Immune Elicitors Research Articles

Exposure to Bacterial Signals Does Not Alter Pea Aphids’ Survival upon a Second Challenge or Investment in Production of Winged Offspring

Pea aphids have an obligate nutritional symbiosis with the bacteria Buchnera aphidicola and frequently also harbor one or more facultative symbionts. Aphids are also susceptible to bacterial pathogen infections, and it has been suggested that aphids have a limited immune response towards such pathogen infections compared to other, more well-studied insects. However, aphids do possess at least some of the genes known to be involved in bacterial immune responses in other insects, and immune-competent hemocytes. One possibility is that immune priming with microbial elicitors could stimulate immune protection against subsequent bacterial infections, as has been observed in several other insect systems. To address this hypothesis we challenged aphids with bacterial immune elicitors twenty-four hours prior to live bacterial pathogen infections and then compared their survival rates to aphids that were not pre-exposed to bacterial signals. Using two aphid genotypes, we found no evidence for immune protection conferred by immune priming during infections with either Serratia marcescens or with Escherichia coli. Immune priming was not altered by the presence of facultative, beneficial symbionts in the aphids. In the absence of inducible immune protection, aphids may allocate energy towards other defense traits, including production of offspring with wings that could escape deteriorating conditions. To test this, we monitored the ratio of winged to unwinged offspring produced by adult mothers of a single clone that had been exposed to bacterial immune elicitors, to live E. coli infections or to no challenge. We found no correlation between immune challenge and winged offspring production, suggesting that this mechanism of defense, which functions upon exposure to fungal pathogens, is not central to aphid responses to bacterial infections.

Immunogenic and Antioxidant Effects of a Pathogen-Associated Prenyl Pyrophosphate in Anopheles gambiae

Despite efficient vector transmission, Plasmodium parasites suffer great bottlenecks during their developmental stages within Anopheles mosquitoes. The outcome depends on a complex three-way interaction between host, parasite and gut bacteria. Although considerable progress has been made recently in deciphering Anopheles effector responses, little is currently known regarding the underlying microbial immune elicitors. An interesting candidate in this sense is the pathogen-derived prenyl pyrophosphate and designated phosphoantigen (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), found in Plasmodium and most eubacteria but not in higher eukaryotes. HMBPP is the most potent stimulant known of human Vγ9Vδ2 T cells, a unique lymphocyte subset that expands during several infections including malaria. In this study, we show that Vγ9Vδ2 T cells proliferate when stimulated with supernatants from intraerythrocytic stages of Plasmodium falciparum cultures, suggesting that biologically relevant doses of phosphoantigens are excreted by the parasite. Next, we used Anopheles gambiae to investigate the immune- and redox- stimulating effects of HMBPP. We demonstrate a potent activation in vitro of all but one of the signaling pathways earlier implicated in the human Vγ9Vδ2 T cell response, as p38, JNK and PI3K/Akt but not ERK were activated in the A. gambiae 4a3B cell line. Additionally, both HMBPP and the downstream endogenous metabolite isopentenyl pyrophosphate displayed antioxidant effects by promoting cellular tolerance to hydrogen peroxide challenge. When provided in the mosquito blood meal, HMBPP induced temporal changes in the expression of several immune genes. In contrast to meso-diaminopimelic acid containing peptidoglycan, HMBPP induced expression of dual oxidase and nitric oxide synthase, two key determinants of Plasmodium infection. Furthermore, temporal fluctuations in midgut bacterial numbers were observed. The multifaceted effects observed in this study indicates that HMBPP is an important elicitor in common for both Plasmodium and gut bacteria in the mosquito.

Activation of the immune defence of the freshwater snailLymnaea stagnalisby different immune elicitors

Understanding the outcomes of host-parasite interactions in nature is in high demand as parasites and pathogens are important for several ecological and evolutionary processes. Ecological immunology (ecoimmunology) has a key role in reaching this goal because immune defence is the main physiological barrier against infections. To date, ecoimmunological studies largely lean on measuring constitutive immune defences (components of defence that are always active). However, understanding the role of inducible components of immune function is important as the immune system is largely an inducible defence. Measuring such defences can be complicated as different parasites may activate different immune cascades, and expression of different immune traits may not be independent. We examined the suitability of different immune activation techniques for the freshwater snail Lymnaea stagnalis. By experimentally challenging snails with different immune elicitors [injection with snail saline (i.e. wounding), lyophilized Escherichia coli cells, lyophilized Micrococcus lysodeikticus cells, healthy snail gonad, and trematode-infected snail gonad; maintenance in microorganism-enriched water] and measuring phenoloxidase-like and antibacterial activity of their haemolymph, we found increased immune activity against some immune elicitors, but also decreased activity. Our findings suggest potentially complicated relationships among immune traits, and propose suitable techniques for ecological studies in this study system.

FEELING ILL: A SNAIL'S COMPLEX IMMUNE SYSTEM

All animals are plagued by parasites of some variety, but parasites all have one thing in common – profiteering at their host's expense. Naturally, hosts aren't too happy about this and will engage their immune systems to fight back. However, the outcome of the ensuing battle can also be affected by ecological and environmental factors. These factors can then modify the host–parasite relationship, causing changes in host's life choices as well as driving evolution. However, this growing field of ecoimmunology – immunology in the context of ecology – has been hampered by limited knowledge of how different immune elicitors activate the immune system. Without this knowledge, knowing which elicitor to use for your specific experiment can be tricky, so Otto Seppälä and Katja Leicht both from Eawag, Switzerland, decided to investigate how the freshwater snail Lymnaea stagnalis reacted to different threats (p. 2902).The team injected their snails with two different types of lyophilized bacteria, Escherichia coli and Microccocus lysodeikticus, as well as ground-up gonads from an unlucky snail infected with a trematode parasite. Some snails escaped these treatments and just received innocuous injections of snail saline or ground-up uninfected gonads. Six hours post-treatment, the duo collected haemolymph samples and began testing the immune reaction, looking at phenoloxidase and antimicrobial activity. Merely pricking the snail and injecting harmless snail saline induced phenoloxidase activity but to their surprise injection with trematode-infected gonads didn't increase this reaction. What's more, this activity decreased when the snails were injected with bacteria. This may represent a trade-off between phenoloxidase activity and antimicrobial activity, as this latter immune response was heightened after Microccous infection.Next, the duo kept their snails in either clean water or bacteria-ridden water and repeated the same measurements of the immune system. This time, the presence of micro-organisms induced a strong phenoloxidase response but no antimicrobial activity. Their results overall highlight the complexity of the snail's immune system, with trade-offs occurring between different pathways. It seems that the immune system of the snail remains a mystery!

Trehalose Biosynthesis Promotes Pseudomonas aeruginosa Pathogenicity in Plants

Pseudomonas aeruginosa strain PA14 is a multi-host pathogen that infects plants, nematodes, insects, and vertebrates. Many PA14 factors are required for virulence in more than one of these hosts. Noting that plants have a fundamentally different cellular architecture from animals, we sought to identify PA14 factors that are specifically required for plant pathogenesis. We show that synthesis by PA14 of the disaccharide trehalose is required for pathogenesis in Arabidopsis, but not in nematodes, insects, or mice. In-frame deletion of two closely-linked predicted trehalose biosynthetic operons, treYZ and treS, decreased growth in Arabidopsis leaves about 50 fold. Exogenously co-inoculated trehalose, ammonium, or nitrate, but not glucose, sulfate, or phosphate suppressed the phenotype of the double ΔtreYZΔtreS mutant. Exogenous trehalose or ammonium nitrate does not suppress the growth defect of the double ΔtreYZΔtreS mutant by suppressing the plant defense response. Trehalose also does not function intracellularly in P. aeruginosa to ameliorate a variety of stresses, but most likely functions extracellularly, because wild-type PA14 rescued the in vivo growth defect of the ΔtreYZΔtreS in trans. Surprisingly, the growth defect of the double ΔtreYZΔtreS double mutant was suppressed by various Arabidopsis cell wall mutants that affect xyloglucan synthesis, including an xxt1xxt2 double mutant that completely lacks xyloglucan, even though xyloglucan mutants are not more susceptible to pathogens and respond like wild-type plants to immune elicitors. An explanation of our data is that trehalose functions to promote the acquisition of nitrogen-containing nutrients in a process that involves the xyloglucan component of the plant cell wall, thereby allowing P. aeruginosa to replicate in the intercellular spaces in a leaf. This work shows how P. aeruginosa, a multi-host opportunistic pathogen, has repurposed a highly conserved “house-keeping” anabolic pathway (trehalose biosynthesis) as a potent virulence factor that allows it to replicate in the intercellular environment of a leaf.

Infection-Induced Interaction between the Mosquito Circulatory and Immune Systems

Insects counter infection with innate immune responses that rely on cells called hemocytes. Hemocytes exist in association with the insect's open circulatory system and this mode of existence has likely influenced the organization and control of anti-pathogen immune responses. Previous studies reported that pathogens in the mosquito body cavity (hemocoel) accumulate on the surface of the heart. Using novel cell staining, microdissection and intravital imaging techniques, we investigated the mechanism of pathogen accumulation in the pericardium of the malaria mosquito, Anopheles gambiae, and discovered a novel insect immune tissue, herein named periostial hemocytes, that sequesters pathogens as they flow with the hemolymph. Specifically, we show that there are two types of endocytic cells that flank the heart: periostial hemocytes and pericardial cells. Resident periostial hemocytes engage in the rapid phagocytosis of pathogens, and during the course of a bacterial or Plasmodium infection, circulating hemocytes migrate to the periostial regions where they bind the cardiac musculature and each other, and continue the phagocytosis of invaders. Periostial hemocyte aggregation occurs in a time- and infection dose-dependent manner, and once this immune process is triggered, the number of periostial hemocytes remains elevated for the lifetime of the mosquito. Finally, the soluble immune elicitors peptidoglycan and β-1,3-glucan also induce periostial hemocyte aggregation, indicating that this is a generalized and basal immune response that is induced by diverse immune stimuli. These data describe a novel insect cellular immune response that fundamentally relies on the physiological interaction between the insect circulatory and immune systems.

Age‐dependent trade‐offs between immunity and male, but not female, reproduction

Immune function is costly and must be traded off against other life-history traits, such as gamete production. Studies of immune trade-offs typically focus on adult individuals, yet the juvenile stage can be a highly protracted period when reproductive resources are acquired and immune challenges are ubiquitous. Trade-offs during development are likely to be important, yet no studies have considered changes in adult responses to immune challenges imposed at different stages of juvenile development. By manipulating the timing of a bacterial immune challenge to the larvae of the cotton bollworm moth, we examined potential trade-offs between investment into immunity at different stages of juvenile development (early or late) and subsequent adult reproductive investment into sperm or egg production. Our data reveal an age-dependent trade-off between juvenile immune function and adult male reproductive investment. Activation of the immune response during late development resulted in a reduced allocation of resources to eupyrene (fertilizing) sperm production. Immune activation from the injection procedure itself (irrespective of whether individuals were injected with an immune elicitor or a control solution) also caused reproductive trade-offs; males injected early in development produced fewer apyrene (nonfertilizing) sperm. Contrary to many other studies, our study demonstrates these immune trade-offs under ad libitum nutritional conditions. No trade-offs were observed between female immune activation and adult reproductive investment. We suggest the differences in trade-offs observed between male sperm types and the absence of reproductive trade-offs in females may be the result of ontogenetic differences in gamete production in this species. Our data reveal developmental windows when trade-offs between immune function and gametic investment are made, and highlight the importance of considering multiple developmental periods when making inferences regarding the fundamental trade-offs expected between immune function and reproduction.

Immune Challenge and Pre- and Post-copulatory Female Choice in the Cricket Teleogryllus commodus

Life history theory predicts a trade off between the expression of male sexual traits and the immune system. To test for this trade off, male crickets Teleogryllus commodus were injected with bacterial lipopolysaccharides (LPS) to induce an immune response and their subsequent pre- and post-copulatory sexual attractiveness to virgin and non-virgin females was assessed. Pre-copulatory attractiveness was quantified based on the time taken for males to court and mate with a female. Post-copulatory attractiveness was measured as the time that elapsed between mating and a female interrupting sperm transfer by removing the externally attached spermatophore. We found no difference in pre- or post-copulatory attractiveness between LPS and control males. In contrast, virgin females retained spermatophores for almost twice as long as non-virgins, presumably to enhance fertilization and begin egg-laying. Finally, we note that although LPS is a widely used immune elicitor in insects, its effect might be transitory. After 24 h there was no detectable elevation in haemolymph antibacterial activity of LPS injected crickets compared to that of controls.

Identification of innate immunity elicitors using molecular signatures of natural selection.

The innate immune system is an ancient and broad-spectrum defense system found in all eukaryotes. The detection of microbial elicitors results in the up-regulation of defense-related genes and the elicitation of inflammatory and apoptotic responses. These innate immune responses are the front-line barrier against disease because they collectively suppress the growth of the vast majority of invading microbes. Despite their critical role, we know remarkably little about the diversity of immune elicitors. To address this paucity, we reasoned that hosts are more likely to evolve recognition to "core" pathogen proteins under strong negative selection for the maintenance of essential cellular functions, whereas repeated exposure to host-defense responses will impose strong positive selective pressure for elicitor diversification to avoid host recognition. Therefore, we hypothesized that novel bacterial elicitors can be identified through these opposing forces of natural selection. We tested this hypothesis by examining the genomes of six bacterial phytopathogens and identifying 56 candidate elicitors that have an excess of positively selected residues in a background of strong negative selection. We show that these positively selected residues are atypically clustered, similar to patterns seen in the few well-characterized elicitors. We then validated selected candidate elicitors by showing that they induce Arabidopsis thaliana innate immunity in functional (virulence suppression) and cellular (callose deposition) assays. These finding provide targets for the study of host-pathogen interactions and applied research into alternative antimicrobial treatments.

Wolbachia surface protein induces innate immune responses in mosquito cells

BackgroundWolbachia endosymbiotic bacteria are capable of inducing chronic upregulation of insect immune genes in some situations and this phenotype may influence the transmission of important insect-borne pathogens. However the molecules involved in these interactions have not been characterized. Results Here we show that recombinant Wolbachia Surface Protein (WSP) stimulates increased transcription of immune genes in mosquito cells derived from the mosquito Anopheles gambiae, which is naturally uninfected with Wolbachia; at least two of the upregulated genes, TEP1 and APL1, are known to be important in Plasmodium killing in this species. When cells from Aedes albopictus, which is naturally Wolbachia-infected, were challenged with WSP lower levels of upregulation were observed than for the An. gambiae cells. Conclusions We have found that WSP is a strong immune elicitor in a naturally Wolbachia-uninfected mosquito species (Anopheles gambiae) while a milder elicitor in a naturally-infected species (Aedes albopictus). Since the WSP of a mosquito non-native (nematode) Wolbachia strain was used, these data suggest that there is a generalized tolerance to WSP in Ae. albopictus.

Cloning and induction patterns of Cu/Zn superoxide dismutase in responses to immune elicitors and nucleopolyhedrovirus in the beet armyworm Spodoptera exigua

AbstractSuperoxide dismutase (SOD) is a metalloenzyme that catalyzes the dismutation of the superoxide anion to oxygen and hydrogen peroxide, and has accordingly been known to play an important role in reducing oxidative stresses induced by various stresses and infection. In an attempt to investigate whether it is involved in antiviral immune responses in insects, the full‐length cDNA of SeCu/ZnSOD was obtained from the cDNA library of Spodoptera exigua. It is 1,008 bp long (excluding poly‐A tail) with the open reading frame of 459 bp encoding 152 amino acids. Sequence analysis with BLAST shows identities to various insects such as Bombyx mori (80%), Hyphantria cunea (80%), Plutella xylostella (77%), Aedes aegypti (73%), Apis mellifera (71%), Lasius niger (70%), Drosophila melanogaster (69%) and Gryllotalpa orientalis (67%). During development, S. exigua expressed SeCu/ZnSOD predominantly at embryonic stage, pupal stage and adult female stage, whereas it was slightly expressed in larvae and adult male. In addition, SeCu/ZnSOD was highly expressed in the fat body, hemocyte, silk gland and Malpighian tubule, although the levels of SeCu/ZnSOD transcripts were very low in the gut. Furthermore, SeCu/ZnSOD mRNA was slightly induced in response to either lipopolysaccharide or laminarin. Finally, SeCu/ZnSOD mRNA was induced in carcass in response to S. exigua nucleopolyhedrovirus (SeNPV) infection, whereas it was not strikingly induced in the gut. The precise roles of SeCu/ZnSOD in antiviral immune response remains to be further studied.

Molecular cloning and expression pattern of 14‐3‐3ζ from the malaria vector, Anopheles sinensis

Abstract14‐3‐3 proteins are known to play a pivotal role in cell survival, apoptosis and signal transduction. The 14‐3‐3ζ isoform has been cloned and characterized from many eukaryotic organisms, including the fruit fly and silkworm. However, no study on mosquito 14‐3‐3 has been reported to date. In an attempt to investigate the function of 14‐3‐3 in midgut epithelial cells undergoing apoptosis, a cDNA library was generated from the malaria vector, Anopheles sinensis, which was treated with apoptosis‐inducing Actinomycin‐D. We were able to identify and obtain A. sinensis 14‐3‐3ζ cDNA (Ansi14‐3‐3ζ) from expressed sequence tags (EST) analysis after conducting massive sequencing of the A. sinensis cDNA library. Ansi14‐3‐3ζ has very high homology to 14‐3‐3 homologs of various insects, such as Anopheles gambiae (100%), Aedes aegypti (100%), Drosophila melanogaster (96%), Bombyx mori (93%), Apis mellifera (93%) and Mus musculus (81%), indicating that mosquito 14‐3‐3ζ is a highly conserved gene in diverse organisms. Analysis of temporal expression patterns showed that Ansi14‐3‐3ζ mRNA is highly expressed in egg, early pupae and adult stages and is also expressed, although at low levels, in fourth instar larvae and late pupae. In response to two immune elicitors (lipopolysaccharide and laminarin), no striking induction of 14‐3‐3ζ mRNA was observed in A. sinensis. Further studies of the precise biological function, inducibility and subcellular distribution of 14‐3‐3ζ are required in Plasmodium invasion‐induced apoptotic midgut cells in A. sinensis in the context of the Time Bomb model.

Molecular Phenotyping of Mannosyltransferases-Deficient Candida albicans Cells by High-Resolution Magic Angle Spinning NMR

The yeast Candida albicans is an opportunistic pathogen that causes infections in immunocompromised individuals with a high morbidity and mortality levels. Recognition of yeasts by host cells is directly mediated by cell wall components of the yeast, including a wide range of abundantly expressed glycoconjugates. Of particular interest in C. albicans are the beta-mannosylated epitopes that show a complex expression pattern on N-glycan moiety of phosphopeptidomannans and are absent in the non-pathogenic species Saccharomyces cerevisiae. Being known as potent antigens for the adaptive immune response and elicitors of specific infection-protective antibodies, the exact delineation of beta-mannosides regulation and expression pathways has lately become a major milestone toward the comprehension of host-pathogen interplay. Using the newly developed HR-MAS NMR methodology, we demonstrate the possibility of assessing the general profiles of cell-surface-exposed glycoconjugates from intact living yeast cells without any prior purification step. This technique permitted to directly observe structural modifications of surface expressed phosphodiester-linked beta-mannosides on a series of deletion strains in beta-mannosyltransferases and phospho-mannosyltransferases compared with their parental strains.

The immunogenic properties of protozoan glycosylphosphatidylinositols in the mosquito Anopheles gambiae

In contrast to humans, mosquitoes do not have an adaptive immune response to deal with pathogens, and therefore must rely on their innate immune system to deal with invaders. This facilitates the recognition of different microbes on the basis of surface components or antigens. Such antigens have been identified in various types of microbe such as bacteria and fungi, yet none has been identified in the genus protozoa, which includes pathogens such as the malaria parasite, Plasmodium falciparum and Toxoplasma gondii. This study allowed us to test the antigenic properties of protozoan glycosylphosphatidylinositol (GPI) on the mosquito immune system. We found that both P. falciparum GPI and T. gondii GPI induce the strong expression of several antimicrobial peptides following ingestion, and that as a result of the immune response against the GPIs, the number of eggs produced by the mosquito is reduced dramatically. Such effects have been associated with malaria infected mosquitoes, but never associated with a Plasmodium specific antigen. This study demonstrates that protozoan GPIs can be considered as protozoan specific immune elicitors in mosquitoes, and that P. falciparum GPI plays a critical role in the malaria parasite manipulation of the mosquito vector to facilitate its transmission.

How Do Flies Tolerate Microorganisms in the Gut?

Although gut epithelia are in constant contact with a large number of microbe-derived immune elicitors such as peptidoglycan, they do not mount an intense immune response. In this issue of Cell Host & Microbe, Lhocine et al. (2008) report that the PIMS gene product induces immune tolerance by reducing the availability of the peptidoglycan receptor in the plasma membrane. These findings provide a novel insight into the molecular mechanisms by which the host gut maintains balanced host-microbe interactions.

Temporal patterns in immune responses to a range of microbial insults ( Tenebrio molitor)

Much work has elucidated the pathways and mechanisms involved in the production of insect immune effector systems. However, the temporal nature of these responses with respect to different immune insults is less well understood. This study investigated the magnitude and temporal variation in phenoloxidase and antimicrobial activity in the mealworm beetle Tenebrio molitor in response to a number of different synthetic and real immune elicitors. We found that antimicrobial activity in haemolymph increased rapidly during the first 48 h after a challenge and was maintained at high levels for at least 14 days. There was no difference in the magnitude of responses to live or dead Escherichia coli or Bacillus subtilis. While peptidoglylcan also elicited a long-lasting antimicrobial response, the response to LPS was short lived. There was no long-lasting upregulation of phenoloxidase activity, suggesting that this immune effector system is not involved in the management of microbial infections over a long time scale.

Resistance is skin‐deep: innate immunity may help amphibians to survive a deadly fungus

Resistance is skin‐deep: innate immunity may help amphibians to survive a deadly fungus

Changes in immune gene expression and resistance to bacterial infection in lobster ( Homarus gammarus) post-larval stage VI following acute or chronic exposure to immune stimulating compounds

Real-time PCR was used to measure changes in transcript abundance of genes encoding important immune proteins, namely prophenoloxidase ( proPO gene), β-1,3-glucan binding protein ( βGBP gene) and a 12.2 kDa antimicrobial peptide ( amp gene) in post-larval stage VI (PLVI) juveniles of the European lobster, Homarus gammarus. Gene expression was studied in both healthy PLVI and following single or repeat exposure to a range of compounds claimed to induce immune reactivity. A single acute (3-h) exposure to any of the tested stimulants did not produce a significant increase in expression of either the proPO or βGBP genes, measured 6 h after stimulation. However, there were a small sub-group of positive responders, identified mainly from βGBP expression, within the experimental groups stimulated with either a β-1,3-glucan or an alginate. There was also no significant increase in the expression of any of the three genes tested 24 h after repeated weekly (3-h) exposures to a either the β-1,3-glucan or the alginate over the longer (36-day) period. The results do show that amp is expressed at an extremely high level compared to proPO or βGBP in healthy animals and a significant correlation was found between the expression of proPO and both βGBP and amp, irrespective of whether or not the larvae were stimulated. None of the immune stimulated compounds improved survival of PLVI challenged with the opportunistic pathogen, Listonella anguillarum, or the lobster pathogen, Aerococcus viridans var. homari. Thus, we found no evidence to support recent claims that immunity and disease resistance can be primed or promoted within a given population of crustaceans or that these animals exhibit functional immune memory to some soluble immune elicitors.

Peptidoglycan Molecular Requirements Allowing Detection by the Drosophila Immune Deficiency Pathway

Innate immune recognition of microbes is a complex process that can be influenced by both the host and the microbe. Drosophila uses two distinct immune signaling pathways, the Toll and immune deficiency (Imd) pathways, to respond to different classes of microbes. The Toll pathway is predominantly activated by Gram-positive bacteria and fungi, while the Imd pathway is primarily activated by Gram-negative bacteria. Recent work has suggested that this differential activation is achieved through peptidoglycan recognition protein (PGRP)-mediated recognition of specific forms of peptidoglycan (PG). In this study, we have further analyzed the specific PG molecular requirements for Imd activation through the pattern recognition receptor PGRP-LC in both cultured cell line and in flies. We found that two signatures of Gram-negative PG, the presence of diaminopimelic acid in the peptide bridge and a 1,6-anhydro form of N-acetylmuramic acid in the glycan chain, allow discrimination between Gram-negative and Gram-positive bacteria. Our results also point to a role for PG oligomerization in Imd activation, and we demonstrate that elements of both the sugar backbone and the peptide bridge of PG are required for optimum recognition. Altogether, these results indicate multiple requirements for efficient PG-mediated activation of the Imd pathway and demonstrate that PG is a complex immune elicitor.

In vivo dynamics of an immune response in the bumble bee Bombus terrestris

Concepts from evolutionary ecology have recently been applied to questions of immune defences. However, an important but often neglected aspect is the temporal dynamics of the simple immune measures used in ecological studies. Here, we present observations for workers of the bumble bee Bombus terrestris on the dynamics of the phenoloxidase (PO) system, antibacterial activity, and the total number of haemocytes following a challenge with immune elicitors (LPS, Laminarin), over a time-span ranging from 1 min to 14 days. The dynamics of the PO measurement showed a complex pattern and was correlated with haemocyte counts. Antibacterial activity, on the other hand, increased sharply between 2 and 24 h post-challenge followed by a slow decrease. Surprisingly, the effects of a challenge lasted up to 14 days.