Identification of a late-lineage neutrophil precursor population and dynamics of their differentiation and proliferation

Abstract

Neutrophils, blood circulating granulocytes characterized with numerus granules, are the most abundant immune cells. Neutrophils serve as the first responders to infection and tissue injury which initiate an immune response. A multi-staged differentiation process of granulopoiesis should be properly regulated for the homeostasis of neutrophils, and the failure results into disease. Pathologic or iatrogenic neutropenia causes a dynamic alteration of neutrophil differentiation process to compensate a neutrophil loss. This process is described as demand-adapted granulopoiesis. The regulation mechanism of this alternative differentiation program is yet to be determined, however the lack of technique to define and purify the neutrophil precursors hinders the research. This study presents a novel way to identify a late-lineage neutrophil precursor population, defined as $lineage^{-}CD11b^{+}Ly6G^{lo}Ly6B^{int}CD115^{-}$, and purified this neutrophil precursor population from the bone marrow. These newly identified NeuPs(neutrophil precursors) were able to exclusively differentiate into functional neutrophils both in vitro and in vivo. Transcriptomic profiling of NeuPs enabled identification of NeuP stage-specific genes and allowed characterization of gene regulation patterns throughout the granulopoiesis. NeuPs were highly proliferative population that can contribute to expansion of neutrophil precursor pool. Instead, the proliferation of NeuP significantly decreased in different hematopoietic stress settings. NeuPs are regarded as a critical step for regulation of granulopoiesis.