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(Journal of Leukocyte Biology. 2000;68:464-470.)
© 2000 by Society for Leukocyte Biology

Impaired splenic erythropoiesis in phlebotomized mice injected with CL2MDP-liposome: an experimental model for studying the role of stromal macrophages in erythropoiesis

Yoshito Sadahira^*, Tatsuji Yasuda, Tadashi Yoshino, Toshiaki Manabe^*, Toshiyuki Takeishi, Yoshiaki Kobayashi, Yusuke Ebe and Makoto Naito

^* Department of Pathology, Kawasaki Medical School, Kurashiki;
Department of Cell Chemistry, Institute of Molecular Biology and Cell Biology;
Department of Pathology, Okayama University Medical School, Okayama; and
Department of Pathology, Niigata University School of Medicine, Niigata, Japan

Correspondence: Yoshito Sadahira, M.D., Department of Pathology, Kawasaki Medical School, 577 Matsushima, Kurashiki 701-0192, Japan. E-mail: sadapath{at}med.kawasaki-m.ac.jp

Erythropoiesis occurs in the presence of erythropoietin (EPO) without macrophages in vitro. In hematopoietic tissues, however, erythroid cells associate closely with stromal macrophages, forming erythroblastic islands via interactions with adhesion molecules. To elucidate the role of macrophages in erythropoiesis, we selectively abrogated stromal macrophages of splenic red pulp of phlebotomized mice by injection with dichloromethylene diphosphonate encapsulated in multilamellar liposomes (CL2MDP-liposome). In the spleen, no erythropoietic activity occurred until 5 days after the treatment. Colony assay revealed that the erythropoiesis was suppressed at the level of CFU-E. The splenic erythropoietic activity gradually developed from day 6 after the treatment, when F4/80⁺ macrophages began to appear in the red pulp. EPO mRNA was expressed in kidney but not in liver or spleen of phlebotomized mice injected with CL2MDP-liposome, and the serum EPO concentration in these mice was higher than that in phlebotomized mice. These findings suggest that abrogation of stromal macrophages by injection with CL2MDP-liposome impairs the splenic microenvironment for erythropoiesis induced by hypoxic stress, and this may be an excellent experimental model for further characterization of the in vivo role of splenic macrophages in erythropoiesis.

Key Words: hypoxia • erythroblasts • erythropoietin • adhesion • microenvironment

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