BM neutropenia wasinvariably coupled to increased HSPC proliferation, regardless of how neutrophilnumbers were reduced (Fig. 2).Neutrophil depletion with Gr-1 mAb induced rapid increases in HSC, MPP, and GMPproliferation followed by supranormal BM neutrophil numbers (Fig. 2); mice rendered chronically neutropenic byinactivation of Mcl-1 in myeloid cells [30] had constitutively elevatedrates of HSPC proliferation (Fig.2C-E) and a surplus of immature BM neutrophils (Table S1). Here, MCL1 is linked to neutropenia.