Liver-associated macrophage precursor cells proliferate under impairment of regular hemopoiesis.

We reported previously that immature macrophage precursor cells can be isolated from spleen and liver of cyclophosphamide or pyran copolymer-pretreated mice. We now extended our investigations to livers of normal, untreated specific pathogen-free mice. Using the response to the macrophage growth factor colony-stimulating factor-1 (CSF-1) and the presence of the mouse macrophage-specific F4/80 antigen as criteria of definition, in the liver of normal mice we could demonstrate macrophage precursor (M phi P) cells by means of proliferation assays and flow cytometric analysis. The amount of M phi P present in the normal liver was significantly increased after administration of pyran copolymer. Also an enhanced proliferative response to CSF-1 as well as augmented natural killer activity and cytostasis of Candida albicans was noted in liver nonparenychymal cells (LNPC) after treatment of bone marrow (BM)-irradiated, splenectomized mice with pyran copolymer. Since the irradiated BM was actually proven to be silent by assessment of BM number and proliferative capacity and by scoring white blood cells, our findings suggest a response of endogenous liver M phi P under the applied conditions. Further evidence for the presence of endogenous liver hemopoietic cells was obtained from transplantation experiments in which LNPC brought about the survival of lethally irradiated mice. The data point towards a significance of the liver in disposing hemopoietic cells to the organism under impairment of regular hemopoiesis.