Abstract
Toxoplasma gondii (T. gondii) is an obligate intracellular protozoan parasite that infects a variety of mammals, including humans. An effective vaccine for this parasite is therefore needed. In this study, RH strain T. gondii rhoptry protein 17 was expressed in bacteria as a fusion with glutathione S-transferase (GST) and the recombinant proteins (rTgROP17) were purified via GST-affinity chromatography. BALB/c mice were nasally immunised with rTgROP17, and induction of immune responses and protection against chronic and lethal T. gondii infections were investigated. The results revealed that mice immunised with rTgROP17 produced high levels of specific anti-rTgROP17 IgGs and a mixed IgG1/IgG2a response of IgG2a predominance. The systemic immune response was associated with increased production of Th1 (IFN-γand IL-2) and Th2 (IL-4) cytokines, and enhanced lymphoproliferation (stimulation index, SI) in the mice immunised with rTgROP17. Strong mucosal immune responses with increased secretion of TgROP17-specific secretory IgA (SIgA) in nasal, vaginal and intestinal washes were also observed in these mice. The vaccinated mice displayed apparent protection against chronic RH strain infection as evidenced by their lower liver and brain parasite burdens (59.17% and 49.08%, respectively) than those of the controls. The vaccinated mice also exhibited significant protection against lethal infection of the virulent RH strain (survival increased by 50%) compared to the controls. Our data demonstrate that rTgROP17 can trigger strong systemic and mucosal immune responses against T. gondii and that ROP17 is a promising candidate vaccine for toxoplasmosis.
Highlights
Toxoplasma gondii is an obligate intracellular parasite of the phylum Apicomplexa [1] that is found worldwide
To evaluate the systemic immune responses in rTgROP17immunized mice, the levels of antigen-specific IgG, IgG1 and IgG2a antibodies in the sera and in the spleen cell supernatants were detected using enzyme linked immunosorbent assays (ELISAs)
The results revealed that 25 mg rTgROP17 but not 15 mg rTgROP17 elicited elevated IgG antibody levels compared to the control groups (P, 0.05)
Summary
Toxoplasma gondii is an obligate intracellular parasite of the phylum Apicomplexa [1] that is found worldwide. T. gondii has a gigantic intermediate host range that comprises nearly any bird and mammal, including humans. Symptoms associated with Toxoplasma infection in humans range from none to severe and can be fatal. When T. gondii infects immunocompromised hosts, such as AIDS patients or malignancy patients, it can lead to severe or even lethal damage [2,3]. T. gondii infection of livestocks can result in serious economic losses due to abortion, stillbirth, and neonatal death. Infected livestock are a major route of T. gondii transmission to humans [4]. The development of effective and safe methods, such as vaccines [5], to control T. gondii infection is crucial for human health and animal husbandry
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