Effect of 89Sr-induced monocytopenia on splenic and pulmonary alveolar macrophage populations in a normal steady state.

A bone-seeking radioisotope, 89Sr eliminates blood monocytes and their precursors in the bone marrow after a selective deposition in the skeletal bone. In the present study, we investigated whether or not such a prominent monocyte depletion can induce any alterations in tissue macrophage populations in 89Sr-injected mice. The number of monocytes or leukocytes possessing a macrophage differentiation antigen, Mac-1, phagocytic or Fc receptor (FcR) activity was significantly reduced in the blood and the bone marrow for about 6 weeks after 89Sr administration. Splenic macrophages characterized by these phenotypic or functional markers were not, however, altered in number during the post-injection period, despite the fact that the total number of spleen cells recovered significantly increased together with macrophage colony forming stem cells (M-CFC) and cells under DNA synthesis. The population of lavaged pulmonary alveolar macrophages (PAM) was invariable not only in the number recovered but also in DNA synthesis. Colony formation by PAM was consistently noted, and the total number of M-CFC in the lung was not reduced during the 8 weeks post-injection period. These results indicate that 89Sr-induced depletion of bone marrow-derived monocytes/macrophages or their precursors has little effect at least on the number of splenic and pulmonary alveolar macrophage populations in a normal steady state.