Both granulocyte-macrophage CSF and macrophage CSF control the proliferation and survival of the same subset of alveolar macrophages

The effect of granulocyte-macrophage (GM)-CSF on the proliferation of murine pulmonary alveolar macrophages in vitro was investigated. About 20% of freshly isolated alveolar macrophages formed colonies in both liquid and soft agar cultures in the presence of GM-CSF. GM-CSF was also found to be capable of maintaining the survival of these colony-forming cells in vitro. Moreover, GM-CSF could substitute for CSF-1 in maintaining the survival of CSF-1-responding pulmonary alveolar macrophage colony-forming cells in the absence of CSF-1. The concentration of GM-CSF required for maintaining the survival of colony-forming cells without proliferation was much lower than that required for the proliferation of these cells in vitro. It also enhanced the CSF-1-dependent clonal growth of alveolar macrographes. These data suggest that the colony-forming cells that respond to GM-CSF are the same subset of macrophages that form colonies in the presence of CSF-1. GM-CSF did not inhibit the binding of ¹²⁵I-CSF-1 to alveolar macrophages at 0°C. However, the preincubation of macrophages with GM-CSF at 37°C resulted in a transient down-regulation of CSF-1 binding activity.