Plasmodium Infection and Endotoxic Shock Induce the Expansion of Regulatory Dendritic Cells

During an acute Plasmodium infection, uncontrolled proinflammatory responses can cause morbidity and mortality. Regulation of this response is required to prevent immunopathology. We therefore decided to investigate a recently characterized subset of regulatory dendritic cells (DCs) that expresses low levels of CD11c and high levels of CD45RB. During a Plasmodium yoelii infection, these regulatory CD11clowCD45RBhigh DCs become the prevalent CD11c-expressing cells in the spleen, overtaking the conventional CD11chigh DCs. Furthermore, the regulatory CD11clowCD45RBhigh DCs induce IL-10-expressing CD4 T cells. A similar change in splenic DC subsets is seen when mice are injected with sublethal doses of LPS, suggesting that shifting the splenic DC subsets in favor of regulatory CD11clowCD45RBhigh DCs can be triggered solely by a high inflammatory stimulus. This is the first time regulatory DCs have been observed in a natural immune response to an infectious disease or endotoxic shock.