Figure 1.

Macrophage origin in the mouse. Classically, macrophages derive from circulating monocytes, in turn descending from bone marrow progenitors. In the bone marrow, HSCs differentiate into LPs or MPs. LPs further differentiate into B cells, T cells, and NK cells. MPs give rise to DCs, granulocytes, mast cells, megakaryocytes, and erythrocytes, or to Ly6C⁺ inflammatory and Ly6C⁻ resident or patrolling monocytes. After tissue infiltration, Ly6C⁺ monocytes give rise to either DCs or macrophages. Although less documented, Ly6C⁻ monocytes can also differentiate into macrophages. Alternatively, adult tissue macrophages can also descend from yolk sac-derived macrophages, independently of HSCs. As such, tissue macrophages in the adult are mainly a mix of bone marrow-derived and yolk sac-derived macrophages. Abbreviations: DCs, dendritic cells; HSCs, hematopoietic stem cells; LPs, lymphoid committed precursors; MPs, myeloid committed precursors; NK, natural killer (cells).