The aim of this thesis was firstly to investigate the possibility of local antibody in urine samples from HEPS individuals to evaluate the theory that such individuals may develop a protective local anti-HIV-l antibody response, detectable in urine. Since elicitation of mucosal immunity is important in preventing viral infection by sexual transmission, development of a vaccine which is effective for the induction of mucosal immune responses may provide protection to mucosal surfaces against HIV-1 transmission. Transgenic plants expressing foreign protein has been demonstrated to be an inexpensive and easily delivered system for the production of animal and human vaccines which can effectively induce mucosal immune response. The second aim of this work was to develop a transgenic plant system expressing HIV-1 gp160 protein to exploit the feasibility of HIV-1 oral vaccine. The specificity of IgG, IgA and sIgA anti-HIV antibodies to different HIV-1 viral proteins present in paired urine and serum samples from 3 HIV-1 seropositive and 9 HEPS individuals were profiled using Western blot immunoassay. Specific sIgA antibodies to HIV-1 gpl60, p65, gp4l, p31 and p24were detected in urine or the corresponding vaginal swab samples from HIV-1 seropositive individuals, which suggested that a local mucosal immune response was induced by HIV-1 infection. For samples from HEPS individuals, specific IgG antibodies to HIV-1 gp160, gpl2O and p51, and IgA antibody to HIV-1 p51 were detected in 1 of 9 urine but not the corresponding serum samples, respectively. These results suggested that local mucosal immune responses may be elicited in those HEPS individuals. Furthermore, IgG are the predominant isotype of anti-HIV antibodies present in the genitourinary tract of those HEPS subjects and may be associated with a natural protection mechanism in some individuals.

The aim of this thesis was to investigate a broad variety of factors, in a cohort of EU heterosexual partners of HIV<SUP>+</SUP> individuals (indexes), which may affect heterosexual transmission. The immune function of the EUs was assessed and compared to normal controls, by monitoring proliferative responses to mitogen, recall and alloantigens and a combination of recombinant HIV proteins. Cytokine responses to these stimuli were also monitored. The EUs were also confirmed to be uninfected by polymerase chain reaction (PCR). The EUs had similar proliferative responses to controls for both the allogenic and recall antigens and showed a minor difference in the response to the mitogen, phytohaemagglutinin (PHA), which may reflect differences in the kinetics of the response. An increase in the amount of interferon-γ (IFN-γ) produced in response to alloantigen was seen in EUs compared to controls, which could potentially inhibit HIV replication. The proportion of lymphocytes expressing the MHC Class II protein, human leucocyte antigen-DR (HLA-DR), was also elevated in the EUs compared to controls and may reflect an overall increase in the activation status of the EU' lymphocytes. Genetic factors which were investigated included the HLA antigens and the recently reported mutations in the CC chemokine receptors (CCR), CCR-2 and CCR-5, utilised by certain strains of HIV as co-receptors for entry. The HLA allele DR5 was elevated in frequency in the EU cohort compared to population controls and to HIV<SUP>+</SUP> individuals who were infected by heterosexual exposure.

Malaria transmission is increasing due to insecticide resistance of the malaria-carrying mosquito, control programme failures, drug resistance of the malaria parasite and perhaps even global warming. Therefore, a greater understanding of the genetics and molecular biology of the parasite is urgently needed in order to develop novel chemotherapeutic and vaccine based control strategies. The research aims of this thesis were to study genes and proteins which regulate the development of the malaria parasite, <I>Plasmodium falciparum, </I>through its intra-erythrocytic life cycle. A <I>Plasmodium falciparum</I> homologue of one of the components of a Chromatin-Remodelling Complex which controls binding of transcription factors to nucleosome core particles has been cloned and characterised. This sequencing effort has been broadened into a genome data bank-based review of intons and promotor sequences in <I>Plasmodium falciparum. </I>Immunofluorescence microscopy also shows that the PfNF2L protein is expressed throughout the asexual stage of the cell cycle and is localised within nucleus. A proteolytic process and granular pattern on the infected red blood cell membrane is revealed by using anti-PfSNF2L polyclonal antibodies on western blotting and immunoflourescence assay. Biological experiments on the cell cycle of malaria parasite have also been carried out. Process through the cell cycle has been shown to be retarded by heat shock and blocked at certain specific cell stage by drugs known to block certain key cell cycle regulatory processes in other cells. The nature of the cell death process in cycle arrested cells has also been investigated and its role in apoptosis-like cell death in malaria cells has been investigated.

The main aim of this study was to develop a fast and efficient way of expressing <i>P. falciparum </i>antigenic epitopes as conformationally conserved antigenic structures whose expression can be readily ‘scaled-up’ for clinical testing. The <i>E. coli</i> and <i>P. pastoris</i> systems were used, both singly and as linked production systems using ‘shuttle vectors’ that can be dually expressed in both microorganisms. Initially a proof-of-principle experiment to express the CIDRI domain of PfEMP1 has been conducted. It was expressed and purified in good quantity and used to immunize rabbits. The sequenced 3D7 <i>P. falciparum</i> genome was then exploited to construct degenerate primers for several domains of PfEMPl (namely DBL α, β and γ). These primers were used to amplify targets from FCR3CSA parasites. PCR products were then ligated into the dual expression vector pPICHOLI1 plasmid. Several erythrocyte surface antigen expression libraries were constructed. Development and optimisation of microarray and high-throughput screening assays in malaria vaccine development was carried out to accelerate the process of identifying malaria vaccine candidates. Growth of colonies of <i>P. pastoris</i> on filters on agar plates for high-throughput screening, a novel procedure, was optimized. These libraries were screened using patients’ pooled sera from endemic areas in Sudan, as well as sera from male and pregnant women suffering from the pregnancy malaria syndrome from a holo-endemic malaria transmission zone, Ghana. Different domains from a gene of particular interest, the NF54 <i>var</i>2CSA gene were also amplified for study. The domains of DBL3X and DBL4e have been produced and purified from mid-scale induction experiments.

No description available.

Drug resistance is one of the major obstacles facing malaria control. Resistance to the combination sulfadoxine/pyrimethamine (S/P) (Fansidar) is now widespread, although the mechanism by which this arises is still not fully understood. Therefore, the molecular basis of S/P resistance was studied in the rodent malaria parasite, <i>Plasmodium chadaubi</i>. S/P resistant mutants were selected from a clone already resistant to the pyrimethamine, AS (PYR), caused by the presence of an asparagine at position 106 in its dihydrofolate reductase (DHFR). Two S/P resistant clones, AS (50S/P) and AS (75S/P), were selected and chosen for further analysis. AS (PYR) parasites were eliminated by S/P treatment, whereas AS (50S/P) and AS (75S/P) recrudesced following S/P pressure. However, each mutant possessed a different drug resistant phenotype. The AS (75S/P) clone always recrudesced before the AS (50S/P) clone following treatment with S/P, while AS (50S/P) always appeared before AS (75S/P) when treated with either sulfadoxine or pyrimethamine alone. Mutations in the genes encoding the targets of sulfadoxine and pyrimethamine, dihydropteroate synthase (DHPS) and DHFR, have been implicated in the mechanism of S/P resistance in <i>P. falciparum</i>. The <i>P. chabaudi</i> <i>dhps</i> gene was cloned by homology and sequenced. The sequence analysis of the both <i>dhfr</i> and <i>dhps</i> genes of AS (75S/P) and AS(50S/P) did not reveal any polymorphisms when compared to the sequences of the AS (PYR) genes. The mechanism of resistance of S/P in these drug-selected lines is not therefore conferred by additional mutations in these genes. To determine the genetic basis of the S/P resistance, AS (50S/P) was crossed with a drug sensitive clone, AJ. Sixteen independent recombinant progeny clones were phenotyped for their susceptibility to S/P and pyrimethamine and genotyped for the influence of 30 chromosome-specific markers. Linkage analysis shows that mutant <i>dhfr</i> is a major determinant of S/P resistance in <i>P. chabaudi</i>. Quantitative trait analysis suggested that other loci, which may be involved in S/P resistance, are present on chromosomes 4, 5, and 9.

Gametocytes, the transmission stage of malaria parasites, are generally rare in infections. I explore whether this may be a parasite adaptation that paradoxically maximises fitness. I present an optimality analysis of gametocyte investment based on a discretely formulated within-host model. I show that low gametocyte investment is predicted as a result of the trade-off that exists between producing gametocytes and increasing parasite numbers. I predict that gametocyte investment should decrease as maximum asexual density occurs later in infections and also as parasite fecundity rises. I address statistical problems with estimating gametocyte investment from blood smears. I also consider the simpler case of estimating parasitaemias and gametocytaemias. Traditional methods of counting parasites in smears can produce biased estimates of parasitaemia, gametocytaemia and gametocyte conversion. I introduce an alternative method of counting based on inverse sampling. This method is unbiased, is consistently precise and the most time-efficient method of counting. I used the inverse sampling method to estimate gametocyte conversion (the observed outcome of investment) in <i>P. chabaudi</i> infections in mice, which had been manipulated to alter the time of maximum asexual density. Gametocyte conversion showed two peaks. The timing of the peaks depended on the time of maximum asexual density. Maximum conversion decreased as the time to maximum asexual density rose as predicted by my optimality analysis. An interesting finding was that gametocyte conversion decreased after reaching a maximum. This result is counter to most life history theory. I suggest this indicates that survival of infections into a chronic phase may be an important component of fitness. Maximum conversion occurred after maximum asexual density. This leads me to propose that contrary to the common view, gametocyte investment may be suppressed at times when there is a high risk of parasite clearance. Understanding the reasons for gametocyte rarity may help to predict how <i>P. falciparum</i> will respond to intervention and suggest new methods of malaria control.

This thesis experimentally tests the within-host competitive interactions between malaria strains of <i>Plasmodium chabaudi</i> in laboratory mice, a system widely used as a model for human malaria. A real-time quantitative PCR assay was developed to track different parasite clones in mixed-clone infections over time. Several experiments were then carried out using this molecular tool. In all these experiments, it was shown that intense competition occurs between <i>Plasmodium</i> clones occupying the same host: this competition as most likely the result of a limited amount of resources, such as red blood cells, and cross-reactive immune responses. There was a direct relationship between virulence and in-host competitiveness, thus supporting a fundamental theoretical assumption. Host genotype also was an important determinant: competition was shown to be more intense in a resistant than a susceptible mouse strain. Timing of infection was very important too: the later a parasite clone arrived after another had established, the more it suffered from competition. How in-host competitiveness related to between-host transmission, was assessed by feeding infected mice to <i>Anopheles stephensi</i> mosquitoes. This showed a straight relationship between in-host competitiveness and mosquito transmission, thus suggesting that competitive suppression in the mouse host translated into reduced transmission in the mosquito vector. Finally, it was shown that drug treatment could disrupt competitive interactions between drug-resistant and –sensitive clones: the result could be competitive release of drug resistant strains followed by an enhanced spread of drug resistance. The results from this thesis confirm many assumptions underlying models on the evolution of virulence and drug resistance. They thereby suggest that reducing the number of mixed malaria infections could have beneficial effects by reducing the evolutionary selection for increased virulence.

<i>Cryptosporidium parvum</i> is an obligate intracellular protozoan which infects the gastrointestinal tract of a wide range of mammalian species. It is a common cause of diarrhoeal illness in humans and neonatal ruminants. Despite the medical and veterinary importance of <i>C. parvum</i> studies of this organism at the genetic level have begun only recently. This is due to the lack of interest shown in the parasite until it was recognised as a cause of human and animal disease, and also to the difficulty in producing sufficient parasite material in order to carry out such studies. The aim of this study was to identify, by screening a DNA library with anti-C. <i>parvum</i> antisera, genes or gene fragments encoding antigens of <i>C.parvum</i>. A <i>C. parvum</i> λgt 11 expression library was constructed using <i>Eco</i>RI-digested genomic DNA prepared from <i>in vitro</i>-excysted oocysts. Screening the library resulted in the isolation of two immunopositive clones, λCPR1, recognised by rat serum raised against excysted <i>C. parvum</i> oocysts, and λCPS10 recognised by serum from a gnotobiotic lamb experimentally infected with <i>C. parvum</i>. The DNA inserts from these clones (CPR1 and CPS10 respectively) were subcloned into the pMS plasmid expression vectors, and the recombinant peptides expressed by the resulting subclones analysed by Western blotting. Subclones containing CPS10 expressed a peptide which was recognised by some, but not all, lambs infected with <i>C. parvum</i>. When CPR1 was subcloned into pMS1S the resulting subclone expressed a 200kDa β-galactosidase fusion protein. This fusion protein was partially purified and used to raise polyclonal antiserum in a rabbit. Western blotting indicated that this serum recognised a 190kDa peptide constituent of the <i>C. parvum</i> oocyst wall. The CPR1 DNA fragment was sequenced in both directions and found to consist of 2359 nucleotides, 2358 of which form a continuous open reading frame. The DNA sequence has a realtively low G+ C content (39.1%) and there is a corresponding bias towards the use of codons ending in A or T (82.1%) within this open reading frame.

No description available.