Bhlhe40 limits early IL-10 production from CD4⁺ T cells during Plasmodium yoelii 17X infection

The cytokine IL-10 suppresses T-cell-mediated immunity, which is required to control infection with Plasmodium yoelii. Consequently, IL-10 can delay the time needed to resolve this infection, leading to a higher parasite burden. While the pathways that lead to IL-10 production by CD4⁺ T cells are well defined, much less is known about the mediators that suppress the expression of this potent anti-inflammatory cytokine. Here, we show that the transcription factor basic helix-loop-helix family member e40 (Bhlhe40) contributes to controlling parasite burden in response to P. yoelii infection in mice. Loss of Bhlhe40 expression in mice results in higher Il10 expression, higher peak parasitemia, and a delay in parasite clearance. The observed phenotype was not due to defects in T-cell activation and proliferation or the humoral response. Nor was it due to changes in regulatory T-cell numbers. However, blocking IL-10 signaling reversed the outcome in Bhlhe40^{-/ -} mice, suggesting that excess IL-10 production limits their ability to control the infection properly. In addition to suppressing Il10 expression in CD4⁺ T cells, Bhlhe40 can promote Ifng expression. Indeed, IFN-γ production by CD4⁺ T cells isolated from the liver was significantly affected by the loss of Bhlhe40. Lastly, Bhlhe40 deletion in T cells resulted in a phenotype similar to that observed in the Bhlhe40^{-/ -} mice, indicating that Bhlhe40 expression in T cells contributes to the ability of mice to control infection with P. yoelii.