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Alveolar macrophages exist in the lung airspaces, and their differentiation and function are considerably regulated by the microenvironment. In this study, we examine the important role of resident neutrophil/IL-23/granulocyte/macrophage colony-stimulating factor (GM-CSF) axis in the development and preferential phenotype of alveolar macrophages under physiological conditions. Using CD18-deficient (CD18(-/-) ) mice, we show a correlation between increased granulopoiesis and enhanced alveolar macrophage development in an IL-23- and GM-CSF-dependent manner. The apoptotic neutrophils could inhibit the secretion of IL-23 from alveolar macrophages, which is important for the production of GM-CSF, and depletion of neutrophils disrupted the regulation of IL-23 and GM-CSF. This study reveals a mechanism for the regulation of the local alveolar macrophage population and function by neutrophil apoptosis in the circulatory system.