Christopher A. Hunter

Eric N. Villegas

Guifang Cai

Robert Kastelein

Thad Radzanowski

Abstract
               The capacity of IL-12 to stimulate T and NK cell production of IFN-γ is required for resistance to Toxoplasma gondii. To identify the transcription factors involved in this mechanism of resistance, mice deficient in STAT4, a protein involved in IL-12 signaling, were infected with T. gondii and their immune responses were analyzed. STAT4−/− mice were unable to control parasite replication and died during the acute phase of infection, whereas wild-type mice controlled parasite replication and survived this challenge. The susceptibility of STAT4−/− mice to toxoplasmosis correlated with a defect in their ability to produce IFN-γ in response to infection, whereas administration of IFN-γ to these mice inhibited parasite replication and delayed time to death. Interestingly, analysis of infected STAT4−/− mice revealed that these mice did produce low levels of IFN-γ during infection, and the ability of splenocytes from infected or uninfected STAT4−/− mice to produce IFN-γ was enhanced by the addition of IL-2 plus IL-18. Moreover, administration of IL-2 plus IL-18 to STAT4−/− mice resulted in elevated serum levels of IFN-γ associated with a decreased parasite burden and delayed time to death. In vivo depletion studies demonstrated that the ability of IL-2 plus IL-18 to mediate STAT4-independent resistance to T. gondii is dependent on NK cell production of IFN-γ. Together, these studies identify STAT4 as an important transcription factor required for development of the innate NK and adaptive T cell responses necessary for resistance to T. gondii. However, other signaling pathways can be used to bypass STAT4-dependent production of IFN-γ and enhance innate resistance to T. gondii.</jats:p

Identification of STAT4-Dependent and Independent Mechanisms of Resistance to Toxoplasma gondii

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