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Different functional and morphological characteristics in a nonadherent subpopulation of human macrophages recovered
C M Sköld1, C Barck, J Lundahl
1Institution of Medicine, Lung Section, Karolinska Hospital, Stockholm, Sweden.
Abstract:
The alveolar macrophages (AMs) constitute a morphologically and functionally heterogenous cell population. The adhesive properties of these cells are important for their role in host defence. To focus on the heterogeneity, a population of nonadherent macrophages were characterized functionally and morphologically. These cells were then compared with the total alveolar macrophage population. Alveolar cells (> 95% alveolar macrophages), were recovered by bronchoalveolar lavage (BAL) from healthy smokers. Nonadherent macrophages were separated by adhesion. The phagocytic capacity and the autofluorescent properties of the cell populations were determined in flow cytofluorometric assays. In addition, electron microscopic evaluation was performed. The alveolar macrophage adhesion to wells coated with albumin increased in a time-dependent manner. After 15 min, median 47%, interquartile range 42-52% (uncoated wells 68%, 67-72%) of the alveolar macrophages were attached; and after 60 min, 56%, 51-58% (uncoated wells 73%, 71-76%) of the alveolar macrophages were attached. The nonadherent alveolar macrophage population had less phagocytic capacity. The cell autofluorescence increased with increasing cell size and cell complexity/granularity in both populations. The nonadherent cells were more autofluorescent, indicating an increased granularity/complexity. These findings were confirmed with electron microscopy. Thus, the nonadherent alveolar macrophages had more cytoplasmic inclusions than the total alveolar macrophage population (volume density median 0.39, interquartile range 0.35-0.46 and 0.31, 0.26-0.34, respectively), but less surface protusions. We conclude that in lavage fluid from human smokers there is an ultrastructurally specific subpopulation of alveolar macrophages, showing less adhesive properties and impaired phagocytic capacity in vitro. These macrophages may be older alveolar cells or, alternatively, airway macrophages. Since only alveolar macrophages from smokers were investigated, we cannot draw any conclusions regarding alveolar cells from nonsmokers. Nevertheless, the heterogeneity of the lavaged cells should be taken into consideration when the functional ability of the alveolar macrophages are evaluated.
Insights
Smokers
Area of Science:
- Pulmonary immunology and cell biology.
- Investigating heterogeneity within alveolar macrophage populations.
Background:
- Alveolar macrophages (AMs) are crucial for lung defense but exhibit heterogeneity.
- Understanding AM subpopulations is vital for interpreting lung immunity studies.
Purpose of the Study:
- To characterize the functional and morphological differences of nonadherent AMs compared to the total AM population in human smokers.
- To identify specific subpopulations within bronchoalveolar lavage (BAL) fluid.
Main Methods:
- Bronchoalveolar lavage (BAL) was performed on healthy smokers.
- Nonadherent macrophages were isolated by differential adhesion.
- Phagocytic capacity and autofluorescence were assessed via flow cytometry.
- Ultrastructural analysis was conducted using electron microscopy.
Main Results:
- Nonadherent AMs displayed reduced phagocytic capacity compared to the total AM population.
- Nonadherent AMs showed increased autofluorescence, indicating greater granularity/complexity.
- Electron microscopy confirmed more cytoplasmic inclusions and fewer surface protrusions in nonadherent AMs.
- AM adhesion to albumin-coated surfaces increased over time.
Conclusions:
- A distinct subpopulation of nonadherent AMs exists in smokers' lungs.
- These nonadherent AMs have reduced adhesion and impaired in vitro phagocytic function.
- This subpopulation may represent older cells or airway-derived macrophages.
- AM heterogeneity must be considered when evaluating lung immune function in smokers.
