Abstract
BackgroundToxoplasma gondii is an obligate intracellular parasite that can pose a serious threat to human health by causing toxoplasmosis. There are no drugs that target the chronic cyst stage of this infection; therefore, development of an effective vaccine would be an important advance. Aspartic proteases play essential roles in the T. gondii lifecycle. The parasite has four aspartic protease encoding genes, which are called toxomepsin 1, 2, 3 and 5 (TgASP1, 2, 3 and 5, respectively).MethodsBioinformatics approaches have enabled us to identify several promising linear-B cell epitopes and potential Th-cell epitopes on TgASP1, thus supporting its potential as a DNA vaccine against toxoplasmosis. We expressed TgASP1 in Escherichia coli and used the purified protein to immunize BALB/c mice. The antibodies obtained were used to determine where TgASP1 was localized in the parasite. We also made a TgASP1 DNA vaccine construct and evaluated it for the level of protection conferred to mice against infection with the virulent RH strain of T. gondii.ResultsTgASP1 appears to be a membrane protein located primarily at the tip of the T. gondii tachyzoite. Investigation of its potential as a DNA vaccine showed that it elicited strong humoral and cellular immune responses in mice, and that these responses were mediated by Th-1 cells. Mice immunized with the vaccine had greater levels of protection against mortality following challenge with T. gondii RH tachyzoites than did those immunized with PBS or the empty vector control.ConclusionsTgASP1 is a novel candidate DNA vaccine that merits further investigation.
Highlights
Toxoplasma gondii is an obligate intracellular parasite that can pose a serious threat to human health by causing toxoplasmosis
T. gondii possesses five genes encoding a family of polytopic membrane rhomboid-like serine proteases, which are known as TgROM 1 to 5 [5]
GENSCAN was used to search for the open reading frame (ORF) structure of the TgASP1 gene, whilst the physical and chemical properties of the protein were analyzed by ProtParam
Summary
Toxoplasma gondii is an obligate intracellular parasite that can pose a serious threat to human health by causing toxoplasmosis. The parasite has four aspartic protease encoding genes, which are called toxomepsin 1, 2, 3 and 5 (TgASP1, 2, 3 and 5, respectively). Toxoplasma gondii, a coccidian apicomplexan, is an obligate intracellular parasite of humans and other warmblooded animals [1,2]. T. gondii expresses several proteases, including cysteine proteases, aspartic proteases and serine proteases. T. gondii has four aspartic protease encoding genes that are designated toxomepsin 1, 2, 3 and 5 (TgASP1, 2, 3 and 5, respectively) and two subtilases (TgSUB1 and TgSUB2). T. gondii possesses five genes encoding a family of polytopic membrane rhomboid-like serine proteases, which are known as TgROM 1 to 5 [5]
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