 receptors on suboptimal PHA-stimulated mononuclear cells. The suppressive factor(s) has not been characterized in molecular terms, but suppressive activity was recovered in fractions with a molecular weight of about 67,000 and in both the glycoprotein fraction and in the glycoprotein-depleted fraction of the HIV lysate. Sera from one-third of a small series (N = 13) of individuals with antibodies to HIV seem to be able to neutralize the suppressive properties of HIV lysate in cultures.     

Blood–Brain Barrier Permeability to Sodium. Modification by Glucose or Insulin?

In order to explore the pathogenetic mechanism underlying the changes in blood-brain barrier sodium transport in experimental diabetes, the effects of hyperglycemia and of hypoinsulinemia were studied in nondiabetic rats. In untreated diabetes, the neocortical blood-brain barrier permeability for sodium decreased by 20% (5.6 +/- 0.7 versus 7.0 +/- 0.8 X 10(5) ml/g/s) as compared to controls. Intravenous infusion of 50% glucose for 2 h was associated with a decrease in the blood-brain barrier permeability to sodium (5.4 +/- 1.2 X 10(5) ml/g/s), whereas rats treated with an inhibitor of insulin-secretion (SMS 201-995, a somatostatin-analogue) had normal sodium permeability (7.3 +/- 2.0 X 10(5) ml/g/s). Acute insulin treatment of diabetic rats normalized the sodium permeability within a few hours as compared to a separate control group (7.7 +/- 1.1 versus 6.9 +/- 1.4 X 10(5) ml/g/s). To elucidate whether the abnormal blood-brain barrier passage is caused by a metabolic effect of glucose or by the concomitant hyperosmolality, rats were made hyperosmolar by intravenous injection of 50% mannitol. Although not statistically significant, blood-brain barrier sodium permeability increased in hyperosmolar rats as compared to the control rats (8.3 +/- 1.0 and 7.0 +/- 1.9 X 10(5) ml/g/s, respectively). It is concluded that either hyperglycemia per se or a glucose metabolite is responsible for the blood-brain barrier abnormality which occurs in diabetes. Further, we suggest that the specific decrease of sodium permeability could be the result of glucose-mediated inhibition of the Na+K+-ATPase localized at the blood-brain barrier.     

Analysis of functional domain organization in DNA topoisomerase II from humans and Saccharomyces cerevisiae.

The functional domain structure of human DNA topoisomerase IIalpha and Saccharomyces cerevisiae DNA topoisomerase II was studied by investigating the abilities of insertion and deletion mutant enzymes to support mitotic growth and catalyze transitions in DNA topology in vitro. Alignment of the human topoisomerase IIalpha and S. cerevisiae topoisomerase II sequences defined 13 conserved regions separated by less conserved or differently spaced sequences. The spatial tolerance of the spacer regions was addressed by insertion of linkers. The importance of the conserved regions was assessed through deletion of individual domains. We found that the exact spacing between most of the conserved domains is noncritical, as insertions in the spacer regions were tolerated with no influence on complementation ability. All conserved domains, however, are essential for sustained mitotic growth of S. cerevisiae and for enzymatic activity in vitro. A series of topoisomerase II carboxy-terminal truncations were investigated with respect to the ability to support viability, cellular localization, and enzymatic properties. The analysis showed that the divergent carboxy-terminal region of human topoisomerase IIalpha is dispensable for catalytic activity but contains elements that specifically locate the protein to the nucleus.     

Influence of Temperature and Floret Age on Nectar Secretion in Trifolium repens L.

The influence of temperature on nectar secretion in non-pollinatedflorets of Trifolium repens was investigated in growth chambersat 10, 14, 18 and 22°C. The effect of temperature on therate of nectar secretion was significant in all clones. Theoptimum temperature for secretion in three clones varied from10°C for a clone of Icelandic origin, to 18°C in a cloneselected from a Danish variety. Similarly, the average nectaryield varied significantly among clones of different geographicalorigin. One clone secreted two to four times more than othersat 10°C. The optimum day temperature for nectar secretionwas higher when the plants were exposed to low night temperature,presumably a result of decreased night respiration. Nectar accumulatedat the floret base until senescence. Evidence for reabsorptionof nectar was obtained in four clones. Sucrose, fructose andglucose were identified as the major sugars in the nectar. Highnight temperatures led to decreased sucrose percentage in favourof glucose and fructose. The frequency of new florets openingper day was not influenced by temperatures between 10 and 22°Cin one clone, whereas low temperatures significantly decreasedthe number of new florets in another. Few or no modified stomatawere observed in the epidermis of the nectary. The high variationwith respect to nectar secretion at low temperatures, alongwith the high heritability of this quality, suggests that breedingfor high nectar production at low temperature is plausible.The significance of nectar yield in pollination biology is discussed.Copyright1994, 1999 Academic Press Trifolium repens, white clover, nectar, temperature, floret age, flowering, nectary     

The effect of acetic acid and specific growth rate on acetic acid tolerance and trehalose content of Saccharomyces cerevisiae

Summary The effects of acetic acid and specific growth rate on acetic acid tolerance and trehalose content of Saccharomyces cerevisiae CBS 2806 were studied using anaerobic chemostat cultures. Cells grown in the presence of acetic acid at a defined specific growth rate showed a higher acetic acid tolerance and a slightly lower trehalose content. Cells grown at a low specific growth rate showed a lower energy demand, a higher acetic acid tolerance, and a higher trehalose content. These results indicate that trehalose plays a growth rate dependent role in the tolerance of S. cerevisiae to acetic acid.     

Direct application of carbendazim and propiconazole at field rates to the external mycelium of three arbuscular mycorrhizal fungi species: effect on 32P transport and succinate dehydrogenase activity

 The influence of the systemic fungicides propiconazole (Tilt 250E) and carbendazim (Bavistin) at field application rates on the functioning of three arbuscular mycorrhizal fungi was studied. Short-term fungal ³²P transport and succinate dehydrogenase (SDH) activity in external hyphae of Glomus intraradices Schenck and Smith, G. claroideum Schenck and Smith and G. invermaium Hall in symbiosis with pea (Pisum sativum L.) were measured. In the experimental system used, the hyphae grew into two root-free hyphal compartments (HCs). The fungicides were applied to each HC 24 days after sowing and ³²P was added to one HC of each pot. Four days later, the fungicide effect on fungal P transport was measured as the difference in ³²P content of treated and untreated plants. SDH activity in fungal hyphae was determined in the HCs given no ³²P. Carbendazim severely inhibited ³²P transport and SDH activity in external hyphae at an application rate of 0.5 μg g^–1 soil. The ergosterol inhibitor propiconazole affected none of these parameters. The fungicides had similar effects on all three fungal species, although P transport efficiency and SDH activity differed markedly between the fungi. Accepted: 12 December 1996     

Concentration-dependent effects of potassium dichromate on the cell cycle

Hexavalent chromium is found to be a strong mutagen, and it also is a potential carcinogen in man. DNA flow cytometry, growth measurements, and determinations of mitotic index show that 1-2 microM K2Cr2O7 produces a prolongation of the G2 phase of the cell cycle in NHIK 3025 cells. By increasing the chromate concentrations (greater than 2 microM K2Cr2O7) the cells are also arrested in G2 phase. We have found, using synchronized cells and measuring cell cycle time, that the most chromate-sensitive part of the cell cycle is S phase. This phase is also somewhat prolonged, and the cells became arrested in early S phase at high toxic K2Cr2O7 concentrations (8 microM). Our results thus indicate that K2Cr2O7 has an effect within S phase--maybe on DNA/RNA synthesis--and also interferes with processes necessary for progression through the G2 phase.