Vaccination-induced protection of lambs against the parasitic nematode Haemonchus contortus correlates with high IgG antibody responses to the LDNF glycan antigen

Lambs respond to vaccination against bacteria and viruses but have a poor immunological response to nematodes. Here we report that they are protected against the parasitic nematode Haemonchus contortus after vaccination with excretory/secretory (ES) glycoproteins using Alhydrogel as an adjuvant. Lambs immunized with ES in Alhydrogel and challenged with 300 L3 larvae/kg body weight had a reduction in cumulative egg output of 89% and an increased percentage protection of 54% compared with the adjuvant control group. Compared to the adjuvant dimethyl dioctadecyl ammonium bromide, Alhydrogel induced earlier onset and significantly higher ES- specific IgG, IgA, and IgE antibody responses. In all vaccinated groups a substantial proportion of the antibody response was directed against glycan epitopes, irrespective of the adjuvant used. In lambs vaccinated with ES in Alhydrogel but not in any other group a significant increase was found in antibody levels against the GalNAcbeta1,4 (Fucalpha1,3)GlcNAc (fucosylated LacdiNAc, LDNF) antigen, a carbohydrate antigen that is also involved in the host defense against the human parasite Schistosoma mansoni. In lambs the LDNF-specific response increased from the first immunization onward and was significantly higher in protected lambs. In addition, an isotype switch from LDNF-specific IgM to IgG was induced that correlated with protection. These data demonstrate that hyporesponsiveness of lambs to H. contortus can be overcome by vaccination with ES glycoproteins in a strong T-helper 2 type response-inducing aluminum adjuvant. This combination generated high and specific antiglycan antibody responses that may contribute to the vaccination-induced protection.     

Leucine-rich repeat-mediated intramolecular interactions in nematode recognition and cell death signaling by the tomato resistance protein Mi

The root-knot nematode resistance gene Mi from tomato encodes a nucleotide-binding/leucine-rich repeat (NB/LRR) protein with a novel amino-terminal domain compared to related disease-resistance genes. The closely linked paralog Mi-1.1, which does not confer nematode resistance, encodes a protein 91% identical to the functional copy, Mi-1.2. The chimeric construct Mi-DS3, which encodes the 161 amino-terminal residues from Mi-1.1 fused to the remainder of Mi-1.2, induces localized necrosis when transiently expressed in Nicotiana benthamiana leaves. We produced mutant constructs that exchanged sequences encoding each of the 40 amino acid differences from the Mi-1.1 LRR region into Mi-DS3 and into Mi-1.2. For 23 of the substitutions, necrosis was lost upon transient expression of the mutated Mi-DS3 in N. benthamiana, and nematode resistance was lost when the altered Mi-1.2 was expressed in the tomato roots. One substitution, R961D, failed to give Mi-DS3-induced necrosis, but produced a dominant lethal phenotype when introduced into Mi-1.2. This gain-of-function phenotype was suppressed by co-expression with the amino-terminal region of Mi-1.1, suggesting that residue 961 is critical for negative regulation by the corresponding N-terminal region. Substitutions of Mi-1.1 residues 984-986 retained the ability to cause necrosis in Mi-DS3, but resulted in loss-of-nematode resistance in Mi-1.2, suggesting that these residues are essential for nematode recognition. None of the loss-of-function mutations in Mi-1.2 had a dominant negative phenotype. These results indicate that the Mi-1.2 LRR is involved in regulation of the transmission of the resistance response as well as in recognition of the nematode.     

Short-term changes in consumption and oviposition rates of Neoseiulus californicus strains (Acari: Phytoseiidae) after a diet shift

Short-term effects on consumption and oviposition rates of four strainsof Neoseiulus californicus (McGregor) after a diet shiftwere evaluated. The new feeding conditions experienced by the predators weresixfixed densities of eggs or protonymphs of Tetranychusurticae Koch placed on excised strawberry leaflet discs andmaintained under laboratory conditions (25±1°C,75–85% RH, 16L: 8D). The observations were made on the first and thefifthday of the experiment. The phytoseiids came from three long-term mass-rearedstrains fed on T. urticae, Dermatophagoides farinaeHughes,or Quercus spp. pollen, respectively. The fourth strainwascollected directly in a strawberry field. Time since diet transfer can be addedto the factors (i.e. feeding history and prey density) already known to affectthe functional and numerical responses of N. californicus,both when it feeds on prey eggs and protonymphs. If consumption rates wereaveraged over all strains and densities, 9.04 and 11.41 eggs, and 6.97 and 6.48protonymphs were consumed on the first and the fifth day, respectively. If thesame was done for oviposition rates, predators feeding on eggs produced 1.46and2.36 eggs/female/day, whereas predators feeding on protonymphs produced 1.35and2.29 eggs/female/day. Time had the greatest impact on the functional responseofthe strain that had previously fed on tetranychids, while an effect of time onthe numerical response was detectable in all strains.     

Effects of Thallus Temperature and Hydration on Photosynthetic Parameters of Cetraria Islandica from Contrasting Habitats

Two methods of induced in vivo chlorophyll (Chl) fluorescence were used to investigate the effects of varying thallus temperature and hydration on the performance of photosynthetic apparatus of a foliar lichen Cetraria islandica: slow Chl fluorescence induction kinetic with the analysis of quenching mechanisms, and rapid irradiance response curves of photosynthesis derived from quantum yield of photochemical reactions of photosystem 2 (₂) recorded at increasing irradiances. We compared responses of photosynthetic apparatus in populations of C. islandica growing in lower altitude (LAP: 1 350 m a.s.l.) and in higher altitude (HAP: 2 000 m a.s.l.). At each altitude, the samples were collected both in fully irradiated sites (HI) and in shade (LI). Temperature optimum of photosynthetic processes was the same for LAP and HAP thalli of LI populations (18 °C), while it was significantly lower for HI HAP (14 °C). Gradual dehydration of fully hydrated thalli led to initial increase (up to 20 % of water saturation deficit, WSD) in F_V/F_M and ₂, no change at 20–50 % WSD, and a dramatic decrease of the parameters within 50–80 % of WSD. LI HAP of C. islandica was the best adapted population to low temperature having higher rates of photochemical processes of photosynthesis than HI HAP within temperature range of –5 to +5 °C. The differences between populations were apparent also in Chl content and thallus morphology.     

Conformation-dependent antibody response to Pseudomonas aeruginosa outer membrane proteins induced by immunization in humans

Outer membrane proteins (OMPs) of pathogenic bacteria have been used as protective antigens in developing bacterial vaccines. In the present study, we compared the antibody responses to a Pseudomonas aeruginosa OMP vaccine elicited in humans and rabbits by immunization. Immunization with the vaccine induced high titers of serum IgG antibody both in rabbits and humans but reactivities of the induced antibodies with the OMPs were different. The rabbit immune sera recognized most of the OMPs in the vaccine both in immunoblot and immunoprecipitation analyses. In contrast, a great variation in band pattern and intensity was observed among the human immune sera in immunoblot analysis, but not in immunoprecipitation analysis. Denaturation of the OMPs did not affect the binding activity of the rabbit immune sera as determined by ELISA, but substantially reduced those of the human immune sera and anti-OMP IgG purified from a pooled normal human plasma. These data suggest that antibody response to P. aeruginosa OMPs elicited by immunization in humans is mainly directed against discontinuous or conformation-dependent epitopes, which should be taken into account in developing vaccines, especially for OMP-derived synthetic peptides.     

Should we take measurements at an intermediate design point?

It is well known that, for estimating a linear treatment effect with constant variance, the optimal design divides the units equally between the two extremes of the design space. If the dose-response relation may be nonlinear, however, intermediate measurements may be useful in order to estimate the effects of partial treatments. We consider the decision of whether to gather data at an intermediate design point: do the gains from learning about nonlinearity outweigh the loss in efficiency in estimating the linear effect? Under reasonable assumptions about nonlinearity, we find that, unless sample size is very large, the design with no interior measurements is best, because with moderate total sample sizes, any nonlinearity in the dose-response will be difficult to detect. We discuss in the context of a simplified version of the problem that motivated this work-a study of pest-control treatments intended to reduce asthma symptoms in children.     

Counterpoint. Cancer vaccines: single-epitope anti-idiotype vaccine versus multiple-epitope antigen vaccine

Anti-idiotype (Id) vaccine therapy has been tested and shown to be effective, in several animal models, for triggering the immune system to induce specific and protective immunity against bacterial, viral and parasitic infections. The administration of anti-Id antibodies as surrogate tumor-associated antigens (TAA) also represents another potential application of the concept of the Id network. Limited experience in human trials using anti-Id to stimulate immunity against tumors has shown promising results. In this “counterpoint” article, we discuss our own findings showing the potential of anti-Id antibody vaccines to be novel therapeutic approaches to various human cancers and also discuss where anti-Id vaccines may perform better than traditional multiple-epitope antigen vaccines. Received: 27 December 1999 / Accepted: 27 January 2000     

Overview of the physiological ecology of carbon metabolism in seagrasses

The small but diverse group of angiosperms known as seagrasses form submersed meadow communities that are among the most productive on earth. Seagrasses are frequently light-limited and, despite access to carbon-rich seawaters, they may also sustain periodic internal carbon limitation. They have been regarded as C3 plants, but many species appear to be C3–C4 intermediates and/or have various carbon-concentrating mechanisms to aid the Rubisco enzyme in carbon acquisition. Photorespiration can occur as a C loss process that may protect photosynthetic electron transport during periods of low CO₂ availability and high light intensity. Seagrasses can also become photoinhibited in high light (generally>1000 μE m⁻² s⁻¹) as a protective mechanism that allows excessive light energy to be dissipated as heat. Many photosynthesis–irradiance curves have been developed to assess light levels needed for seagrass growth. However, most available data (e.g. compensation irradiance I_c) do not account for belowground tissue respiration and, thus, are of limited use in assessing the whole-plant carbon balance across light gradients. Caution is recommended in use of I_k (saturating irradiance for photosynthesis), since seagrass photosynthesis commonly increases under higher light intensities than I_k; and in estimating seagrass productivity from H_sat (duration of daily light period when light equals or exceeds I_k) which varies considerably among species and sites, and which fails to account for light-limited photosynthesis at light levels less than I_k. The dominant storage carbohydrate in seagrasses is sucrose (primarily stored in rhizomes), which generally forms more than 90% of the total soluble carbohydrate pool. Seagrasses with high I_c levels (suggesting lower efficiency in C acquisition) have relatively low levels of leaf carbohydrates. Sucrose-P synthase (SPS, involved in sucrose synthesis) activity increases with leaf age, consistent with leaf maturation from carbon sink to source. Unlike terrestrial plants, SPS apparently is not light-activated, and is positively influenced by increasing temperature and salinity. This response may indicate an osmotic adjustment in marine angiosperms, analogous to increased SPS activity as a cryoprotectant response in terrestrial non-halophytic plants. Sucrose synthase (SS, involved in sucrose metabolism and degradation in sink tissues) of both above- and belowground tissues decreases with tissue age. In belowground tissues, SS activity increases under low oxygen availability and with increasing temperatures, likely indicating increased metabolic carbohydrate demand. Respiration in seagrasses is primarily influenced by temperature and, in belowground tissues, by oxygen availability. Aboveground tissues (involved in C assimilation and other energy-costly processes) generally have higher respiration rates than belowground (mostly storage) tissues. Respiration rates increase with increasing temperature (in excess of 40°C) and increasing water-column nitrate enrichment (Z. marina), which may help to supply the energy and carbon needed to assimilate and reduce nitrate. Seagrasses translocate oxygen from photosynthesizing leaves to belowground tissues for aerobic respiration. During darkness or extended periods of low light, belowground tissues can sustain extended anerobiosis. Documented alternate fermentation pathways have yielded high alanine, a metabolic ‘strategy’ that would depress production of the more toxic product ethanol, while conserving carbon skeletons and assimilated nitrogen. In comparison to the wealth of information available for terrestrial plants, little is known about the physiological ecology of seagrasses in carbon acquisition and metabolism. Many aspects of their carbon metabolism — controls by interactive environmental factors; and the role of carbon metabolism in salt tolerance, growth under resource-limited conditions, and survival through periods of dormancy — remain to be resolved as directions in future research. Such research will strengthen the understanding needed to improve management and protection of these environmentally important marine angiosperms.     

In vivo imaging of an elicitor-induced nitric oxide burst in tobacco

A growing body of evidence suggests that nitric oxide (NO), an important signalling and defence molecule in mammals, plays a key role in activating disease resistance in plants, acting as signalling molecule and possibly as direct anti-microbial agent. Recently, a novel fluorophore (diaminofluorescein diacetate, DAF-2 DA) has been developed which allows bio-imaging of NO in vivo. Here we use the cell-permeable DAF-2 DA, in conjunction with confocal laser scanning microscopy, for real-time imaging of NO in living plant cells. Epidermal tobacco cells treated with cryptogein, a fungal elicitor from Phytophthora cryptogea, respond to the elicitor with a strong increase of intracellular NO. NO-induced fluorescence was found in several cellular compartments, and could be inhibited by a NO scavenger and an inhibitor of nitric oxide synthase. The NO burst was triggered within minutes, reminiscent of the oxidative burst during hypersensitive response reactions. These results reveal additional similarities between plant and animal host responses to infection.