Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

    We have a manual that explains all the features 

Current refinement(s):

Records 1 - 20 / 59

  • help
  • print

    Print search results

  • export

    Export search results

  • alert
    We will mail you new results for this query: keywords==immuniteit
Check title to add to marked list
Virulence contribution and recognition of homologs of the Verticillium dahliae effector Ave1
Boshoven, Jordi C. - \ 2017
University. Promotor(en): Bart Thomma; Pierre de Wit. - Wageningen : Wageningen University - ISBN 9789463436441 - 183
verticillium dahliae - plant pathogenic fungi - plant pathogens - disease resistance - virulence factors - virulence - immunity - host parasite relationships - plant-microbe interactions - symbiosis - mutagenesis - resistance breeding - plantenziekteverwekkende schimmels - plantenziekteverwekkers - ziekteresistentie - virulente factoren - virulentie - immuniteit - gastheer parasiet relaties - plant-microbe interacties - symbiose - mutagenese - resistentieveredeling

Disease resistance in crops is an important aspect of securing global food security. Resistant plants carry immune receptors that sense pathogen invasion often through the recognition of important pathogen virulence factors, known as effectors. Thus, identification and characterization of effectors is important for the fundamental understanding of virulence mechanisms and to aid in resistance breeding. In this thesis the VdAve1 effector of the soil-borne fungal pathogen Verticillium dahliae is studied that is recognized by tomato immune receptor Ve1. Homologs were found in other plant pathogens and the role in virulence in these pathogens was analyzed. Ave1 homologs are differentially recognized by Ve1 and with a combination of domain swaps and truncations a surface exposed patch was identified that contributes to the recognition by Ve1. Knowledge of specific effector-receptor combinations and knowledge of effectors in general can be exploited to aid in breeding for durable resistance in crops.

On the role of vaccine dose and antigenic distance in the transmission dynamics of Highly Pathogenic Avian Influenza (HPAI) H5N1 virus and its selected mutants in vaccinated animals
Sitaras, Ioannis - \ 2017
University. Promotor(en): Mart de Jong, co-promotor(en): Ben Peeters. - Wageningen : Wageningen University - ISBN 9789463438063 - 209
avian influenza viruses - avian influenza - disease transmission - vaccines - vaccination - dosage - antigenic variation - mutants - mutations - immunity - vaccine development - virology - epidemiology - aviaire influenzavirussen - aviaire influenza - ziekteoverdracht - vaccins - vaccinatie - dosering - antigene variatie - mutanten - mutaties - immuniteit - vaccinontwikkeling - virologie - epidemiologie

Influenza virus infections can cause high morbidity and mortality rates among animals and humans, and result in staggering direct and indirect financial losses amounting to billions of US dollars. Ever since it emerged in 1996 in Guangdong province, People’s Republic of China, one particular highly pathogenic avian influenza (HPAI) H5N1 virus has spread globally, and is responsible for massive losses of poultry, as well as human infections. For these reasons, HPAI H5N1 is considered as one of the viruses possible to cause a future influenza pandemic.

One of the main reasons why influenza is a recurring problem is its ability to constantly evolve through the selection of mutants that are able to avoid immunity (be it natural or acquired). Due to the accumulation of mutations during genome replication, diverse/variant influenza genome sequences co-exist in a virus pool (quasispecies). These sequences can contain mutations that are able to confer selective advantages to the influenza virus given the opportunity. As a consequence, whenever a situation arises that places the virus under any type of pressure that the dominant virus sequence cannot cope with (i.e. immune pressure, selective receptor binding, etc.), the virus with the genome sequence that allows it to better adapt to that particular pressure becomes selected and takes over.

Because of the influenza virus’s high rate of mutations, a global surveillance network is in place to monitor changes in circulating strains among humans that would warrant an update of the vaccines used. For human influenza strains, vaccines are updated frequently (every one or two years) and a similar situation holds true for racehorse vaccination. For avian influenza vaccination, however, the situation is different. In most countries, vaccination against avian influenza is not used, and in the countries where vaccines are used (either as routine or emergency measures), they are not updated as frequently as human vaccines are. In addition, in many instances vaccination against avian influenza viruses has met with some spectacular failures, since it failed to produce a level of immunity that would protect against circulating field strains. These vaccination failures have often been attributed to the fact that without constant vaccine updating (as is done for human influenza), the vaccines used are not able to keep up with continuously evolving antigenic variants selected in the field, and thus to protect poultry against them. In addition, since it is known that immune pressure resulting from vaccination can be a driving force in the evolution of influenza viruses and the selection of immune-escape mutants, there is a school of thought that posits that vaccination against avian influenza is not only a very expensive affair (especially if vaccines need to be frequently updated), but can also lead to selection of mutants that are able to avoid vaccination-induced immunity.

The research reported in this thesis started with addressing the gaps in the knowledge regarding the role of vaccination-induced immunity in the selection of immune-escape mutants of HPAI H5N1, and if there is a way for vaccines to still be able to protect against antigenically-distant variants of the vaccine seed strain, without the need for frequent vaccine updates.

Our first step in studying influenza virus evolution and selection of immune-escape mutants was to investigate how antigenic pressure may drive the selection of such mutants, and what the effect of the selected mutations on the pathogenicity and transmissibility of the mutants may be. Although there exist a variety of methods to select for influenza virus mutations (i.e. monoclonal antibodies, site-directed mutagenesis, reverse genetics, etc.), none of them is representative of selection as it happens in a vaccinated animal. In Chapter 2, we discuss in detail a laboratory-based system we have developed, in which immune-escape mutants are selected using homologous polyclonal chicken sera, similar to how they are selected in the field due to vaccination- induced immune pressure. We find that selection takes place early on, and additional mutations are selected when immune pressure is increased. Antigenic distances between the selected mutants and their parent strains are also increased throughout the selection process, but not in a linear fashion. Our selection system proved to be robust and replicable, and to be representative of selection in the field, since the mutations we selected for are also found in naturally-selected field isolates, and the antigenic distances between our selected mutants and their parent strains are similar to antigenic distances between vaccine strains and field isolates.

We continued our research by addressing the roles played by vaccine dose (and resulting immunity) and antigenic distance between vaccine and challenge strains, in the transmission of HPAI H5N1 viruses, by employing transmission experiments using vaccinated chickens (Chapter 3). To our surprise, we found that the effect of antigenic distances between vaccine and challenge strains on transmission is very small compared to the effect of vaccine dose. We then quantified, for the first time, the minimum level of immunity and minimum percentage of the vaccinated population exhibiting said immunity, in order for vaccines to be able to protect against transmission even of strains that are antigenically distant to the vaccine seed strain. Transmission of such strains in well-vaccinated populations would allow for a scenario where vaccination- induced immunity may drive the selection of immune-escape mutants. Our results show that in order for vaccines to prevent transmission of antigenically distant strains (such as the ones resulting from selection due to immune pressure), the threshold level of immunity against these strains should be ≥23 haemagglutination inhibition units (HIU), in at least 86.5% of the vaccinated population. This level of immunity can be estimated by knowing the antigenic distance between the vaccine and challenge (field) strain, and the HI titre against the vaccine strain, which would then allow the approximate level of immunity against the field strain to be deduced. For example, assuming the HI titre against a vaccine strain is 210 HIU, and the distance with the challenge (field) strain is 24 HIU, according to our results the vaccine should be able to protect against the challenge strain, because the difference in HI titres should be around 26 HIU (i.e. above 23 HIU). These results, taken together with our previous work on selection of mutants, where we showed that the antigenic distances between our mutants and their parent strains are representative of distances found in the field, point to the fact that it is unlikely that vaccination-induced immunity can lead to selection of mutants able to escape it, given that a threshold level of immunity in a minimum percentage of the vaccinated population is achieved. As a consequence, we believe that constant vaccine updating may not be necessary for avian influenza viruses, as long as a threshold level of immunity is maintained. This makes vaccination a more attractive control measure, both from a health perspective and a financial one, than just applying biosecurity measures.

To examine the effect the mutations in the haemagglutinin protein of our selected mutants may have in their transmission among chickens vaccinated with the parent strain, we used reverse genetics techniques to insert the HA gene of our most antigenically distant mutant into the parent strain backbone (Chapter 4). We vaccinated animals with a sub-optimal dose of vaccine, and we concluded that the mutations we selected for did not allow the mutant to avoid even low levels of immunity, such as the ones resulting from a sub-optimal vaccine dose (which resembles a poor field vaccination scenario). At the same time, the HA mutations we selected for did not appear to have a negative effect either on the pathogenicity of the mutant, or its ability to transmit to unvaccinated animals, since both parameters were comparable to the parent strain.

Finally, we studied the role inter-animal variation in immunity – as measured by HI titres – has in the accuracy of antigenic cartography calculations (Chapter 5). We found that using sera from more than one animal significantly increased the accuracy of antigenic distance calculations, since it takes into account individual differences in immune responses to vaccination, an inevitable phenomenon documented in both humans and animals. In addition, we increased the accuracy of antigenic maps by avoiding the use of dimension-reducing algorithms as is currently done. By not reducing the dimensionality of virus positioning in space, our maps retain the original geometry between strains or sera, leading to more accurate positioning (Chapters 2 and 5). We hope that improving the accuracy of antigenic cartography can lead to a more precise surveillance of influenza evolution and better informed decisions regarding the need to update vaccines.

Taken collectively, our results can improve field vaccination outcomes, since they provide guidelines on how to increase vaccination efficiency in stopping transmission of even antigenically-distant strains. In addition, our method for selecting for immune- escape mutants can be a valuable addition to research on influenza virus evolution. Moreover, policy making decisions regarding vaccination against any type of influenza can also benefit from our improvement on antigenic cartography accuracy, saving unnecessary costs in vaccine updating, and reducing morbidity and mortality of both animals and humans.

Recognition of Verticillium effector Ave1 by tomato immune receptor Ve1 mediates Verticillium resistance in diverse plant species
Song, Yin - \ 2017
University. Promotor(en): Bart Thomma; Pierre de Wit. - Wageningen : Wageningen University - ISBN 9789463437950 - 231
disease resistance - defence mechanisms - immunity - plant-microbe interactions - plant pathogens - verticillium dahliae - verticillium - tomatoes - solanum lycopersicum - receptors - genes - tobacco - nicotiana glutinosa - potatoes - solanum tuberosum - solanum torvum - humulus lupulus - cotton - gossypium hirsutum - transgenic plants - arabidopsis thaliana - ziekteresistentie - verdedigingsmechanismen - immuniteit - plant-microbe interacties - plantenziekteverwekkers - tomaten - receptoren - genen - tabak - aardappelen - katoen - transgene planten

Plant-pathogenic microbes secrete effector molecules to establish disease on their hosts, whereas plants in turn employ immune receptors to try and intercept such effectors in order to prevent pathogen colonization. Based on structure and subcellular location, immune receptors fall into two major classes; cell surface-localized receptors that comprise receptor kinases (RKs) and receptor-like proteins (RLPs) that monitor the extracellular space, and cytoplasm-localized nucleotide-binding domain leucine-rich repeat receptors (NLRs) that survey the intracellular environment. Race-specific resistance to Verticillium wilt in tomato (Solanum lycopersicum) is governed by the tomato extracellular leucine-rich repeat (eLRR)-containing RLP-type cell surface receptor Ve1 upon recognition of the effector protein Ave1 that is secreted by race 1 strains of the soil-borne vascular wilt Verticillium dahliae. Homologues of V. dahliae Ave1 (VdAve1) are found in plants and in a number of plant pathogenic microbes, and some of these VdAve1 homologues are recognized by tomato Ve1. The research presented in this thesis aims to characterize the role of the tomato cell surface-localized immune receptor Ve1, and its homologues in other diverse plant species, in Verticillium wilt resistance.

Adapting to change : on the mechanism of type I-E CRISPR-Cas defence
Künne, Tim A. - \ 2017
University. Promotor(en): John van der Oost, co-promotor(en): Stan Brouns. - Wageningen : Wageningen University - ISBN 9789463436649 - 239
immunity - defence mechanisms - rna - bacteria - escherichia coli - analytical methods - priming - immuniteit - verdedigingsmechanismen - bacteriën - analytische methoden - zaadbevochtiging

Host-pathogen interactions are among the most prevalent and evolutionary important interactions known today. The predation of prokaryotes by their viruses is happening on an especially large scale and had a major influence on the evolutionary history of prokaryotes. Since most viruses are lytic at some point in their life-cycle, there is a high selection pressure for prokaryotes to develop defense mechanisms. As described in Chapter 1, the CRISPR-Cas system is a relatively recently discovered defense system and is also the first adaptive defense system discovered in prokaryotes. CRISPR-Cas systems are widespread, occurring in the majority of archaea and also a considerable fraction of bacteria. This diversity is also reflected in the diversity of different types of CRISPR-Cas systems, currently being divided into 6 major types with a large number of subtypes. The type I-E system of Escherichia coli is a well-studied model system and of high relevance, since it is a major subtype of type I systems which make up around 50 % of all discovered CRISPR-Cas systems. CRISPR-Cas systems basically comprise the CRISPR array, made up of repeats and foreign derived spacers, and a set of cas genes. Immunity is commonly divided into three functional stages, adaptation, expression and interference. Adaptation is the acquisition of new spacers from the foreign nucleic acid and its incorporation into the CRISPR array. During expression, the CRISPR array is transcribed, processed and assembled with Cas proteins into CRISPR RNA (crRNA) guided ribonucleoprotein complexes (crRNP). Interference is the detection, binding and destruction of foreign nucleic acids by the crRNP and in type I systems the Cas3 nuclease. The type I-E system contains another function, called primed adaptation. Primed adaptation is a more rapid and efficient version of regular (naïve) adaptation. In addition to the adaptation machinery, primed adaptation also requires the interference machinery.

Chapter 2 describes and compares a fundamental feature of most, if not all, CRISPR-Cas systems and also many other small RNA based systems. The mode of action of small RNAs relies on protein-assisted base pairing of the guide RNA with target mRNA or DNA to interfere with their transcription, translation or replication. Several unrelated classes of small non-coding RNAs have been identified including eukaryotic RNA silencing associated small RNAs, prokaryotic small regulatory RNAs and prokaryotic CRISPR (clustered regularly interspaced short palindromic repeats) RNAs. All three groups identify their target sequence by base pairing after finding it in a pool of millions of other nucleotide sequences in the cell. In this complicated target search process, a region of 6 to 12 nucleotides of the small RNA termed the ‘seed’ plays a critical role. The seed is often a structurally pre-ordered region that increases accessibility and lowers the energy barrier of RNA-DNA duplex formation. Furthermore, the length of the seed is optimally chosen to allow rapid probing and also rejection of potential target sites. The seed is a perfect example of parallel evolution, showing that nature comes up with the same strategy independently multiple times.

Chapter 3 provides a description and protocol of the Electrophoretic Mobility Shift Assay (EMSA) and its use for studying crRNPs. EMSA is a straightforward and inexpensive method for the determination and quantification of protein–nucleic acid interactions. It relies on the different mobility of free and protein-bound nucleic acid in a gel matrix during electrophoresis. Nucleic acid affinities of crRNPs can be quantified by calculating the dissociation constant (Kd ). Protocols for two types of EMSA assays are described using the Cascade ribonucleoprotein complex from Escherichia coli as an example. One protocol uses plasmid DNA as substrate, while the other uses short linear oligonucleotides. Plasmids can be easily visualized with traditional DNA staining, while oligos have to be radioactively labelled using the 32Phosphate isotope. The EMSA method and these protocols are applied throughout the other chapters of this thesis.

Chapter 4 focusses on the processes of interference and primed adaptation, specifically on their tolerance of mutations. Invaders can escape Type I-E CRISPR-Cas immunity in E. coli by making point mutations in the protospacer (especially in the seed) or its adjacent motif (PAM), but hosts quickly restore immunity by integrating new spacers in a positive feedback process termed priming. Here, we provide a systematic analysis of the constraints of both direct interference and subsequent priming in E. coli. We have defined a high-resolution genetic map of direct interference by Cascade and Cas3, which includes five positions of the protospacer at 6 nt intervals that readily tolerate mutations. Importantly, we show that priming is an extremely robust process capable of utilizing degenerate target regions with up to at least eleven mutations throughout the PAM and protospacer region. Priming is influenced by the number of mismatches, their position and is nucleotide dependent. Our findings imply that even out-dated spacers containing many mismatches can induce a rapid primed CRISPR response against diversified or related invaders, giving microbes an advantage in the co- evolutionary arms race with their invaders.

In Chapter 5 we elucidate the mechanism of priming. Specifically, we determine how new spacers are produced and selected for integration into the CRISPR array during priming. We show that priming is directly dependent on interference. Rapid priming occurs when the rate of interference is high, delayed priming occurs when the rate of interference is low. Using in vitro assays and next generation sequencing, we show that Cas3 couples CRISPR interference to adaptation by producing DNA breakdown products that fuel the spacer integration process in a two-step, PAM-associated manner. The helicase-nuclease Cas3 pre-processes target DNA into fragments of about 30–100 nt enriched for thymine-stretches in their 3’ ends. By reconstituting the spacer integration process in vitro, we show that the Cas1-2 complex further processes these fragments and integrates them sequence- specifically into CRISPR repeats by coupling of a 3’ cytosine of the fragment. Our results highlight that the selection of PAM-compliant spacers during priming is enhanced by the combined sequence specificities of Cas3 and the Cas1-2 complex, leading to an increased propensity of integrating functional CTT-containing spacers.

In Chapter 6 we look deeper into a nucleotide specific effect on priming that was discovered in Chapter 4. Immunity is based on the complementarity of host encoded spacer sequences with protospacers on the foreign genetic element. The efficiency of both direct interference and primed acquisition depends on the degree of complementarity between spacer and protospacer. Previous studies focused on the amount and positions of mutations, not the identity of the substituted nucleotide. In Chapter 4, we describe a nucleotide bias, showing a positive effect on priming of C substitutions and a negative effect on priming of G substitutions in the basepairing strand of the protospacer. Here we show that these substitutions rather directly influence the efficiency of interference and therefore indirectly influence the efficiency of interference dependent priming. We show that G substitutions have a profoundly negative effect on interference, while C substitutions are readily tolerated when in the same positions. Furthermore, we show that this effect is based on strongly decreased binding of the effector complex Cascade to G mutants, while C mutants only minimally affect binding. In Chapter 5 we showed a connection between the rate of interference and the time of occurrence of priming. Here, we also quantify the extent of priming and show that priming is very prevalent in a population that shows intermediate levels of interference, while high or low levels of interference lead to a lower prevalence of priming.

Chapter 7 describes an attempt to make use of our knowledge about the Cascade complex and develop it into a genome editing tool. The development of genome editing tools has made major leaps in the last decade. Recently, RNA guided endonucleases (RGENs) such as Cas9 or Cpf1 have revolutionized genome editing. These RGENs are the hallmark proteins of class II CRISPR-Cas systems. Here, we have explored the possibility to develop a new genome editing tool that makes use of the Cascade complex from E. coli. This RNA guided protein complex is fused to a FokI nuclease domain to sequence specifically cleave DNA. We validate the tool in vitro using purified protein and two sets of guide RNAs, showing specific cleavage activity. The tool requires two target sites of 32 nt each at a distance of 30-40 nt and inward facing three nucleotide flexible PAM sequences. Cleavage occurs in the middle between the two binding sites and primarily creates 4 nt overhangs. Furthermore, we show that an additional RFP can be fused to FokI-Cascade, allowing visualization of the complex in target cells. Unfortunately, we were not able to successfully apply the tool in vivo in eukaryotic cells.

Evasion of chitin-triggered immunity by fungal plant pathogens
Rövenich, Hanna J. - \ 2017
University. Promotor(en): Bart Thomma; Pierre de Wit. - Wageningen : Wageningen University - ISBN 9789463436137 - 133
plant-microbe interactions - immunity - receptors - verticillium dahliae - cladosporium - plant pathogens - chitin - arabidopsis thaliana - fungi - plant-microbe interacties - immuniteit - receptoren - plantenziekteverwekkers - chitine - schimmels

Plants establish intricate relationships with microorganisms that range from mutualistic to pathogenic. In order to prevent colonization by potentially harmful microbes, plant hosts employ surface-localized receptor molecules that perceive ligands, which are either microbe-derived or result from microbe-mediated plant manipulation. This recognition ultimately leads to the activation of host immunity. In order to circumvent recognition or suppress immune responses, microbes secrete effector proteins that deregulate host physiological processes. While the number of identified putative effectors has rapidly increased in recent years, their functions and the mechanisms governing their recognition have largely remained unexplored. To enhance our understanding of the molecular interplay between host and microbe, the work presented here was designed to identify further components involved in the recognition of the two fungal pathogens Verticillium dahliae and Cladosporium fulvum, as well as to characterize the functions of effector proteins produced by these pathogens during tomato infection.

Innate immunity of carp : fishing for receptors
Fink, Inge - \ 2017
University. Promotor(en): Geert Wiegertjes; Huub Savelkoul, co-promotor(en): Maria Forlenza. - Wageningen : Wageningen University - ISBN 9789463430753 - 240
carp - cyprinus - immunity - platelets - macrophage activation - receptors - polarization - immunostimulation - immunology - karper - immuniteit - bloedplaatjes - macrofaag activering - receptoren - polarisatie - immunostimulatie - immunologie

Recent decades have seen a significant intensification of aquaculture leading to increased risk of infections with several pathogenic organisms. On economical and ethical grounds it is more appropriate to improve general welfare conditions and prevent infections rather than treating disease outbreaks once they have occurred. Immunostimulation through feed can provide more efficient and sustainable control of diseases in aquaculture through enhancing the immunocompetence of fish; however, the underlying mechanisms are poorly characterized. The overall aim of this thesis was to perform a molecular and functional characterization of how pathogen-associated molecular patterns (PAMPs), such as β-glucans, affect the innate immune response of carp and which receptors on carp leukocytes are likely candidates to play a role in sensing such PAMPs.

In chapter 1 we provide a framework for this thesis by introducing different classes of PAMPs, including β-glucans. These molecules were the centrepiece of an intra-European training network called NEMO (Protective immune modulation in warm water fish by feeding glucans), which this PhD project was part of. The scientific aim of the NEMO network was to develop a sustainable and cost-effective use of β-glucans as immunostimulants for aquaculture, using common carp as the model fish species, since on a global scale common carp is the most cultured fish species for food consumption. Our aims within the NEMO project entailed both the characterization of carp leukocytes and the characterization of candidate pattern recognition receptors (PRRs) that could play a role in sensing PAMPs and initiating immune responses. Chapter 1 therefore introduces the thrombocytes and macrophages pertinent to this thesis, as well as important classes of PRRs.

In our first experimental study, described in chapter 2, we investigated the relevance of thrombocytes for the immune system of carp. We found that thrombocytes from healthy carp express a large number of immune-relevant genes, among which several cytokines and Toll-like receptors (Tlrs). Furthermore, we dissected the role of thrombocytes during infections with two different, albeit related, protozoan parasites, Trypanoplasma borreli and Trypanosoma carassii, and found thrombocytes were massively depleted from blood and spleen of fish infected with T. borreli. The pathology of this infection is associated with elevated levels of tissue nitration, prompting us to investigate, ex vivo, the effect of nitric oxide on thrombocytes. Our studies revealed that nitric oxide can induce a clear and rapid apoptosis of thrombocytes from healthy carp, supporting a role for nitric oxide-mediated control of immune-relevant thrombocytes during infection with T. borreli. Thereby, this particular study provided an excellent example of interplay between pathogen and the innate immune system of carp.

We reviewed in chapter 3 another cell type central to innate immunity: the macrophage. We focused on the heterogeneity of macrophage activation states as these cells, at least in humans and mice, have the ability to polarize in several directions during an immune response. Based on the signals that lead to activation and the effector functions and cytokine profile as a result thereof, macrophages can be broadly divided into two types: classically activated macrophages induced in a T helper 1 (TH1) cytokine environment, and alternatively activated macrophages, induced in a TH2 cytokine environment. Mirroring the TH1–TH2 dichotomy, classically activated macrophages have also been termed M1, whereas alternatively activated macrophages have been termed M2. Classically activated macrophages are typically induced by stimulation with microbial ligands such as LPS in combination with pro-inflammatory cytokines such as IFNγ, and can be viewed as an extension of innate activated macrophages which are induced by microbial ligands only, thus are independent of cytokines. Alternatively activated macrophages are generated in the presence of IL4 and/or IL13. In addition to M1 and M2, one can distinguish regulatory macrophages, which are associated with the presence of the cytokine IL10. In this chapter, we reviewed the evidence of existence of polarized macrophages in teleost fish, among other things based on observations of the fundamentally different immune responses elicited by the parasites T. borreli and T. carassii.

We further investigated the polarization of carp macrophages in chapter 4, where we obtained gene signature profiles of carp macrophages via a transcriptome approach. Independently of cytokines, carp macrophages showed the ability to differentiate into cells with functional characteristics highly comparable to those of mammalian M1 and M2, consistent with a conserved ability of macrophages to polarize into distinct subsets. In addition to obtaining a global view of gene expression, our transcriptome approach identified gene signatures for M1 and M2 macrophages which appear conserved from fish to mammals. We selected a number of these interesting genes that were differentially regulated between M1 and M2 macrophages and discussed in detail five potential M1 markers; il1β, ptx3a, saa, nos2b, and il12a – as well as five potential M2 markers; cyr61, inhba, timp2, tgm2, and arg2. These transcriptome studies may pave the way for future studies of polarized macrophages during immune responses in fish. Furthermore, additional analyses of the datasets described in this chapter will undoubtedly lead to the characterization of more genes relevant to macrophage polarization and recognition of immunostimulants.

As part of the characterization of candidate PRRs that could play a role in sensing PAMPs and initiating immune responses, we studied the scavenger receptor Cd36 (chapter 5), which in mammals is expressed by many different (immune) cell types and plays a role in highly diverse processes, both homeostatic and pathologic. Among other things, it is often found associated with sensing of β-glucans and also with M2 macrophage activation, sparking our interest in this molecule in fish. We studied Cd36 in common carp as well as in zebrafish, a closely related cyprinid fish species. Whereas a single cd36 gene is present in zebrafish, carp was shown to have two paralogs of cd36. Although all genes show conserved synteny compared to mammalian CD36, unexpectedly we could not detect gene expression of cyprinid cd36 in macrophages or any other immune cell type or immune organ. Yet, because gene expression of cd36 was down-regulated during Mycobacterium marinum infection of zebrafish, and knockdown of cd36 in zebrafish embryos led to higher bacterial burden upon such infection, our data imply a role for Cd36 in immune responses of fish. Future studies are needed to clarify the exact mechanisms involved.

As characterization of candidate PRRs we also examined the Toll-like receptors Tlr1 and Tlr2 (chapter 6). We identified a full-length, expressed tlr1 gene, a tlr1 pseudogene, and a second tlr2 gene next to the tlr2 which had been described previously. Sequence, phylogenetic and synteny analyses supported the conserved nature of these genes, and three-dimensional modelling showed a good fit with the mammalian TLR1/TLR2 heterodimer including the potential to bind to the prototypical ligand Pam3CSK4. However, we were unable to demonstrate Tlr1/Tlr2-mediated ligand binding in transfected cell lines through NFκB activation, despite showing the expression and co-localization of Tlr1 and Tlr2. This prompted a discussion of methods available for studying ligand-binding properties of fish Tlrs.

Finally, we discuss in chapter 7 the findings of this thesis in the context of the NEMO project. We present the concept of trained immunity, which could provide the conceptual framework within which the immune-stimulating ability of compounds such as β-glucans could be explained. We discuss recent advances in the field of TLR research as well as that of macrophage polarization, and highlight immunometabolism as a new area of interest which may help to illuminate the molecular events occurring in immune cells during health and disease. In conclusion, we found that carp leukocytes, along with their pattern recognition receptors, are central players of the innate immune system of carp. Our findings contribute to the understanding of mechanisms of immunostimulation, and expect this will enable the valorisation and use of immunostimulants for sustainable aquaculture and improvement of fish health.

Biomarkers and mechanisms of natural disease resistance in dairy cows
Altena, S.E.C. van - \ 2016
University. Promotor(en): Huub Savelkoul, co-promotor(en): Edwin Tijhaar. - Wageningen : Wageningen University - ISBN 9789462578005 - 158 p.
dairy cows - biomarkers - disease resistance - immunity - antibodies - proteomics - immune response - dendritic cells - immunology - melkkoeien - ziekteresistentie - immuniteit - antilichamen - eiwitexpressieanalyse - immuniteitsreactie - dendritische cellen - immunologie

The aim of this thesis was to define and test biomarkers for disease resistance in dairy cows and to determine the underlying mechanism in natural disease resistance. The health status of the cows is an important issue in dairy farming. Due to the mandatory reduction in the use of antibiotics, alternatives are required to prevent the development and expression of illness in dairy cows. The identification of biomarkers associated with such disease offers the opportunity to adapt the management of cows at risk, and in this way, prevent them from developing overt disease. Previously, natural antibodies (NAbs) in serum and milk were used as candidate biomarkers for natural disease resistance in cows. In this thesis, we continue on the occurrence and mode of action of NAbs and also focus on their source: the B-1 cells. We performed a literature study on the identification and function of B-1 cells in different species and defined the limitations in the current identification of these cells in pigs, sheep and cows (Chapter 2). B-1 cells were described in cows by using widely accepted cell surface markers CD5 and CD11b. However, in literature several findings suggest that these cell surface markers are not unique markers for B-1 identification. The similarities between mice and veterinary animals in foetal B-cell development and antibody production, implies that B-1 cells are present in cows. In chapter 3, we carefully studied new markers to selectively identify B-1 cells in cows. The combination of B-1 cell markers IgM++ and pSYK++ (indicator constitutive intracellular signalling) identifies a distinct cell population with essential B-1 characteristics such as high CD80 expression. In addition, the development of these B-1 cells in calves before colostrum intake and 3 weeks afterwards shows the same kinetics as the development of NAbs represented by IgM antibodies binding to the well-accepted NAb-antigen phosphatidylcholine (PtC). In calves up to half a year of age, it is shown that the production of such NAbs increases from birth and stabilises from 6 weeks onwards. This implies an endogenous NAb production, which follows the same age-related kinetics as can be expected from B-1 cell development. In contrast, the development of total IgM antibody levels in calves shows a bimodal distribution, which is caused by the uptake and breakdown of maternally-derived IgM and simultaneous endogenous production of specific and natural IgM. Chapter 4 describes the role of such NAbs in bovine immunity. NAbs were represented by the binding of IgM to the naïve antigen keyhole limpet hemocyanin (KLH). Cows with high serum NAb levels were shown to have more IgM and IgG antibodies binding to common microbial structures LPS, LTA and PGN, than cows with low serum NAb levels. In addition, they also have more IgM antibodies binding to intact, fixed E. coli and S. Typhimurium bacteria. However, the killing of live E. coli and S. Typhimurium bacteria via antibody-mediated complement killing does not differ between cows with high and low NAb levels. The antibody-mediated complement killing was determined in a newly developed serum bactericidal test. Cows that performed less in the bactericidal test were more likely to develop mastitis in the future. This association was observed for the killing of E. coli and S. Typhimurium and the development of mastitis within the next one year. For S. Typhimurium the association was still present for the cases of mastitis occurring within four years after testing. Alternative biomarkers for disease resistance in cows were defined in chapter 5 by using a contemporary proteomics approach. Milk samples from high and low disease resistant cows were selected from the “Resilient Cattle” (Weerbaar Vee) biobank. Comparing the spectrum of milk proteins of high and low disease-resistant cows showed potential candidate biomarkers that were elevated in the milk of low-resistant cows. Two candidate marker proteins were validated with ELISA in a new and larger group of high- and low-resistant cows. Lactoferrin (LF) levels were significantly increased in milk of low-resistant cows. In addition, LF levels in milk were associated with clinical manifestations of lameness and had a predictive value for subsequent culling.

In conclusion, we found that also in cows NAbs are produced by B-1 cells that can be identified based on the combined expression of cell surface IgM and internal pSYK. In addition, the frequency of these B-1 cells after birth follows a similar kinetics as described before in mice. These NAbs can be more precisely identified based on their PtC binding ability and their functional activity in a bactericidal test. However, the true predictive value of B-1 cells and NAbs for the health status and immunocompetence of dairy cattle remains to be established. Proteomics turned out to be a useful approach for identifying potential new biomarkers for health and disease in milk of cows. Application and further development of their predictive capacity is dependent on the availability of robust, sensitive and quantitative assays. This project was part of the “Resilient Cattle” project providing biological samples and essential data on the health status during respective lactation periods of individual dairy cows. The impact of this research now requires translation into management tools and principles for the individual farmer impacting on the overall health status and economic performance of his herd of dairy cattle.

Tospovirus : induction and suppression of RNA silencing
Hedil, Marcio - \ 2016
University. Promotor(en): Just Vlak, co-promotor(en): Richard Kormelink. - Wageningen : Wageningen University - ISBN 9789462577848 - 137 p.
tospovirus - rna - plants - immunity - gene silencing - biochemical pathways - rna interference - viral proteins - plant viruses - planten - immuniteit - uitschakelen van genexpressie - biochemische omzettingen - rna-interferentie - viruseiwitten - plantenvirussen

While infecting their hosts, viruses must deal with host immunity. In plants the antiviral RNA silencing pathway is an important part of plant innate immunity. Tospoviruses are segmented negative-stranded RNA viruses of plants. To counteract the antiviral RNA silencing response in plants, tospoviruses have evolved a silencing suppressor function via its NSs protein. This viral protein has previously been shown to bind dsRNA that likely arises from secondary RNA folding structures in viral RNAs. The aim of the present research was to further investigate the interaction between tospoviruses and the plant antiviral RNA silencing response, including the target sequences in the viral RNA and the further role of the NSs protein as part of the tospovirus counterdefence strategy.

In order to identify the target and inducer for RNA silencing against tospoviruses, small RNAs purified from plants infected with three tospoviral species, tomato spotted wilt virus (TSWV), groundnut ringspot virus (GRSV) and tomato yellow ring virus (TYRV), were probed against the viral RNA segments of these three different tospoviruses (Chapter 3). Virus-derived siRNAs (vsiRNAs) were found to be derived from all three genomic RNA segments but predominantly the ambisense M and S RNAs. Further profiling on the S RNA sequence revealed that vsiRNAs were found from almost the entire S RNA sequence, except the predicted AU-rich hairpin (HP) structure encoded by the intergenic region (IGR) from where hardly any vsiRNAs were found. Similar profiles were observed with the closely related GRSV as well as the distantly related TYRV. Dicer cleavage assays using Drosophila melanogaster embryo extracts showed that synthetic transcripts of the IGR-HP region were recognized as substrate for Dicer. Transient agroinfiltration assays of a GFP-sensor construct containing the IGR-HP sequence at its 3′-UTR did not show more rapid/strong silencing, and profiling of the corresponding siRNAs generated outside the context of a viral infection still revealed relatively low levels of IGR-HP-derived siRNAs. These data support the idea that the IGR-HP region/structure is a weak inducer of RNA silencing and plays a minor role in the amplification of a strong antiviral RNA silencing response.

Next, a biochemical analysis was performed using E. coli-expressed and purified NSs from GRSV and TYRV. The binding of both purified NSs proteins to small and long dsRNA indicated that this is likely a generic feature of all tospoviral NSs proteins (Chapter 4). Binding of siRNAs to NSs furthermore revealed two shifts on polyacrylamide gels i.e. a first shift at low NSs concentrations followed by a second larger one at higher concentrations. When the NSs protein of TSWV resistant breaker (RB) isolates (of Tsw-gene based resistance), which lack RSS activity when transiently expressed, were analyzed using extracts from infected plants still a major (second) shift of siRNAs was observed, similar to the case with extracts containing TSWV resistant inducer (RI) isolates. In contrast, plant extracts containing transiently expressed NSs proteins alone (no infection) showed only the smaller, first shift for NSsRI but no shift for NSsRB.

The ability of NSs to suppress systemic silencing is demonstrated for the NSs proteins of TSWV, GRSV and TYRV, and their relative strengths to suppress local and systemic silencing were compared (Chapter 5). A system was developed to quantify suppression via GFP silencing constructs, allowing comparison of relative RNA silencing suppressor strength. In this case NSs proteins of all three tospoviruses are suppressors of local and systemic silencing. Unexpectedly, suppression of systemic RNA silencing by NSsTYRV was just as strong as those by NSsTSWV and NSsGRSV, even though NSsTYRV was expressed in lower amounts. Moreover, a set of selected NSsTSWV gene constructs mutated in predicted RNA binding domains, as well as NSs from TSWV isolates 160 and 171 (resistance breakers of the Tsw resistance gene), were analyzed for their ability to suppress systemic GFP silencing. The results indicate another mode of RNA silencing suppression by NSs that acts further downstream of the biogenesis of siRNAs and their sequestration.

In summary, evidence is presented showing that sequences from all three genomic segments from tospovirus are targeted by the plant RNA silencing machinery. The predicted hairpin sequence in the IGR is poorly targeted. Biochemical experiments with purified NSs proteins further support the view that binding to small and long dsRNA is a characteristic common to all tospovirus NSs proteins. Furthermore, tospovirus NSs proteins suppress systemic silencing and there are indications that local and systemic silencing suppression can be uncoupled in NSs. Collectively, these results add to our current understanding of the tospovirus-plant interaction involving antiviral RNA silencing and the viral counter-defence (NSs protein). Lastly, the results of the research presented in this thesis are discussed in light of the current knowledge on RNA silencing and to present some future perspectives and questions that remain open and/or resulted from this thesis (Chapter 6).

Next-generation salmonid alphavirus vaccine development
Hikke, M.C. - \ 2016
University. Promotor(en): Just Vlak, co-promotor(en): Gorben Pijlman. - Wageningen : Wageningen University - ISBN 9789462577404 - 159 p.
alphavirus - atlantic salmon - rainbow trout - vaccine development - immunity - virology - fish culture - aquaculture - biotechnology - alfavirus - europese zalm - regenboogforel - vaccinontwikkeling - immuniteit - virologie - visteelt - aquacultuur - biotechnologie

ABSTRACT

Aquaculture is essential to meet the current and future demands for seafood to feed the world population. Atlantic salmon and rainbow trout are two of the most cultured aquaculture species. A pathogen that threatens these species is salmonid alphavirus (SAV). A current inactivated virus vaccine against SAV provides cross-protection against all SAV subtypes in salmonids and reduces mortality amongst infected fish. However, protection is not 100% and due to virus growth at low temperature, the vaccine production process is time consuming. In addition, the vaccine needs to be injected into the fish, which is a cumbersome process. The work described in this thesis aimed to increase the general knowledge of SAV and to assess current vaccine technologies, and to use this knowledge in designing next-generation vaccines for salmonid aquaculture.

An alternative cell line to support SAV proliferation was identified, however, the virus production time could not yet outcompete the current SAV production system. Making use of the baculovirus insect cell expression system, multiple enveloped virus-like particle (eVLP), and core-like particle (CLP) prototype vaccines were produced in insect cells at high temperature. An in vivo vaccination study showed, however, that these vaccines could not readily protect Atlantic salmon against SAV. The low temperature-dependent replication of SAV was attributed to the glycoprotein E2, and it was found that E2 only correctly travelled to the cell surface at low temperature, and in the presence of glycoprotein E1. The biological impact of this finding was confirmed in the development and in vivo testing of a DNA-launched replicon vaccine. The effective DNA-launched replicon vaccine was extended by delivery of the capsid protein in trans. It was hypothesized that viral replicon particles (VRP) were formed in vivo, which would cause an additional single round of infection and might further elevate the immune response in comparison to the replicon vaccine. A second animal trial indicated that the inclusion of capsid did not yet improve vaccine efficacy. This trial however did show that a DNA vaccine transiently expressing the SAV structural proteins provided superior protection over both replicon vaccines (with and without capsid).

In this thesis, some virus characteristics, such as the cause of temperature-dependency of SAV replication, of an unique aquatic virus were further explored. The production and in vivo testing of multiple next-generation vaccines defined the prerequisites for induction of a potent immune response in Atlantic salmon. A prototype DNA-launched replicon vaccine has shown potential for further development. The research described in this thesis contributes to the development of next-generation vaccines in the challenging area of fish vaccinology.

Effects of early life conditions on immunity in broilers and layers
Simon, K. - \ 2016
University. Promotor(en): Bas Kemp, co-promotor(en): Aart Lammers. - Wageningen : Wageningen University - ISBN 9789462576711 - 188 p.
broilers - hens - ontogeny - poultry feeding - chicken housing - immune response - antibiotics - gastrointestinal microbiota - immunology - immunity - vleeskuikens - hennen - ontogenie - pluimveevoeding - huisvesting van kippen - immuniteitsreactie - antibiotica - microbiota van het spijsverteringskanaal - immunologie - immuniteit

ABSTRACT

The course for later life immune responses is set early in life during the developmental phase of the immune system and accordingly disturbances of immune development may have long-term consequences for host health. In terms of immune activation and immune development the gut microbiota play an important role and consequently disturbances of early life microbial colonization may affect host immunity later in life. In chickens, disturbances of microbial colonization may be caused by various early life conditions which in turn may affect robustness of the chick in the long term. The aim of this thesis was to assess the effects of several early life factors including time of access to feed post hatch (immediately or 72 hours delayed), housing conditions, antibiotic treatment, and intestinal pathology on the intestinal microbiota composition, immune development, and specific antibody response later in life in chickens. Additionally, possible differences between broilers and layers were taken into account as unintentional co-selection of immunological traits may have taken place during the selection process for different production traits. Delayed access to feed and administration of antibiotics early in life led to a shift in early life microbiota composition, which seemed to be restored quite quickly in both cases. Microbiota composition in response to DSS was not investigated, but based on rodent studies was expected to be influenced. Ileal immune development, which was assessed in terms of relative cytokine and immunoglobulin mRNA expression levels was not affected by feeding strategy post hatch (early vs. delayed), but a downregulation of ileal immunoglobulin expression levels could be observed during DSS treatment. All early life factors investigated affected the specific antibody response towards an immunological challenge later in life. Interestingly, there seemed to be an interaction between immediate access to feed post hatch and immune responsiveness towards the environment, thus early feeding may influence the adaptive capacity of chickens in different environments. Regarding the differences between breeds it is interesting to note that broilers seem to have developed a more humoral oriented immune strategy, while layers seem to react in a more pro-inflammatory way. Taken together, results suggested that early life conditions may influence priming of the immune system during its developmental phase, leading to altered antibody responses later in life. Furthermore, broilers and layers seem to have developed different immune strategies. Early life conditions as well as possible differences between breeds should therefore be taken into account in future immunological studies.

The role of microbiota for a balanced immune system
Smits, M.A. ; Jansman, A.J.M. ; Savelkoul, H.F.J. ; Rebel, J.M.J. - \ 2014
Tijdschrift voor Diergeneeskunde 139 (2014)6. - ISSN 0040-7453 - p. 22 - 26.
microbiota van het spijsverteringskanaal - spijsverteringsstoornissen - maagdarmziekten - immuniteit - diergezondheid - immuunsysteem - gastrointestinal microbiota - digestive disorders - gastrointestinal diseases - immunity - animal health - immune system
Central Veterinary Institute, onderdeel van Wageningen UR. Wageningen UR Livestock Research en Wageningen Universiteit hebben hun expertise en onderzoek naar het functioneren van het maagdarmkanaal bij landbouwhuisdieren gebundeld en geïntensiveerd. Zij hebben dit gedaan omdat de processen die in het maagdarmkanaal plaatsvinden, niet alleen van belang zijn voor een efficiënte voervertering en benutting maar ook voor de afweer van landbouwhuisdieren tegen infectieziekten. In het kader van de genoemde samenwerking zijn expertises en onderzoekstechnieken bij elkaar gebracht waarmee complexe processen in het maagdarmkanaal beter kunnen worden ontrafeld.
Mucosal immunity : barriers, bugs, and balance
Neerven, R.J.J. van - \ 2014
Wageningen : Wageningen University, Wageningen UR - ISBN 9789462571952 - 24
immuniteit - immuniteitsreactie - immuunsysteem - immunologie - infectieziekten - ontsteking - orale vaccinatie - voeding - immunity - immune response - immune system - immunology - infectious diseases - inflammation - oral vaccination - nutrition
Understanding the role of L-type lectin receptor kinases in Phytophthora resistance
Wang, Y. - \ 2014
University. Promotor(en): Francine Govers, co-promotor(en): W. Shan; Klaas Bouwmeester. - Wageningen : Wageningen University - ISBN 9789462571327 - 214
phytophthora - phytophthora capsici - oömycota - plantenziekteverwekkende schimmels - plant-microbe interacties - arabidopsis - transgene planten - genexpressie - receptoren - kinasen - genen - ziekteresistentie - immuniteit - oomycota - plant pathogenic fungi - plant-microbe interactions - transgenic plants - gene expression - receptors - kinases - genes - disease resistance - immunity

Abstract

Phytophthora pathogens are notorious for causing severe damage to many agriculturally and ornamentally important plants. Effective plant resistance depends largely on the capacity to perceive pathogens and to activate rapid defence. Cytoplasmic resistance (R) proteins are well-known for activation of plant immunity upon recognition of matching effectors secreted by Phytophthora. However, Phytophthora pathogens are notoriously difficult to control due to their rapid adaptation to evade R protein-mediated recognition. Hence, exploring novel resistance components is instrumental for developing durable resistance. Receptor-like kinases (RLKs) function as important sentinels in sensing exogenous and endogenous stimuli to initiate plant defence. One RLK that was previously identified as a novel Phytophthora resistance component is the Arabidopsis L-type lectin receptor kinase LecRK-I.9. This RLK belongs to a multigene family consisting of 45 members in Arabidopsis but whether or not the other members function in Phytophthora resistance was thus far unknown. The research described in this thesis was aimed at unravelling the role of LecRKs in plant immunity, in particular to Phytophthora pathogens.

Chapter I describes various Phytophthora diseases and the current understanding of the mechanisms underlying plant innate immunity with emphasis on disease resistance to Phytophthora pathogens.

In Chapter II, we describe the development of a new Arabidopsis-Phytophthora pathosystem. We demonstrated that Phytophthora capsici is capable to infect Arabidopsis. Inoculation assays and cytological analysis revealed variations among Arabidopsis accessions in response to different P. capsici isolates. Moreover, infection assays on Arabidopsis mutants with specific defects in defence showed that salicylic acid signaling, camalexin and indole glucosinolates biosynthesis pathways are required for P. capsici resistance (Chapter IIa). The importance of these pathways in Arabidopsis resistance was supported by the finding that the corresponding marker genes are induced upon infection by P. capsici (Chapter IIb). This model pathosystem can be used as an additional tool to pinpoint essential components of Phytophthora resistance.

We then exploited Arabidopsis-Phytophthora pathosystems to uncover the role of LecRKs in Phytophthora resistance. In Chapter III we describe a systematic phenotypic characterization of a large set of Arabidopsis LecRK T-DNA insertion lines. The T-DNA insertion lines were assembled and assayed for their response towards different Phytophthora pathogens. This revealed that next to LecRK-I.9, several other LecRKs function in Phytophthora resistance. We have also analysed whether the LecRKs are involved in response to other biotic and abiotic stimuli. Several T-DNA insertion lines showed altered responses to bacterial or fungal pathogens, but none of the lines showed visible developmental changes under normal conditions or upon abiotic stress treatment. Combining these phenotypic data with LecRK expression profiles obtained from publicly available datasets revealed that LecRKs that are hardly induced or even suppressed upon infection, might still have a function in pathogen resistance. Computed co-expression analysis revealed that LecRKs with similar function display diverse expression patterns.

Arabidopsis LecRK clade IX comprises two members. T-DNA insertion mutants of both LecRK-IX.1 and LecRK-IX.2 showed gain of susceptibility to non-adapted Phytophthora isolates and therefore the role of these two LecRKs in Phytophthora resistance was further investigated. In Chapter IV we describe that overexpression of either LecRK-IX.1 or LecRK-IX.2 in Arabidopsis resulted in increased resistance to Phytophthora, but also induced plant cell death. A mutation in the kinase domain abolished the ability of LecRK-IX.1 and LecRK-IX.2 to induce Phytophthora resistance as did deletion of the lectin domain. Cell death induction however, only required the kinase, not the lectin domain. Since transient expression of both LecRKs in Nicotiana benthamiana also resulted in increased Phytophthora resistance and induction of cell death, we used N. benthamiana to explore downstream components required for LecRK-IX.1- and LecRK-IX.2-mediated Phytophthora resistance and cell death. Virus-induced gene silencing of candidate signaling genes revealed that NbSIPK1/NPT4 is essential for LecRK-IX.1-mediated cell death but not for Phytophthora resistance. Collectively, these results illustrate that the Phytophthora resistance mediated by LecRK-IX.1 and LecRK-IX.2 is independent of the cell death phenotype. By co-immunoprecipitation we identified putative interacting proteins, one of which was an ATP-binding cassette (ABC) transporter. A homolog in Arabidopsis, the ABC transporter ABCG40, was found to interact in planta with both LecRK-IX.1 and LecRK-IX.2. Similar to the LecRK mutants, Arabidopsis ABCG40 mutants showed compromised Phytophthora resistance, indicating that ABCG40 has a function in Phytophthora resistance.

In Chapter V, we describe the generation of stable transgenic N. benthamiana plants expressing Arabidopsis LecRK-I.9 or LecRK-IX.1. Multiple transgenic lines were obtained varying in transgene copy number and transgene expression level. Ectopic expression of LecRK-I.9 resulted in reduced plant sizes and aberrant leaf morphology. In addition, expression of LecRK-IX.1 induced plant cell death. Transgenic N. benthamiana lines expressing either LecRK-I.9 or LecRK-IX.1 showed increased resistance towards P. capsici or Phytophthora infestans. This demonstrated that Arabidopsis LecRK-I.9 and LecRK-IX.1 retained their role in Phytophthora resistance upon interfamily transfer.

Based on the results obtained on Arabidopsis LecRKs, we speculated that LecRKs in other plant species could play a similar role in Phytophthora resistance. In Chapter VI, we focus on LecRKs in two Solanaceous plants, i.e. N. benthamiana and tomato. By exploring genome databases, we identified 38 and 22 LecRKs in N. benthamiana and tomato, respectively. Phylogenetic analysis revealed that both N. benthamiana and tomato lack LecRKs homologous to Arabidopsis LecRKs of clades I, II, III and V, but contain a Solanaceous-specific clade of LecRKs. Functional analysis of various Solanaceous LecRKs using virus-induced gene silencing followed by infection assays revealed that homologs of Arabidopsis LecRK-IX.1 and LecRK-IX.2 in N. benthamiana and tomato are implicated in Phytophthora resistance. These results indicate that the role of clade IX LecRKs in Phytophthora resistance is conserved across plant species.

In Chapter VII, the experimental data presented in this thesis are summarized and discussed in a broader context. We present an overview of the current understanding of LecRKs in plant immunity and discuss how LecRKs can be exploited to improve plant resistance.

Venom allergen-like proteins in secretions of plant-parasitic nematodes activate and suppress extracellular plant immune receptors
Lozano Torres, J.L. - \ 2014
University. Promotor(en): Jaap Bakker, co-promotor(en): Geert Smant; Aska Goverse. - Wageningen University - ISBN 9789461739193 - 201
plantenparasitaire nematoden - nematoda - receptoren - vergiffen - eiwitten - secretie - immuniteit - modulatie - plant parasitic nematodes - receptors - venoms - proteins - secretion - immunity - modulation

Parasitic worms threaten human, animal and plant health by infecting people, livestock and crops worldwide. Animals and plants share an anciently evolved innate immune system. Parasites modulate this immune system by secreting proteins to maintain their parasitic lifestyle. This thesis describes how venom-allergen-like proteins (VAPs) that both animal- and plant-parasitic nematodes release into their hosts, modulate host innate immunity. On the one hand we found that one particular secreted VAP from the potato cyst nematode can activate host defenses in tomato plants, opening an opportunity for plant breeders to generate novel nematode-resistant cultivars. We showed that plants make more efficiently use of their limited repertoire of immune receptors by guarding common virulence targets of multiple unrelated plant pathogens. While on the other hand, we describe how VAPs may be used by parasites to suppress the host defense responses mediated by extracellular immune receptors. In short, this fundamental study contributes to our understanding of the molecular basis of persistent infections by parasitic nematodes in plants and in animals.

Efficiënter voeren en met voeding sturen op immuniteit
Smits, M.A. ; Duinkerken, G. van; Marchal, J.L.M. ; Bruininx, E.M.A.M. - \ 2014
V-focus 2014 (2014)1. - ISSN 1574-1575 - p. 25 - 27.
duurzame veehouderij - veevoeding - diergezondheid - ingrediënten - immuniteit - dierlijke productie - veevoeder - duurzame ontwikkeling - sustainable animal husbandry - livestock feeding - animal health - ingredients - immunity - animal production - fodder - sustainable development
Met voeding valt veel te sturen, zoals de gezondheid van het dier, groeisnelheid, melkgift en melksamenstelling en de efficiëntie waarmee nutriënten worden benut of via mest en urine worden uitgescheiden. Binnen Feed4Foodure wordt gebouwd aan kennis en nieuwe voedingsmodellen om beter te begrijpen welke effecten voeding heeft op het dier.
1Health4Food : focus op gezondheid mens-dier
Kimman, T.G. ; Mevius, D.J. ; Antonis, A.F.G. ; Parée, P. - \ 2014
V-focus 2014 (2014)1. - ISSN 1574-1575 - p. 22 - 24.
veehouderij - dierlijke productie - diergezondheid - volksgezondheid - wetenschappelijk onderzoek - onderzoeksprojecten - diagnostiek - antibioticaresistentie - volksgezondheidsbevordering - verbreed spectrum bèta-lactamases - immuniteit - immuunsysteem - immunologie - voedselveiligheid - voeding en gezondheid - mens-dier relaties - livestock farming - animal production - animal health - public health - scientific research - research projects - diagnostics - antibiotic resistance - sanitation - extended spectrum beta-lactamases - immunity - immune system - immunology - food safety - nutrition and health - human-animal relationships
1Health4Food is een ambitieus onderzoeksprogramma op het gebied van dier- en volksgezondheid. Het landbouwbedrijfsleven heeft in sterke mate bepaald waar de prioriteiten moeten liggen: bij de ESBL’s en de snelle diagnostiek. Binnen 1Health4Food wordt kennis ontwikkeld voor meerdere sectoren, kennis die veehouders en hun adviseurs, zoals dierenartsen, in staat stellen om rendabel te produceren op een wijze die ook veilig is voor de mens. De ambitie is om in de toekomst gezamenlijk een gezonde en veilige veehouderij te realiseren.
Analysis of Tomato spotted wilt virus effector-triggered immunity
Ronde, D. de - \ 2013
University. Promotor(en): Just Vlak, co-promotor(en): Richard Kormelink. - S.l. : s.n. - ISBN 9789461737212 - 190
tomatenbronsvlekkenvirus - plantenvirussen - ziekteresistentie - immuniteit - virulentie - genkartering - genetische merkers - genetische analyse - capsicum annuum - paprika's - tomato spotted wilt virus - plant viruses - disease resistance - immunity - virulence - gene mapping - genetic markers - genetic analysis - sweet peppers

ResistanceinCapsicumagainsttheTomatospottedwiltvirus(TSWV),typespeciesof the Tospovirusgenuswithinthe Bunyaviridaefamily,employsthe singledominant resistancegeneTsw.Thisresistance hasmeanwhilebeenbrokenbyresistance breaking (RB) TSWV isolates and is causing increasing problems in many different (Capsicumcultivating)countries.Theresearchdescribedhereaimedtoidentify andcharacterise theviralproteintriggeringTswresistanceandprovidefurther insightintothemechanismofTsw-mediatedresistance.Knowledgegainedfrom thegeneticandphenotypiccharacterisationofTsw-resistancebreakingisolateswas usedtodevelopdiagnosticmarkersfordetectionofTsw-breakingpathotypesin fieldcultivations.

TheNSsRNAsilencingsuppressor(RSS)proteinwasidentifiedastheavirulence determinant ofTsw-mediatedresistance(Chapter2).WhiletheNSsproteinfrom theTSWVresistanceinducer(RI)isolatewasactiveasRNAsilencingsuppressorand avirulencedeterminant,theNSsproteinfromtwodifferentTSWVRBisolateslacked bothfunctionsasevidencedfromtransientassays.Surprisingly,thecorresponding resistancebreakingvirusisolatesstillexhibitedRNAisuppressoractivity. Noneof the other viral proteins were able to aid in the transient recovery of RSS activity. Electrophoreticmobilityshift assays(EMSAs)usingplantextractscontaining transientlyexpressedNSsproteinsshowedashift ofsiRNAswithNSsRI,indicative forbinding,butnotwithNSsRB.InagreementwiththelocalleafRSSassaysusinga virusinfection,plantextractsofvirusinfectedleaveswereabletoshiftthesiRNAs, showing recovery of the RSS activityduring virus infection.

The linkage of RNAi suppression and avirulence in NSs was further investigated bymutationalanalysis(Chapter3).AlargesetofNSsmutantswasgeneratedusing alaninesubstitutions ofauthenticTSWVNSsaminoacidsandwastestedfortheir abilitytotriggerTsw-mediatedHRandabilitytosuppressRNAi.Theseassaysshowed thatthe N-terminaldomainofNSscarried mostimportantresiduesinvolvedwith bothactivities. However,singlemutationscouldbeintroducedthatdisruptedone function,whilemaintainingtheotheroneandviceversaindicatingthatRSSactivity andavirulencewerenotfunctionally linked.SwappingofdomainsbetweenNSsRI andNSsRB notonlyconfirmedtheimportanceoftheN-terminaldomainbutalso thespecificitywithintheTSWVspecies,sincedomainswapsbetweenNSsRIandNSs fromGRSV,arelatedbutdistinct Tospovirus,couldnottransfertheAvrphenotype toGRSV.MutationofaGW/WG-motifintheNterminalregionofNSsRI leadtoa lossofbothfunctionsandindicatedthatthismotif, knowntobeinvolvedinAGO1 interactionof other viral RSS, was of biological relevance for TSWV NSs.

Theputativeinteraction ofAGO1andNSswasinvestigatedbyusingdifferent approaches to co-immunoprecipitate (Co-IP) on transiently co-expressed tagged- AGO1and(His-)NSs(Chapter4).Initialindicationsforsuchinteraction were obtained,howeverfurthersupportforthisputativeinteraction willhavetocome fromcomplementaryexperiments,e.g. Yeast-2-hybrid (Y2H), FRET-FLIM or BiFC.

Severaladditional TSWVisolateswereanalysedthatbesidestheknownresistance inducing-and resistance breaking-phenotype showed a temperature-dependent phenotype(Chapter5).IsolatesclassifiedtothistypeexhibitedanRIphenotypeat standardgreenhouseconditions (~22°C)whileatelevatedtemperatures(≥28°C), butstillbelowtemperaturesthatinactivatedtheR-geneproduct(≥31°C),wereable tobreaktheresistance.Viruschallengingassaysatvariousconditionsindicatedthat inductionofTswresistanceatalower temperaturebythesesocalledtemperature dependentresistancebreakingisolates(TempRB)involveddenovosynthesisofthe avirulenceprotein,i.e.NSs,andthat proteinfoldingmight play arole. NSsproteins clonedandexpressedfromthisadditional newsetofTSWVresistanceinducing, resistancebreakingandtemperature dependentresistancebreakingisolates revealedvariableresultsregardless oftheircorrespondingvirusphenotype,when tested for their abilitytoinduceTsw-mediated HR andsuppress RNAi at normal greenhouseconditions(22°C).However,similarassaystoanalysetheiractivity attheelevatedtemperature(28°C)failedwhenusingAgrobacteriummediated transientassays.Sofar,themechanismoftemperature dependencyhasnotbeen clarified yetandneedsfurtherinvestigation.Usingtheinformationobtained,a diagnostictoolwasdevelopedtoscreenforthepotential presenceofresistance breakingisolatesofTSWVusingreversetranscription-polymerasechainreaction amplification(RT-PCR).Aprimersetwasdesignedtargetinganimportantcodon ataaposition79andshowedtobeabletodistinguishRB-isolatesfromRI-isolates. However,afewRB-isolatesstillescapedfromdetection indicatingthelimitedand conditionaluse of this tool.

In summary, NSs has been identified as Avr-determinant of Tsw-mediated resistance,butthisfunctionisnottightlylinkedtoitsRNAisuppressor-activity. Preliminarydataindicateaputativeinteraction betweenAGO1andNSs.Besides the typicalRIandRBphenotypes,athirdphenotypicclassofTSWVisolates has beenidentified thatexhibitsatemperaturedependencyontriggeringTsw- mediatedresistance andpossiblyinvolvesanalteredproteinfoldingofNSs.A diagnostic toolhasbeendevelopedtodetectresistancebreakingisolatesinthe fieldbasedonRT-PCR,butthistoolstillallowsforescapesofRBisolates.Theresults onNSsarediscussedinlightofitsroleaseffectorwithinthe‘Zig-zag-model’of planthostdefenceresponses.Finally,TSWVNSsisbriefly discussedandcompared totheanimal-infecting(NSs)paralogsoftheBunyaviridaefamily,alsoinlightof functional andstructuralhomologiesbetweenthesensorsofinnateimmunityin plant(R-genes)and animal (NLRs/TLRs) cell systems.

RegIII proteins as gatekeepers of the intestinal epithelium
Loonen, L.M.P. - \ 2013
University. Promotor(en): Jerry Wells, co-promotor(en): Peter van Baarlen. - S.l. : s.n. - ISBN 9789461736727 - 205
eiwitten - darmen - darmslijmvlies - darmziekten - colitis - bacterieziekten - immuunsysteem - verdedigingsmechanismen - muizen - diermodellen - microbiologie - immuniteit - geneeskunde - proteins - intestines - intestinal mucosa - intestinal diseases - bacterial diseases - immune system - defence mechanisms - mice - animal models - microbiology - immunity - medicine

Mammalian RegIII proteins are expressed in the intestine and in the pancreas in response to inflammation or infection. In the mouse intestine, expression of RegIIIβ and RegIIIγ is increased by microbial colonization, inflammation and infection. At the outset of this thesis human PAP and mouse RegIIIγ were reported to be bactericidal for Gram-positive bacteria. Additionally, human PAP had been shown to attenuate NF-κbsignallingin human monocytes and epithelial cells and administration of anti-PAP antibodies increased inflammation in an experimental rat model of acute pancreatitis. The overarching goals of this thesis were to find out more about the protective role of mouse RegIIIβ and RegIIIγ in the intestine and explore their protective role in colitis and bacterial infection.

In Chapter 2 we investigated expression of RegIIIβ and RegIIIγ in intestine of Muc2 knockout (-/-) mice, which develop colitis after about 4 weeks, due to the absence of a secreted mucus layer in the small intestine or colon. RegIII proteins were expressed in Paneth cells, enterocytes and goblet cells pointing to a new function for goblet cells in innate immunity. Ang4 expression was confined to Paneth cells and goblet cells. Absence of Muc2 increased expression levels of RegIIIβ, RegIIIγ, and Ang4 and colitis appeared first in the distal colon where the RegIII expression is lowest.

In Chapter 3 we investigated the distinct phases of colitis development in Muc2-/- mice from before weaning to 4 and 8 weeks of age, also taking into account the effect that mucin deficiency has in the ileum. Gene set enrichment approaches showed increased expression of innate and adaptive immune pathways associated with colitis over time, whereas in the ileum many immune signalling pathways were down-regulated. Nevertheless, RegIIIβ and RegIIIγ were significantly upregulated, suggesting their proposed antimicrobial and/or anti-inflammatory activities might be related to the suppression of immune pathways and avoidance of immune-mediated damage. Furthermore, we showed that RegIIIβ could specifically bind to mucin and fucosylated glycans in vitro, which may serve to inhibit bacterial binding to membrane bound mucins on the epithelium, and also enable RegIIIβ to be retained in the secreted mucin.

An in vitro approach was used in Chapter 4, where we investigated the activities of RegIIIγ and RegIIIβby expressing and purifying recombinant proteins. Both proteins were insoluble when expressed in E. coli but RegIIIβ could be expressed and secreted in baculovirus as a soluble protein. As previous work reported that RegIII proteins were bactericidal even when produced as inclusion bodies in E. coli and refolded, we followed similar procedures to obtain soluble RegIII proteins. In our hands both the E. coli and baculovirus produced proteins bound strongly to both Gram-positive and Gram-negative bacteria after processing of an N-terminal pro-peptide by trypsin, but lacked any appreciable bactericidal activity. Furthermore these proteins did not influence the growth of Salmonella enteritidis andListeria monocytogenes. Attempts to crystallize the proteins were unsuccessful but structural models of the protein were generated based on the crystal structure of human PAP. These models were used to dock known ligands of RegIIIγ or RegIIIβ. Only one ligand is known for RegIIIγ, which is peptidoglycan, but for RegIIIβ the ligands include peptidoglycan, lipid A and the fucose-containing glycans identified in chapter 3. RegIIIβ was predicted to have two different binding sites which would allow it to bind to mucins and bacteria simultaneously, thereby preventing penetrating of the mucus.

In Chapter 5 a RegIIIβ-/- mouse was used to study the role of the protein during infection with Gram-negative Salmonella enteritidis or Gram-positive Listeria monocytogenes. Whereas recovery of S. enteritidis orL. monocytogenes from faeces was similar in RegIIIβ-/- and wild type (WT) mice, significantly higher numbers of viable S. enteritidis, but not L. monocytogenes, were recovered from the colon, mesenteric lymph nodes, spleen, and liver of the RegIIIβ-/- than the WT mice. The results suggest that mouse RegIIIβ plays a protective role against intestinal translocation of the Gram-negative bacterium S. enteritidis but not against the Gram-positive bacterium L. monocytogenes.

In Chapter 6, the generation of a RegIIIγ-/- mouse is described. One of the main phenotypic differences between the RegIIIγ-/- and WT was an altered distribution of the ileal mucus and increased bacterial contact with the epithelium. Additionally, measurement of innate immune markers in the mucosa suggested heightened inflammation in the RegIIIγ-/- mice. Compared to WT mice, RegIIIγ-/- mice infected with S. enteritidis and L. monocytogenes showed an increase of mucosal inflammatory markers indicating protective, anti-microbial roles of RegIIIγ in defense against both Gram-positive and Gram-negative bacteria.

Chapter 7summarizes and discusses the key results of the thesis in the context of the wider literature and possible directions for future research

Immuunmodulatie door voeding "Van black box naar toolbox"
Wolthuis, A. ; Wichers, H.J. - \ 2013
Immuun 2 (2013)2. - p. 30 - 31.
voeding en gezondheid - immuunsysteem - immuniteit - gezondheidsbevordering - modulatie - immunomodulatoren - bèta-glucaan - voedingsvezels - nutrition and health - immune system - immunity - health promotion - modulation - immunomodulators - beta-glucan - dietary fibres
Prof. dr. Harry Wichers van Wageningen University & Research Centre doet onderzoek naar hoe voeding ons immuunsysteem een oppepper kan geven. "We kijken standaard naar medicijnen wanneer het er om gaat onze gezondheid te verbeteren. De mogelijkheden en het belang van voeding worden onderschat."
On the modulation of innate immunity by plant-parasitic cyst nematodes
Postma, W.J. - \ 2013
University. Promotor(en): Jaap Bakker, co-promotor(en): Geert Smant; Aska Goverse. - S.l. : s.n. - ISBN 9789461735560 - 154
plantenparasitaire nematoden - globodera rostochiensis - heterodera schachtii - planten - interacties - immuniteit - immuunsysteem - modulatie - receptoren - signaaltransductie - moleculaire plantenziektekunde - plant parasitic nematodes - plants - interactions - immunity - immune system - modulation - receptors - signal transduction - molecular plant pathology

Plant-parasitic cyst nematodes are major agricultural pests worldwide. These obligate endoparasites invade the roots of host plants where they transform cells near the vascular cylinder into a permanent feeding site. Plants possess a multilayered innate immune system consisting of different types of extracellular and intracellular immune receptors. These enable detection of most invading nematodes and initiate immune responses that result in resistance. Many plant pathogens use effectors to overcome resistance. Here, modulation of plant innate immunity by plant-parasitic cyst nematodes was investigated. Extracellular immune receptor signaling and hormone-mediated signaling pathways were found to contain infection of susceptible Arabidopsis thalianawith Heterodera schachtii. A large family of effectors was identified in Globodera rostochiensis. One of these so-called SPRYSECs interacted with a novel CC-NB-LRR type resistance protein of a susceptible tomato without inducing resistance responses. Instead, the effector was found to suppress defense-related programmed cell death and resistance mediated by several CC-NB-LRR type resistance proteins. In addition, a secreted antimicrobial peptide was identified in G. rostochiensis. Plant-parasitic cyst nematodes thus most likely secrete effectors that protect against plant immune responses and secondary infections. The current evidence for the existence of immune modulating effectors is reviewed and directions for further research are given.

Check title to add to marked list
<< previous | next >>

Show 20 50 100 records per page

 
Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.