Activated macrophages induce hemopoietic islands in the adult rat liver.

Focal hemopoiesis was induced in the liver of adult rats following treatment with glucan, a macrophage activator. Using endogenous peroxidase cytochemistry for identification of hemopoietic cell types, hemopoietic islands were studied by light and electron microscopy. Hemopoiesis in the islands was either restricted to the erythroid or myeloid lineage. Hemopoietic cells of various maturational stages frequently formed close contacts with macrophages. This indicates that activated macrophages exert a stimulatory effect on hemopoiesis by short-range action of humoral factors or by a close cell-to-cell-contact.