The observation that Bhlhe40−/− CD4+ T cells exhibit a significant increase in IL-10 RNA and protein production suggests that Bhlhe40 acts during the early stages of a P. yoelii infection, to suppress IL-10 expression in CD4+ T cells, as it does in response to other Th1-centric infections (18, 19). Here, BHLHE40 is linked to infection.