Macrophage progenitors in bone marrow. Bone marrow cells isolated from either Agtr1^+/+ mice or Agtr1^–/– mice were cultured for 10 days in semisolid agar culture at a density of 50,000 cells per milliliter in the presence of indicated concentrations of CSF-1. Colonies of macrophages or granulocyte/macrophages were counted (a), and the total number of macrophage progenitors per tibia was determined (b). *P < 0.05.