α-Gal immunization positively impacts Trypanosoma cruzi colonization of heart tissue in a mouse model

Abstract

Chagas disease, caused by the parasite Trypanosoma cruzi, is considered endemic in more than 20 countries but lacks both an approved vaccine and limited treatment for its chronic stage. Chronic infection is most harmful to human health because of long-term parasitic infection of the heart. Here we show that immunization with a virus-like particle vaccine displaying a high density of the immunogenic α-Gal trisaccharide (Qβ-αGal) induced several beneficial effects concerning acute and chronic T. cruzi infection in α1,3-galactosyltransferase knockout mice. Approximately 60% of these animals were protected from initial infection with high parasite loads. Vaccinated animals also produced high anti-αGal IgG antibody titers, improved IFN-γ and IL-12 cytokine production, and controlled parasitemia in the acute phase at 8 days post-infection (dpi) for the Y strain and 22 dpi for the Colombian strain. In the chronic stage of infection (36 and 190 dpi, respectively), all of the vaccinated group survived, showing significantly decreased heart inflammation and clearance of amastigote nests from the heart tissue.

Fig 1. Immunization against high dose of T. cruzi Y strain.

(A) Immunization and analysis schedule. αGalT-KO mice (5 per group) were inoculated (subcutaneous) with two 10 μg doses of of Qβ-αGal, Qβ-WT, or PBS on days 0 and 7. On day 14 (dpi 0), all groups were infected with 10⁶ Y strain. (B) Relative anti-α-Gal IgG serum antibody levels measured by ELISA before infection, Y days before infection (serum dilution = 1/100). (C) Parasite levels in blood checked daily starting at day 1 post-infection (dpi). (D) Mouse survival. All experiments were performed independently in triplicate.

Fig 2. Immunization against moderate dose of T. cruzi Y strain.

αGalT-KO mice (6–10 per group) were inoculated (subcutaneous) with one 10 μg dose of Qβ-αGal, Qβ-WT, or Qβ-Glu (alternate control bearing glucose units instead of α-Gal). Mice were challenged one week after immunization with 10⁴ Y strain. (A) Parasite levels in blood checked daily starting at day 1 post-infection (dpi). Red dashed lines show the upper limit of the standard deviation for each set of data. (B) Mouse survival. (C) Degenerative changes in the heart. (D) Hypertrophy. (E) Inflammation score. (F) Lesion intensity. All experiments were performed independently in triplicate. Significance p < 0.05. ns (not significant). Data plotted as SEM (Standard Error of the Mean).

Fig 3. Immunization against T. cruzi Colombian strain.

αGalT-KO mice (6–10 per group) were inoculated (subcutaneous) with two 10 μg doses of Qβ-αGal or Qβ-WT on days 0 and 7. On day 14, all groups were challenged with 10³ parasites of the Colombian strain. (A) Relative anti-α-Gal IgG serum antibody levels measured by ELISA (serum dilution = 1/100). “Pre-infection” denotes day 7, one week before challenge. (B) Parasite levels in blood checked daily starting at day 2 post-infection (dpi). Red dotted lines show the upper limit of the standard deviation for each set of data. (C) Degenerative changes in the heart. (D) Hypertrophy. (E) Inflammation score. (F) Lesion intensity. All experiments were performed independently in triplicate. Significance p < 0.05. ns (not significant). Data plotted as SEM (Standard Error of the Mean).

Fig 4. TLR activity, cytokine production and histopathology.

(A) Nitric oxide production from stimulated peritoneal macrophages from unvaccinated mice of the indicated strains. Treatment groups refer to 1 μg/mL concentrations of the indicated agent; “medium” = buffer. (B and C) IL-12 and IFN-γ production by heart homogenate from vaccinated or unvaccinated αGalT-KO mice infected with Y strain. (D and E) IL-12 and IFN-γ production by heart homogenate from vaccinated or unvaccinated αGalT-KO mice infected with Colombian strain. (F and G) Average number of T. cruzi amastigote nests found in heart tissue by counting in 100 fields per slide of heart section. (H) Representative histopathological sections from the indicated mice; for example, the top-left panel shows heart tissue from an unvaccinated animal 8 days after infection with T. cruzi Y strain. Arrows point to amastigote colonies. All experiments were performed independently in triplicate.