CSF1 and infection: Ossified vascular channels within the skull allow a direct route for bone marrow–derived myeloid cells to egress from bone marrow to the dura membrane.34, 35, 36 This direct route enables colony stimulation factor 1, produced by injury or infection, to reach calvarial bone marrow reservoirs to modify the immune environment, prompting the trafficking of bone marrow–derived myeloid cells to the dural mater.37