A study on the mechanism of the development of extramedullary hemopoiesis in adult mouse liver

A single withdrawal of blood (about 0.6 ml) from a splenectomized mouse induced extramedullary hemopoiesis in the liver. Twenty days after splenectomy, blood was taken from the retroorbital sinus. Hemopoietic foci in the liver increased in number daily reaching maximum value 6 days after blood withdrawal, then decreased gradually to the initial level with recovery of the hematocrit value and disappearance of reticulocytosis 25 days after blood withdrawal. Hemopoietic foci were pure erythrocytic, granulocytic, megakaryocytic or unclassified, but not mixed. Small unclassified cell foci appeared first, increased in number, followed by the development of erythrocytic, granulocytic and megakaryocytic foci. This suggests that small unclassified cell foci grow to erythrocytic and large granulocytic ones. Most of the liver hemopoietic foci were in the intralobular area. Some were in the portal area; none of these were megakaryocytic. Electron microscopic observation revealed that lymphoid cells having distinct nucleoli migrate into Disse's space through the sinusoidal walls. There they proliferate by cell division to form large foci in the perisinusoidal area. The morphologic characteristics of the lymphoid cell are discussed.