Identification of the Cellular Sensor That Stimulates the Inflammatory Response to Sterile Cell Death

Abstract Cell death provokes a robust inflammatory response. We have previously shown that this response is dependent on IL-1α. In this study, we investigate the cellular mechanism used by a host to sense cell death, produce IL-1α and also the role of IL-1β in this response. In almost all cases examined, the IL-1 that stimulated the death-induced inflammatory response came from the host rather than the cell that was dying. In these situations, host bone marrow-derived cells were the key source of the IL-1α that was required for the inflammatory response. Conditional cellular depletion and reconstitution in CD11b promoter-driven diphtheria toxin receptor transgenic mice revealed that host macrophages played an essential role in the generation of the inflammatory response and were the source of the required IL-1α. In addition, we found a role for IL-1β in the death-induced inflammatory response and that this cytokine was generated by both bone marrow-derived and radioresistant host cells. The one exception to these findings was that when dendritic cells were injected into mice, they provided a portion of the IL-1 that stimulated inflammation, and this was observed whether the dendritic cells were live or necrotic. Together, these findings demonstrate that macrophages play a key role as the primary sentinels that are required to sense and report cell death in ways that initiate the inflammatory response. One key way they accomplish this important task is by producing IL-1α that is needed to initiate the inflammatory response.