Our data show that type I IFN signaling directly and additionally contributes to Blimp-1 induction in cells responding to either Plasmodium or chronic LCMV infection, further supporting that type IFN-mediated induction of Blimp-1 and subsequent expansion of immunosuppressive Tr1 cells represents a generalizable feature of inflammatory Th1-biased infections. This evidence concerns the gene PRDM1 and infection.