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Toll-like receptor (TLR) ligands are attractive adjuvant candidates in vaccine development. Eimeria tenella profilin-like protein has recently been shown to be a potent agonist of the innate immune system through its recognition by Toll-like receptor-11. In this report, we studied the systemic and mucosal adjuvant activity of Eimeria profilin-like protein within a vaccinal strategy against Toxoplasma gondii in mice. Using intraperitoneal (i.p.) immunization, we observed that coadministration of the recombinant Eimeria antigen (rEA) with T. gondii antigen (TAg) effectively elevates plasma levels of IL-12p70 and consequently induced both enhanced specific humoral and Th1 cellular immune responses. The co-administration of TAg plus rEA by i.p route significantly enhanced the protection against T. gondii infection (62% brain cyst reduction) in comparison with control mice and with mice immunized with TAg alone (only 36% brain cyst reduction). After intranasal immunization, humoral and cellular responses were weak. However mice immunized nasally with TAg plus rEA were significantly protected with 50% of brain cyst reduction, conversely TAg immunized mice did not present any brain cyst reduction.These results indicate that Eimeria profilin-like protein would serve as an efficacious systemic and mucosal adjuvant inducing protective immune response against chronical stage of T. gondii infection through TLR11 activation.

Recombinant Eimeria antigen (rEA) has been shown to have potent anticancer and antiviral activity in respective mouse disease models, presumably through robust immune stimulation that occurs via TLR11, a pattern recognition receptor that recognizes profilin-like proteins expressed on apicomplexan protozoans. Comparable immunostimulatory activity in other species has yet to be demonstrated. Since rEA is known to be highly effective in treating Punta Toro virus (PTV) infection in mice, its ability to elicit protective immunity in the hamster PTV infection model was investigated. rEA was given alone, or in combination with IL-18 or IL-2, and virally challenged hamsters were observed for mortality. Cytokine transcript profiles for IL-12p40, IL-21, IFN-gamma and TNF-alpha were assessed to evaluate the induction of these inflammatory mediators known to be induced in mice following exposure to rEA. A dose of 100 microg of rEA, given once 4 h prior to viral challenge, and a second time on day 3 of the infection, was found to be the most effective prophylactic therapy protecting 60% of treated hamsters from mortality, compared to only 5-10% observed in animals receiving placebo. Increased expression of IFN-gamma and IL-12p40 was evident following treatment with rEA. The data suggest that rEA does induce host antiviral responses in hamsters that result in significant protection from death, although determining the most appropriate dose for intervention in other species, including humans, will likely be challenging.

A protein antigen from an Eimeria protozoan has recently been reported to induce antitumor activity in mice. This activity most likely results from the strong induction of interkeukin-12 (IL-12) and gamma interferon (IFN-γ), which are also essential factors in the establishment of protective immunity against viral infection. We evaluated recombinant Eimeria antigen (rEA) as a potential immunotherapeutic agent in mouse and hamster models of acute phleboviral disease. Punta Toro virus (PTV) was highly sensitive to a single dose of nanogram quantities of rEA in the mouse infection model. Intraperitoneal treatment with rEA also reduced virus load and liver damage associated with PTV infection. IL-12 was elicited following exposure of uninfected mice to quantities of rEA of 10 ng or greater, and the levels peaked at between 3 and 8 h postexposure. IFN-γ release was induced more slowly and required less rEA (1 ng) to produce a significant rise in systemic levels. The induction of IL-12 and IFN-γ involved in the coordination of innate and adaptive immune responses to microbial pathogens required myeloid differentiation factor 88, a signaling adaptor shared by most members of the Toll-like receptor (TLR) family. Despite encouraging results in the murine system, rEA failed to protect hamsters challenged with PTV. Our findings suggest that hamsters may lack functional TLR11, which has recently been shown to recognize a profilin-like protein homologous to rEA from the protozoan Toxoplasma gondii . Further investigation into the immunostimulatory capacity of rEA in other mammalian systems is necessary.