No description available.

No description available.

No description available.

Live attenuated <i>Salmonella </i>that express heterologous antigens are attractive vehicles for the presentation of antigens for systemic and mucosal immunity. It is hypothesised that this requires uptake and interaction with DCs although this has yet to be studied in large animal models. This study has used pseudoafferent cannulated sheep to provide physiologically relevant DCs. However, in many other systems <i>in vitro</i> derived DCs are used in studies with <i>Salmonella</i>. Therefore we have cloned and expressed ovine IL-4 and developed protocols for derivation of <i>in vitro</i> generated DCs from comparison with this data. Cannulation of pseudoafferent and efferent lymphatics further allows monitoring of the earliest events of an <i>in vivo</i> <i>Salmonella</i> infection. Following <i>in vitro</i> infection with <i>S. abortus</i> <i>ovis</i> (a sheep specific <i>Salmonella </i>serotype) very few DCs were found to contain intracellular <i>Salmonella</i>. Avirulent <i>Salmonella</i> mutants were rapidly cleared from afferent lymph DCs <i>in vitro</i> unlike their virulent parental strains, which were found to survive and replicate intracellularly. Despite the rapid clearance of attenuated <i>S. abortus</i> <i>ovis</i> mutants from DCs, Maedi Visna virus (MVV) <i>gag</i> antigens expressed in these <i>Salmonella </i>were found to be presented to T cells. Following subcutaneous injection of <i>aroA^-</i> <i>S. abortus</i> <i>ovis</i> expressing MVV gag p25, <i>Salmonella</i> were found in the afferent lymph and cells draining the infection site. However, no bacteria were detected in the efferent lymph or cells. Phenotypic changes indicative of enhanced DC maturation in afferent lymph as well as lymphocyte activation in afferent and efferent lymph were also observed. Functional anti-<i>Salmonella</i> immune responses in efferent lymph were also studied. This study has established that <i>Salmonella </i>can infect afferent lymph dendritic cells of a large animal model. Such cells migrate to the lymph node where they initiate immune responses and can influence the cells' activation and the immune mechanisms invoked.

<I>Trypanosoma brucei</I>, the causal agents of African sleeping sickness contains a membrane bound glycosylphosphatidylinositol-specific phospholipase C (GPI-PLC) which exhibits exquisite specificity for GPI anchors. The enzyme is of interest as its action has the effect of releasing the variant specific surface glycoprotein (VSG) monolayer from the cell membrane <I>in vitro</I>, an event that is possibly analogous to a life cycle stage dependent process occurring <I>in vivo</I>. The regulation of expression of the GPI-PLC gene operates mainly at the post-transcription level and has been investigated through generating transgenic trypanosomes containing GPI-PLC genes with altered regulatory sequences. The results obtained suggest that the 3' (and/or possibly 5') untranslated regions (UTRs) contain elements conferring instability in procyclic forms and that the 5' or 3' UTRs contain elements that confer stability on the coding sequence in bloodstream forms. The function of the gene has been addressed by manipulation of a GPI-PLC null mutant <I>T.brucei</I> generated in the laboratory. The null trypanosomes contain no activity capable of cleaving the GPI anchor to release the VSG from the membrane. Despite this lack the trypanosomes can complete the life-cycle, so the GPI-PLC gene is non-essential. The GPI-PLC is not necessary for the process of antigenic variation as the null trypanosomes can establish a persistent infection in mice. However, the levels of infection (trypanosomes/ml blood) are reduced by one to two orders of magnitude. Experiments have been designed to establish whether this attenuation can be reversed by returning a wild type GPI-PLC gene to the null mutant, and with the aim of determining the phenotype of a dominant null mutation.

This study aimed to establish if the memory response observed in long-term HCMV carriers directly reflects the breadth of the T cell response generated following primary infection or if a broader response early in infection then leads to selection of particular CD8⁺ T cells into the long term memory pool (clonal focussing). In two immunocompetent donors and two renal transplant recipients, the early primary HCMV CD8⁺ peptide-specific T cell pool was composed of multiple T cell receptor (TcR) Vβ family members. This usage rapidly focused predominantly onto T cell clones bearing a single TcR Vβ family. Clones within the dominant TcR Vβ family frequently had public TcR usage (sequence motifs shared between different unrelated donors) whilst subdominant clones and clones which were contracted below the limit of detection often expressed private TcRs. A high TcR avidity for a particular MHC/peptide could be a factor which governs selection of particular T cells into the memory pool. Functional avidities were determined for multiple virus specific T cell clones and it was clear that T cells specific to the same MHC/peptide combination had very high avidities which were very similar regardless of the donor origin. The expression of particular Natural Killer receptors (NKRs) on CD8⁺ T cells has also been associated with entry into the virus-specific memory pool. Different repertoires of NKR expression were detected on pp65-specific clones generated during primary infection than on clones generated in long-term memory. Overall this work demonstrates that the HCMV specific CD8⁺ T cell repertoire seen in long-term virus carriers is established early following primary infection by the rapid selection of public TcR clonotypes which display high functional avidity and often have common NKR expression.

No description available.

Recovery from Hepatitis C virus (HCV) infection is considered infrequent (<20%) in Western populations but reaches 50% in West Africa where genotype 2 infection is predominant. The first objective of this project was to investigate the role of cellular response and host genetics involved in this phenomenon. Plasma samples from 104 Ghanaian blood donors reactive with anti-HCV assays were collected. 81% of subjects with chronic infection carried genotype 2 HVC. Cellular immune responses were studied in frozen peripheral blood mononuclear cell samples from 35 cases. HLA-A, -B and –DR types were determined. HLA-B*57 was significantly more frequent in the group recovered from infection compared with chronically infected donors (<i>p</i> = 0.0053). The dominance of genotype 2 HCV strains and high frequency of HLAA-B*57 may be important factors explaining the high rate of recovery from HCV infection in Ghana. The second objective of this project was to assess the antigenicity of the recombinant genotype 2 F protein in donors with either chronic infection or recovery identified previously. Purified F and core proteins were used to develop immunoassays to detect anti-F and anti-core in titrated plasma samples. The level of HCV antibodies was also titrated using a commercial anti-HCV kit. The results showed that the reactivity of F protein was significantly higher (<i>p</i> <0.001) in donors with chronic infection than recovered infection regardless of genotype. The same difference was observed with anti-core and anti-HCV. This strongly suggested that F protein exists in natural HCV infection. It also showed that antibodies to F protein were not genotype-specific as genotype 2 F protein was recognised by plasma from genotype 1 and 3-infected individuals. Anti-F antibody titre was estimated here for the first time in comparison with anti-core and anti-HCV antibodies.

The life cycle of the parasite and the consequent human disease manifestations are reviewed in Chapter 1. Chapter 2 describes the drug trial in Papua New Guinea which provides most of the data for the dissertation. Chapter 3 demonstrates that data on two aspects of the vector-human interface - density dependence of microfilarial survival, and comparisons of mosquito catching methods - have in the past been manipulated in ways which simplified analysis by reducing the influence of extreme values, but at the cost of unjustified conclusions. Chapter 4 analyses the mean and aggregation of human microfilarial density as functions of age and sex. In particular, data from demographic surveillance are used to investigate the hypothesis that a drop in intensity among women of reproductive age is the result of pregnancy-associated changes. In addition, spatial heterogeneity is shown to be an alternative explanation for intra-family associations which have previously been attributed to <I>in utero</I> effects. The distributions of acute and chronic disease are characterized in Chapters 5 and 6, in order to select statistical models which can accommodate heterogeneity and determine risk factors for the different types of morbidity. Geographical patterns are visualized using satellite mapping techniques, and autoregressive spatial models are used to check that the maps are not unduly dominated by counts with high sampling variability because of small denominators. Chapter 7 returns to the vector to consider possible effects on other mosquito-borne diseases of mass anti-filarial chemotherapeutic control programmes. Chapter 8 provides a concluding synthesis of the work. Overall, this research demonstrates that heterogeneity arises in lymphatic filariasis through a network of factors - including vector contact, innate and acquired host characteristics, and geographical variability - which must be recognized and distinguished in order to properly quantify the epidemiology of the disease.

MicroRNAs (miRNAs) function through targeted binding to the 3’ un-translated region (UTR) of messenger RNAs (mRNAs) in a sequence specific manner. Recent studies have implicated microRNA-155 (miR-155) as an important player in the development and function of a number of immune cells including B and T cells, macrophages and dendritic cells. The aim of this study was to investigate the role of miR-155 in controlling either a mucosal <i>Citrobacter rodentium </i>or a systemic <i>Salmonella enterica </i>serovar Typhimurium infection in the context of the overall immune response. Here we present evidence that miR-155-deficient mice are less competent in their ability to eradicate a mucosal <i>C. rodentium </i>infection compared with wild type control C57BL/6 mice. We show that miR-155-deficient mice have a higher <i>C. rodentium </i>burden in gastrointestinal tissue and also exhibit spread into systemic tissues. Additionally, we demonstrate that germinal centre formation and humoral immune responses are impaired in the absence of miR-155. In view of the fact that this phenotype is largely reproduced in μMT (B cell-deficient) mice reconstituted with miR-155-deficient B cells we conclude that miR-155 is required to control <i>C. rodentium </i>infection. Further, miR-155-deficient mice were able to clear a primary infection with an attenuated strain of <i>S. Typhimurium </i>but were defective in their immune response to <i>Salmonella.</i>