Effective malaria vaccine might help improve control strategies against malaria, but the complexity of interactions between the parasite and its hosts poses challenges. The asexual blood stage P. falciparum antigen Pf332 has potentials as one of the proteins in understanding the complex host-parasite interactions. The interest in Pf332 as a target for parasite neutralizing antibodies, evolved from previous studies demonstrating that Pf332-reactive antibodies inhibits parasite growth in vitro. The presence of natural P. falciparum infection also indicated that Pf332 has the ability to induce protective antibodies. In paper I, we identified and characterized the immunogenicity of a C-terminal region of Pf332. Immunological analyses carried out with this fragment revealed that rabbit anti-C231 antibodies possess parasite in vitro inhibitory capabilities. In paper II, the functional activity of C231 specific antibodies was confirmed with human-affinity purified antibodies, where the antibodies inhibited late stage parasite development, by the presence of abnormal parasites and disintegrated red cell membranes. Epidemiological data from malaria endemic area of Senegal (Paper III & IV), showed that antibodies were reactive with two different fragments of Pf332 (C231 and DBL). Distribution of anti-C231 antibodies in the IgG subclasses, gave similar levels of IgG2 and IgG3. The levels of anti-C231 antibodies were associated with protection from clinical malaria, but with DBL reactive antibodies IgG3 was associated with protection from clinical malaria. We hereby conclude that antigen Pf332 contains immunogenic epitopes, and is a potential target for parasite neutralizing antibodies. The Pf332 protein should thus be considered as a candidate antigen for inclusion in a subunit P. falciparum malaria vaccine. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: Manuscript.

The cationic host defence peptide LL-37 is an immunomodulatory agent that plays an important role in epithelial innate immunity. Previously, concentrations of LL-37 thought to represent levels present during inflammation have been shown to elicit the production of cytokines and chemokines by epithelial cells. To investigate the potential of lower concentrations of LL-37 to alter epithelial cell responses, normal primary keratinocytes and bronchial epithelial cells were treated with pro-inflammatory stimuli in the presence or absence of 1 – 3 μg/ml LL-37. Low, physiologically relevant concentrations of LL-37 synergistically increased IL-8 production by both proliferating and differentiated keratinocytes in response to IL-1β and the TLR5 agonist flagellin, and synergistically increased IL-8 production by bronchial epithelial cells in response to IL-1β, flagellin, and the TLR2/1 agonist PAM3CSK4. Treatment of bronchial epithelial cells with LL-37 and the TLR3 agonist poly(I:C) resulted in synergistic increases in IL-8 release and cytotoxicity. The synergistic increase in IL-8 production observed when keratinocytes were co-stimulated with flagellin and LL-37 was suppressed by pretreatment with inhibitors of Src-family kinase signalling and NF-κB translocation. These data suggest that low concentrations of LL-37 may alter epithelial responses to microbes in vivo. Microarray analysis of keratinocyte transcriptional responses after LL-37 treatment suggest that LL-37 may alter the expression of growth factors and a number of genes important to innate immune responses. LL-37 may thus play a more important role than previously suspected in the regulation of epithelial inflammation; an improved understanding of the mechanisms by which LL-37 alters chemokine responses could lead to the development of novel anti-infective and anti-inflammatory therapeutics.

This study was conducted as part of a parent grantwhich examined the relationship between components of sleep and antibody responses to the flu vaccine in a population of 392 nurses working at two large hospitals. During/after sleep data was collected, nurses had blood drawn at four time points: immediately pre-vaccination, 1-, 6-, and 11-months post vaccine to obtain serum for detection of anti-influenza antibodies measured with an HI (hemagglutination inhibition) assay. Additionally, the inflammatory biomarkers IL6, IL1-β, TNF-α and CRP were measured at the pre-vaccine time point only to determine any correlation between the markers and antibody response. Data was analyzed using a hierarchical regression. In the first step, analyses assessed whether each change/average in cytokines over the one-month period had an impact on vaccine response for each of the four viral strains in the flu vaccine. In a second step, analyses assessed whether variables such as insomnia, stress, age, smoking, BMI, and race had any impact on vaccine response beyond the effects exerted through inflammation. The change in association (β) between the primary independent variable and primary dependent variable were examined in order to determine whether there are any suppression effects caused by baseline covariates on the relationship between inflammation changes or averages and antibody response. No relationship was discovered between circulating inflammatory changes or circulating inflammatory averages and antibody response. There was a weak correlation between CRP at Timepoint A and CRP at Timepoint B. No relationship was observed between age and circulating inflammation. The lack of relationship was likely due to the use of circulating inflammatory biomarkers; this may be an insufficient approach to determine chronic inflammatory status.

Malaria is a life-threatening parasitic disease endemic throughout the world. Control methods for malaria are becoming less reliable; thus, efforts to develop a safe and effective vaccine are critical. Immunity to malaria requires both cell- and humoral-mediated immunity, CMI and HMI, respectively. CD4+ T cells play a central role in protection against blood stage Plasmodium infection. Given that clinical features of malaria are caused by blood stages, a vaccine against this stage will be very effective in reducing morbidity and mortality. During the blood stage, purine nucleotides, which are essential for parasites’ survival and proliferation, are in high demand. The inability of the parasite to engage in de novo synthesis of purine nucleotides makes the enzyme hypoxanthine guanine xanthine phosphoribosyltransferase (HGXPRT) an essential nutrient salvage enzyme. HGXPRT is located in electron-dense regions in merozoites and in vesicles in the red cell cytoplasm. In contrast to other blood stage antigens, those located on the merozoite surface are targets of HMI. To advance HGXPRT as a malaria vaccine candidate, fermentation and purification of the protein from Plasmodium falciparum (PfHGXPRT) was performed using facilities at Q-Gen, the Queensland Institute of Medical Research (QIMR). Escherichia coli carrying PfHGXPRT gene were a gift in-kind from the University of Queensland (UQ). Recombinant PfHGXPRT expressed in E.coli was purified using anion exchange liquid chromatography and gel filtration techniques. Three methods were used to confirm the Q-Gen PfHGXPRT identity: (1) Western blotting showing identical bands of UQ PfHGXPRT and Q-Gen PfHGXPRT at 26 kDa; (2) N terminal sequencing was compatible with the PfHGXPRT sequence; and (3) mass spectrometry showed homogeneity by giving a subunit molecular mass of 26,231 Da. The purification method used is reproducible and affordable, yielding reasonably pure protein for animal experimentation. Following purification of PfHGXPRT, its efficacy as a subunit vaccine candidate in a rodent model of infection was examined. Multiple rodent models of malaria infection were assessed and it was determined that Plasmodium chabaudi AS (P. chabaudi AS) exhibited the highest cross-reactivity against PfHGXPRT in mice. Hence, P. chabaudi AS was chosen as the appropriate rodent model for study in this thesis. Natural immunity against PfHGXPRT during a blood stage P. chabaudi AS infection was assessed by testing sera and splenocyte responses to PfHGXPRT. IFN- and IL-4, as well as antibodies specific for PfHGXPRT, could be detected after infection, suggesting that PfHGXPRT is a target of natural immunity during the blood stage infection. Therefore, further studies of protective immunity generated by immunisation with PfHGXPRT were conducted, specifically to determine their protective efficacy and to determine immune mechanisms elicited by immunisation. Mice immunised with PfHGXPRT and challenged with P. chabaudi AS developed a slightly reduced parasitaemia. T-cell proliferation, but not antibody responses, was detected after immunisation. Protective mechanism(s) were assessed by adoptively transferring immune CD4+ T cells, B cells or sera to naïve SCID mice followed by parasite challenge. Only recipients of immune CD4+ T cells showed extended survival. Nevertheless, immunisation with PfHGXPRT followed by sub-patent infection induced better protection than immunisation with PfHGXPRT alone, which appeared to be related to CD4+ T cells. Reduction of parasitaemia, as well as augmentation of T cell proliferation and IFN-γ production, was evident in PfHGXPRT and sub-patent infected immunised mice. Recipients of CD4+ T cells from PfHGXPRT and sub-patent infection immune mice also showed some degree of protective immunity. PfHGXPRT was shown to induce natural and acquired immunity to P. chabaudi AS. HGXPRT is highly conserved in parasites and humans; therefore, it is essential to define minimal protective epitopes that could be included in a vaccine. Hence, 22 overlapping peptides (termed P1 P22) corresponding to the entire P. chabaudi AS HGPRT sequence were used to define minimal protective epitopes. Following immunisation of mice with seven pools of peptides (P1 P3, P4 P6, P7 P9, P10 P12, P13 P15, P16 P18 and P19 P22), three immunogenic peptides (P11, P13, and P17), which stimulated significant proliferative and IFN-γ responses were chosen for immunisation studies. Peptide P9 (position 76-95 from N-terminal), which induced the highest IFN- levels during P. chabaudi AS infection was also included in the pool of peptides. Mice immunised with P9, P11, P13 and P17 had significantly decreased parasitaemia. Antibody mediated immunity had a partial effect on suppressing parasite growth. CMI, on the contrary, played a central role in adoptively transferred protection by significantly reducing parasitaemia and prolonging survival of recipient SCID mice. Strong T cell proliferation and IFN- secretion were also detected after stimulation of splenocytes from immune mice with P. chabaudi AS antigen. CMI response was significantly increased after immunisation with the peptides followed by sub-patent infection. The findings that four short epitopes of HG(X)PRT confer strong CMI protection suggest that homologues of such epitopes could be included in a multi-component malaria vaccine.

CD4 is a co-receptor for binding of T cells to antigen-presenting cells (APC) and the primary receptor for human immunodeficiency virus-I. The disulfide bond in the second extracellular domain (D2) of CD4 is reduced on the cell surface, which leads to formation of disulfide-linked homodimers. A large conformational change must take place in D2 to allow for formation of the disulfide-linked dimer. Domain swapping of D2 is the most likely candidate for the conformational change leading to formation of two disulfide-bonds between Cysl30 in one monomer and Cysl59 in the other one (Cys133 and Cysl62 in the mouse CD4). Thus, we hypothesized that the domain swapping of D2 in CD4 regulates its co-receptor function of antigenspecific T cell activation. We found that mild reduction of the extracellular part of human CD4 resulted in formation of disulfide-linked dimers. We then tested the functional significance of dimer formation for co-receptor function using the engineered Jurkat T cell system by expressing wild-type or disulfide-bond mutant mouse CD4. Eliminating the D2 disulfide bond markedly impaired CD4's coreceptor function as assessed by antigen-specific IL-2 production. Exogenous wild type thioredoxin, but not redox-inactive thioredoxin, could inhibit the CD4-mediated IL-2 production, suggesting that the redox state of D2 disulfide bond is controlled by this oxidoreductase. Furthermore, structural modeling of the complex ofthe T cell receptor and domain-swapped CD4 dimer bound to class II major histocompatibility complex and antigen supports the domain-swapped dimer as the immune co-receptor. The known involvement of D4 residues Lys318 and Gln344 in dimer formation isalso accommodated by this model. These findings imply that disulfide-linked dimeric CD4 is the preferred functional co-receptor for binding to APC. Strategies to promote dimerisation of CD4 should, therefore, enhance the immune response, while inhibiting dimer formation is predicted to be immunosuppressive.

Title page, table of contents and summary only. The complete thesis in print form is available from the University of Adelaide Library. / Herpes simplex virus type I (HSV-I) produces acute muco-cutaneous infections, followed by spread to sensory nerve ganglia, and establishment of latency. In the peripheral nervous system, primary sensory neurons, which are found in dorsal root ganglia of the of the spinal nerves, are the target for HSV and they may undergo either productive or latent intection. Productive infection of sensory neurons generates the potential for lethal spread of virus through the nervous system but in immunocom petent hosts, viral replication is terminated by limely development of an adaptive immune response. The infection of dorsal root ganglia that follows cutaneous inoculation of the flanks of mice with HSV provides a well-characterized model of peripheral nervous system infection. The mechanisms responsible for clearance of HSV are complex. At mucosal and cutaneous sites, local innate immune mechanisms act to interrupt the initial spread of virus to the nervous system, while adaptive immunity is important in limiting replication in the ganglia and extension of the virus to adjacent dennatomes. Thus actions of both the innate and the adaptive immune systems are vital in defence against replicating HSV-1, while it is thought that latent infection in the ganglia is contained by the surveillance of the adaptive immune system. Natural killer T (NKT) cells are a conserved subpopulation of lymphocytes that recognize glycolipid antigens presented by the invariant MHC class I-like molecule CD1d. Upon activation through their semi-invariant T cell receptor, these cells rapidly release large amounts of immuno-modulating Th1 and Th2 cytokines. NKT cells have, therefore, been implicated in immune responses controlling various diseases, including infection, cancer, and autoimmunity, as well as having an involvement in allo-graft survival. Consideration of the important contributions of innate and adaptive immunity to clearance of HSV prompted this investigation of the role of CD1d and of CD1d-restricted NKT cells in the pathogenesis of HSV infection. The first part of this thesis (Chapter 3 and 4) describes investigations into the role of NKT cells in immunity to HSV-1, using a zosteriform model of infection and two gene knockout strains of C57BL/6 mice. CD1d GKO and Ja18 GKO mice, which are deficient in NKT cells, are compromised in controlling HSV-1 as evidenced by mortality, virus loads in skin and dorsal root ganglia, presence and size of skin lesions, persistence of HSV antigen, neuronal damage and extent of latency. Comparisons between wild type (NKT cell replete), Ja18 GKO (deficient in invariant Va14⁺ NKT cells) and CD1d GKO (deficient in all CD1d-dependant NKT cells) mice allowed assessment of CD1d-dependant NKT cell subsets in defence against the virus at various stages of infection. It was concluded that both subsets play important roles in controlling the virus and in preventing lethal neuro-invasive disease, that both are vital adjuncts to the adaptive immune response and that without them, low doses of neuropathogenic HSV-1 can establish quickly and cause fatal infections. The NKT-cell population appears to be quite dynamic in its response to a range of pathogens and other disease processes. The study described in Chapter 5 presents evidence suggesting that the response of NKT cells during HSV infection is no less dynamic. In the axillary lymph nodes, observations on numbers of cells expressing NK1.1 antigen and the invariant TCR suggest that NKT cells are activated in the regional lymph nodes draining the infection site. Observations on lymphocytes prepared from liver and spleen also suggested activation of NKT cells, indicating that NKT cells at these sites are also activated during the course of acute HSV infection. The role of NKT cells in the control of HSV infection was further examined by adoptive transfer studies, to investigate whether the defect in handling of HSV-1 by Ja18 GKO mice could be complemented by the adoptive transfer of lymphocytes from wt mice (Chapter 6). Finally, the relevance of activated NKT cells in the anti-HSV response was examined by observing the effects of a-GalactosylCeramide therapy on the severity of HSV-1 infection (Chapter 6). Activation of NKT cells by this compound delayed the onset of HSV disease, decreased prevalence and severity of zosteriform lesions and reduced viral titres in skin and ganglia. The beneficial effects of a-GalactosylCeramide on the outcome and severity of HSV infection in the skin were dose-dependent. Collectively, the studies described in this thesis provide insights into how NKT cells, normally a rare population of cells, has the ability to regulate the protective immune response to HSV-1. As more understanding is gained about how NKT cells become activated during HSV-1 infection, and how they mediate their antiviral effects, other ways may be developed to modulate and activate this interesting subset to the benefit of infected individuals. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1277283 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2007

Title page, table of contents and summary only. The complete thesis in print form is available from the University of Adelaide Library. / Herpes simplex virus type I (HSV-I) produces acute muco-cutaneous infections, followed by spread to sensory nerve ganglia, and establishment of latency. In the peripheral nervous system, primary sensory neurons, which are found in dorsal root ganglia of the of the spinal nerves, are the target for HSV and they may undergo either productive or latent intection. Productive infection of sensory neurons generates the potential for lethal spread of virus through the nervous system but in immunocom petent hosts, viral replication is terminated by limely development of an adaptive immune response. The infection of dorsal root ganglia that follows cutaneous inoculation of the flanks of mice with HSV provides a well-characterized model of peripheral nervous system infection. The mechanisms responsible for clearance of HSV are complex. At mucosal and cutaneous sites, local innate immune mechanisms act to interrupt the initial spread of virus to the nervous system, while adaptive immunity is important in limiting replication in the ganglia and extension of the virus to adjacent dennatomes. Thus actions of both the innate and the adaptive immune systems are vital in defence against replicating HSV-1, while it is thought that latent infection in the ganglia is contained by the surveillance of the adaptive immune system. Natural killer T (NKT) cells are a conserved subpopulation of lymphocytes that recognize glycolipid antigens presented by the invariant MHC class I-like molecule CD1d. Upon activation through their semi-invariant T cell receptor, these cells rapidly release large amounts of immuno-modulating Th1 and Th2 cytokines. NKT cells have, therefore, been implicated in immune responses controlling various diseases, including infection, cancer, and autoimmunity, as well as having an involvement in allo-graft survival. Consideration of the important contributions of innate and adaptive immunity to clearance of HSV prompted this investigation of the role of CD1d and of CD1d-restricted NKT cells in the pathogenesis of HSV infection. The first part of this thesis (Chapter 3 and 4) describes investigations into the role of NKT cells in immunity to HSV-1, using a zosteriform model of infection and two gene knockout strains of C57BL/6 mice. CD1d GKO and Ja18 GKO mice, which are deficient in NKT cells, are compromised in controlling HSV-1 as evidenced by mortality, virus loads in skin and dorsal root ganglia, presence and size of skin lesions, persistence of HSV antigen, neuronal damage and extent of latency. Comparisons between wild type (NKT cell replete), Ja18 GKO (deficient in invariant Va14⁺ NKT cells) and CD1d GKO (deficient in all CD1d-dependant NKT cells) mice allowed assessment of CD1d-dependant NKT cell subsets in defence against the virus at various stages of infection. It was concluded that both subsets play important roles in controlling the virus and in preventing lethal neuro-invasive disease, that both are vital adjuncts to the adaptive immune response and that without them, low doses of neuropathogenic HSV-1 can establish quickly and cause fatal infections. The NKT-cell population appears to be quite dynamic in its response to a range of pathogens and other disease processes. The study described in Chapter 5 presents evidence suggesting that the response of NKT cells during HSV infection is no less dynamic. In the axillary lymph nodes, observations on numbers of cells expressing NK1.1 antigen and the invariant TCR suggest that NKT cells are activated in the regional lymph nodes draining the infection site. Observations on lymphocytes prepared from liver and spleen also suggested activation of NKT cells, indicating that NKT cells at these sites are also activated during the course of acute HSV infection. The role of NKT cells in the control of HSV infection was further examined by adoptive transfer studies, to investigate whether the defect in handling of HSV-1 by Ja18 GKO mice could be complemented by the adoptive transfer of lymphocytes from wt mice (Chapter 6). Finally, the relevance of activated NKT cells in the anti-HSV response was examined by observing the effects of a-GalactosylCeramide therapy on the severity of HSV-1 infection (Chapter 6). Activation of NKT cells by this compound delayed the onset of HSV disease, decreased prevalence and severity of zosteriform lesions and reduced viral titres in skin and ganglia. The beneficial effects of a-GalactosylCeramide on the outcome and severity of HSV infection in the skin were dose-dependent. Collectively, the studies described in this thesis provide insights into how NKT cells, normally a rare population of cells, has the ability to regulate the protective immune response to HSV-1. As more understanding is gained about how NKT cells become activated during HSV-1 infection, and how they mediate their antiviral effects, other ways may be developed to modulate and activate this interesting subset to the benefit of infected individuals. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1277283 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2007

Mass mortalities of farmed Sydney rock oyster, Saccostrea glomerata, have been observed in Australia since the 1970s and are attributed to the paramyxean protozoan parasite, Marteilia sydneyi (etiological agent of QX disease). This opportunistic parasite infects S. glomerata when the oyster’s immune system has been compromised due to one or more unknown transient environmental stressor. Management and prevention of the disease is seriously compromised as neither the risk factors for the disease, nor the complete life cycle of M. sydneyi are currently understood. The future of the rock oyster industry relies on the development of QX-resistant oysters. Selection of S. glomerata for resistance to QX disease over several generations has revealed that QX-resistance is heritable and likely to be controlled by multiple genes. The main focuses of this thesis was to improve our knowledge of the genes involved in immunity of S. glomerata to disease. The transcriptome response of hemocytes isolated from S. glomerata selected over four generations for resistance to QX disease (QXR4) was compared to non-selected control oysters (W-type) using suppression, subtractive hybridization (SSH) and quantitative real-time PCR (qRT-PCR). Our data supported that differences in gene expression due to selection was largely attributable to constitutive differences in transcriptional rate. The basal-expression of an extracellular superoxide dismutase (EcSOD) and small heat shock protein (sHsP) was 3.18- and 2.05-fold higher in QXR4 oysters, respectively (p < 0.5). The basal-expression of peroxiredoxin 6 (Prx6) and interferon inhibiting cytokine (IK) was 2.75- and 1.5-fold lower in QXR4 oysters, respectively (p < 0.5). Expression of EcSOD, Prx6 and IK was measured in S. glomerata in response to injection with a range of pathogen associated molecular patterns (PAMPs) to replicate microbial invasion as QX disease cannot be replicated in the laboratory due to the complex life cycle of M. sydneyi. The expression of IK was induced 2.2-fold in S. glomerata in response to injection with double stranded RNA when compared to control oysters (p < 0.05). However, changes in the expression of EcSOD and Prx6 could not be induced with any of the tested PAMPs (p > 0.5), suggesting the difference in basal-expression of these two genes between QXR4 and W-type oysters would be maintained during infection with M. sydneyi. It was concluded that QXR4 oysters would be able to generate the anti-parasitic compound, hydrogen peroxide (H2O2) faster due to the elevated levels of EcSOD and that the H2O2 would reach higher concentrations due to the reduced levels of Prx6 to detoxify it. Attempts were made to understand why the basal expression of EcSOD and Prx6 is different between QXR4 and W-type oysters. Identification of DNA variants within the promoter regions of these genes would provide greater insight into the gene network(s) involved in disease resistance and possibly lead to identification of QX-resistant markers that can be applied to the Sydney rock oyster breeding program. The differential expression of EcSOD and Prx6 is likely to originate from either modifications in transcriptional rate or mRNA stability as the percentage of hemocytes that express these two genes was shown to be equal between QXR4 and W-type oysters using in-situ hybridization (p > 0.5). Attempts to amplify and assemble the full-length EcSOD gene from S. glomerata were unsuccessful. The full Prx6 gene was amplified and the frequency of polymorphisms that affected mRNA stability and transcriptional rate were determine between QX-resistant and –susceptible S. glomerata (N = 15). Notably, the frequency of a single nucleotide polymorphism (SNP) in the promoter region (-240A>G) affected the binding of a heat shock factor. The genotypic frequency of -240G/G was 0.400 in resistant oysters compared to 0.067 in susceptible oysters (p = 0.059). Further validation of this SNP is now required using a larger data set. Monitoring survival and histological observations of S. glomerata over the 2006/2007 and 2007/2008 QX disease risk period in the Pimpama River, SE Queensland provided further support to anecdotal evidence that mortality of S. glomerata occurs after heavy summer rainfall in SE Queensland. It is presumed that heavy rainfall causes the immune system of S. glomerata to become compromised, presumably by a reduction in salinity and/or estuarine acidification from a rising water table leading to leaching of acid sulfate soils. Laboratory trials revealed a drop in salinity from 35 ppt to 15 ppt affected immune gene expression and inhibition of the Prx6 gene could still be detected five days after oysters were returned to normal seawater. Acid sulfate soil leachate had no effect on the expression of immune genes or immunological parameters tested. This result provides further support to existing evidence that reduced salinity causes the immune system of S. glomerata to be compromised, possibly resulting in higher mortality of S. glomerata when subsequently challenged with M. sydneyi. Examination of S. glomerata during the QX disease risk period revealed oysters were often infected with other parasites. The microsporidian parasite, Steinhausia sp. was frequently observed infecting the gonad tissue of female S. glomerata in histological sections. This infection resulted in hemocytic infiltration and re-absorption of gonad tissue, possibly resulting in reduced growth rates, condition index and marketablity. The frequency of this parasite in oyster samples taken from Moreton Bay, SE Queensland, suggests this parasite could be an emerging problem for oyster farmers in SE Queensland. Differences in the bacterial community within the digestive gland of S. glomerata infected and un-infected with M. sydneyi was observed using non-culture techniques. Healthy oysters had a diverse bacterial community with 23 different operational taxonomic units (OTUs) identified. In contrast, S. glomerata infected with M. sydneyi had only one OTU present in the digestive gland, which was closely related to a Rickettsiales-like prokaryote (RLP) based on phylogenetic analysis of its 16S rDNA sequence. This RLP may be detrimental to its host during concurrent infection with M. sydneyi and warrants further investigation. Overall, this project demonstrated resistance of S. glomerata to M. sydneyi is likely to involve constitutive differences in gene expression. Identification of DNA variants within the promoter regions of differentially expressed genes may provide further insight into gene regulation within oysters and allow identification of DNA markers for selecting QX-resistant brood-stock. Results presented in this thesis support anecdotal evidence that S. glomerata are more susceptible to M. sydneyi following periods of high rainfall as a result of reduced salinity compromising the immune system of S. glomerata. Histological observation of S. glomerata over the QX-disease risk period revealed that oysters were often infected with a range of other parasites. The presence of these parasites may also compromise the immune system of S. glomerata during the QX-disease risk period. The implications of their presence must be factored in to future breeding and research programmes.

Diss. (sammanfattning) Göteborg : Univ. , 2007. / Härtill 3 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 5 uppsatser.