Abstract
Toxoplasma gondii is the causative agent for toxoplasmosis. The rhoptry protein 1 (ROP1) is secreted by rhoptry, an apical secretory organelle of the parasite. ROP1 plays an important role in host cell invasion. In this study, the efficacy of ROP1 as a vaccine candidate against toxoplasmosis was evaluated through intramuscular or subcutaneous injection of BALB/c mice followed by immunological characterization (humoral- and cellular-mediated) and lethal challenge against virulent T. gondii RH strain in BALB/c mice. Briefly, a recombinant DNA plasmid (pVAX1-GFP-ROP1) was expressed in CHO cells while expression of recombinant ROP1 protein (rROP1) was carried out in Escherichia coli expression system. Immunization study involved injection of the recombinant pVAX1-ROP1 and purified rROP1 into different group of mice. Empty vector and PBS served as two different types of negative controls. Results obtained demonstrated that ROP1 is an immunogenic antigen that induced humoral immune response whereby detection of a protein band with expected size of 43 kDa was observed against vaccinated mice sera through western blot analysis. ROP1 antigen was shown to elicit cellular-mediated immunity as well whereby stimulated splenocytes with total lysate antigen (TLA) and rROP1 from pVAX1-ROP1 and rROP1-immunized mice, respectively, readily proliferated and secreted large amount of IFN-γ (712 ± 28.1 pg/ml and 1457 ± 31.19 pg/ml, respectively) and relatively low IL-4 level (94 ± 14.5 pg/ml and 186 ± 14.17 pg/ml, respectively). These phenomena suggested that Th1-favored immunity was being induced. Vaccination with ROP1 antigen was able to provide partial protection in the vaccinated mice against lethal challenge with virulent RH strain of tachyzoites. These findings proposed that the ROP1 antigen is a potential candidate for the development of vaccine against toxoplasmosis.
Highlights
Toxoplasma gondii is an obligate intracellular parasite that infects various cell types to cause an infection known as toxoplasmosis (Kim and Weiss, 2004)
Full length open reading frame of rhoptry protein 1 (ROP1) gene was successfully amplified from T. gondii genomic DNA producing an amplified product of 1191 bp
Mice vaccinated with pVAX1-ROP1 and recombinant ROP1 protein (rROP1) survived longer than the controls when challenged with lethal dose of virulent T. gondii RH strain
Summary
Toxoplasma gondii is an obligate intracellular parasite that infects various cell types to cause an infection known as toxoplasmosis (Kim and Weiss, 2004). Current therapies against T. gondii are toxic and expensive They are designed to control newly acquired infections, but not for treating chronic toxoplasmosis. The only available vaccine for toxoplasmosis to date is derived from live attenuated T. gondii (non-cystforming S48 strain). It is only used for sheep in Europe and New Zealand (Buxton et al, 1991; Jongert et al, 2009). It is not suitable for human use because of the risks associated with reversion of the parasite to its pathogenic form (WeeksLevy et al, 1991; Bourguin et al, 1993). Various T. gondii antigens, such as microneme proteins (Lourenco et al, 2006; Peng et al, 2009; Yan et al, 2012), dense granule proteins (Golkar et al, 2007; Jongert et al, 2008; Hiszczynska-Sawicka et al, 2011b; Sun et al, 2011), rhoptry antigens (Chen et al, 2003; Yuan et al, 2011a; Dziadek et al, 2012), matrix proteins (Di Cristina et al, 2004), and surface antigens (Khan et al, 1991; Mevelec et al, 2005; Lau et al, 2011) have been assessed as potential vaccination candidates
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