Malaria is a widespread parasitic disease, causing 300-500 million infections per year and resulting in over 1 million deaths. There is widespread resistance of the parasite to most of the antimalarial treatments available, indicating the need for a vaccine (http://www.rbm.who.int/wmr2005/). The translationally controlled tumour protein (TCTP) family are highly conserved eukaryotic proteins that have been assigned a variety of functions. While most studies have focused on the intracellular functions of TCTP, human, malarial and other parasitic TCTPs have also been reported to have extracellular functions in the induction of histamine release from immune cells (e.g. MacDonald et al., 2001; Rao et al., 2002). Malarial TCTP has been detected in the sera of malaria-infected individuals (MacDonald et al., 2001) and is also known to bind to the antimalarial drug artemisinin (Bhisutthibhan et al., 1998). In this study, TCTP was investigated as a malarial vaccine candidate due to a previously observed protective effect in mice infected with Plasmodium yoelii YM. In that study, PfTCTP immunisation conferred a significant delay in disease progression, as judged by reduced parasitemia and prolonged survival (Taylor, 2002). It was thought that the protective effect might have been due to the inhibition of the extracellular actions of malarial TCTP by the acquired host immune response. P. falciparum and P. yoelii TCTP were initially expressed in S. cerevisiae, as in the previous study. The recombinant proteins were used to vaccinate mice, which were then challenged with two strains of P. yoelii. No protective effect was observed for either vaccine, and so the previous results using PfTCTP could not be confirmed. The TCTP of P. yoelii and P. berghei were then expressed in E. coli, which increased yield and decreased proteolysis. The recombinant proteins were used as vaccines in mice challenged with P. yoelii YM, P. c. chabaudi AS, or P. berghei ANKA. A significant delay in disease progression was observed in PyTCTP-immunised mice challenged with the non-lethal P.c. chabaudi, as determined by a significantly reduced parasitemia at each day post-infection leading up to a delayed peak parasitemia. A significant reduction in parasitemia was also observed in the early stages of P. yoelii YM infection in PyTCTP-immunised mice. P. berghei ANKA was used to challenge C57BL/6 mice to determine whether PbTCTP immunisation could protect mice from cerebral malaria development, no protective effect was observed. P. berghei ANKA was also used as a second lethal malaria challenge model in BALB/c mice, no significant differences in disease progression were observed in immunised mice. To further assess the functions of malarial TCTP, several attempts were made to create a TCTP-knockout strain of P. berghei ANKA. A TCTP-knockout malaria strain could be assessed for alterations in morphology, infectivity and artemisinin sensitivity compared with wild-type parasites. Initial genotype analysis of parasites resulting from several transfection experiments indicated that TCTP disruption had been successful, however TCTP-disrupted parasites were strongly selected against, and stable knockout strains could not be obtained. This indicates that TCTP performs an important role within the malaria parasite.
| Identifer | oai:union.ndltd.org:ADTP/246511 |
| Date | January 2009 |
| Creators | Taylor, Kim, kim.taylor@y7mail.com |
| Publisher | RMIT University. Applied Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.rmit.edu.au/help/disclaimer, Copyright Kim Taylor |
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