O papel do epítopo α-Gal (Galα1-3Galβ1-4GlcNAc-R) no diagnóstico sorológico e na infecção experimental pelo Trypanosoma cruzi

Abstract

The protozoan parasite Trypanosoma cruzi has a cell surface covered by immunogenic glycoconjugates expressing the α-Gal epitope, which triggers high levels of protective anti-α- Gal antibodies in infected individuals, representing excellent targets for the serological diagnosis. The use of bovine serum albumin (BSA) and Qβ virus-like particle (Qβ-VLP) platforms, which increase the number of displayed α-Gal epitope, was evaluated as a tool for the serological diagnosis of T. cruzi infection in chronic phase. For this purpose, ~22 units of α-Gal epitope were coupled to BSA and this neoglycoprotein was used as antigen, showing that purified anti-α-Gal antibodies from chagasic patients were ~230-fold more reactive than purified anti-α-Gal antibodies from healthy individuals. Similarly, the pooled sera from chagasic patients were recognized ~20-fold more strongly than pooled sera from health individuals. On the other platform used, 540 molecules of the α-Gal epitope were coupled to Qβ-VLP and this antigen was tested against a panel of sera from patients chronically infected with T. cruzi, both untreated and benznidazole-treated, and compared with sera from patients with leishmaniasis and from healthy donors. The results showed excellent discrimination between chagasic and non-chagasic patients, regardless of parasitemia, degree of chronic chagasic cardiopathy and age, as well as the absence of cross-reactivity. Moreover, the anti-α- Gal IgG levels decreased substantially in patients receiving treatment with benznidazole, suggesting that the assessment of serum levels of this highly abundant type of antibody can report on disease status in individual patients. Taken together, these results indicate that α-Gal coupled to BSA or Qβ-VLP could be a potential diagnostic candidate for T. cruzi infection. Since α-Gal is highly immunogenic and human cells or tissues are not able to produce it, it was hypothesized that this epitope could be used as a vaccine. Therefore, the last part of this work aimed to evaluate mice that do not express the α-Gal epitope in their tissues as experimental models in T. cruzi infection. These mice were more efficient at controlling the infection, showing a more organized immune response, and the high levels of lytic anti-α-Gal antibodies may be responsible by this protection, as well as by the greater survival found when these animals were challenged with a lethal dose of T. cruzi trypomastigotes (Y strain).