Characterization of murine lung and peritoneal macrophages

Tissue macrophage populations have a common origin in the bone marrow and yet are adapted to their specific anatomical loci and display characteristic differences in metabolism, biochemical activity, and other parameters. In this study, immunologic and nonimmunologic receptor-mediated functions of lung (LM) and peritoneal (PM) macrophages were compared. With sheep erythrocytes as challenge particles, both cell populations exhibited Fc and cytophilic Ab-mediated rosetting and phagocytosis. However, LM showed greater rosetting and phagocytic activity mediated by either immune-complexed or free IgG. Complement receptor (CR₁ and CR₃) activity was lacking in LM, while PM displayed high rosetting ability for these receptors. Neither LM nor PM demonstrated CR₂ receptors. Conversely, a considerable percentage of LM demonstrated nonimmunologic Candida rosettes, whereas PM showed a paucity of this ability. Phagocytosis and killing of Candida krusei was greater in LM than in PM. Cytochemical staining for acid phosphatase revealed higher enzyme activity in LM. These results support the view that LM and PM are distinct cell populations which demonstrate functional manifestations of adaptation from circulating monocytes to region-specific tissue macrophages. With the exception of complement-mediated rosetting and phagocytosis, LM had greater activity in all parameters measured. Although the lack of active CR₁ and CR₃ receptors on murine LM is not clearly understood, the generally higher activity displayed by LM may be associated with the greater environmental assault faced by the lung in contrast to the peritoneum.