Gradients in embolism resistance within stems driven by secondary growth in herbs

The stems of some herbaceous species can undergo basal secondary growth, leading to a continuum in the degree of woodiness along the stem. Whether the formation of secondary growth in the stem base results in differences in embolism resistance between the base and the upper portions of stems is unknown. We assessed the embolism resistance of leaves and the basal and upper portions of stems simultaneously within the same individuals of two divergent herbaceous species that undergo secondary growth in the mature stem bases. The species were Solanum lycopersicum (tomato) and Senecio minimus (fireweed). Basal stem in mature plants of both species displayed advanced secondary growth and greater resistance to embolism than the upper stem. This also resulted in significant vulnerability segmentation between the basal stem and the leaves in both species. Greater embolism resistance in the woodier stem base was found alongside decreases in the pith-to-xylem ratio, increases in the proportion of secondary xylem, and increases in lignin content. We show that there can be considerable variation in embolism resistance across the stem in herbs and that this variation is linked to the degree of secondary growth present. A gradient in embolism resistance across the stem in herbaceous plants could be an adaptation to ensure reproduction or basal resprouting during episodes of drought late in the lifecycle.

Abscisic acid acts essentially on stomata, not on the xylem, to improve drought resistance in tomato

Drought resistance is essential for plant production under water-limiting environments. Abscisic acid (ABA) plays a critical role in stomata but its impact on hydraulic function beyond the stomata is far less studied. We selected genotypes differing in their ability to accumulate ABA to investigate its role in drought-induced dysfunction. All genotypes exhibited similar leaf and stem embolism resistance regardless of differences in ABA levels. Their leaf hydraulic resistance was also similar. Differences were only observed between the two extreme genotypes: sitiens (sit; a strong ABA-deficient mutant) and sp12 (a transgenic line that constitutively overaccumulates ABA), where the water potential inducing 50% embolism was 0.25 MPa lower in sp12 than in sit. Maximum stomatal and minimum leaf conductances were considerably lower in plants with higher ABA (wild type [WT] and sp12) than in ABA-deficient mutants. Variations in gas exchange across genotypes were associated with ABA levels and differences in stomatal density and size. The lower water loss in plants with higher ABA meant that lethal water potentials associated with embolism occurred later during drought in sp12 plants, followed by WT, and then by the ABA-deficient mutants. Therefore, the primary pathway by which ABA enhances drought resistance is via declines in water loss, which delays dehydration and hydraulic dysfunction.

Carbon gain is coordinated with enhanced stomatal conductance and hydraulic architecture in coffee plants acclimated to elevated [CO2]: The interplay with irradiance supply

We recently demonstrated that, under elevated [CO2] (eCa), coffee (Coffea arabica L.) plants grown at high light (HL), but not at low light (LL), display higher stomatal conductance (gs) than at ambient [CO2] (aCa). We then hypothesized that the enhanced gs at eCa/HL, if sustained at the long-term, would lead to adjustments in hydraulic architecture. To test this hypothesis, potted plants of coffee were grown in open-top chambers for 12 months under HL or LL (ca. 9 or 1 mol photons m-2 day-1, respectively); these light treatments were combined with two [CO2] levels (ca. 437 or 705 μmol mol-1, respectively). Under eCa/HL, increased gs was closely accompanied by increases in branch and leaf hydraulic conductances, suggesting a coordinated response between liquid- and vapor-phase water flows throughout the plant. Still under HL, eCa also resulted in increased Huber value (sapwood area-to-total leaf area), sapwood area-to-stem diameter, and root mass-to-total leaf area, thus further improving the water supply to the leaves. Our results demonstrate that Ca is a central player in coffee physiology increasing carbon gain through a close association between stomatal function and an improved hydraulic architecture under HL conditions.

Growth and Leaf Gas Exchange Upregulation by Elevated [CO2] Is Light Dependent in Coffee Plants

Coffee (Coffea arabica L.) plants have been assorted as highly suitable to growth at elevated [CO₂] (eC_a), although such suitability is hypothesized to decrease under severe shade. We herein examined how the combination of eC_a and contrasting irradiance affects growth and photosynthetic performance. Coffee plants were grown in open-top chambers under relatively high light (HL) or low light (LL) (9 or 1 mol photons m^-2 day^-1, respectively), and aC_a or eC_a (437 or 705 μmol mol^-1, respectively). Most traits were affected by light and CO₂, and by their interaction. Relative to aC_a, our main findings were (i) a greater stomatal conductance (g_s) (only at HL) with decreased diffusive limitations to photosynthesis, (ii) greater g_s during HL-to-LL transitions, whereas g_s was unresponsive to the LL-to-HL transitions irrespective of [CO₂], (iii) greater leaf nitrogen pools (only at HL) and higher photosynthetic nitrogen-use efficiency irrespective of light, (iv) lack of photosynthetic acclimation, and (v) greater biomass partitioning to roots and earlier branching. In summary, eC_a improved plant growth and photosynthetic performance. Our novel and timely findings suggest that coffee plants are highly suited for a changing climate characterized by a progressive elevation of [CO₂], especially if the light is nonlimiting.

An abrupt increase in foliage ABA levels on incipient leaf death occurs across vascular plants

Forest mortality during drought has been attributed to hydraulic failure, which can be challenging to measure. A limited number of alternative proxies for incipient leaf death exist. Here we investigate whether a terminal increase in abscisic acid (ABA) levels in leaves occurs across vascular land plants and is an indicator of imminent leaf death. For different species across vascular plants, we monitored ABA levels during lethal drought as well as leaf embolism resistance, across the canopy as leaves die following senescence, or when leaves are exposed to a heavy, lethal frost late in the growing season. We observed a considerable increase in foliage ABA levels once leaves showed signs of incipient leaf death. This increase in ABA levels upon incipient leaf death, could be induced by embolism during drought, by freezing or as leaves age naturally, and was observed in species spanning the phylogeny of vascular land plants as well as in an ABA biosynthetic mutant plant. A considerable increase in foliage ABA levels may act as an indicator of impending leaf death.

Exploring leaf hydraulic traits to predict drought tolerance of Eucalyptus clones

Ongoing changes in climate, and the consequent mortality of natural and cultivated forests across the globe, highlight the urgent need to understand the plant traits associated with greater tolerance to drought. Here, we aimed at assessing key foliar traits, with a focus on the hydraulic component, that could confer a differential ability to tolerate drought in three commercial hybrids of the most important Eucalyptus species utilized in tropical silviculture: E. urophyla, E. grandis and E. camaldulensis. All genotypes exhibited similar water potential when the 90% stomatal closure (Ψgs90) occurs with Ψgs90 always preceding the start of embolism events. The drought-tolerant hybrid showed a higher leaf resistance to embolism, but the leaf hydraulic efficiency was similar among all genotypes. Other traits presented by the drought-tolerant hybrid were a higher cell wall reinforcement, lower value of osmotic potential at full turgor and greater bulk modulus of elasticity. We also identified that the leaf capacitance after the turgor loss, the ratio between cell wall thickness (t) and lumen breadth (b) ratio (t/b)3, and the minimal conductance might be good proxies for screening drought-tolerant Eucalyptus genotypes. Our findings suggest that xylem resistance to embolism can be an important component of drought tolerance in Eucalyptus in addition to other traits aimed at delaying the development of high tensions in the xylem. Highlight Drought tolerance in tropical Eucalyptus hybrids encompasses a high leaf resistance to embolism and a suite of traits aimed at delaying the development of high tensions in the xylem.

Seeing is believing: what visualising bubbles in the xylem has revealed about plant hydraulic function

Maintaining water transport in the xylem is critical for vascular plants to grow and survive. The drought-induced accumulation of embolism, when gas enters xylem conduits, causes declines in hydraulic conductance (K ) and is ultimately lethal. Several methods can be used to estimate the degree of embolism in xylem, from measuring K in tissues to directly visualising embolism in conduits. One method allowing a direct quantification of embolised xylem area is the optical vulnerability (OV) technique. This method has been used across different organs and has a high spatial and temporal resolution. Here, we review studies using the OV technique, discuss the main advantages and disadvantages of this method, and summarise key advances arising from its use. Vulnerability curves generated by the OV method are regularly comparable to other methods, including the centrifuge and X-ray microtomography. A major advantage of the OV technique over other methods is that it can be simultaneously used to determine in situ embolism formation in leaves, stems and roots, in species spanning the phylogeny of land plants. The OV method has been used to experimentally investigate the spreading of embolism through xylem networks, associate embolism with downstream tissue death, and observe embolism formation in the field.

Impaired auxin signaling increases vein and stomatal density but reduces hydraulic efficiency and ultimately net photosynthesis

Auxins are known to regulate xylem development in plants, but their effects on water transport efficiency are poorly known. Here we used tomato plants with the diageotropica mutation (dgt), which has impaired function of a cyclophilin 1 cis-trans isomerase involved in auxin signaling, and the corresponding wild type (WT) to explore the mutation's effects on plant hydraulics and leaf gas exchange. The xylem of the dgt mutant showed a reduced hydraulically weighted vessel diameter (Dh) (24-43%) and conduit number (25-58%) in petioles and stems, resulting in lower theoretical hydraulic conductivities (Kt); on the other hand, no changes in root Dh and Kt were observed. The measured stem and leaf hydraulic conductances of the dgt mutant were lower (up to 81%), in agreement with the Kt values; however, despite dgt and WT plants showing similar root Dh and Kt, the measured root hydraulic conductance of the dgt mutant was 75% lower. The dgt mutation increased the vein and stomatal density, which could potentially increase photosynthesis. Nevertheless, even though it had the same photosynthetic capacity as WT plants, the dgt mutant showed a photosynthetic rate c. 25% lower, coupled with a stomatal conductance reduction of 52%. These results clearly demonstrate that increases in minor vein and stomatal density only result in higher leaf gas exchange when accompanied by higher hydraulic efficiency.

Xylem embolism spread is largely prevented by interconduit pit membranes until the majority of conduits are gas-filled

Xylem embolism resistance varies across species influencing drought tolerance, yet little is known about the determinants of the embolism resistance of an individual conduit. Here we conducted an experiment using the optical vulnerability method to test whether individual conduits have a specific water potential threshold for embolism formation and whether pre-existing embolism in neighbouring conduits alters this threshold. Observations were made on a diverse sample of angiosperm and conifer species through a cycle of dehydration, rehydration and subsequent dehydration to death. Upon rehydration after the formation of embolism, no refilling was observed. When little pre-existing embolism was present, xylem conduits had a conserved, individual embolism-resistance threshold that varied across the population of conduits. The consequence of a variable conduit-specific embolism threshold is that a small degree of pre-existing embolism in the xylem results in apparently more resistant xylem in subsequent dehydrations, particularly in angiosperms with vessels. While our results suggest that pit membranes separating xylem conduits are critical for maintaining a conserved individual conduit threshold for embolism when little pre-existing embolism is present, as the percentage of embolized conduits increases, gas movement, local pressure differences and connectivity between conduits increasingly contribute to embolism spread.

Limited plasticity in embolism resistance in response to light in leaves and stems in species with considerable vulnerability segmentation

Xylem resistance to embolism is a key metric determining plant survival during drought. Yet, we have a limited understanding of the degree of plasticity in vulnerability to embolism. Here, we tested whether light availability influences embolism resistance in leaves and stems. The optical vulnerability method was used to assess stem and leaf resistance to embolism in Phellodendron amurense and Ilex verticillata acclimated to sun and shade microenvironments within the same canopy. In both species, we found considerable segmentation in xylem resistance to embolism between leaves and stems, but only minor acclimation in response to light availability. With the addition of a third species, Betula pubescens, which shows no vulnerability segmentation, we sought to investigate xylem anatomical traits that might correlate with strong vulnerability segmentation. We found a correlation between the area fraction of vessels in the xylem and embolism resistance across species and tissue types. Our results suggest that minimal acclimation of embolism resistance occurs in response to light environment in the same individual and that the degree of vulnerability segmentation between leaves and stems might be determined by the vessel lumen fraction of the xylem.

The interplay between irrigation and fruiting on branch growth and mortality, gas exchange and water relations of coffee trees

The overall coordination between gas exchanges and plant hydraulics may be affected by soil water availability and source-to-sink relationships. Here we evaluated how branch growth and mortality, leaf gas exchange and metabolism are affected in coffee (Coffea arabica L.) trees by drought and fruiting. Field-grown plants were irrigated or not, and maintained with full or no fruit load. Under mild water deficit, irrigation per se did not significantly impact growth but markedly reduced branch mortality in fruiting trees, despite similar leaf assimilate pools and water status. Fruiting increased net photosynthetic rate in parallel with an enhanced stomatal conductance, particularly in irrigated plants. Mesophyll conductance and maximum RuBisCO carboxylation rate remained unchanged across treatments. The increased stomatal conductance in fruiting trees over nonfruiting ones was unrelated to internal CO2 concentration, foliar abscisic acid (ABA) levels or differential ABA sensitivity. However, stomatal conductance was associated with higher stomatal density, lower stomatal sensitivity to vapor pressure deficit, and higher leaf hydraulic conductance and capacitance. Increased leaf transpiration rate in fruiting trees was supported by coordinated alterations in plant hydraulics, which explained the maintenance of plant water status. Finally, by preventing branch mortality, irrigation can mitigate biennial production fluctuations and improve the sustainability of coffee plantations.

Drought-induced lacuna formation in the stem causes hydraulic conductance to decline before xylem embolism in Selaginella

Lycophytes are the earliest diverging extant lineage of vascular plants, sister to all other vascular plants. Given that most species are adapted to ever-wet environments, it has been hypothesized that lycophytes, and by extension the common ancestor of all vascular plants, have few adaptations to drought. We investigated the responses to drought of key fitness-related traits such as stomatal regulation, shoot hydraulic conductance (K_shoot ) and stem xylem embolism resistance in Selaginella haematodes and S. pulcherrima, both native to tropical understory. During drought stomata in both species were found to close before declines in K_shoot , with a 50% loss of K_shoot occurring at -1.7 and -2.5 MPa in S. haematodes and S. pulcherrima, respectively. Direct observational methods revealed that the xylem of both species was resistant to embolism formation, with 50% of embolized xylem area occurring at -3.0 and -4.6 MPa in S. haematodes and S. pulcherrima, respectively. X-ray microcomputed tomography images of stems revealed that the decline in K_shoot occurred with the formation of an air-filled lacuna, disconnecting the central vascular cylinder from the cortex. We propose that embolism-resistant xylem and large capacitance, provided by collapsing inner cortical cells, is essential for Selaginella survival during water deficit.

Osmotic adjustment and hormonal regulation of stomatal responses to vapour pressure deficit in sunflower

Dynamic variation of the stomatal pore in response to changes in leaf-air vapour pressure difference (VPD) constitutes a critical regulation of daytime gas exchange. The stomatal response to VPD has been associated with both foliage abscisic acid (ABA) and leaf water potential (Ψ  _l ); however, causation remains a matter of debate. Here, we seek to separate hydraulic and hormonal control of stomatal aperture by manipulating the osmotic potential of sunflower leaves. In addition, we test whether stomatal responses to VPD in an ABA-deficient mutant (w-1) of sunflower are similar to the wild type. Stomatal apertures during VPD transitions were closely linked with foliage ABA levels in sunflower plants with contrasting osmotic potentials. In addition, we observed that the inability to synthesize ABA at high VPD in w-1 plants was associated with no dynamic or steady-state stomatal response to VPD. These results for sunflower are consistent with a hormonal, ABA-mediated stomatal responses to VPD rather than a hydraulic-driven stomatal response to VPD.

Xylem Embolism Resistance Determines Leaf Mortality during Drought in Persea americana

The driver of leaf mortality during drought stress is a critical unknown. We used the commercially important tree Persea americana, in which there is a large variation in the degree of drought-induced leaf death across the canopy, to test whether embolism formation in the xylem during drought drives this leaf mortality. A large range in the number of embolized vessels in the petioles of leaves was observed across the canopy of plants that had experienced drought. Despite considerable variation between leaves, the amount of embolized vessels in the xylem of the petiole strongly correlated with area of drought-induced tissue death in individual leaves. Consistent with this finding was a large interleaf variability in xylem resistance to embolism, with a 1.45 MPa variation in the water potential at which 50% of the xylem in the leaf midrib embolized across leaves. Our results implicate xylem embolism as a driver of leaf mortality during drought. Moreover, we propose that heterogeneity in drought-induced leaf mortality across a canopy is caused by high interleaf variability in xylem resistance to embolism, which may act as a buffer against complete canopy death during prolonged drought in P. americana.

Misleading conclusions from exogenous ABA application: a cautionary tale about the evolution of stomatal responses to changes in leaf water status

Stomatal responses to changes in leaf water status are critical for minimizing excessive water loss during soil drought. A major debate has surrounded the evolution of stomatal responses to water status and this debate has particularly focused on the evolution of the regulatory role of the drought hormone abscisic acid (ABA). Studies relying on the application of high levels of exogenous ABA have occasionally concluded that all stomata respond to ABA and that stomatal regulation in response to this hormone has not evolved over the past 450 million years. In contrast, studies which have investigated stomatal function in intact plants, as well as the role of endogenous ABA in regulating stomatal aperture, have found major evolutionary transitions in the functional regulation of stomata across land plant lineages. We show that endogenous ABA plays no role in closing the stomata of the fern Nephrolepis exaltata during natural soil drought, in contrast to a recent finding using isolated epidermis and exceptionally high levels of exogenous ABA. We conclude that stomatal behavior in intact plants has evolved over time, and may have shaped the evolutionary and ecological success of successive land plant lineages.

Hydraulics Regulate Stomatal Responses to Changes in Leaf Water Status in the Fern Athyrium filix-femina

Stomatal responses to changes in leaf water status are important for the diurnal regulation of gas exchange and the survival of plants during drought. These stomatal responses in angiosperm species are well characterized, yet in species of nonseed plants, an ongoing debate surrounds the role of metabolism, particularly the role of the hormone abscisic acid (ABA), in functionally regulating stomatal responses to changes in leaf water status. Here, we measured the stomatal response to changes in vapor pressure difference (VPD) in two natural forms of the fern species Athyrium filix-femina, recently suggested to have stomata that are regulated by ABA. The two forms measured had considerable differences in key hydraulic traits, including leaf hydraulic conductance and capacitance, as well as the kinetics of stomatal response to changes in VPD. In both forms, the stomatal responses to VPD could be accurately predicted by a dynamic, mechanistic model that assumes guard cell turgor changes in concert with leaf turgor in the light, and not via metabolic processes including the level of ABA. During drought, endogenous ABA did not play a role in stomatal closure, and exogenous ABA applied to live, intact leaves did not induce stomatal closure. Our results indicate that functional stomatal responses to changes in leaf water status in ferns are regulated by leaf hydraulics and not metabolism. With ferns being sister to seed plants, this result has implications for the evolutionary reconstruction of functional stomatal responses across vascular land plant lineages.

Extended differentiation of veins and stomata is essential for the expansion of large leaves in Rheum rhabarbarum

PREMISE OF THE STUDY

The densities of veins and stomata govern leaf water supply and gas exchange. They are coordinated to avoid overproduction of either veins or stomata. In many species, where leaf area is greater at low light, this coordination is primarily achieved through differential cell expansion, resulting in lower stomatal and vein density in larger leaves. This mechanism would, however, create highly inefficient leaves in species in which leaf area is greater at high light. Here we investigate the role of cell expansion and differentiation as regulators of vein and stomatal density in Rheum rhabarbarum, which produces large leaves under high light.

METHODS

Rheum rhabarbarum plants were grown under full sunlight and 7% of full sunlight. Leaf area, stomatal density, and vein density were measured from leaves harvested at different intervals.

KEY RESULTS

Leaves of R. rhabarbarum expanded at high light were six times larger than leaves expanded at low light, yet vein and stomatal densities were similar. In high light-expanded leaves, minor veins were continuously initiated as the leaves expanded, while an extended period of stomatal initiation, compared to leaves expanded at low light, occurred early in leaf development.

CONCLUSIONS

We demonstrate that R. rhabarbarum adjusts the initiation of stomata and minor veins at high light, allowing for the production of larger leaves uncoupled from lower vein and stomatal densities. We also present evidence for an independent control of vein and stomatal initiation, suggesting that this adjustment must involve some unknown developmental mechanism.

Coordinated plasticity maintains hydraulic safety in sunflower leaves

The xylem cavitation threshold water potential establishes a hydraulic limit on the ability of woody species to survive in water-limiting environments, but herbs may be more plastic in terms of their ability to adapt to drying conditions. Here, we examined the capacity of sunflower (Helianthus annuus L.) leaves to adapt to reduced water availability by modifying the sensitivity of xylem and stomata to soil water deficit. We found that sunflower plants grown under water-limited conditions significantly adjusted leaf osmotic potential, which was linked to a prolongation of stomatal opening as soil dried and a reduced sensitivity of photosynthesis to water-stress-induced damage. At the same time, the vulnerability of midrib xylem to water-stress-induced cavitation was observed to be highly responsive to growth conditions, with water-limited plants producing conduits with thicker cell walls which were more resistant to xylem cavitation. Coordinated plasticity in osmotic potential and xylem vulnerability enabled water-limited sunflowers to safely extract water from the soil, while protecting leaf xylem against embolism. High plasticity in sunflower xylem contrasts with data from woody plants and may suggest an alternative strategy in herbs.

Similar geometric rules govern the distribution of veins and stomata in petals, sepals and leaves

Investment in leaf veins (supplying xylem water) is balanced by stomatal abundance, such that sufficient water transport is provided for stomata to remain open when soil water is abundant. This coordination is mediated by a common dependence of vein and stomatal densities on cell size. Flowers may not conform to this same developmental pattern if they depend on water supplied by the phloem or have high rates of nonstomatal transpiration. We examined the relationships between veins, stomata and epidermal cells in leaves, sepals and petals of 27 angiosperms to determine whether common spacing rules applied to all tissues. Regression analysis found no evidence for different relationships within organ types. Both vein and stomatal densities were strongly associated with epidermal cell size within organs, but, for a given epidermal cell size, petals had fewer veins and stomata than sepals, which had fewer than leaves. Although our data support the concept of common scaling between veins and stomata in leaves and flowers, the large diversity in petal vein density suggests that, in some species, petal veins may be engaged in additional functions, such as the supply of water for high cuticular transpiration or for phloem delivery of water or carbohydrates.

Physiological and Agronomic Performance of the Coffee Crop in the Context of Climate Change and Global Warming: A Review

Coffee is one of the most important global crops and provides a livelihood to millions of people living in developing countries. Coffee species have been described as being highly sensitive to climate change, as largely deduced from modeling studies based on predictions of rising temperatures and changing rainfall patterns. Here, we discuss the physiological responses of the coffee tree in the context of present and ongoing climate changes, including drought, heat, and light stresses, and interactions between these factors. We also summarize recent insights on the physiological and agronomic performance of coffee at elevated atmospheric CO₂ concentrations and highlight the key role of CO₂ in mitigating the harmful effects of heat stress. Evidence is shown suggesting that warming, per se, may be less harmful to coffee suitability than previously estimated, at least under the conditions of an adequate water supply. Finally, we discuss several mitigation strategies to improve crop performance in a changing world.

Leaves, not roots or floral tissue, are the main site of rapid, external pressure-induced ABA biosynthesis in angiosperms

Rapid biosynthesis of abscisic acid (ABA) in the leaf, triggered by a decrease in cell volume, is essential for a functional stomatal response. However, it is not known whether rapid biosynthesis of ABA is also triggered in other plant tissues. Through the application of external pressure to flower, root, and leaf tissues, we test whether a reduction in cell volume can trigger rapid increases in ABA levels across the plant body in two species, Solanum lycopersicum and Passiflora tarminiana. Our results show that, in contrast to rapid ABA synthesis in the leaf, flower and root tissue did not show a significant, increase in ABA level in response to a drop in cell volume over a short time frame, suggesting that rapid ABA biosynthesis occurs only in leaf, not in flower or root tissues. A gene encoding the key, rate-limiting carotenoid cleavage enzyme (9-cis-epoxycarotenoid dioxygenase, NCED) in the ABA biosynthetic pathway in S. lycopersicum, NCED1, was upregulated to a lesser degree in flowers and roots compared with leaves in response to applied pressure. In both species, floral tissues contained substantially lower levels of the NCED substrate 9'-cis-neoxanthin than leaves, and this ABA precursor could not be detected in roots. Slow and minimal ABA biosynthesis was detected after 2 h in petals, indicating that floral tissue is capable of synthesizing ABA in response to sustained water deficit. Our results indicate that rapid ABA biosynthesis predominantly occurs in the leaves, and not in other tissues.

Activities and participation in children with developmental coordination disorder: a systematic review

PURPOSE

To systematically review all literature published in peer reviewed journals from January 1995 to July 2008 in order to summarize and describe the activity limitations and participation restrictions of children with developmental coordination disorder (DCD).

METHODS

Multiple databases were systematically searched for articles related to DCD; only descriptive, intervention or qualitative articles were retained. Articles were coded using the International Classification of Function, Disability and Health (ICF) and descriptions of the activity and participation issues of individuals with DCD were identified.

RESULTS

Data analysis revealed that, from 371 articles that met inclusion criteria, only 44 (14.4%) presented any data related to activity or participation issues. Information was inconsistent and only 18 articles used published measurement tools. Most frequently cited issues were poor handwriting, difficulties playing ball games, getting dressed and participating in organized sports.

CONCLUSION

Evidence concerning activity and participation issues for children with DCD is limited in both volume and scope. Improved understanding of participation and of activity limitations in children with DCD is essential for clarifying diagnostic criteria, guiding assessment, and making evidence-based decisions regarding intervention. Researchers working with this population should make every effort to measure and consistently report the impact of children's motor impairments on function.

Measurements and modeling of reactive nitrogen deposition in southeast Brazil

Increased reactive nitrogen (Nr) deposition due to expansion of agro-industry was investigated considering emission sources, atmospheric transport and chemical reactions. Measurements of the main inorganic nitrogen species (NO2, NH3, HNO3, and aerosol nitrate and ammonium) were made over a period of one year at six sites distributed across an area of ∼130,000 km2 in southeast Brazil. Oxidized species were estimated to account for ∼90% of dry deposited Nr, due to the region's large emissions of nitrogen oxides from biomass burning and road transport. NO2-N was important closer to urban areas, however overall HNO3-N represented the largest component of dry deposited Nr. A simple mathematical modeling procedure was developed to enable estimates of total Nr dry deposition to be made from knowledge of NO2 concentrations. The technique, whose accuracy here ranged from <1% to 29%, provides a useful new tool for the mapping of reactive nitrogen deposition.

Indoor NO2 air pollution and lung function of professional cooks

Studies of cooking-generated NO2 effects are rare in occupational epidemiology. In the present study, we evaluated the lung function of professional cooks exposed to NO2 in hospital kitchens. We performed spirometry in 37 cooks working in four hospital kitchens and estimated the predicted FVC, FEV1 and FEF(25-75), based on age, sex, race, weight, and height, according to Knudson standards. NO2 measurements were obtained for 4 consecutive days during 4 different periods at 20-day intervals in each kitchen. Measurements were performed inside and outside the kitchens, simultaneously using Palm diffusion tubes. A time/exposure indicator was defined as representative of the cumulative exposure of each cook. No statistically significant effect of NO2 exposure on FVC was found. Each year of work as a cook corresponded to a decrease in predicted FEV1 of 2.5% (P = 0.046) for the group as a whole. When smoking status and asthma were included in the analysis the effect of time/exposure decreased about 10% and lost statistical significance. On predicted FEF(25-75), a decrease of 3.5% (P = 0.035) was observed for the same group and the inclusion of controllers for smoking status and asthma did not affect the effects of time/exposure on pulmonary function parameter. After a 10-year period of work as cooks the participants of the study may present decreases in both predicted FEV1 and FEF(25-75) that can reach 20 and 30%, respectively. The present study showed small but statistically significant adverse effects of gas stove exposure on the lung function of professional cooks.

Rapid, reliable and inexpensive quality assessment of biotinylated cRNA

The interpretation of oligonucleotide array experiments depends on the quality of the target cRNA used. cRNA target quality is assessed by quantitative analysis of the representation of 5' and 3' sequences of control genes using commercially available Test arrays. The Test array provides an economically priced means of determining the quality of labeled target prior to analysis on whole genome expression arrays. This manuscript validates the use of a duplex RT-PCR assay as a faster (6 h) and less expensive (<10 US dollars) but equally accurate alternative to the Test arrays in determining biotinylated cRNA quality. Forty-one different cRNA samples were hybridized to HG-U133A microarrays from Affymetrix. Ten cRNA samples with a beta-actin 3'/5' ratio >6 were chosen and classified as degraded cRNAs, and 31 samples with a beta-actin 3'/5' ratio <6 were selected as good quality cRNAs. Blinded samples were then used for the RT-PCR assay. After gel electrophoresis, optical densities of the amplified 3' and 5' fragments of beta-actin were measured and the 3'/5' ratio was calculated. There was a strong correlation (r(2) = 0.6802) between the array and the RT-PCR beta-actin 3'/5' ratios. Moreover, the RT-PCR 3'/5' ratio was significantly different (P < 0.0001) between undegraded (mean +/- SD, 0.34 +/- 0.09) and degraded (1.71 +/- 0.83) samples. None of the other parameters analyzed, such as i) the starting amount of RNA, ii) RNA quality assessed using the Bioanalyzer Chip technology, or iii) the concentration and OD260/OD280 ratio of the purified biotinylated cRNA, correlated with cRNA quality.

Immunotherapy with acute leukemia cells modified into antigen-presenting cells: ex vivo culture and gene transfer methods

Adult patients with acute leukemia have, in general, a poor prognosis, with long-term, disease-free survival achieved in only approximately one-third of cases. One of the proposed mechanisms for this poor overall response is the inability of the immune system to detect and eliminate residual malignant leukemia cells, which subsequently serve as a source of leukemic relapse. This review discusses the rationale of immunotherapy for acute leukemia and presents in vitro and in vivo model systems that were devised for pre-B acute lymphocytic leukemia (ALL) and acute myeloid leukemia (AML). New advances in the ex vivo manipulation of acute leukemia cells are presented, which attempt to modify these cells into functional antigen-presenting cells. These cells can then be used as autologous vaccines at the time of minimal residual disease after standard chemotherapy, to stimulate host immune responses against their own leukemia cells. The various approaches toward this aim include incubation of leukemia cells with cytokines or growth factors and gene manipulation of these cells. In particular, ex vivo culture of ALL cells with CD40 ligand, incubation of AML cells with granulocyte-macrophage colony-stimulating factor and interleukin-4 (GM-CSF/IL-4) and lentiviral transduction of ALL and AML cells for expression of immunomodulators (CD80 and GM-CSF) are current approaches under investigation for the development of autologous acute leukemia cell vaccines.

MCP-1 modulates chemotaxis by follicular lymphoma cells

The localization and establishment of follicular lymphoma (FL) cells in distinct anatomic sites probably involves chemokine and adhesion receptors on the neoplastic cells and appropriate chemokines and adhesion receptor ligands in the microenvironment. Several chemokines play an important role in normal B-cell trafficking and differentiation. Monocyte chemoattractant protein-1 (MCP-1) is a C-C chemokine that induces chemotaxis of a variety of lymphoid cells through its receptor CCR2. CCR2 is also expressed on B cells, and MCP-1 induces chemotaxis of normal B cells. In this report, we investigated expression and function of CCR2 on FL cells. We found FL cells as well as the t(14; 18)+ B-cell lymphoma line H2 expressed CCR2. MCP-1 potentiated SDF-1-induced chemotaxis of FL cells and H2 cells, but MCP-1 alone did not induce chemotaxis. The specificity of the effects of MCP-1 and SDF-1 was demonstrated by antibody blocking studies. Because FL cells are generally associated with follicular dendritic cells (FDCs), FDCs may be an important source of chemokines. We found that cultured FDCs produced MCP-1, and this production was enhanced by tumour necrosis factor. These data implicate MCP-1 in the migration and localization of FL cells.

Identification of HER-2/neu immunogenic epitopes presented by renal cell carcinoma and other human epithelial tumors

HER-2/neu is a tumor-associated antigen overexpressed in a large variety of human tumors. Eight HER-2/neu peptides displaying HLA-A*0201 anchoring motifs were selected and tested for their binding affinity to HLA-A*0201 and their capacity to elicit cytotoxic T lymphocyte (CTL) responses in both HLA-A*0201 transgenic mice and in HLA-A*0201(+) healthy donors. Two high-affinity (p5 and p48) and one intermediate-affinity (p1023) peptides triggered CTL responses in both transgenic mice and humans, comparable to those observed for the well-known HER2/neu dominant peptide p369. CTL induced in transgenic mice lysed HLA-A*0201(+) RMA cells infected with recombinant HER-2/neu but not cells infected with wild-type vaccinia virus. Human CTL lysed HLA-A*0201(+) HER-2/neu(+) tumor cells of different origins (breast, colon, lung and renal cancer) irrespective of the expression levels of HER-2/neu. Importantly, primed CTL specific for these epitopes were detected in freshly isolated tumor-infiltrating lymphocytes from three renal cell carcinoma patients. Therefore, the HER-2/neu peptides p5, p48 and p1023 may be good candidates for immunotherapy of a broad spectrum of tumors, including renal cell carcinoma.

Mortality and morbidity trends in ischemic heart disease in the autonomous region of Madeira in the ten-year period 1987-1996

The increase in absolute number of deaths from ischemic heart disease (IHD) in the population aged > or = 65 years, in both sexes, in Madeira, when comparing the years 1987 and 1996, led to significant increases in the corresponding standardized death rates that go against the stabilization seen at national level. Significant increases in these rates for the same years were also seen in the district of Beja and in the Azores. The aim of this study was to ascertain the trends for the incidence, morbidity and mortality from acute myocardial infarction (AMI) in patients admitted in Madeira and its contribution to the increase in these rates, particularly in the population aged < 65 years of both sexes, which the number of deaths from ischemic heart disease did not increase. We studied 119 pts with AMI admitted in 1987 (year A), of whom 53 were aged < 65 years, and 186 pts with AMI admitted in 1996 (year B), of whom 72 were aged < 65 years, whose data were included in the Madeira Ischemic Heart Disease Register (RECIMA), an IHD hospital register that covers 1792 patients admitted with AMI in the Coronary Intensive Care Unit of the Department of Medical and Surgical Cardiology of Funchal Hospital over a period of 15 years (1984-1998). Mortality by the 28th day (fatal AMI admissions) in all ages fell slightly in both sexes in the two years studied (A = 19.3%; B = 16.1%). The number of fatal AMI admissions rose among females in the two age groups considered A = 11; B = 20; delta% = +45) and fell among males (A = 12; B = 10; delta% = -20). In males aged > or = 65 years, this number remained the same (A = 7; B = 7) and fell in males aged > or = 65 years (A = 5; B = 3; delta% = -40). The number of pts who survived to the 28th day (non-fatal AMI admissions) rose in all age groups for both sexes (A = 96; B = 156; delta% = +38.46), as did the ratios with deaths from IHD. These increases were roughly double in the group of patients aged 65 years compared to patients aged < 65 years. We found highly significant positive correlations in the population aged < 65 years between the number of non-fatal AMI admissions (morbidity data) and the number of deaths from IHD (mortality data) recorded in every year of the 10-year period 1987-96, these values being highly significant in both sexes (r = 0.89; p < 0.0001), in males (r = 0.87; p < 0.0001) and in females (r = 0.77; p < 0.0001). Since our study was carried out on an island on which all AMI cases are admitted to a single treatment center, we can conclude that these positive correlations represent a trend towards worsening of morbidity and mortality from IHD in Madeira in the population aged < 65 years, even though the number of deaths from IHD did not rise. The establishment of IHD registers similar to RECIMA in other regions of the country would help to identify trends in morbidity, mortality, and morbidity plus mortality in this population that would be useful in improving the orientation of resources allocated to the prevention and treatment of cardiovascular diseases.

Interleukin-7 promotes survival and cell cycle progression of T-cell acute lymphoblastic leukemia cells by down-regulating the cyclin-dependent kinase inhibitor p27(kip1)

In normal T-cell development interleukin-7 (IL-7) functions as an antiapoptotic factor by regulating bcl-2 expression in immature thymocytes and mature T cells. Similar to what occurs in normal immature thymocytes, prevention of spontaneous apoptosis by IL-7 in precursor T-cell acute lymphoblastic leukemia (T-ALL) cells correlates with up-regulation of bcl-2. IL-7 is also implicated in leukemogenesis because IL-7 transgenic mice develop lymphoid malignancies, suggesting that IL-7 may regulate the generation and expansion of malignant cells. This study shows that in the presence of IL-7, T-ALL cells not only up-regulated bcl-2 expression and escaped apoptosis but also progressed in the cell cycle, resulting in sequential induction of cyclin D2 and cyclin A. Down-regulation of p27kip1 was mandatory for IL-7-mediated cell cycle progression and temporally coincided with activation of cyclin-dependent kinase (cdk)4 and cdk2 and hyperphosphorylation of Rb. Strikingly, forced expression of p27kip1 in T-ALL cells not only prevented cell cycle progression but also reversed IL-7-mediated up-regulation of bcl-2 and promotion of viability. These results show for the first time that a causative link between IL-7-mediated proliferation and p27kip1 down-regulation exists in malignant T cells. Moreover, these results suggest that p27kip1 may function as a tumor suppressor gene not only because it is a negative regulator of cell cycle progression but also because it is associated with induction of apoptosis of primary malignant cells.

Chemoattractants MDC and TARC are secreted by malignant B-cell precursors following CD40 ligation and support the migration of leukemia-specific T cells

The use of tumor cells as vaccines in cancer immunotherapy is critically dependent on their capacity to initiate and amplify tumor-specific immunity. Optimal responses may require the modification of the tumor cells not only to increase their immunogenicity but also to improve their ability to recruit effector cells to the tumor sites or sites of tumor antigen exposure. It has been reported that CD40 cross-linking of acute lymphoblastic leukemia (ALL) cells significantly increases their immunogenicity and allows the generation and expansion of autologous antileukemia cytotoxic T lymphocytes. This study demonstrates that the CD40 ligation of these tumor cells also induces the secretion of the CC-chemokines MDC and TARC. Supernatants from malignant cells cultured in the presence of sCD40L promote the migration of activated T cells that express CCR4, the common specific receptor for MDC and TARC. More importantly, the supernatants from CD40-stimulated tumor cells also support the transendothelial migration of autologous CCR4(+) antileukemia T cells. Therefore, the results demonstrate that the delivery to leukemia cells of a single physiologic signal, that is, CD40 cross-linking, simultaneously improves tumor cell immunogenicity and induces potent chemoattraction for T cells. (Blood. 2001;98:533-540)

Colorimetric determination of formaldehyde in air using a hanging drop of chromotropic acid

A simple and sensitive method to determine parts per billion (ppb) of atmospheric formaldehyde in situ, using chromotropic acid, is described. A colorimetric sensor, coupled to a droplet of 15.5 microL chromotropic acid, was constructed and used to sample and quantify formaldehyde. The sensor was set up with two optical fibers, a light emitting diode (LED) and two photodiodes. The reference and transmitted light were measured by a photodetection arrangement that converts the signals into units of absorbance. Air was sampled around the chromotropic acid droplet. A purple product was formed and measured after the sampling terminated (typically 7 min). The response is proportional to the sampling period, analyte concentration and sample flow rate. The detection limit is approximately 2 ppb and can be improved by using longer sampling times and/or a sampling flow rate higher than that used in this work, 200 mL min-1. The present technique affords a simple, inexpensive near real-time measurement with very little reagent consumption. The method is selective and highly sensitive. This sensor could be used either for outdoor or indoor atmospheres.

Lentiviral vectors for efficient delivery of CD80 and granulocyte-macrophage- colony-stimulating factor in human acute lymphoblastic leukemia and acute myeloid leukemia cells to induce antileukemic immune responses

Cell vaccines engineered to express immunomodulators have shown feasibility in eliminating leukemia in murine models. Vectors for efficient gene delivery to primary human leukemia cells are required to translate this approach to clinical trials. In this study, second-generation lentiviral vectors derived from human immunodeficiency virus 1 were evaluated, with the cytomegalovirus (CMV) promoter driving expression of granulocyte-macrophage-colony-stimulating factor (GM-CSF) and CD80 in separate vectors or in a bicistronic vector. The vectors were pseudotyped with vesicular stomatitis virus G glycoprotein and concentrated to high titers (10(8)-10(9) infective particles/mL). Human acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), and chronic myeloid leukemia cell lines transduced with the monocistronic pHR-CD80 vector or the bicistronic pHR-GM/CD vector became 75% to 95% CD80 positive (CD80(+)). More important, transduction of primary human ALL and AML blasts with high-titer lentiviral vectors was consistently successful (40%-95% CD80(+)). The average amount of GM-CSF secretion by the leukemia cell lines transduced with the pHR-GM-CSF monocistronic vector was 2182.9 pg/10(6) cells per 24 hours. Secretion was markedly lower with the bicistronic pHR-GM/CD vector (average, 225.7 pg/10(6) cells per 24 hours). Lower amounts of CMV-driven messenger RNA were detected with the bicistronic vector, which may account for its poor expression of GM-CSF. Primary ALL cells transduced to express CD80 stimulated T-cell proliferation in an autologous mixed lymphocyte reaction. This stimulation was specifically blocked with monoclonal antibodies reactive against CD80 or by recombinant cytotoxic T-lymphocyte antigen 4-immunoglobulin fusion protein. These results show the feasibility of efficiently transducing primary leukemia cells with lentiviral vectors to express immunomodulators to elicit antileukemic immune responses. (Blood. 2000;96:1317-1326)

[Magnifying colonoscopy in the diagnosis of colorectal carcinoma invading the submucosa in familial adenomatous polyposis]

The development of colonoscopy with image magnification has enable to study the colonic mucosa in detail and to do differential diagnosis between neoplastic and non-neoplastic lesions from the observation of pit patterns. The results are comparable to stereomicroscopy being possible to predict the histologic diagnosis. In a patient with familial adenomatous polyposis magnifying colonoscopy was performed and this method demonstrated a wide variation of benign polypoid lesions and the morphological features of early colorectal cancer. In this patient, the evaluation by image magnification, together with indigo carmin 0.4% chromoscopy, showed a wide variety of lesions in the colon and rectum: laterally spreading tumor in the cecum, with IIIL + IV pits, subpediculate polyp in the transverse colon with approximately 2.0 cm diameter and IV + V pits, flat elevated lesions IIIL type, and in the sigmoid colon IIa + IIc lesion with V type of Kudo's classification were observed. The evaluation of pit patterns of the lesions in the transverse and sigmoid colon has enable to do the endoscopic diagnosis of the lesion with submucosal invasion.

Adoptive T-cell therapy for B-cell acute lymphoblastic leukemia: preclinical studies

We have previously shown that leukemia-specific cytotoxic T cells (CTL) can be generated from the bone marrow of most patients with B-cell precursor acute leukemias. If these antileukemia CTL are to be used for adoptive immunotherapy, they must have the capability to circulate, migrate through endothelium, home to the bone marrow, and, most importantly, lyse the leukemic cells in a leukemia-permissive bone marrow microenvironment. We demonstrate here that such antileukemia T-cell lines are overwhelmingly CD8(+) and exhibit an activated phenotype. Using a transendothelial chemotaxis assay with human endothelial cells, we observed that these T cells can be recruited and transmigrate through vascular and bone marrow endothelium and that these transmigrated cells preserve their capacity to lyse leukemic cells. Additionally, these antileukemia T-cell lines are capable of adhering to autologous stromal cell layers. Finally, autologous antileukemia CTL specifically lyse leukemic cells even in the presence of autologous marrow stroma. Importantly, these antileukemia T-cell lines do not lyse autologous stromal cells. Thus, the capacity to generate anti-leukemia-specific T-cell lines coupled with the present findings that such cells can migrate, adhere, and function in the presence of the marrow microenvironment enable the development of clinical studies of adoptive transfer of antileukemia CTL for the treatment of ALL.

The BB1 monoclonal antibody recognizes both cell surface CD74 (MHC class II-associated invariant chain) as well as B7-1 (CD80), resolving the question regarding a third CD28/CTLA-4 counterreceptor

The identification of all CD28/CTLA-4 counterreceptors is critical to our understanding of this pivotal pathway of T cell activation. Clouding our understanding has been the reported discrepancies in expression and function of the B7-1 (CD80) molecule based upon the use of the BB1 vs other anti-B7-1 mAbs. To resolve this issue, we have cloned a BB1-binding molecule from the BB1+B7-1(-) NALM-6 pre-B cell line. Here, we demonstrate that this BB1-binding molecule is identical to the cell surface form of CD74 (MHC class II-associated invariant chain). CD74-transfected cells bound the BB1 mAb but not other anti-CD80 mAbs, CD28-Ig, or CTLA4Ig. Absorption and blocking experiments confirmed the reactivity of BB1 mAb with CD74. A region of weak homology was identified between CD74 and the region of B7-1 encoding the BB1 epitope. Therefore, the BB1 mAb binds to a protein distinct from B7-1, and this epitope is also present on the B7-1 protein. Many of the puzzling observations in the literature concerning the expression of human B7-1 are resolved by an understanding that BB1 staining is the summation of CD74 plus B7-1 expression. This observation requires the field to reconsider studies using BB1 mAb in the analysis of CD80 expression and function.

Unbalanced expression of bcl-2 family proteins in follicular lymphoma: contribution of CD40 signaling in promoting survival

Although highly responsive, advanced stage follicular lymphoma (FL) is not curable with conventional treatment. This relative resistance is thought to be due to the t(14;18) that results in the constitutive overexpression of the death-inhibiting protein bcl-2. However, the observation that FL cells are sensitive to treatment in vivo and prone to apoptosis on in vitro culture questions whether bcl-2 alone is responsible for the pathogenesis and clinical behavior of this disease. Therefore, multiple genes are likely to be involved in both the lymphomagenesis and the clinical course of FL. We examined whether expression of other bcl-2 family genes might also be operative. Here, we show that FL cells display a different pattern of expression of bcl-2 family proteins from normal germinal center (GC) B cells that are thought to be their normal counterpart. FL cells express the death-suppressor proteins bcl-2, bcl-xL, and mcl-1; whereas GC B cells express bcl-xL and mcl-1 but also the proapoptotic proteins bax-alpha and bad. Although maintaining constitutive levels of bcl-2 and mcl-1, FL cells are not protected from apoptosis when cultured in vitro. Their propensity to undergo apoptosis is temporally associated with downregulation of bcl-xL. More importantly, activation of FL cells via CD40 not only prevents downregulation but increases the level of bcl-xL expression and results in promotion of survival. These results support the hypothesis that the overexpression of bcl-2 is not the only antiapoptotic mechanism responsible for the pathogenesis of FL. Survival of FL cells is determined by a number of death-inhibiting proteins, among which bcl-xL appears to have the most critical role. Moreover, these findings are consistent with the hypothesis that, although FL cells are malignant, they respond to microenvironmental signals such as CD40L that appear to contribute to their survival through the upregulation of death-inhibiting proteins.

Ex vivo generation of human anti-pre-B leukemia-specific autologous cytolytic T cells

In contrast to other neoplasms, antigen-specific autologous cytolytic T cells have not been detected in patients with human pre-B-cell leukemias. The absence of efficient B7 family (B7-1/CD80; B7-2/CD86) -mediated costimulation has been shown to be a major defect in tumor cells' capacity to function as antigen-presenting cells. We show here the generation of autologous anti-pre-B-cell leukemia-specific cytolytic T-cell lines from the marrows of 10 of 15 patients with pre-B-cell malignancies. T-cell costimulation via CD28 is an absolute requirement for the generation of these autologous cytolytic T cells (CTL). Although costimulation could be delivered by either bystander B7 transfectants or professional antigen-presenting cells (indirect costimulation), optimal priming and CTL expansion required that the costimulatory signal was expressed by the tumor cell (direct costimulation). These anti-pre-B-cell leukemia-specific CTL lysed both unstimulated and CD40-stimulated tumor cells from each patient studied but did not lyse either K562 or CD40-stimulated allogeneic B cells. Cytolysis was mediated by the induction of tumor cell apoptosis by CD8+ T cells via the perforin-granzyme pathway. Although we were able to generate anti-leukemia-specific CTL from the bone marrow, we were unable to generate such CTL from the peripheral blood of these patients. These studies show that antigen-specific CTL can be generated from the bone marrow of patients with pre-B-cell leukemias and these findings should facilitate the design of adoptive T-cell-mediated immunotherapy trials for the treatment of patients with B-cell precursor malignancies.

Kupffer cell activation with BCG. Corynebacterium parvum or zymosan protects against acute liver injury induced by carbon tetrachloride in rats

Kupffer cells have been implicated in the pathogenesis of liver injury, but there is controversy about the effects of activation of these cells on the hepatotoxicity of chemicals and endotoxin. It has been shown that injection of Corynebacterium parvum in rats induces macrophage activation that protects against toxic effects of carbon tetrachloride and acetaminophen, five days after injection, and this protection is due to inhibition of microsomal oxidizing enzymes and increased production of glutathion. To verify if the protective effect occurs soon after Kupffer cell activation, with different activators, male albino rats were treated with intravenous injection of BCG (0.5 ml with 7.5.10(8) bacilli), Corynebacterium parvum (30 mg/kg) or zymosan (7.5.10(6) yeast cells). Fourty-eight hours after the injection of one of the macrophage activators, the animals and rats treated with intravenous injection of saline (controls) received carbon tetrachloride by subcutaneous route (1 ml/kg of CCl4, 3:1 in soybean oil). Fourty-eight hours after the animals were killed after ether anesthesia and fragments of the liver were fixed, paraffin embedded and the sections stained with hematoxylin and eosin. A Weibel grid with 168 points was used to estimate the percent volume of necrosis and severe hydropic degeneration. The results showed that the volume density of necrosis and severe hydropic degeneration were significatively lesser in rats treated with the three Kupffer cells activators. The protection was greater with BCG and Corynebacterium parvum than with zymosan. These results confirm that activation of Kupffer cell with three different activators can induce protection against liver cell injury produced by carbon tetrachloride in rats soon as 48 h after injection of activators.

Biologic response modifiers in acute lymphoblastic leukemia

Despite the presence of tumor antigens, the paucity of clinically significant T-cell mediated immune responses against human tumors is striking. This may, in part, be because of the inability of cancer cells to function as efficient antigen-presenting cells. For full activation, T cells must receive two signals delivered by antigen-presenting cells. The first is antigen-specific and is delivered by presentation of antigenic peptide by the major histocompatibility complex molecules to the T-cell receptor. This signal, although necessary, is in itself insufficient to mediate T-cell activation, cytokine release, and subsequent T-cell proliferation and function. For full T-cell activation, T cells require delivery of a secondary, costimulatory signal, such as that delivered by members of the B7 family to their receptor on the T-cell, CD28. Delivery of an antigen signal in the absence of costimulation does not result in productive immunity, but rather in anergy, a state of antigen-specific T-cell nonresponsiveness. To induce T-cell proliferation against B-cell malignancies, the tumor cell must first be induced to express B7 or the tumor antigen must be presented by an efficient antigen-presenting cell. Simple expression of B7 on the tumor cell alone, however, cannot reverse anergy. Reversal of anergy is a complex process involving stepwise repair of the T-cell defect and can be accomplished by prolonged exposure to interleukin-2, signaling through the CD2 pathway, followed by antigen presentation with B7-mediated costimulation. Successful immunotherapeutic strategies in the B-cell malignancies will likely require steps to reverse established anergy in the tumor-bearing host as well as effective tumor-antigen presentation.

CD4-induced interaction of primary HIV-1 gp120 glycoproteins with the chemokine receptor CCR-5

For efficient entry into target cells, primary macrophage-tropic and laboratory-adapted human immunodeficiency viruses type 1 (HIV-1) require particular chemokine receptors, CCR-5 and CXCR-4, respectively, as well as the primary receptor CD4 (refs 1-6). Here we show that a complex of gp120, the exterior envelope glycoprotein, of macrophage-tropic primary HIV-1 and soluble CD4 interacts specifically with CCR-5 and inhibits the binding of the natural CCR-5 ligands, macrophage inflammatory protein (MIP)-1alpha and MIP-1beta (refs 7, 8). The apparent affinity of the interaction between gp120 and CCR-5 was dramatically lower in the absence of soluble CD4. Additionally, in the absence of gp120, an interaction between a two-domain CD4 fragment and CCR-5 was observed. A gp120 fragment retaining the CD4-binding site and overlapping epitopes was able to interact with CCR-5 only if the V3 loop, which can specify HIV-1 tropism and chemokine receptor choice, was also present on the molecule. Neutralizing antibodies directed against either CD4-induced or V3 epitopes on gp120 blocked the interaction of gp12O-CD4 complexes with CCR-5. These results suggest that HIV-1 attachment to CD4 creates a high-affinity binding site for CCR-5, leading to membrane fusion and virus entry.

Human CD100, a novel leukocyte semaphorin that promotes B-cell aggregation and differentiation

Herein we describe the molecular characterization of the human leukocyte activation antigen CD100 and identify it as the first semaphorin, to our knowledge, in the immune system. Semaphorins have recently been described as neuronal chemorepellants that direct pioneering neurons during nervous system development. In this study we demonstrate that CD100 induces B cells to aggregate and improves their viability in vitro. We show that CD100 modifies CD40-CD40L B-cell signaling by augmenting B-cell aggregation and survival and down-regulating CD23 expression. Thus, these results suggest that semaphorins as exemplified by CD100 also play a functional role in the immune system.

Pre-B acute lymphoblastic leukemia cells may induce T-cell anergy to alloantigen

Even if neoplastic cells express tumor associated antigens they still may fail to function as antigen presenting cells (APC) if they lack expression of one or more molecules critical for the induction of productive immunity. These cellular defects can be repaired by physiologic activation, transfection, or fusion of tumor cells with professional APC. Although such defects can be repaired, antitumor specific T cells may still fail to respond in vivo if they may have been tolerized. Here, human pre-B cell acute lymphoblastic leukemia (pre-B ALL) was used as a model to determine if primary human tumor cells can function as alloantigen presenting cells (alloAPC) or alternatively whether they induce anergy. In the present report, we show that pre-B cell ALL express alloantigen and adhesion molecules but uniformly lack B7-1 (CD80) and only a subset express B7-2 (CD86). Pre-B ALL cells are inefficient or ineffective alloAPC and those cases that lack expression of B7-1 and B7-2 also induce alloantigen specific T-cell unresponsiveness. Under these circumstances, T-cell unresponsiveness could be prevented by physiologic activation of tumor cells via CD40, cross-linking CD28, or signaling through the common gamma chain of the interleukin-2 receptor on T cells. Taken together, these results suggest that pre-B ALL may be incapable of inducing clinically significant T-cell-mediated antileukemia responses. This defect may be not only due to their inability to function as APC, but also due to their potential to induce tolerance. Attempts to induce clinically significant antitumor immune responses may then require not only mechanisms to repair the antigen presenting capacity of the tumor cells, but also reversal of tolerance.