Estudo de novos peptídeos preditos in silico visando a indução de resposta imune protetora contra a infecção experimental de camundongos C57BL/6 por Toxoplasma gondii

Abstract

Toxoplasmosis is a parasitic disease caused by Toxoplasma gondii, an intracellular protozoan capable of infecting a wide range of hosts. The infection usually causes no disease in healthy individuals, but it is especially severe for immunocompromised patients or during pregnancy, situations when the parasite could have an environment more favorable for its multiplication. Several species of animals also are infected by this parasite, causing abortion and livestock economic losses as well. The existing treatment consists of drugs with high toxicity to patient, being not appropriate particularly for the fetuses. Therefore, a vaccine capable of prevent the disease or reducing the consequences would be extremely beneficial, both from medical and veterinary point of view. So far, there is no vaccine available to prevent the disease and only one vaccine capable of reducing abortion induced by this parasite is used currently only in sheeps. Considering these points, we proposed to evaluate in the present study the immune response induced by synthetic peptides derived from immunodominant proteins (SRS, ROP, MIC and GRA) of this parasite. First, 22 peptides were selected considering the highest scores for B cell epitope prediction by analysis in silico. All of them were screened, it was selected 11 of them, according with their higher reactivity against serum samples from infected animals, based on their organelle location and used to immunize C57Bl/6 mice. Afterwards, animals immunized were infected with a sublethal dose of 10 cysts of ME49 strain 45 days after the first step of immunization, blood and brains from immunized animals were collected, being posteriorly used to measure cytokines production, antibody titers and to quantify the parasite. Cytokines analysis showed that all experimental groups had IL-10, IL-4, IL-6, IL-2, IFN-ɣ and IL-17 levels lower than non-immunized group. Also, the cytokines levels from SRS and MIC immunized groups were similar to soluble Toxoplasma antigen (STAg) group. The immunized group with peptides from surface antigen proteins related sequences (SRS) and micronemes (MIC) had significant lower parasite DNA than non-immunized group (PBS), similarly to the results obtained from STAg immunized group. Another groups of immunized animals were immunized with the same peptide groups and submitted to challenge with 40 cysts. The group SRS had the longest survival time, but the results were not statistically different from PBS group. In summary, peptides from SRS and MIC proteins showed promising results as vaccine antigens in a murine model and further studies are needed to confirm their potential.