Estudo da imunogenicidade das proteínas SAG1, SAG2 e SAG3 de Toxoplasma gondii expressas em vírus recombinantes e mapeamento de seus epítopos protetores

Abstract

The tachyzoite SAG proteins are involved in activation of protective immune responses against the parasite T. gondii in infected individuals. In the present study, we have evaluated the activation of humoral and cellular immunity in mice vaccinated with recombinant adenoviruses coding for SAG1, SAG2 or SAG3 from T. gondii. Peptides corresponding to MHCI-binding epitopes, specific for the H2-Db and H2-Ld haplotype, were predicted in SAG1, SAG2 and SAG3 proteins by sequence analysis on SYFPEITHI software. Those peptides were produced by solid-phase synthesis employing the Fmoc methodology. BALB/c and C57BL/6 mice received two 109 p.f.u. doses of AdSAG1, AdSAG2, AdSAG3 or AdCTRL, six weeks apart. Serum samples obtained from C57BL/6, four weeks after the last immunization, were submitted to Western-blot assays, against total tachyzoite lysate (TLA). Two to four weeks after the last immunization, spleens from both mice lineages were collected for ELISPOT assays. Splenocytes were stimulated in vitro with synthetic peptides corresponding to epitopes predicted on SYFPEITHI software. Vaccinated mice were challenged with an oral dose ME49 strain two weeks after the last immunization. Results show that immunization elicited specific IgG antibodies against the three proteins in C57BL/6 mice. Also, immunization with AdSAG1 induced specific activation of IFN-g producing CD8+ T cells in both mice. Those cells showed to be responsive to an epitope predicted on SAG1 sequence. The same level of activation was not observed in mice from the AdSAG2, AdSAG3 or AdCTRL groups. Further, the immune responses observed in AdSAG1-vaccinated mice were related to protection against an oral challenge with the ME49 strain. It was observed higher survival rate and less cysts numbers in that group. These results indicate that vaccination with recombinant viruses is feasible approach for development of anti-toxoplasma vaccines.