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Updated: Aug 19, 2026
Isolation and In Vitro Culture of Murine and Human Alveolar Macrophages
Published on: April 20, 2018
The ontogeny of pulmonary alveolar macrophages in parabiotic mice
Abstract:
A bilateral distribution of labeled blood monocytes was achieved by unilaterally labeling donor members of surgically parabiosed B6D2F1/J mice with tritiated thymidine (3HTdR). Labeled pulmonary alveolar macrophages (PAM) were found in lung lavage fluid of donors. By contrast, no labeled PAM were found in lung lavage fluid from unstimulated recipients, even 12 days after labeling. Contralateral 3HTdR flash labeling showed that in recipients 3%, or about 10(4), PAM were in S phase of the cell cycle. Contralateral intratracheal challenge of recipient members with either Corynebacterium parvum vaccine or with Salmonella typhimurium lipopolysaccharide induced the emigration of labeled blood monocytes of donor origin into recipient alveoli. These data show that in parabiotic mice, blood monocytes do not regularly enter the alveolar compartment. It may be concluded that monocytes are not needed on a daily basis to sustain PAM populations.
Insights
Blood monocytes do not regularly enter the lung
Area of Science:
- Immunology
- Cell Biology
- Pulmonary Medicine
Background:
- Pulmonary alveolar macrophages (PAM) are critical immune cells in the lungs.
- The origin and replenishment of PAM populations are not fully understood.
- Investigating monocyte contribution to PAM is essential for understanding lung immunity.
Purpose of the Study:
- To determine if blood monocytes regularly replenish the pulmonary alveolar macrophage population in mice.
- To investigate the conditions under which blood monocytes may enter the alveolar space.
Main Methods:
- Utilized parabiosis in B6D2F1/J mice, labeling donor monocytes with tritiated thymidine (3HTdR).
- Analyzed lung lavage fluid from donors and recipients for labeled cells.
- Administered inflammatory stimuli (Corynebacterium parvum or Salmonella typhimurium lipopolysaccharide) to recipients to assess monocyte recruitment.
Main Results:
- No labeled monocytes were found in recipient PAM populations under unstimulated conditions, even after 12 days.
- A small percentage (3%) of recipient PAM were in S phase, indicating endogenous proliferation.
- Inflammatory stimuli induced the emigration of labeled donor monocytes into recipient alveoli.
Conclusions:
- Blood monocytes do not routinely infiltrate the alveolar compartment to sustain the resident pulmonary alveolar macrophage population.
- The resident PAM population is likely maintained through self-renewal rather than daily monocyte influx.
- Monocyte recruitment into the alveoli can be induced by specific inflammatory challenges.
