Isolation and antigenic identification of hamster lung interstitial macrophages

Lung interstitial macrophages (IMs) are a large, distinctive population of cells with important proliferative capacities. Characterization of their role in health and disease has been hampered by inadequate methods to separate interstitial from residual alveolar macrophages (AMs) in preparations of individual mononuclear cells from lung tissue. In this study, a specific cell-surface antigen (HAM1) present on more than 90% of hamster AMs, but not expressed by hamster IMs, was used to distinguish these populations. After collagenase digestion of lung tissue slices from exhaustively lavaged and perfused hamster lungs, mononuclear phagocytes were isolated by density gradient centrifugation. The mean yield of lung digest macrophages (3.9 +/- 1.9 (SD) x 10(6] was comparable to the yield of lavaged AMs (4.2 +/- 1.9 x 10(6]. The proliferative capacity of lavaged AMs, blood monocytes, and lung digest macrophages was compared using a soft-agar colony-forming unit (CFU) assay. Both lung digest macrophages and blood monocytes had significantly more CFUs (68.7 +/- 2.6 and 53.5 +/- 8.4 CFU/10(3) cells [mean +/- SEM], respectively) than did AMs (16.5 +/- 1.7) (p less than 0.01). To further define the composition of the lung digest macrophage population, flow cytometric analysis of fixed cells from six experiments was performed using a mouse monoclonal antibody specific for the HAM1 antigen found only on AMs. The lung digest macrophage population consisted of both antigen-negative IMs (78.2% +/- 3.7% [SEM]; n = 6) and antigen-positive, residual AMs (21.8% +/- 3.7%). Morphometric counts confirmed that substantial numbers of AMs are left behind after lavage and contribute to macrophages obtained from lung tissue.(ABSTRACT TRUNCATED AT 250 WORDS)