PRDM1 and malaria: However, Blimp-1 deficiency in Treg cells has minimal impact on immune responses and disease outcome in mice infected with L. donovani. Data from malaria [30,31] and VL [29] patients indicates that Tr1 cells are a major regulatory T cell population during protozoan diseases, and our results show a critical role for Blimp-1 in Tr1 cell function by promoting IL-10 production.