Correlation of lung macrophage age and surface antigen in the hamster

A monoclonal antibody specific for a surface antigen found on hamster lung macrophages has been produced. Macrophages obtained from LSH Syrian golden hamsters by pulmonary lavage have varying amounts of this antigen on their surface. We compared the age of alveolar macrophages (using 3H-thymidine) with the amount of surface antigen. Lung macrophages were obtained by repeated saline lavage at 1, 3, 5, and 10 days after 3H-thymidine injection. Monoclonal antibody was then reacted with these cells followed by fluorescein isothiocyanate-conjugated protein A. Cell size and fluorescence were analyzed by flow cytometry. A wide range of fluorescent intensity was observed; the cells were sorted into four subpopulations (SPs). SP1 had the lowest fluorescence per cell, and SP4 had the highest. The sorted cells were placed on glass slides, and autoradiographs were made. The percentage of labeled macrophages in each SP was determined. At 1 day after thymidine injection, cells with a paucity of antigen (SP1) were the most highly labeled; 12.5% of SP1 macrophages were labeled, but only 1.4 and 1.1% of SP3 and SP4 were labeled, respectively. The labeling was relatively even in all four SPs at 3 days, but at 5 days the labeling of cells in SP2 and SP3 was highest. By day 10, labeled macrophages had large amounts of surface antigen and were in SP3 and SP4. These findings suggest that pulmonary macrophages that have recently synthesized DNA lack surface antigen. As time passes, cells mature and more antigen is acquired. The amount of surface antigen reflects cell age and provides a useful tool to isolate and study macrophage SPs.