Caenorhabditis elegans as a biomonitor for immunological stress in nematodes

Mapping the pharyngeal and intestinal pH of Caenorhabditis elegans and real-time luminal pH oscillations using extended dynamic range pH-sensitive nanosensors

Extended dynamic range pH-sensitive ratiometric nanosensors, capable of accurately mapping the full physiological pH range, have been developed and used to characterize the pH of the pharyngeal and intestinal lumen of Caenorhabditis elegans in real-time. Nanosensors, 40 nm in diameter, were prepared by conjugating pH-sensitive fluorophores, carboxyfluorescein (FAM) and Oregon Green (OG) in a 1:1 ratio, and a reference fluorophore, 5-(and-6)-carboxytetramethylrhodamine (TAMRA) to an inert polyacrylamide matrix. Accurate ratiometric pH measurements were calculated through determination of the fluorescence ratio between the pH-sensitive and reference fluorophores. Nanosensors were calibrated with an automated image analysis system and validated to demonstrate a pH measurement resolution of ±0.17 pH units. The motility of C. elegans populations, as an indicator for viability, showed nematodes treated with nanosensors, for concentrations ranging from 50.00 to 3.13 mg/mL, were not statistically different to nematodes not challenged with nanosensors up to a period of 4 days (p < 0.05). The nanosensors were also found to remain in the C. elegans lumen >24 h after nanosensor challenge was removed. The pH of viable C. elegans lumen was found to range from 5.96 ± 0.31 in the anterior pharynx to 3.59 ± 0.09 in the posterior intestine. The pharyngeal pumping rate, which dictates the transfer of ingested material from the pharynx to the intestine, was found to be temperature dependent. Imaging C. elegans at 4 °C reduced the pharyngeal pumping rate to 7 contractions/min and enabled the reconstruction of rhythmic pH oscillations in the intestinal lumen in real-time with fluorescence microscopy.

Immunity-mediated regulation of fecundity in the nematode Heligmosomoides polygyrus--the potential role of mast cells

Previous studies have shown that host immunity regulates the fecundity of nematodes. The present study was aimed at clarifying the reversible nature of fecundity in response to changes of immunological status and to determine which effector cells are responsible for compromising fecundity in Heligmosomoides polygyrus. Enhanced fecundity was observed in immunocompromised SCID and nu/nu mice compared to those in the corresponding wild-type mice, with significantly fewer numbers of intrauterine eggs produced in the wild-type than in the immunodeficient mice. When 14-day-old adult worms from BALB/c mice were transplanted into naïve BALB/c mice, their fecundity increased significantly as early as 24 h post-transplantation, but not when they were transferred into immune mice, suggesting the plastic and reversible nature of fecundity in response to changes in host immunological status. In mast cell-deficient W/W(v) mice, nematode fecundity was significantly higher than in mast cell-reconstituted W/W(v) or +/+ mice. The serum levels of the mast-cell protease mMCP1 were markedly increased in the wild-type as well as the mast cell-reconstituted W/W(v), but not in the W/W(v), SCID, or nu/nu mice during infection. These findings raise the interesting possibility that certain activities of mast cells, either directly or indirectly, regulate parasite fecundity during infection.

The innate allergenicity of helminth parasites

Helminth parasites are well known to induce an immune response in their hosts characterised by elevated IgE, peripheral blood or local tissue eosinophilia, and in some cases, intestinal mastocytosis. This immunological response has a strong T-helper 2 (Th2) cytokine bias and is reminiscent of the immunological constellation found in allergic diseases. However, the molecular forces driving the Th2 response to helminth parasites are still not understood. By using the human hookworm parasite Necator americanus as an example, the authors of the current article propose that in the course of its life cycle, this parasite becomes innately allergenic through the secretion of a molecular array designed to promote tissue migration and homing, feeding and survival against immunological attack. This complex array comprises proteases, lectins and other classes of molecules. Subsequent immunological and physiological events seemingly protect the host from both the allergic sequelae of exposure to environmental allergens and, moreover, from the parasite itself.

Monoclonal antibodies reactive with secreted-excreted products from the amphids and the cuticle surface of Globodera pallida affect nematode movement and delay invasion of potato roots

This paper describes Excreted-secreted proteins (ES) proteins that were immunolocalised in the cuticle, amphids and subventral glands of second stage juveniles of the two species of potato cyst nematodes (Globodera pallida and Globodera rostochiensis). Monoclonal antibodies reactive with these ES proteins were used in a bioassay to investigate their effect on nematode movement and on their ability to invade potato roots. Antibodies recognising the nematode cuticle surface and the amphids affected nematode movement and delayed nematode penetration of roots. These effects were temporary, since the nematodes were able to recover and infect potato roots. Movement of second stage juveniles treated with the antibodies was impaired for the first 30 min after inoculation: the juveniles remained close to the point of introduction and moved slowly and abnormally. They recovered normal movement after 1-2 h, possibly because the turnover rate of the secreted proteins meant that they were no longer blocked by the monoclonal antibodies. No effect was observed on second stage juveniles treated with an antibody reactive with secretions from the oesophageal glands. Nematodes treated with antibodies reactive with the nematode cuticle surface were notably more affected than those treated with other antibodies; nematodes failed to recover movement when in continuous contact with the antibodies. It is possible that the physical presence of the antibodies on the nematode surface affected their motility. Nematodes treated with antibodies reactive with secretions from the amphids were temporarily unable to move towards potato roots and their exploratory behaviour was greatly affected by the antibody treatment. Whether these antibodies were able to inhibit temporarily the function of the amphids or this effect was due to physical presence of the antibodies blocking the amphidial pore remains to be determined.

Hormesis and debilitation effects in stress experiments using the nematode worm Caenorhabditis elegans: the model of balance between cell damage and HSP levels

In this article, we discuss mechanisms responsible for the effects of heat treatment on increasing subsequent survival in the nematode worm Caenorhabditis elegans. We assume that the balance between damage associated with exposure to thermal stress and the level of heat shock proteins produced plays a key role in forming the age-pattern of mortality and survival in stress experiments. We propose a stochastic model of stress, which describes the accumulation of damage in the cells of the worm as the worm ages. The model replicates the age trajectories of experimental survival curves in three experiments in which worms were heat-treated for 0, 1, 2, 4, 6, or 8h. We also discuss analytical results and directions of further research. The proposed method of stochastic modelling of survival data provides a new approach that can be used to model, analyse and extrapolate experimental results.

The contribution of molecular biology to the development of vaccines against nematode and trematode parasites of domestic ruminants

Rapid developments in molecular biology have had an enormous impact on the prospects for the development of vaccines to control the major nematode and trematode infestations of livestock. Vaccine candidates are purified using conventional protein chemistry techniques but the limitations imposed by the scarcity of parasite material provide an insurmountable barrier for commercial vaccine production by this means. The ability to purify mRNA from different parasite life-cycle stages and to prepare cDNA expression libraries from it has proven central to the identification of immunogenic parasite proteins. Potentially, protective parasite antigens can now be produced in recombinant form in a variety of vectors and this represents a key breakthrough on the road to commercial vaccine production. The contribution of molecular biology to this process is discussed using several examples, particularly in vaccine development against the pathogenic abomasal nematode of sheep and goats, Haemonchus contortus, and the liver fluke of sheep and cattle, Fasciola hepatica. The difficulties of producing recombinant proteins in the correct form, with appropriate post-translational modification and conformation, are discussed as well as emerging means of antigen delivery including DNA vaccination. The opportunities offered by genome and expressed sequence tag analyses programmes for antigen targeting are discussed in association with developing microarray and proteomics technologies which offer the prospect of large scale, rapid antigen screening and identification.

Toxicity of the dithiocarbamate fungicide mancozeb to the nontarget soil nematode, Caenorhabditis elegans

We have previously shown that the dithiocarbamate fungicide, Mancozeb, strongly induces lacZ reporter expression from an endogenous heat-shock promoter (hsp16) in the PC72 transgenic strain of the nematode Caenorhabditis elegans. Such evidence of organismal stress, in a nontarget species at subapplication concentrations, was much less apparent for the related fungicide, Maneb, which only weakly induced reporter expression. We now show that reporter induction by Mancozeb is marginal (<60%) after a few hours' exposure, but increases substantially (to almost 10-fold) after overnight exposure. In conjunction with our previous results using intermediate exposure periods, this suggests that the factor limiting reporter responses is likely to be a slow rate of uptake and/or metabolism of the fungicide. We confirm that a potentially toxic metabolite of dithiocarbamate fungicides, namely ethylenethiourea (ETU), has minimal toxicity toward C. elegans, even after prolonged exposure at high concentrations. We demonstrate that exposure to Mancozeb (but not ETU) significantly inhibits larval growth in C. elegans, although this parameter is not markedly more sensitive than reporter induction as a toxicological endpoint. Finally, we have used two-dimensional electrophoresis to show that high concentrations of both Maneb and Mancozeb drastically simplify the protein spot profile compared with controls. However, only in the latter case is there evidence of novel proteins being induced. Both fungicides appear toxic to C. elegans, but only Mancozeb induces a strong heat-shock response.