Macrophage-Derived IL-1β Regulates Emergency Myelopoiesis via the NF-κB and C/ebpβ in Zebrafish

Myeloid phagocytes, neutrophils in particular, are easily consumed when they fight against a large number of invading microbes. Hence, they require efficient and constant replenishment from their progenitors via the well-orchestrated emergency myelopoiesis in the hematopoietic organs. The cellular and molecular details of the danger-sensing and warning processes to activate the emergency myelopoiesis are still under debate. In this study, we set up a systemic infection model in zebrafish ( Danio rerio ) larvae via circulative administration of LPS. We focused on the cross-talk of macrophages with myeloid progenitors in the caudal hematopoietic tissue. We revealed that macrophages first detected LPS and sent out the emergency message via il1β The myeloid progenitors, rather than hematopoietic stem and progenitor cells, responded and fulfilled the demand to adapt myeloid expansion through the synergistic cooperation of NF-κB and C/ebpβ. Our study unveiled a critical role of macrophages as the early "whistle blowers" to initiate emergency myelopoiesis.