Characterization of cytokine production in murine Trypanosoma cruzi infection by in situ immunocytochemistry: Lack of association between susceptibility and type 2 cytokine production

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Abstract
Cytokine production in the spleens of mice infected with the protozoan parasite Trypanosoma cruzi was analyzed in three models which differ in the outcome of the infection. Using immunocytochemical techniques to detect cytokine‐producing cells, the production of type 1 [interleukin‐2 (IL‐2) and interferon (IFN)‐γ], type 2 (IL‐4, IL‐5, IL‐10), inflammatory [tumor necrosis factor (TNF)‐α, IL‐1α, IL‐6] and regulatory (transforming growth factor‐β) cytokines were examined. With the exception of IL‐4 and IL‐5, cells producing all of the cytokines assayed were detected in both the resistant and susceptible models of T. cruzi infection. Cells producing IL‐4 and IL‐5 were not detected until later in infection in the resistant mice (>34 days), at about the time animals of the susceptible strain succumb to the infection. Mice of the susceptible model showed a slight delay in the appearance of cells producing the type 1 cytokines IL‐2 and IFN‐γ and an earlier appearance of TNF‐producing cells, in comparison to resistant mice. Cells producing IL‐2 or IL‐10 were transient in their appearance in the spleen while cells producing IL‐1, IL‐4, IL‐5, IL‐6, IFN‐γ, TNF, or TGF‐β were first detectable in either the acute or post‐acute stage of the infection and persisted up to 700 days post infection in two different resistant models of the infection. Cells producing IFN‐γ, TNF‐α and TGF‐β were particularly numerous even very late in the infection. Double‐staining techniques were used to show that the vast majority of the IFN‐γ‐producing cells in the spleen were CD4−, CD8− α/β TCR+ T cells. This study confirms the transience of IL‐2 production in the acute stage of T. cruzi infection and the persistent and simultaneous production of type 1 and type 2 cytokines during the late‐acute and chronic stages of the infection. Susceptibility or resistance to T. cruzi infection does not associate with a Th2 pattern of cytokine production in the three models examined in this study. The overlapping pattern of type 1 and type 2 cytokine‐producing cells in both the acute and chronic stages of T. cruzi infection demonstrates that longterm infections do not necessarily lead to a dominance of either type 1 or type 2 cytokine production.

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