Toxoplasma gondii upregulates interleukin-12 to prevent Plasmodium berghei-induced experimental cerebral malaria

A chronic infection with the parasite Toxoplasma gondii has previously been shown to protect mice against subsequent viral, bacterial, or protozoal infections. Here we have shown that a chronic T. gondii infection can prevent Plasmodium berghei ANKA-induced experimental cerebral malaria (ECM) in C57BL/6 mice. Treatment with soluble T. gondii antigens (STAg) reduced parasite sequestration and T cell infiltration in the brains of P. berghei-infected mice. Administration of STAg also preserved blood-brain barrier function, reduced ECM symptoms, and significantly decreased mortality. STAg treatment 24 h post-P. berghei infection led to a rapid increase in serum levels of interleukin 12 (IL-12) and gamma interferon (IFN-γ). By 5 days after P. berghei infection, STAg-treated mice had reduced IFN-γ levels compared to those of mock-treated mice, suggesting that reductions in IFN-γ at the time of ECM onset protected against lethality. Using IL-10- and IL-12βR-deficient mice, we found that STAg-induced protection from ECM is IL-10 independent but IL-12 dependent. Treatment of P. berghei-infected mice with recombinant IL-12 significantly decreased parasitemia and mortality. These data suggest that IL-12, either induced by STAg or injected as a recombinant protein, mediates protection from ECM-associated pathology potentially through early induction of IFN-γ and reduction in parasitemia. These results highlight the importance of early IL-12 induction in protection against ECM.