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The current view on the origin of pulmonary macrophages
Abstract:
In the present contribution the current view on the origin of macrophages is briefly summarized. Recent studies on the kinetics of pulmonary macrophages in the normal steady state and during an inflammatory reaction induced by heat-killed BCG applied intravenously or by aerosol are reported in more detail, and the effect of glucocorticosteroids on the kinetics of these cells is described. The results support the general conclusion that pulmonary macrophages derive mainly from circulating monocytes, exclude the existence of an interstitial pool of dividing precursors cells, and provide evidence that the limited local production of pulmonary macrophages is the result of division of mononuclear phagocytes recently derived from the circulation.
Insights
Pulmonary macrophages primarily originate from circulating monocytes, not local dividing cells. Limited local production results from monocytes recently entering the lungs.
Area of Science:
- Immunology
- Cell Biology
- Respiratory Medicine
Background:
- Macrophages are crucial immune cells in the lungs.
- Understanding their origin is key to lung immunity and disease.
- Existing theories on macrophage origins require further investigation.
Purpose of the Study:
- To investigate the origin and kinetics of pulmonary macrophages.
- To examine macrophage behavior during inflammation and under glucocorticosteroid treatment.
- To clarify the role of circulating monocytes versus local precursors.
Main Methods:
- Kinetic studies of pulmonary macrophages in normal and inflammatory states.
- Intravenous and aerosol administration of heat-killed BCG to induce inflammation.
- Assessment of glucocorticosteroid effects on macrophage kinetics.
- Utilizing techniques to track cell origins and proliferation.
Main Results:
- Pulmonary macrophages predominantly originate from circulating monocytes.
- Evidence against an interstitial pool of dividing precursor cells.
- Demonstrated limited local proliferation of recently arrived monocytes.
- Glucocorticosteroids impact macrophage kinetics.
Conclusions:
- Circulating monocytes are the main source of pulmonary macrophages.
- Local proliferation of macrophages is limited and derived from monocytes.
- Challenges the concept of a self-sustaining interstitial macrophage population.