Trypanosoma cruzi induces strong IL-12 and IL-18 gene expression in vivo: correlation with interferon-gamma (IFN-γ) production

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Abstract
IFN-γ, produced after infection with Trypanosoma cruzi, has been shown to be crucial in the determination of resistance or susceptibility. We have performed a detailed study on the expression of IFN-γ and of the IFN-γ-inducing cytokines IL-12 and IFN-γ-inducing factor (IGIF)/IL-18 with regard to time course and tissue localization. IFN-γ was present in high amounts in the serum and in the supernatants of unseparated spleen cells and isolated CD4+ and CD8+ T cells from the spleens of infected mice which were stimulated ex vivo with T. cruzi. Using the in situ hybridization technique we demonstrate that IL-12 p40 messages were expressed in the spleen and increased during infection, correlating with the expression of IFN-γ transcripts. Furthermore, we show for the first time that the mRNA for the cytokine IL-18 was induced by a parasitic infection and that this expression increased during infection with T. cruzi. Interestingly, the message for IL-18 was produced earlier during infection and already had declined until day 38, when IFN-γ and IL-12 p40 transcripts were optimally expressed. Surprisingly, the changes in IL-12 and IL-18 mRNA production were clearly seen only by in situ hybridization, but less clearly by quantitative reverse-transcriptase polymerase chain reaction (RT-PCR). This is possibly due to the extensive activation and proliferation of spleen cells observed during infection leading to a dilution of these specific mRNAs.

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