Alveolar macrophages: functional heterogeneity within macrophage populations from rat lung

Alveolar macrophages were obtained from the unstimulated lungs of rats by repeated endobronchial lavage and an interstitial macrophage population prepared by mincing the lungs subsequent to the lavage process. Considerable heterogeneity was observed within these macrophage populations with respect to cell size, surface morphology and cytochemistry. Functional studies, involving assessment of IgG-Fc receptor density/avidity and the expression of cytostatic activity in cultures of mitogen-stimulated lymphocytes, revealed comparable heterogeneity, and further indicated a considerably higher degree of apparent stimulation in the alveolar versus the interstitial macrophage population. Parallel assessment of the functional activity of blood monocytes, the immediate precursors of these latter macrophages, indicated a lower state of activation again. This suggests that the lung interstitium normally provides an intermediate environment between the blood and the alveolar spaces, wherein blood monocytes may undergo maturational changes before their efflux into the alveoli.