FUNCTIONAL-CHARACTERIZATION OF INTERSTITIAL MACROPHAGES AND SUBPOPULATIONS OF ALVEOLAR MACROPHAGES FROM RAT LUNG

The specific function of interstitial macrophages (IM) in the lung is poorly understood because of difficulties in isolating these cells in high purity or large number. In the present studies, a pure population of enzymatically isolated IM and lung macrophages obtained mechanical ly from the lung were compared functionally with alveolar macrophages recovered by lavage (AM). Macrophages isolated mechanically from the t issue and AM displayed similarly high levels of Fc-receptor mediated p hagocytosis. In contrast, IM phagocytized significantly fewer opsonize d sheep red blood cells per macrophage than AM. In addition, although some variations in the amounts of nitric oxide and superoxide anion pr oduced by AM and macrophages obtained by mechanical tissue disruption were observed, these subpopulations released significantly more of the se mediators than IM. These data support the concept that macrophages isolated by mechanical disruption of the tissue represent a subpopulat ion of AM. We also found that, in contrast to AM, IM did not respond s ynergistically to combinations of IFN-gamma and lipopolysaccharide (LP S) or tumor necrosis factor alpha in terms of nitric oxide production. Furthermore, regulation of superoxide anion release in AM and IM by L PS and/or IFN-gamma was distinct. Taken together, these studies demons trate that IM are functionally different from other macrophage subpopu lations which might reflect their unique location within the lung.