Related Experiment Video
Updated: Oct 9, 2026
In Vivo Assessment of Alveolar Macrophage Efferocytosis Following Ozone Exposure
Published on: October 22, 2019
Surfactant protein A enhances alveolar macrophage phagocytosis of apoptotic neutrophils
T L Schagat1, J A Wofford, J R Wright
1Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA.
Abstract:
Surfactant protein A (SP-A) is an innate immune molecule that binds foreign organisms that invade the lungs and targets them for phagocytic clearance by the resident pulmonary phagocyte, the alveolar macrophage (AM). We hypothesized that SP-A binds to and enhances macrophage uptake of other nonself particles, specifically apoptotic polymorphonuclear neutrophils (PMNs). PMNs are recruited into the lungs during inflammation, but as inflammation is resolved, PMNs undergo apoptosis and are phagocytosed by AMs. We determined that SP-A increases AM phagocytosis of apoptotic PMNs 280 +/- 62% above the no protein control value. The increase is dose dependent, and heat-treated SP-A still enhanced uptake, whereas deglycosylated SP-A had significantly diminished ability to enhance phagocytosis. Surfactant protein D also increased phagocytosis of apoptotic PMNs by approximately 125%. However, other proteins that are structurally homologous to SP-A, mannose-binding lectin and complement protein 1q, did not. SP-A enhances phagocytosis via an opsonization-dependent mechanism and binds apoptotic PMNs approximately 4-fold more than viable PMNs. Also, binding of SP-A to apoptotic PMNs does not appear to involve SP-A's lectin domain. These data suggest that the pulmonary collectins SP-A and SP-D facilitate the resolution of inflammation by accelerating apoptotic PMN clearance.
Insights
Surfactant protein A (SP-A) enhances the clearance of apoptotic neutrophils by lung macrophages. This innate immune molecule aids in resolving inflammation by promoting the uptake of these cellular debris.
Area of Science:
- Pulmonary immunology
- Innate immunity
- Cellular biology
Background:
- Surfactant protein A (SP-A) is a key innate immune molecule in the lungs.
- Alveolar macrophages (AMs) clear foreign invaders and apoptotic cells.
- Resolution of inflammation involves efficient clearance of apoptotic polymorphonuclear neutrophils (PMNs).
Purpose of the Study:
- To investigate if SP-A enhances the phagocytosis of apoptotic PMNs by AMs.
- To determine the mechanism by which SP-A influences this process.
- To compare SP-A's effect with other related proteins.
Main Methods:
- Quantification of AM phagocytosis of apoptotic PMNs with and without SP-A.
- Dose-response experiments with SP-A.
- Assessment of heat-treated and deglycosylated SP-A effects.
- Comparison with Surfactant protein D (SP-D), mannose-binding lectin, and complement protein 1q.
Main Results:
- SP-A significantly increased AM phagocytosis of apoptotic PMNs by 280%.
- This enhancement was dose-dependent and required SP-A's glycosylation.
- SP-D also enhanced phagocytosis, but SP-A showed a greater effect.
- SP-A binds apoptotic PMNs more avidly than viable PMNs, independent of its lectin domain.
Conclusions:
- SP-A acts as an opsonin, enhancing the clearance of apoptotic PMNs by AMs.
- SP-A and SP-D contribute to the resolution of lung inflammation by facilitating apoptotic cell clearance.
- The mechanism involves SP-A binding to apoptotic PMNs, but not solely through its lectin domain.
Related Concept Videos
01:17Phagocytosis of Apoptotic Cells
Normal cells contain receptors that prevent them from being recognized by phagocytes.
01:27Immune Surveillance by NK Cells and Phagocytes
Natural Killer Cells: The Fast Responders
NK cells are large granular lymphocytes found in the blood and lymphatic system. These...