Our finding that IL-10 is critical during the first 96 hours of Plasmodium blood-stage infection is consistent with the notion that B cells must respond to IL-10 well before anatomical formation of germinal centers within B cell follicles, which are only histologically detectable in our system by day ~10 p.i. Our results stand in striking contrast to studies of acute and chronic virus infections. Here, IL10 is linked to infection.