Thymic selection of CD4+CD25+ regulatory T cells induced by an agonist self-peptide.

Despite accumulating evidence that regulatory T cells play a crucial role in preventing autoimmunity, the processes underlying their generation during immune repertoire formation are unknown. We show here that interactions with a single self-peptide can induce thymocytes that bear an autoreactive T cell receptor (TCR) to undergo selection to become CD4+CD25+ regulatory T cells. Selection of CD4+CD25+ thymocytes appears to require a TCR with high affinity for a self peptide because thymocytes that bear TCRs with low affinity do not undergo selection into this pathway. Our findings indicate that specificity for self-peptides directs the selection of CD4+CD25+ regulatory thymocytes by a process that is distinct from positive selection and deletion.

Virus-induced maturation and activation of autoreactive memory B cells.

We have examined B cell populations that participate in distinct phases of the immune response to the influenza virus A/PR/8/34 hemagglutinin (HA) for their susceptibility to negative selection in mice that express the HA as a neo-self-antigen (HA104 mice). We demonstrated previously that specificity for the neo-self-HA causes a population of immunoglobulin G antibody-secreting cells, which dominate the primary response to virus immunization in BALB/c mice, to be negatively selected in HA104 mice. We find here that in contrast to these primary response B cells, HA-specific memory response B cells developed equivalently in HA104 and nontransgenic (BALB/c) mice. Indeed, there was no indication that HA-specific B cells were negatively selected during memory formation in influenza virus-immunized HA104 mice, even though the neo-self-HA can be recognized by memory B cells. Furthermore, HA-specific autoantibodies were induced in the absence of virus immunization by mating HA104 mice with mice transgenic for a CD4(+) HA-specific T cell receptor. These findings indicate that specificity for a self-antigen does not prevent the maturation of autoreactive B cells in the germinal center pathway. Rather, the availability of CD4(+) T cell help may play a crucial role in regulating autoantibody responses to the HA in HA104 mice.

Impaired CD4 T cell activation due to reliance upon B cell-mediated costimulation in nonobese diabetic (NOD) mice.

Diabetes in nonobese diabetic (NOD) mice results from the activation of I-A(g7)-restricted, islet-reactive T cells. This study delineates several characteristics of NOD CD4 T cell activation, which, independent of I-A(g7), are likely to promote a dysregulated state of peripheral T cell tolerance. NOD CD4 T cell activation was found to be resistant to antigenic stimulation via the TCR complex, using the progression of cell division as a measure. The extent of NOD CD4 T cell division was highly sensitive to changes in Ag ligand density. Moreover, even upon maximal TCR complex-mediated stimulation, NOD CD4 T cell division prematurely terminated. Maximally stimulated NOD CD4 T cells failed to achieve the threshold number of division cycles required for optimal susceptibility to activation-induced death, a critical mechanism for the regulation of peripheral T cell tolerance. Importantly, these aberrant activation characteristics were not T cell-intrinsic but resulted from reliance on B cell costimulatory function in NOD mice. Costimulation delivered by nonautoimmune strain APCs normalized NOD CD4 T cell division and the extent of activation-induced death. Thus, by disrupting the progression of CD4 T cell division, polarization of APC costimulatory function to the B cell compartment could allow the persistence and activation of diabetogenic cells in NOD mice.

The impact of religious faith and practice on patients suffering from a major affective disorder: a cost analysis.

Presents empirical data showing the relationship between religious beliefs and practices and lengths of stay in the hospital for patients suffering from one form of mental illness. Includes a spiritual injury scale which measures guilt, anger or resentment, sadness/grief, lack of meaning, feeling God/life has treated one unfairly, religious doubt, and fear of death. Shows in statistical form the relationship between these spiritual injuries and length of stay in the hospital. Indicates that spiritual injury issues are positively associated with longer lengths of hospital stay and that an inverse relationship exists between religious faith as measured by church attendance and cost for health care.

Electron microscopic studies of magnetosomes in magnetotactic bacteria.

Electron microscopic studies on magnetosomes in magnetotactic bacteria have revealed much information on their composition, structure, and even the formation of their mineral phase. The mineral phases of the magnetosomes are of two general types: iron oxides and iron sulfides. Iron oxide-type magnetosomes contain particles of the ferrimagnetic mineral magnetite (Fe3O4) while the iron sulfide-type contain ferrimagnetic greigite (Fe3S4), greigite and non-magnetic pyrite (FeS2), or possibly ferrimagnetic pyrrhotite (Fe7S8). Regardless of their composition, the crystalline particles in magnetosomes have a narrow size range: approximately 35 to 120 nm. Magnetite crystals in this size range are single-magnetic-domains and confer a permanent magnetic dipole moment to the cell. The single-domain size range for greigite is not known but is probably similar to that for magnetite. The morphology of the particles in the bacterial magnetosomes appears to be species-specific. Morphologies of magnetite crystals in different species of magnetotactic bacteria include cubo-octahedra, parallelepipedal (truncated hexahedral or octahedral prisms), and tooth- or bullet-shaped (anisotropic). Morphologies of greigite particles include cubo-octahedra and rectangular prismatic. The greigite-pyrite particles are generally pleomorphic with no consistent crystalline morphology. A membrane has been shown to surround the particles in some organisms and may be involved in the formation of the crystalline phase while also providing physical constraints on the size and the shape of the crystal. These results clearly indicate that the biomineralization process involved in the bacterial magnetosome, a good example of a self-assembled structure on a nanometer scale, is highly controlled by the organism.

Takayasu arteritis in a middle-aged Caucasian woman: clinical course correlated with duplex ultrasound and angiography.

Takayasu arteritis, an occlusive arteritis usually involving the aorta and its major branches, occurs most commonly in young oriental women. The authors report the case of a 54-year-old caucasian woman with Takayasu arteritis who initially presented with the inflammatory manifestations of fever and markedly accelerated erythrocyte sedimentation rate. Over 2 months she developed evidence of vascular insufficiency with arm claudication, diminished radial pulses, and decreased blood pressure in the arms, suggestive of an occlusive arteritis. Arteriography revealed the typical findings of Takayasu arteritis, which involved the brachial and axillary arteries but spared the aorta and its major branches. Changes in the patient's clinical course were correlated with sedimentation rate, angiography, and Duplex sonography.

Roles of carbohydrate supply and phytohormones in maize kernel abortion.

Kernels at the ear tip of field grown maize (Zea mays L.) often abort during flowering, resulting in significant yield loss. The objective of this study was to determine if abortion is initiated by an inadequate supply of carbohydrates for growth of ear tip kernels, and/or by a hormonal signal. Field grown maize plants were either unshaded or shaded during flowering to increase kernel abortion. Nonstructural carbohydrates, indoleacetic acid (IAA), abscisic acid (ABA), and cytokinins were measured in aborting and nonaborting kernels, before and after abortion occurred. Kernel abortion was initiated 8 days after anthesis (DAA) and was complete by 12 DAA, when kernels ceased dry weight accumulation. Concentrations of reducing sugars, sucrose, and starch in aborting kernels were not significantly different from those in nonaborting kernels up to 12 DAA. Also, total carbohydrate concentrations were higher in the cob of aborting than of nonaborting kernels from 8 to 26 DAA. These data suggest that kernel abortion is not initiated by an inadequate supply of carbohydrates. However, accumulation of reducing sugars in the cob of aborting kernels suggests that transfer of sugars from cob to kernels is impaired early in the abortion process. Differences in IAA, ABA, and cytokinin concentrations between aborting and nonaborting kernels were only observed after abortion was complete. Kernel abortion is apparently not initiated by a signal of these hormones. After completion of abortion, aborted kernels contained higher concentrations of ABA and lower concentrations of IAA than nonaborted kernels. There was also a trend toward higher concentrations of zeatin riboside in nonaborted kernels. Abscisic acid may promote kernel abortion after the process has been initiated. A mechanism for kernel abortion is discussed.

Assimilation of [N]Nitrate and [N]Nitrite in Leaves of Five Plant Species under Light and Dark Conditions.

Light dependency of nitrate and nitrite assimilation to reduced-N in leaves remains a controversial issue in the literature. With the objective of resolving this controversy, the light requirement for nitrate and nitrite assimilation was investigated in several plant species. Dark and light assimilation of [(15)N]nitrate and [(15)N]nitrite to ammonium and amino-N was determined with leaves of wheat, corn, soybean, sunflower, and tobacco. In dark aerobic conditions, assimilation of [(15)N]nitrate as a percentage of the light rate was 16 to 34% for wheat, 9 to 16% for tobacco, 26% for corn, 35 to 76% for soybean, and 55 to 63% for sunflower. In dark aerobic conditions, assimilation of [(15)N]nitrite as a percentage of the light rate was 11% for wheat, 7% for tobacco, 13% for corn, 28 to 36% for soybeans, and 12% for sunflower. It is concluded that variation among plant species in the light requirement for nitrate and nitrite assimilation explains some of the contradictory results in the literature, but additional explanations must be sought to fully resolve the controversy.In dark anaerobic conditions, the assimilation of [(15)N]nitrate to ammonium and amino-N in leaves of wheat, corn, and soybean was 43 to 58% of the dark aerobic rate while dark anaerobic assimilation of [(15)N]nitrite for the same species was 31 to 41% of the dark aerobic rate. In contrast, accumulation of nitrite in leaves of the same species in the dark was 2.5-to 20-fold higher under anaerobic than aerobic conditions. Therefore, dark assimilation of nitrite cannot alone account for the absence of nitrite accumulation in the in vivo nitrate reductase assay under aerobic conditions. Oxygen apparently inhibits nitrate reduction in the dark even in leaves of plant species that exhibit a relatively high dark rate of [(15)N]nitrite assimilation.

Light and Dark Controls of Nitrate Reduction in Wheat (Triticum aestivum L.) Protoplasts.

Protoplasts were isolated from the leaves of nitrate-cultured wheat (Triticum aestivum L. var. Frederick) seedlings. When incubated in the dark, protoplasts accumulated nitrite under anaerobic, but not under aerobic, conditions. The assimilation of [(15)N]nitrite by protoplasts was strictly light-dependent, and no loss of nitrite from the assay medium was observed under dark aerobic conditions. Therefore, the absence of nitrite accumulation under dark aerobic conditions was the result of an O(2) inhibition of nitrate reduction and not a stimulation of nitrite reduction. In the presence of antimycin A, protoplasts accumulated nitrite under dark aerobic conditions. The oxygen inhibition of nitrate reduction was apparently due to a competition between nitrate reduction and dark respiration for cytoplasmic-reducing equivalents.Oxygen control of nitrate reduction was not observed in the light, since protoplasts assimilated [(15)N]nitrate to amino-N under light aerobic conditions. It has been proposed that the increase of the ATP-to-ADP ratio in the light inhibits dark respiration and allows nitrate reduction to occur under aerobic conditions. To test this hypothesis, protoplast N and C assimilation was assayed in the presence of nigericin, an uncoupler of photophosphorylation. The dark to light increase of the protoplast energy charge was not observed in the presence of nigericin, and CO(2) fixation was completely inhibited by the uncoupler. In contrast, rates of in vivo nitrate reduction (N(2) and air) and nitrite reduction were relatively unaffected by nigericin, and light-driven nitrate assimilation was inhibited by only 20%. Nigericin had no effect on the dark-to-light increase of protoplast NADH and NADPH levels. It is proposed that the light-induced increase of cytoplasmic-reducing equivalents suppresses the competition between nitrate reduction and dark respiration and allows nitrate reduction to occur under aerobic conditions. Dark-to-light changes of the ATP-to-ADP ratio apparently are not critical to the regulation of nitrate reduction.

Availability of reduced N and carbohydrates for ear development of maize.

Changes in dry weights, reduced N, nitrate, and nitrate reductase activity of various plant parts of the above ground vegetation (stover) and ears of field grown maize were measured at intervals between anthesis and grain maturity. Nonstructural carbohydrate contents were also measured in some instances. Changes in dry weight and reduced N content were used to approximate net in situ photosynthetic and nitrate assimilation activities and to determine whether the availability of photosynthate or reduced N was limiting grain production.Of the five hybrids studied, all showed extensive remobilization (loss) of reduced N from the stover during grain development. This loss of stover N was initiated by 18 to 21 days after anthesis. Most of this loss of N (about 70%) was from the leaves. In contrast, three of the five hybrids had more vegetative dry weight at grain maturity than at anthesis, while the loss of stover dry weight by the other two hybrids was negligible. By 42 days after anthesis when the bulk of the ear weight had been acquired, the average gain in stover dry weight for the five hybrids was 12% while the loss of stover reduced N was 28%. Where measured, the increase in stover dry weight was largely due to deposition of carbohydrates in the stalk. These results show that the photosynthetic capacity was adequate while nitrate reduction capacity was inadequate for ear demands. The changes in the rate of accumulation of dry weight and reduced N by the ear indicated that the rate of supply of reduced N to the ear could have limited ear development for one of the five hybrids. The dry weight and carbohydrate (where measured) accumulation in the vegetation during the first 42 days after anthesis infers that the rate of supply of photosynthate to the ear was probably not a limiting factor for any of the five hybrids.The maximum remobilization of stover N during grain development was 1.8 g N plant(-1) for the genotypes examined, while the amount of reduced N accumulated by the grain varied from 1 to 5 g plant(-1). The amount of newly reduced N (nitrate reduced after anthesis) provided from 48 to 72% of the total N accumulated by the ear. The relative amounts of newly reduced N and remobilized N vary with genotype and environment. With respect to insuring high productivity, it was concluded that there is more flexibility in the system (genotype and environment) for increasing the supply of newly reduced N than in enhancing the remobilization of vegetative N.

Relationship between Nitrate Uptake, Flux, and Reduction and the Accumulation of Reduced Nitrogen in Maize (Zea mays L.): I. GENOTYPIC VARIATION.

The study presented here was an extension of a preceding field project concerned with changes in N metabolism of four maize hybrids during grain development. The objectives were to relate uptake, flux, and reduction of nitrate to accumulation of reduced N in growth-chamber-grown seedlings of the same four hybrids and to compare these results with those obtained in the field study.Hybrid D took up more nitrate than the other three hybrids, primarily because of a larger root system. The correlations between total N (nitrate plus reduced N plant(-1)) accumulated by harvest and root dry weight or shoot to root ratios were r = +0.97 and -0.90, respectively. Correlations with shoot dry weight were low. Although the larger root system indicates enhanced partitioning of photosynthate to the root of hybrid D, the observations made do not elucidate the role of photosynthate in increasing nitrate uptake. There was no genetic difference in partitioning of nitrate (per cent of total) among the plant parts; however, the hybrids differed in amounts of nitrate stored in stalks and midribs. Hybrids D and B accumulated more nitrate than A and C.Although two of the hybrids (A and C) with highest nitrate reductase activity had the lowest concentrations of nitrate in all plant parts, nitrate reductase activity was not correlated with accumulation of nitrate or reduced N for the four hybrids. Uptake and flux of nitrate were not numerically related to accumulation of reduced N for the four hybrids. Among the four hybrids, nitrate flux was not associated with level of leaf nitrate reductase activity. None of the individual parameters, as measured, would serve as an index for reduced N accumulation for these four hybrids. When the hybrid pairs were compared separately, it was evident that both rate of nitrate flux and level of nitrate reductase activity affect the accumulation of reduced N by the plant.Relative to the other hybrids, hybrid D that accumulated the most reduced N and nitrate as a 23-day-old seedling had the least reduced N in grain plus stover at maturity under field conditions. Hybrid C that had high nitrate reductase activity as a seedling had low nitrate reductase activity after anthesis under field conditions. These changes in metabolic activities with plant development and different environments illustrate the problems encountered in attempting to develop simple physiological or biochemical screening criteria useful in identifying superior cultivars at the seedling stage.

Relationship between Nitrate Uptake, Flux, and Reduction and the Accumulation of Reduced Nitrogen in Maize (Zea mays L.): II. EFFECT OF NUTRIENT NITRATE CONCENTRATION.

Two maize hybrids were grown under growth chamber conditions on solution or vermiculite medium that contained 2.5, 7.5, or 15 millimolar nitrate. The objectives were to determine: (a) the effect of nitrate supply on N metabolism and growth and (b) the interrelationship between nitrate uptake, flux, and reduction on the accumulation of reduced N and nitrate by the various plant parts and for the whole plant.Increases in nutrient nitrate concentration caused increases in (a) shoot, but not root, dry weight and (b) nitrate uptake, flux, and reduction and accumulation of nitrate and reduced N by the aerial plant parts of both hybrids. Increases in nitrate supply resulted in decreases in nitrate reductase activity and negligible increases in reduced N in the roots of both hybrids. At 2.5 and 15 millimolar, but not at 7.5 millimolar, external nitrate, hybrid B had higher rates of nitrate uptake and flux. Hybrid B also had lower nitrate reductase activity at all levels of external nitrate and accumulated less reduced N than did hybrid C, except when the plants were grown at 2.5 millimolar nitrate. Correlation values between nitrate uptake and flux were significant for each hybrid and for both hybrids, whereas correlations between nitrate reductase activity and flux and nitrate reductase activity and uptake were significant only for a given hybrid. The correlation values (pooling of all data) between (a) nitrate uptake, flux, or reduction and the accumulation of reduced N by the whole plant, and (b) flux x nitrate reductase activity and accumulation of reduced N were all positive and statistically significant. Because nitrate uptake, flux, and reduction (as measured) were all closely associated with the accumulation of reduced N by the plant, all three parameters should be measured in attempts to estimate the genetic potential of a maize genotype to accumulate reduced N.

Grain Protein Accumulation and the Relationship between Leaf Nitrate Reductase and Protease Activities during Grain Development in Maize (Zea mays L.): I. VARIATION BETWEEN GENOTYPES.

Four maize hybrids, two with high and two with low levels of postanthesis nitrate reductase activity were grown under field conditions. The characteristic enzyme patterns had been established in previous work. Nitrate reductase and proteases were measured in three representative leaves (ear leaf, fourth leaf above and fourth leaf below the ear) at intervals throughout the period of grain development. Concurrent with enzyme sampling, other plants were harvested and subdivided into top, middle and lower leaves, husks, stalks, and ear. Dry weights, nitrate, and reduced N were determined on all plant parts for each sampling. These data established the rate of N accumulation by the grain and depletion from the vegetative material and provide some insight into the relation between newly reduced and remobilized N and accumulation of grain N. Other plants were harvested at maturity for yield and harvest indices for dry weight and N.Nitrate reductase activity was higher in comparable leaves from the high than from the low nitrate reductase genotypes throughout the grain development period. There was no mathematical correlation between nitrate reductase activity and nitrate content of the leaves or stalks, however the high nitrate reductase genotypes maintained a higher amount of nitrate per plant (largely in the stalk) during the later stages of grain development. From the patterns of plant nitrate content it was deduced that the low nitrate reductase genotypes terminated nitrate absorption sooner than the high nitrate reductase types. Proteolytic activities (casein as substrate at pH 5.5 and 7.5) were higher and increased earlier in the low than in the high nitrate reductase genotypes. The "low nitrate reductase-high protease" genotypes had a higher percentage of grain N, and higher harvest index for N than did the "high nitrate reductase-low protease" genotypes. These results permit the tentative conclusions that: (a) redistribution of vegetative N accounted for more of the grain N in the low than in the high nitrate reductase genotypes; and (b) leaf protease activities are more closely related to the accumulation of grain N than leaf nitrate reductase activity.

Some New Aspects of the in Vivo Assay for Nitrate Reductase in Wheat (Triticum aestivum L.) Leaves: I. REEVALUATION OF NITRATE POOL SIZES.

Experiments were carried out to clarify problems encountered in measuring metabolic and storage pool sizes of nitrate in wheat leaf sections with an in vivo nitrate reductase assay. The leaf sections were from seedlings grown on 15 millimolar nitrate. Data obtained show that the cessation of nitrite accumulation, used as an index of the active nitrate pool size, could be caused by lack of anaerobiosis in the assay system, the lack of energy for nitrate reduction, or a loss of nitrate reductase activity. Availability of nitrate was never the limiting factor in this system. It is concluded that pool sizes of nitrate cannot be determined in wheat leaves with the in vivo assays employed.

Preliminary report on effect of topical applications of titanium tetrafluoride on dental caries.

An annual, one-minute application of a 1% solution of titanium tetrafluoride to the teeth on one side of the mouth of each of 110 children offered greater protection against caries after three years than was given to teeth on the other side of the mouth treated with a four-minute application of acid phosphate fluoride.