During acute Trypanosoma cruzi infection highly susceptible mice deficient in natural killer cells are protected by a single alpha-galactosylceramide treatment

Abstract

The protective immune response against Trypanosoma cruzi is improved by treatment with the natural killer (NK) T-cell glycolipid antigen alpha-galactosylceramide (alpha-GalCer). A single alpha-GalCer treatment of mice before T. cruzi infection decreases parasitaemia and prolongs survival. This protection is dependent on CD1d-restricted NKT cells and interferon-gamma (IFN-gamma) suggesting that alpha-GalCer-activated NKT cells produce IFN-gamma, which stimulates the cells of the innate and adaptive immune responses to provide protection. To learn which cells provide protection we investigate here alpha-GalCer treatment of mice deficient in different immune cells. Surprisingly, although NK cells provide protection against T. cruzi, and are a major source of IFN-gamma following alpha-GalCer treatment, NK cells are not required for the alpha-GalCer-induced protection. The alpha-GalCer treatment of NK-cell-depleted mice controlled parasitaemia and prevented death. In contrast, phagocytes, helper T cells and cytotoxic T cells are required. Furthermore, alpha-GalCer treatment of MHC II(-/-) or CD8alpha(-/-) mice exacerbated the infection, demonstrating that alpha-GalCer treatment induces some responses that favour the parasite. In summary alpha-GalCer protection against T. cruzi required multiple cellular responses, but not the response of NK cells. These results provide useful information because alpha-GalCer is being developed as therapy for infections, autoimmune diseases, allergy and cancers.

Figure 1

α-GalCer-induced Trypanosoma cruzi protection does not require NK cells. Mice were injected with 80 μg anti-asialo GM1 antibody or PBS, 1 day later they were treated with 5 μg α-GalCer or diluent and the next day they were inoculated with 1 × 10⁵ trypomastigotes. (a) Spleen and liver mononuclear cells of mice treated with anti-asialo GM1 antibody or PBS were stained with anti-TCR mAb and anti-NK1.1 mAb and analysed by flow cytometry. In each flow cytometry plot the upper left ellipse indicates the NK cells and the central ellipse indicates the NKT cells. The number indicates the percentage of cells (NK cells) present in the left ellipse. (b) Mean parasitaemia and SE per group; (c) survival curves of five mice per group. Results are representative of three similar experiments.

Figure 2

α-GalCer-mediated protection against Trypanosoma cruzi is not observed in MHC II^–/–, CD8α^–/–, perforin^–/– or silica-treated mice. Mice were treated with 5 μg α-GalCer or diluent and the next day were inoculated with 2 × 10⁵ trypomastigotes. Five mice per group were monitored for parasitaemia (mean and SE) and five or more mice per group were monitored for survival. The results are representative of two or more experiments for each mouse strain.

Figure 3

α-GalCer-treated mice exhibit weight loss. Wild-type, NK-cell-depleted, MHC II^–/–, CD8α^–/–, perforin^–/– and silica-treated mice were treated with 5 μg α-GalCer or diluent. Five mice per group were monitored for weight just before α-GalCer treatment and 24 hr later (just before T. cruzi infection) and weight change is presented as the mean and SE of the per cent weight change., The results are representative of two or more experiments for each mouse strain; *P < 0·05 and **P < 0·01, versus same strain, diluent-treated.