Purified viral neuraminidase vaccine to control influenza.

The control of influenza by immunoprophylaxis is difficult because of the antigenic mutability of the influenza virus and the unpredictability of its epidemiologic behaviour. The inactivated whole-virus vaccine currently used is not ideal. Vaccination with pure neuraminidase is suggested. The induced antineuraminidase antibody will restrict viral invasion. Mild illness may or may not occur. On subsequent exposure to influenza virus the individual will produce antihemagglutinin and antineuraminidase antibodies and will be resistant to both infection and illness. Since antigenic changes are less frequent in the viral neuraminidase than in the viral hemagglutinin, the vaccine would be usable for longer periods than the presently used inactivated whole-virus vaccine.     

A photoaffinity label for the thromboxane A2/prostaglandin H2 receptor in human blood platelets

A photoactive iodoarylazide derivative (I-APA-PhN3) of the competitive thromboxane A2/prostaglandin H2 (TXA2/PGH2) antagonist 13-azaprostanoic acid is evaluated. Upon photoactivation, the compound was found to inhibit specifically and irreversibly human platelet aggregation induced by the TXA2/PGH2 mimetic U46619. In receptor-binding studies using [3H]U46619, I-APA-PhN3 exhibited an IC50 of 300 nM for inhibition of U46619 binding. Photoactivation of I-APA-PhN3 resulted in an irreversible 58% reduction in specific binding of U46619. This compound and its corresponding ratio-iodinated form will prove to be useful tools for the isolation and purification of the TXA2/PGH2-binding protein in human platelets.     

"Pyruvate recycling" and its influence on the estimation of the pentose pathway in intact liver and Morris hepatoma 5123TC cells

The phenomenon of "pyruvate recycling" is demonstrated in perfused rat liver, rabbit liver in situ and in Morris Hepatoma 5123TC cells and quantitatively measured using [2-14C]pyruvate and the method of Friedmann et al. (1971). Various metabolites, viz. lactate, DHAP, glucose, glucose 6-P and fructose 6-P were isolated and degraded following the metabolism of [2-14C]pyruvate and [2-14C]glycerol in order to assess the 14C-distributions imparted by "pyruvate recycling" reactions. The labelling of DHAP, lactate, glucose and glucose 6-P showed 14C randomizations consistent with the operation and the quantitative extent of "pyruvate recycling". These findings support the proposal that the actions of "pyruvate recycling" may account for the failure to find significant levels of 14C isotope at C-1 of glucose 6-P following the metabolism of [4,5,6-14C]- or [6-14C]glucose by L-type pentose pathway metabolism in aerobic intact tissues. "Pyruvate recycling" diminishes the measured value of the L-type pentose cycle in intact tissues and qualifies one of the mechanistic predictions of the L-type pentose pathway which was unravelled by tracing its reactions with labelled ribose 5-P and liver enzymes (Horecker et al., 1954; Williams et al., 1978a,b) in vitro. The demonstration of an association of L-type pentose pathway reactions with "pyruvate recycling" by way of the common reactions of their triose-P intermediates qualifies the superficial acceptance of the predictions of the L-type pathway in vitro for the distribution of isotopic labels by aerobic tissues in vivo.     

Mechanism and quantitative contribution of the pentose pathway to the glucose metabolism of Morris hepatoma 5123C

An investigation of the mechanism and quantitative contribution of the pentose phosphate pathway in the glucose metabolism of Morris Hepatoma 5123C is reported. Morris Hepatoma 5123C has an active non-oxidative segment of pentose pathway as judged by its ability to convert ribose 5-P to hexose 6-P in a standard assay. Based on compliance with qualitative and quantitative criteria, the cells exhibit the L-type pentose pathway reaction sequence rather than the F-type pathway. This compliance included the formation of intermediates characteristic of the L-type pathway, namely arabinose 5-P, octulose mono- and bisphosphates and sedoheptulose 1,7-bisphosphate, during the dissimilation of ribose 5-P to hexose 6-P. The intermediary role of arabinose 5-P was suggested by the incorporation of its carbon into various intermediates and products of the pentose pathway. Intermediary roles for ido octulose mono- and bisphosphates were supported by their participation in the reaction catalyzed by the phosphotransferase enzyme of the L-type pentose pathway. Presence of L-type PP reactions was further affirmed by 14C-prediction labelling experiments using [5-14C]- and [2-14C]glucose as specifically labelled substrates. Using two methods of measurement, the F-type pentose cycle made a negligibly small contribution to glucose metabolism, while the measured value of the L-type pentose pathway accounted for 30% (approx.) of the total glucose metabolism of these cells, a value consistent with the high activity of the enzymes of the L-type pentose pathway in Morris Hepatoma 5123C cells and the very high activity of the non-oxidative segment of the pathway in vitro. The findings validate the proposal that the L-type pentose pathway reactions constitute the non-oxidative segment of the pathway in Morris Hepatoma 5123C cells. Reasons involving pyruvate recycling reactions show why there is low incorporation of 14C-isotope in C-1 of glucose 6-P, when [4,5,6-14C]glucose and [6-14C]glucose are L-type PP test substrates in intact cells.     

Relative sensitivity of photosynthesis and respiration to freeze-thaw stress in herbaceous species : importance of realistic freeze-thaw protocols

The relative effect of a freeze-thaw cycle on photosynthesis, respiration, and ion leakage of potato leaf tissue was examined in two potato species, Solanum acaule Bitt. and Solanum commersonii Dun. Photosynthesis was found to be much more sensitive to freezing stress than was respiration, and demonstrated more than a 60% inhibition before any impairment of respiratory function was observed. Photosynthesis showed a slight to moderate inhibition when only 5 to 10% of the total electrolytes had leaked from the tissue (reversible injury). This was in contrast to respiration which showed no impairment until temperatures at which about 50% ion leakage (irreversible injury) had occurred. The influence of freeze-thaw protocol was further examined in S. acaule and S. commersonii, in order to explore discrepancies in the literature as to the relative sensitivities of photosynthesis and respiration. As bath cooling rates increased from 1°C/hour to about 3 or 6°C/hour, there was a dramatic increase in the level of damage to all measured cellular functions. The initiation of ice formation in deeply supercooled tissue caused even greater damage. As the cooling rates used in stress treatments increased, the differential sensitivity between photosynthesis and respiration nearly disappeared. Examination of agriculturally relevant, climatological data from an 11 year period confirmed that air cooling rates in the freezing range do not exceed 2°C/hour. It was demonstrated, in the studies presented here, that simply increasing the actual cooling rate from 1.0 to 2.9°C/hour, in frozen tissue from paired leaflet halves, meant the difference between cell survival and cell death.     

Stress modulates calcium mobilization in immune cells

Both acute and chronic restraint stress modulated mitogen-induced increases in cytoplasmic free-calcium concentrations ([Ca2+]i) in mouse spleen cells. Dual-color analysis of lymphocyte subpopulations demonstrated that acute (2 hour) restraint stress suppressed mitogen-stimulated increases in [Ca2+]i in CD4+ T cells, but enhanced [Ca2+]i in CD8+ T cells. Chronic restraint stress (2 hours daily for up to 21 days) resulted in a significant suppression of mitogen-stimulated increases in [Ca2+]i in CD4+ T cells at 3 and 7 days, but not at 21 days. CD8+ T cells were unaffected by chronic stress. Chronic stress (for 7 days) had a modest suppressive effect on mitogen-induced Ca2+ responses in B cells. Within T lymphocyte subpopulations, both acute and chronic stress predominantly affected CD4+ T cells, which may induce a functional reversal of the CD4/CD8 ratios in vivo. Such a reversal could result in suppression of a variety of immune responses such as lymphocyte proliferation and antigen-specific antibody production. These findings indicate that the inhibitory effects of stress on calcium mobilization in lymphocytes may be an early event mediating stress-induced immunosuppression.     

Nutrient levels in malformed and healthy tissues of mango (Mangifera indica L.)

Samples of malformed and healthy panicles of mango (Mangifera indica L.) as well as leaves and shoots bearing them were collected at different stages of development (fully swollen buds, bud inception, fully grown panicles prior to full bloom and at full bloom) over two consecutive years and were analysed for their macro- and micronutrient status. In addition, malformed and healthy seedlings were collected and analysed. Malformed panicles were found to be significantly higher in N at all the developmental stages except at bud inception. Phosphorus and K also tended to accumulate in malformed panicles at later stages of their development. In general, malformed panicles exhibited lower levels of P, K and Ca than healthy panicles. The differences in levels of Mg and S in malformed and healthy panicles were not significant. All micronutrients were in much lower concentrations in malformed panicles except for Mn which appears to accumulate in malformed panicles particularly at the early stages of development. The leaves on the shoots bearing malformed panicles also showed a tendency to accumulate N, while P, Mg and S were always higher in leaves on shoots bearing healthy panicles. The leaves on shoots bearing healthy panicles had lower levels of Fe, Cu and Mn, whereas levels of Zn and B tended to be higher in leaves on shoots bearing malformed panicles. The nutrient concentration differences between the two kinds of shoots were generally nonsignificant (P=0.05), except for K and S which were significantly lower in shoots bearing malformed panicles. The shoots bearing malformed panicles showed significantly (P=0.05) higher levels of almost all nutrients compared with shoots bearing healthy panicles. Vegetative malformation was found to be associated significantly (p=0.05) with higher amounts of all nutrients except Ca which was significantly higher in healthy seedlings. The present study, therefore, seems to point to lower Ca as one of the pre-disposing factors causing malformation in mango.A part of Ph.D. thesis of the senior author.A part of Ph.D. thesis of the senior author.