To test whether the increase in endothelial IL-6 production during atherosclerosis contributes to the leukocytosis that fuels arterial inflammation19–22,25, we induced atherosclerosis in Cdh5CreERT2;Il6fl/fl mice using an atherogenic diet and adeno-associated virus (AAV)-mediated gene transfer of mutant human PCSK9. Compared to Cdh5CreERT2 littermate controls, endothelial cell-specific Il6 deletion reduced HSPC numbers and proliferation in the bone marrow and lowered systemic myeloid cell numbers (Fig. 8a–c), while splenic hematopoiesis remained unchanged (Extended Data Fig. 7d,e). Here, PCSK9 is linked to atherosclerosis.