Inflammatory responses must be tightly coordinated with the activation of emergency myelopoiesis to produce potent myeloid cells that fight infection without causing excessive host damage. Here, we show that GM-CSF programs myeloid committed progenitors to produce trained macrophages (increased cytokine response), but programs the upstream non-committed LKS+ progenitors to produce tolerized macrophages (decreased cytokine response). In myeloid progenitors, GM-CSF strongly activates STAT5, …