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Role of activation in alveolar macrophage-mediated suppression of the plaque-forming cell response
1Department of Microbiology, School of Medicine, Georgetown University, Washington, D.C. 20007.
Abstract:
Alveolar macrophages (AM) are highly suppressive of the in vitro plaque-forming cell (PFC) response of spleen cells obtained from mice primed with sheep erythrocytes. Comparison of macrophage populations obtained from disparate anatomical sites revealed that although in both cases there was a cell-concentration-dependent suppression of the PFC response, resident AM or AM activated as a result of intravenous injection of Mycobacterium bovis BCG were equally suppressive at the doses examined. Although there was a similar dose-dependent suppression with peritoneal macrophages, BCG-activated cells were more suppressive of the PFC response than were resident cells. In contrast, splenic macrophages at comparable concentrations were not at all suppressive. Resident AM exhibited significantly lower levels of 5'-nucleotidase activity than did resident peritoneal macrophages. Macrophage-mediated suppression of the in vitro PFC response could not be attributed to the release of toxic oxygen metabolites (H2O2, O2- ,and .OH) or prostaglandins, since the addition of catalase, superoxide dismutase, 2-mercaptoethanol, or indomethacin did not completely reverse suppression. These results suggest that the lung microenvironment may maintain AM in an activated state which contributes to their potential immunoregulatory functions.
Insights
Alveolar macrophages (AM) suppress immune responses, unlike splenic macrophages. The lung environment may keep AM in an activated state, influencing their immunoregulatory roles.
Area of Science:
- Immunology
- Cell Biology
- Respiratory Medicine
Background:
- Alveolar macrophages (AM) play a crucial role in lung immunity.
- AM exhibit potent immunosuppressive properties on the in vitro plaque-forming cell (PFC) response.
- Understanding macrophage function across different anatomical sites is key to immune regulation.
Purpose of the Study:
- To compare the immunomodulatory functions of alveolar macrophages (AM) with macrophages from other sites.
- To investigate the mechanisms underlying macrophage-mediated suppression of the PFC response.
- To explore the influence of the lung microenvironment on AM activation and function.
Main Methods:
- Comparison of in vitro PFC response suppression by resident and activated AM, peritoneal macrophages, and splenic macrophages.
- Assessment of macrophage-derived factors, including oxygen metabolites and prostaglandins, in mediating suppression.
- Enzyme activity assays (5'-nucleotidase) to characterize macrophage populations.
Main Results:
- Resident and BCG-activated AM demonstrated significant dose-dependent suppression of the PFC response.
- BCG-activated peritoneal macrophages were more suppressive than resident peritoneal macrophages.
- Splenic macrophages showed no suppressive activity at comparable concentrations.
- Suppression was not fully reversed by catalase, superoxide dismutase, 2-mercaptoethanol, or indomethacin, suggesting non-oxidative and non-prostaglandin mechanisms.
Conclusions:
- Alveolar macrophages possess potent immunosuppressive capabilities distinct from splenic macrophages.
- The lung microenvironment may contribute to maintaining AM in a chronically activated, immunoregulatory state.
- Macrophage-mediated suppression involves mechanisms beyond reactive oxygen species and prostaglandins.