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Keywords:

  • Babesia;
  • bovine;
  • IFN-γ;
  • innate immunity;
  • NK cells;
  • regulatory cytokines

SUMMARY

The spleen is a critical effector organ functioning, in haemoparasitic diseases like babesiosis, to destroy the pathogen and clear the host of infected erythrocytes. It has an important role in both innate responses and adaptive immune responses. Young calves demonstrate a strong spleen-dependent innate response to an initial infection with Babesia bovis involving the type-1 regulating cytokines IL-12 and IFN-γ. However, the specific splenic cell types that produce IFN-γ in response to infection and the cellular factors that regulate the induction have not been fully determined. Splenic NKp46+ NK cells were identified and purified. They consisted of CD3, CD2+/–, and CD8+/– populations. NK cells responded to exogenous IL-12 and IL-18 with the production of IFN-γ. Functionally, IL-18 served as a potent co-stimulant with IL-12 for IFN-γ production. Finally, innate IFN-γ production was induced in splenic NK cells in the presence of supernatants from B. bovis merozoite-exposed monocytes in an IL-12 pathway-dependent manner.